Better Sailing
Best Sailboats Under 25 Feet
Love fishing, going out on open water, and love the gentle rocking of waves? Then, now is the time to think of investing in a sailboat. Sailboats are silent, eco-friendly, and a great mode of transportation for water lovers. In addition, you can choose smaller boats for family sailing excursions.
Why Get a Sailboat Under 25 Feet?
Owning a sailboat can be amazing for those who like an adventure. Having a small sailboat for some weekend fun can be a big achievement for people who like boats, water, and adventurous outings. These sailboats are a great way to have fun on the water, but they can also often accommodate a couple or a small family for a weekend. Here are some reasons why owning a sailboat is not a bad idea:
- Eco-friendly : Sailboats use wind energy to sail on water. This makes these boats eco-friendly because it is safer for the environment. This keeps the water clean and the marine life safe from any pollutants. The sailboats are also less noisy.
- Power : Modern sailboats are quite different from the older versions. These days, boats have engineer power included. Yes, most of the navigation is done manually using the sails. Still, the engine gives a certain boost to the performance. This makes sailing an easier task and also provides more enjoyment for people on board.
- Right-of-Way : When it comes to sailboats, they do not stop easily. That means they are required to have the right-of-way while on the water. You can easily pass through the water because nobody expects the sailboat to stop.
- Affordable: Most sailboats in the 25-and-under feet category are affordable and much cheaper to have fun with than pretty much any other weekend vehicle. You do not have to worry about fuel expenses or anything like that and
- Travel : A small sailboat under 25 feet can be a great way to go through the water for those who like to travel. Those who love sailing the water’s calmness and want to drift through less traffic should invest in a beautiful sailboat. Also, you can take your family with you without having to pay for separate tickets.
- Variety : Lastly, you can choose from a large variety of boats. There are hundreds of types to pick from based on their size, features, and ability to sail in various water bodies. This gives you a choice based on your budget, making it a convenient mode of transportation without spending too much.
Here Are The 5 Best Sailboats Under 25 Feet:
Catalina 22 sport.
Catalina 22 is a very popular choice for smaller sailboats that can be trailered easily. The Catalina 22 sport is the updated version that has some added features. This sailboat is perfect for the weekend sailing excursion.
- Retractable keel made of lead
- Roller furling jib
- The fractional rig has the mainsail
- The large cabin that can sleep four people
- Engine, cloth cushions, and swim ladders are optional
>>Also Read: Best Sailboats Under 100k
Montgomery 17
This is another smaller pocket sailboat. This sailboat can be trailered easily when required. It is a bit stout in looks, and the entire body is made of fiberglass.
- The deck-stepped mast can be used with a 4-part tackle
- The boat is about 2 feet in depth
- Comes in 15 and 23-foot models
- Bunk beds in the cabin
- Has a portable toilet
- The boat has a lot of storage space
- DC power is optional
>>Also Read: Best Small Sailboats To Sail Around The World
This is one of the best family vacation sailboats in a smaller size. It has an open transom cockpit, which is quite large and comfortable. This is a perfect two-person sailboat:
- Hull and deck have laminated fiberglass
- The centerboard can be lifted through hydraulics
- The deck is molded as nonskid
- Has a cuddy cabin with a bunk bed
- Portable toilet screened ports and an optional electrical system
>>Also Read: Best Small Sailboats Under 20 Feet
Norseboat 17.5
This is Canadian-made and is fit for both sailing and rowing. This is a comparatively recent addition to the sailboat market. It has an open cockpit that is enough for a two-man team.
- The rig has a curved raff type
- Two rowing stations
- Carbon fiber mast
- Fiberglass hull with ply interiors
- 9-foot oars as well
>>Also Read: Best Small and Trailerable Sailboats
Small Sailboat Buying Guide
Finding the right sailboat is not child’s play. These are not some simple appliances for the kitchen. Sailboats are large vehicles with many components and specifications. That is why you should pay attention to the overall features and details regarding the sailboat before. Choosing the right sailboat is about the size and the power, navigation controls, space, deck, and durability. Here are a few things that should be paid attention to when picking a sailboat for traveling:
- Used or new : The first question you need to ask is whether to choose a new boat or a used one. New sailboats are expensive and are going to cost more than buying a used one. Also, the new ones will depreciate quickly as compared to the older boats. With new boats, you can take them to the water almost immediately. But with old ones, you will probably have to hire someone to make repairs and maybe upgrades. This will cost you some extra money too. It is always wiser to check the engine; the hull and deck should be dry and intact. Also, you should hire an experienced electrician to get the electric system upgraded. I am always a big believer in used sailboats, but you need to shop around for a good deal.
- Small or big : Another big question that needs to be answered is whether the boat should be small or big. You can easily find smaller-sized boats under 25 feet, but also lavish 40-foot sailboats. Yes, the bigger ones do look great and enticing. But the larger the boat, the larger the expenses on it. If you are new to sailboats, then buying a smaller one is the best option. It will be easier to learn. Another thing to keep in mind is that larger boats are not that safe and beginner-friendly. It requires a lot of practice to navigate a bigger boat.
- Ocean or lake : You should also consider where you will sail. Sailing on a calm lake is much different than sailing on an open ocean. Therefore, the boat choice should be decided based on that. You should ask whether you will sail inland or offshore. If you will sail on the ocean, then choose one sturdy and built for ocean sailing. Smaller sailboats work just fine if you plan to sail on a lake because they don’t need to be too bulky or fancy.
- Leisure or adventure : Some people are serious sailors who like to reach the bigger waves and have an adventure on rough ocean waters. Others like to go fishing with their family on a lake. Now, the choice of sailboat should be made, considering the purpose of the sailboat. You should also consider how many people will be on board before buying a boat. Users should pick a boat that will be comfortable for everyone, especially for longer vacations.
- Cheap or expensive : Lastly, consider the cost of owning a sailboat. The sailboat cost is not just the buying price you need to pay. The cost of owning a sailboat will include all the upkeep, maintenance, and upgrading costs that the sailboat will incur over time. Always keep in mind the time you are planning to keep the sailboat. If the sailboat is for a shorter time, then investing too much is not smart. Also, you should be careful of the repair costs for older sailboats that need to be paid.
Best Sailboats Under 25 Ft – Final Thoughts
Sailboats are a great way to have memorable vacations even when they are under 25 feet long. You can enjoy open waters, comfortable sailing, and some fun and quality family time on them. The best thing is that there are so many of them to choose from. Smaller sailboats are best for inland water sailing, weekend trips, and during holidays for a great fishing experience. Get ready to become a sailboat owner!
Peter is the editor of Better Sailing. He has sailed for countless hours and has maintained his own boats and sailboats for years. After years of trial and error, he decided to start this website to share the knowledge.
Related Posts
The Ultimate Guide to Choosing the Best Fishing Line for Trolling
Lagoon Catamaran Review: Are Lagoon Catamarans Good?
Best Inboard Boat Engine Brands
Are O’Day Sailboats Good? A Closer Look at a Classic Brand
- Buyer's Guide
- Destinations
- Maintenance
- Sailing Info
Hit enter to search or ESC to close.
| Featured Sailboat:
| ||||||||||||||||
30 Year: 1972 Asking: $12,000
31 Year: 1998 Asking: $10,000
2003 2 cabin, boat has brand new US SPars rigging, roller furling, mast, boom. due to insurance claim for ice splitting the mast. Freshwater boat entire life on lake erie and Lake Michigan. Stored Winters. 39 Year: 2003 Asking: $105,000
19.6' Year: 1967 Asking: $2,950
53 Year: 1983 Asking: $95,000
40 Year: 2012 Asking: $349,000
Standard Sailboat Ads:
35 Year: 2005 Asking: $109,000
14' 6 Year: 2019 Asking: $7,500
28 Year: 1985 Asking: $49,900
33 Year: 1984 Asking: $32,000
30 Year: 1980 Asking: $23,000
30 Year: 1979 Asking: $6,500
50 Year: 2023 Asking: $1,330,000
28 Year: 1977 Asking: $9,900
18.3 Year: 2014 Asking: $14,990
| .com
If you are serious about selling your boat, ! There are no catches. And we don't charge any commission. We allow buyers to contact sellers direct. For a very economical one-time fee you can feature your sailboat here where hundreds of potential buyers can see your ad each and every day! |
.com provides an extensive listing of sailboats: cruising yachts, daysailers, raceboats, catamarans, trimarans, and custom yachts. Each photo sailboat listing includes specs-at-a-glance as well as a detailed description and contact information.
|
|
|
|
life sciences essays grade 12
Academia.edu no longer supports Internet Explorer.
To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to upgrade your browser .
Enter the email address you signed up with and we'll email you a reset link.
- We're Hiring!
- Help Center
LIFE SCIENCES ESSAYS GRADE 10-12
The document provides a clear structure on how to write the essays. This document has been created from information available from the internet and it is not meant for any business purposes (FREE SUPPLY) but to help South African Life sciences Learners by gathering all the important information together. Not for market purposes only meant at assisting the Learners with a simple clear alternative in the essay writing, With a compilation of essays from Grade 12-10. You have to read the essays with understanding and never try to memorize them, as that is never part of learning. We aimed at creating independent and innovative thinkers of the south African as non-profit organization. Sources 1. I’solezwe lesiXhosa, 17 September, 2015 page 11 2. Life Sciences Academics (Facebook page), DR Marian Ross 3. http://www.testtakingpa.com/study/ 4. South African Department Basic Education Exam question papers and memorandums available from WWW.dbe.gov.za 5. Mr. Chaple's Science Class Blog http://chaplescienceclass.blogspot.com/2017/09/dnastructure.html 6. Eastern Cape Department of Education https://www.ecexams.co.za/ExaminationPapers.htm
Related Papers
Life Sciences have always been a fundamental area of science. The exponential increase in the quantity of scientific information and the rate, at which new discoveries are made, require very elaborate, interdisciplinary and up-to-date information and their understanding. This fourth edition of Life sciences, Fundamentals and practice includes extensive revisions of the previous edition. We have attempted to provide an extraordinarily large amount of information from the enormous and ever-growing field in an easily retrievable form. It is written in clear and concise language to enhance self-motivation and strategic learning skill of the students and empowering them with a mechanism to measure and analyze their abilities and the confidence of winning. We have given equal importance to text and illustrations. The fourth edition has a number of new figures to enhance understanding. At the same time, we avoid excess detail, which can obscure the main point of the figure. We have retained the design elements that have evolved through the previous editions to make the book easier to read. Sincere efforts have been made to support textual clarifications and explanations with the help of flow charts, figures and tables to make learning easy and convincing. The chapters have been supplemented with self-tests and questions so as to check one’s own level of understanding. Although the chapters of this book can be read independently of one another, they are arranged in a logical sequence. Each page is carefully laid out to place related text, figures and tables near one another, minimizing the need for page turning while reading a topic. I have given equal importance to text and illustrations as well. We hope you will find this book interesting, relevant and challenging.
Life Sciences have always been a fundamental area of science. The exponential increase in the quantity of scientific information and the rate, at which new discoveries are made, require very elaborate, interdisciplinary and up-to-date information and their understanding. This fourth edition of Life sciences, Fundamentals and practice includes extensive revisions of the previous edition. We have attempted to provide an extraordinarily large amount of information from the enormous and ever-growing field in an easily retrievable form. It is written in clear and concise language to enhance self-motivation and strategic learning skill of the students and empowering them with a mechanism to measure and analyze their abilities and the confidence of winning. We have given equal importance to text and illustrations. The fourth edition has a number of new figures to enhance understanding. At the same time, we avoid excess details, which can obscure the main point of the figure. We have retained the design elements that have evolved through the previous editions to make the book easier to read. Sincere efforts have been made to support textual clarifications and explanations with the help of flow charts, figures and tables to make learning easy and convincing. The chapters have been supplemented with self-tests and questions so as to check one’s own level of understanding. We hope you will find this book interesting, relevant and challenging.
Halus Satriawan
Bekele Gebreamanule
Joyce Wawira
By the end of the course, the learner should be able to: 1. communicate biological information in a precise, clear and logical manner 2. develop an understanding of interrelationships between plants and animals and between humans and their environment 3. apply the knowledge gained to improve and maintain the health of the individual, family and the community 4. relate and apply relevant biological knowledge and understanding to social and economic situations in rural and urban settings 5. observe and identify features of familiar and unfamiliar organisms, record the observations and make deductions about the functions of parts of organisms 6. develop positive attitudes and interest towards biology and the relevant practical skills 7. demonstrate resourcefulness, relevant technical skills and scientific thinking necessary for economic development 8. design and carry out experiments and projects that will enable them understand biological concepts 9. create awareness of the value of cooperation in solving problems 10. acquire a firm foundation of relevant knowledge, skills and attitudes for further education and for training in related scientific field.
Science & Education
Eneku Ronald
Farah Ramzi
TRISNA AMELIA
This book contains concept of biology and the exercise in English language that can help the readers to improve their English skill in biology. There are eight main contents in this book, which are the chemistry of life, an introduction of metabolisms, biotechnology, mechanisms of evolution, classification of living things,reproduction in plant, thermoregulation, and ecology. Hopefully, this book can help the readers to expand their knowledge about English for Biology.
Nature Reviews Genetics
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.
RELATED PAPERS
David Ozugha
salihath shafeer
Shanaya Patel
tarak pramanick
ADVANCES IN LIFE SCIENCES JOURNAL
TRENDS IN BIOSCIENCES JOURNAL
Quinn Francesca
marc Silberstein
Dr Dipankar Dey
KENNEDY N Y E S E H OFORI
Manoj Brahmane
Guaracy Tadeu Rocha
Edukacja Biologiczna i Środowiskowa
South African Journal of Libraries and Information Science
Omwoyo Bosire Onyancha
Maria Salih
Boris Barreno
Natasha Govender
Ezz Eldin A Shalaby
Angela Bianca Carido
Edith R Dempster , Kathryn Johnson
Khilesh Sinha
ANNASTASIA ORAEGBUNEM
Yayuk Putri Rahayu
Britta Rutert
RELATED TOPICS
- We're Hiring!
- Help Center
- Find new research papers in:
- Health Sciences
- Earth Sciences
- Cognitive Science
- Mathematics
- Computer Science
- Academia ©2024
- Life Sciences Grade 12 Latest Essays and Topics Guide CAPS
Life Sciences Grade 12 Latest Essays and Topics Guide for CAPS Curriculum (Syllabus) South Africa: A National Curriculum and Assessment Policy Statement (CAPS) is a single, comprehensive, and concise policy document introduced by the Department of Basic Education for all the subjects listed in the National Curriculum Statement for Grades R – 12. CAPS gives detailed guidance for teachers on what they should teach and how to assess.
On this page you will find Life Sciences Grade 12 Essays and Topics Guide for Term 1, Term 2, Term 3, and Term 4.
View all # Life-Sciences-Grade12 Study Resources
We have compiled great resources for Life Sciences Grade 12 students in one place. Find all Question Papers, Notes, Previous Tests, Annual Teaching Plans, and CAPS Documents.
Available Essays and Topics Guide Life Sciences Grade 12
Below is a list of Grade 12 Essay Topics and a downloadable answer guide for the Life Sciences Subject: (Compiled by France Chavngwane):
Protein Synthesis And Dna Replication Essay Grade 12
Protein Sythesis And Mutation Essay Grade 12
Nephron Essay Grade 12
Forelimbs Modification And Functions Essay Grade 12
Allien Plants Essay
The Heart Essay
Ecoutourism Essay
Breast Cancer Essay
Resource Manangement Essay
Metabolic Rate, Co2 And Glucose Essay
Mutation On Protein Sythesis And Evolution Essay
Accomodation, Hearing And Balance Essay
Meiosis, Mutation And Natural Selection Essay
Adrenalin & Hearing Essay
Out Of Africa Hypothesis Essay
Osmoregulation And Balance Essay
Natural Selection And Speciation Essay
Spermatogenesis Essay
Chromosomes And Meiosis Essay
Dna Replication And Protein Synthesis Essay
Genetic Variation Essay
Food Security, Gmo & Farming Essay
Petrified Fossils Esssays
Invansive Species & Water Quality Esssay
Solid Waste Manangement Essay
Eutrophication Acid Mine Drainage Essay
Hypothalamus (Thermoregulation) Essay
Breathing Essay
Stem Cell Essay
Glucose Regulation Essay
Nephron Homeostatic Control Essay
Digestion And Absorption Esssay
Hearing And Reflex Action Essay
Lamarckism And Darwinism Essay
Meiosis And Dna Repplication Essay Ii
Reproductive Strategies Essay
Threath To Biodiversity Essay
Homeostasis Essay
Blood Groups Essay
Speciation Essay
Pregnancy Essay
Hormones Essay
Evolution Essay (Lamarkism, Darwinism, Gradualism Vs Puntcuated Equlibrium)
Speciation And Evolution Essay
Natural Selection Vs Artificial Selection Essay
Contraceptive Methods Essay (Preg Prevention)
Air Pollution Essay
Overfishing Essay
Contraceptives Essay (Prevention Of Std’s)
Drinking Water Quality Essay
Gonorrhea And Hiv/Aids Essay
Over-Exploitation Of Idegeneous Plants Essay
Meiosis Essay (Genetic Variation,Down Syndromme And Polyploidy) Essay
Punctuated Equilibrium Vs Gradualism
Genetic Variation And Mutation Essay
Foetus Essay
Skull Essay
Genetic Engineering Essay
Clonning Essay
Photosynthesis Essay
Cellular Respiration Essay.
Mutation Essay (Harmful And Useful Mutation)
Excrection Essay
Carrying Capacicty,Competion And Predation Essay
Kidney Essay
Message To The Life Sciences Learners
Download a guide on how to answer the above essay questions here
Life Science Grade 12 Resources
- Genetics and Inheritance Grade 12 Notes
- Life Sciences Grade 12 2020 Past Exam Papers and Memos November
- Life Sciences Grade 12 Question Papers and Memorandums for Previous Years
- Grade 12 Life Sciences Study Guide pdf Download – Mind the Gap Study
- Life Sciences Grade 12 Past Papers and Memos 2020 and 2019
Life Sciences Questions and Answers For Revision
Do a free online revision:
- A structure in the eye that absorbs light to prevent internal reflection
- The branch of the autonomic nervous system that restores an increased heart rate back to normal
- A small device that is inserted in the ear to drain fluids caused by a middle-ear infection
- The blood vessel that transports deoxygenated blood from the foetus towards the placenta
More Life Sciences Revision Questions can be found from MorningAnswers.com
Looking for something specific?
Leave a comment.
Save my name, email, and website in this browser for the next time I comment.
You May Also Like
Lewenswetenskappe (Life Sciences) CAPS Document – Lesson Plans for FET Phase Grade 10 – 12
Life Sciences Grade 12 2021 November Paper 1 Paper 2 Exam Question Papers and Memorandum for downloads in PDF format
Life Sciences Grade 12 2020 Past Exam Papers and Memos November pdf download
Life sciences grade 12 june 2023 exam question papers and memorandum pdf download.
LIFE SCIENCES OVERVIEW GRADE 12 NOTES - LIFE SCIENCES STUDY GUIDES
OVERVIEW LIFE SCIENCES STUDY GUIDES AND NOTES GRADE 12
Dear Grade 12 learner
This Mind the Gap study guide helps you to prepare for the end-of-year CAPS Life Sciences Grade 12 exam. The study guide does NOT cover the entire CAPS curriculum, but it does focus on core content of each knowledge area and points out where you can earn easy marks. You must work your way through this study guide to improve your understanding, identify your areas of weakness and correct your own mistakes. To ensure a good pass, you should also cover the remaining sections of the curriculum using other textbooks and your class notes.
OVERVIEW OF THE EXAM FOR CAPS LIFE SCIENCES GRADE 12
The following topics make up each of the TWO Life Sciences exam papers that you write at the end of the year:
| Meiosis | 7 | 11 |
| Reproduction in Vertebrates | 4 | 6 |
| Human Reproduction | 21 | 31 |
Responding to the Environment (Humans) | 27 | 40 |
| ||
| Human Endocrine System | 10 | 15 |
| Homeostasis in Humans | 7 | 11 |
Responding to the Environment (Plants) | 7 | 11 |
| ||
Human Impact (Grade 11) | 17 | 25 |
| 100 | 150 | |
| ||
| DNA: Code of Life | 19 | 27 |
| Meiosis | 7 | 12 |
| Genetics and Inheritance | 30 | 45 |
| ||
| Evolution | 44 | 66 |
| 100 | 150 | |
Both Paper 1 and Paper 2 will include the following types of questions:
|
|
|
| Short answer, objective questions such as multiple-choice questions, terminology, columns/statement and items | 50 |
| A variety of question types. There will be two questions of 40 marks each. Both of these questions will be divided into two to four subsections. | 2 × 40 |
| Essay | 20 |
How to use this study guide
This study guide covers selected parts of the different topics of the CAPS Grade 12 Life Sciences curriculum in the order they are usually taught during the year. The selected parts of each topic are presented in the following way:
- An explanation of terms and concepts;
- Worked examples to explain and demonstrate;
- Activities with questions for you to answer; and
- Answers for you to use to check your own work.
- A checklist from the exam guidelines for Life Sciences has been provided on page xvii for you to keep track of your progress. Once you have mastered the core concepts and have confidence in your answers to the questions provided, tick the last column of the checklist.
- The activities are based on exam-type questions. Cover the answers provided and do each activity on your own. Then check your answers. Reward yourself for the things you get right. If you get any incorrect answers, make sure you understand where you went wrong before moving on to the next section.
- In Chapter 12, you will find a section on graphing skills which you must master when preparing for both Paper 1 and Paper 2. This chapter also provides guidelines on how to answer essay-type questions in the exam.
- You will be asked to draw a labelled diagram in the exam. On page 115 to 132 are a set of blank diagrams that you can use to practise your drawing and labelling skills. Filling in these blank diagrams is a good way to test yourself and work out what you know well and what you still need more practice in.
- Use this study guide as a workbook. Make notes, draw pictures and highlight important concepts.
- Exemplar Exam papers are included in the study guide for you to do. Check your answers by looking back at your notes and the exam memoranda. Past exam papers go a long way in preparing you for what to expect and help reduce exam anxiety. Go to https://www.elimuza.com/ to download past exam papers.
Top 10 study tips
- Have all your materials ready before you begin studying - pencils, pens, highlighters, paper, etc.
- Be positive. Make sure your brain holds on to the information you are learning by reminding yourself how important it is to remember the work and get the marks.
- Take a walk outside. A change of scenery will stimulate your learning. You’ll be surprised at how much more you take in after being outside in the fresh air.
- Break up your learning sections into manageable parts. Trying to learn too much at one time will only result in a tired, unfocused and anxious brain.
- Keep your study sessions short but effective and reward yourself with short, constructive breaks.
- Teach your concepts to anyone who will listen. It might feel strange at first, but it is definitely worth reading your revision notes aloud.
- Your brain learns well with colours and pictures. Try to use them whenever you can.
- Be confident with the learning areas you know well and focus your brain energy on the sections that you find more difficult to take in.
- Repetition is the key to retaining information you have to learn. Keep going - don’t give up!
- Sleeping at least 8 hours every night, eating properly and drinking plenty of water are all important things you need to do for your brain. Studying for exams is like strenuous exercise, so you must be physically prepared.
Study skills to boost your learning
This guide includes 3 study techniques you can use to help you learn the material:
- Mobile notes
Mobile notes
Mobile notes are excellent techniques will tools for learning all the key help you to study concepts in the study guide. smarter! Mobile notes are easy to make and you can take them with you wherever you go:
- Fold a blank piece of paper in half. Fold it in half again. Fold it again.
- Open the paper. It will now be divided into 8 parts.
- Cut or tear neatly along the folded lines.
- On one side of each of these 8 bits of paper, write the basic concept.
- On the other side, write the meaning or the explanation of the basic concept.
- Use different colours and add pictures to help you remember.
- Take these mobile notes with you wherever you go and look at them whenever you can.
- I know this information well.
- I’m getting there.
- I need more practice.
- The more you learn them, the better you will remember them.
A mnemonic code is a useful technique for learning information that is difficult to remember. Below are two examples of mnemonics. Here is a made-up word to help you remember the structure of a sperm cell - each letter of the word stands for a part of the cell:
M - Mitochondria
A - acrosome, n - nucleus.
Here is a sentence to help you remember the 4 nitrogenous bases in DNA - each word in the sentence begins with the same letter as one of the nitrogenous bases:
All Teachers Get Chocolate Adenine Thymine Guanine Cytosine
Mnemonics code information and make it easier to remember. The more creative you are and the more you link your ‘codes’ to familiar things, the more helpful your mnemonics will be. This guide provides ideas for using mnemonics. Be sure to make up your own.
Mind maps work because they show information that we have to learn in the same way that our brains ‘see’ information. As you study the mind maps in the guide, add pictures to each of the branches to help you remember the content. You can make your own mind maps as you finish each section. How to make your own mind maps:
- Turn your paper sideways so your brain has space to spread out in all directions.
- Decide on a name for your mind map that summarises the information you are going to put on it.
- Write the name in the middle and draw a circle, bubble or picture around it.
- Write only key words on your branches, not whole sentences. Keep it short and simple.
- Each branch should show a different idea. Use a different colour for each idea. Connect the information that belongs together. This will help build your understanding of the learning areas.
- Have fun adding pictures wherever you can. It does not matter if you can’t draw well.
On the day of the exam …
- Make sure you have all the necessary stationery for your exam, i.e. pens, pencils, eraser, protractor, compass, calculator (with new batteries). Make sure you bring your ID document and examination admission letter.
- Arrive on time, at least one hour before the start of the exam.
- Go to the toilet before entering the exam room. You don’t want to waste valuable time going to the toilet during the exam.
- Use the 10 minutes reading time to read the instructions carefully. This helps to ‘open’ the information in your brain. Start with the question you think is the easiest to get the flow going.
- Break the questions down to make sure you understand what is being asked. If you don’t answer the question properly you won’t get any marks for it. Look for the key words in the question to know how to answer it. A list of these words is on page xiv of this study guide.
- Try all the questions. Each question has some easy marks in it so make sure that you do all the questions in the exam.
- Never panic, even if the question seems difficult at first. It will be linked with something you have covered. Find the connection.
- Question 1: 50 marks = 45 minutes
- Question 2: 40 marks = 35 minutes
- Question 3: 40 marks = 35 minutes
- Question 4: 20 marks = 15 minutes The remaining 20 minutes can be used to check your answers and attempt to answer any question that you might have left out.
- Check weighting - how many marks have been allocated for your answer? Take note of the ticks in this study guide as examples of marks allocated. Do not give more or less information than is required.
- Write big and bold and clearly. You will get more marks if the marker can read your answer clearly.
Question words to help you answer questions
It is important to look for the question words (the words that tell you what to do) to correctly understand what the examiner is asking. Use the words in the table below as a guide when answering questions.
|
|
| Separate, examine and interpret |
| This means a numerical answer is required - in general, you should show your working, especially where two or more steps are involved |
| Group things based on common characteristics |
| Point out or show both similarities and differences between things, concepts or phenomena |
| Give a clear meaning |
| State in words (using diagrams where appropriate) the main points of a structure/process/phenomenon/investigation |
| To calculate something, or to discover the answer by examining evidence |
| Use differences to qualify categories |
| Consider all information and reach a conclusion |
| Make clear; interpret and spell out |
| Name the essential characteristics |
| Identify on a diagram or drawing |
| Write a list of items, with no additional detail |
| Refer to relevant points |
| Give the name (proper noun) of something |
| Write down information without discussion |
| Offer an explanation or a solution |
| Draw a table and indicate the answers as direct pairs |
Learner’s checklist
Use this checklist to monitor your progress when preparing for the examination. The ticks (✔) tell you which aspects of the curriculum are covered in this study guide. The stars (*) tell you to go to textbooks and class notes.
|
| |||
DNA: The code of life | Discovery of DNA structure | * | ||
Nucleic acids terminology | ✔ | |||
Structure of DNA and RNA | ✔ | |||
Differences between DNA and RNA | ✔ | |||
DNA replication and the importance thereof | ✔ | |||
DNA profiling | ✔ | |||
Protein synthesis | ✔ | |||
Meiosis | The process of meiosis using diagrams | ✔ | ||
Significance of meiosis | ✔ | |||
Abnormal meiosis | ✔ | |||
Differences between meiosis I and meiosis II | ✔ | |||
Reproduction in vertebrates | Diversity in reproductive strategies | ✔ | ||
Human reproduction | Male reproductive system | ✔ | ||
Female reproductive system | ✔ | |||
Puberty | ✔ | |||
Menstrual cycle | ✔ | |||
Development of the foetus | ✔ | |||
Gestation | ✔ | |||
Role of placenta | ✔ | |||
Genetics and inheritance | Genetic terminology | ✔ | ||
Complete dominance | ✔ | |||
Incomplete dominance | ✔ | |||
Co-dominance | ✔ | |||
Inheritance of sex | ✔ | |||
Sex-linked characteristics | ✔ | |||
Dihybrid crossing | ✔ | |||
Mutations | ✔ | |||
Pedigree diagrams | ✔ | |||
Genetic engineering | ✔ | |||
Genetic counselling | ✔ | |||
Paternity testing and DNA fingerprinting | ✔ | |||
Responding to the environment: Humans | The brain | ✔ | ||
Neurons, reflex actions and reflex arcs | ✔ | |||
Peripheral nervous system | * | |||
Autonomic nervous system | * | |||
Brain disorders and injuries | * | |||
Effects of drugs on the central nervous system | * | |||
Structure and functions of parts of the eye | ✔ |
Responding to the environment: Humans | Accommodation | ✔ | ||
Pupillary mechanism | ✔ | |||
Visual defects | ✔ | |||
Structure and functions of parts of the ear | ✔ | |||
Hearing | ✔ | |||
Balance | ✔ | |||
Hearing defects | ✔ | |||
Human endocrine system | Glands and the hormones they secrete | ✔ | ||
Negative feedback - glucose | ✔ | |||
Negative feedback - thyroxin | ✔ | |||
Homeostasis in humans | Negative feedback - glucose | ✔ | ||
Negative feedback - carbon dioxide | ✔ | |||
Negative feedback - water | ✔ | |||
Negative feedback - salts | ✔ | |||
The role of the skin on hot and cold days | ✔ | |||
Responding to the environment: Plants | Functions of auxins, gibberillins and abscisic acid | ✔ | ||
Role of auxins in phototropism and geotropism | ✔ | |||
Plant defence mechanisms is included | ✔ | |||
Evolution | Evidence for evolution | ✔ | ||
Sources of variation | ✔ | |||
Lamarck and Darwin’s theories | ✔ | |||
Natural and artificial selection | ✔ | |||
Punctuated equilibrium | ✔ | |||
Speciation | ✔ | |||
Mechanisms for reproductive isolation | ✔ | |||
Evolution in present times | ✔ | |||
Human evolution: similarities to African apes | ✔ | |||
Human evolution: differences from African apes | ✔ | |||
Major phases in hominid evolution | ✔ | |||
Out of Africa hypothesis | ✔ | |||
Phylogenetic trees | ✔ | |||
Human impact on the environment | Atmosphere and climate change | ✔ | ||
Water availability | ✔ | |||
Water quality | ✔ | |||
Food security | ✔ | |||
Loss of biodiversity | ✔ | |||
Waste disposal | ✔ | |||
Skills | Draw a line graph | ✔ | ||
Draw a bar graph | ✔ | |||
Draw a histogram | ✔ | |||
Draw a pie chart | ✔ | |||
Answering essay questions | ✔ |
GOOD LUCK!!!
Related items.
- LIFE SCIENCES GRADE 12 MEMORANDUM - NSC PAST PAPERS AND MEMOS JUNE 2022
- LIFE SCIENCES GRADE 12 QUESTIONS - NSC PAST PAPERS AND MEMOS JUNE 2022
- LIFE SCIENCES PAPER 2 GRADE 12 MEMORANDUM - NSC PAST PAPERS AND MEMOS NOVEMBER 2021
- LIFE SCIENCES PAPER 2 GRADE 12 QUESTIONS - NSC PAST PAPERS AND MEMOS NOVEMBER 2021
- LIFE SCIENCES PAPER 1 GRADE 12 MEMORANDUM - NSC PAST PAPERS AND MEMOS NOVEMBER 2021
- Interactivity
- AI Assistant
- Digital Sales
- Online Sharing
- Offline Reading
- Custom Domain
- Branding & Self-hosting
- SEO Friendly
- Create Video & Photo with AI
- PDF/Image/Audio/Video Tools
- Art & Culture
- Food & Beverage
- Home & Garden
- Weddings & Bridal
- Religion & Spirituality
- Animals & Pets
- Celebrity & Entertainment
- Family & Parenting
- Science & Technology
- Health & Wellness
- Real Estate
- Business & Finance
- Cars & Automobiles
- Fashion & Style
- News & Politics
- Hobbies & Leisure
- Recipes & Cookbooks
- Photo Albums
- Invitations
- Presentations
- Newsletters
- Sell Content
- Fashion & Beauty
- Retail & Wholesale
- Presentation
- Help Center Check out our knowledge base with detailed tutorials and FAQs.
- Learning Center Read latest article about digital publishing solutions.
- Webinars Check out the upcoming free live Webinars, and book the sessions you are interested.
- Contact Us Please feel free to leave us a message.
Understanding Life Sciences 12
Description: flipbook (undefined description), read the text version.
No Text Content!
CONTENTS Topic Page About the Book ………….……………………………………………………………………………………………………………… i Assessment in the Life Sciences ……………………………………………………………………………..……………… iv Topic 1 DNA – The Code of Life ……………………………………………………………………………… ………. 1 Topic 2 Cell Division: Meiosis ……………………………………………………………………………………………… 19 Topic 3 Reproduction in Vertebrates: Diversity of Reproductive Strategies …………………… 37 Topic 4 Human Reproduction …………………………………………………………………………………………. 43 Assessment Test One – Practice Paper ………………….………………………………………………………………… 61 Topic 5 Genetics and Inheritance …………………………………………………………………………………… 65 Topic 6 Human Nervous System and Sense Organs …………………………………………………………… 103 Assessment Test Two – Practice Paper …………….……………………………………………………………..……… 135 Assessment June Exam – Practice Paper ……………………….………………………………………………………… 139 Topic 7 Human Endocrine System …………………………………………………………………………………… 149 Topic 8 Homeostasis in Humans ………………………………………………………………………………………. 167 Topic 9 Plant Responses to the Environment ……………………………………………………………………. 177 Topic 10 Evolution by Natural Selection ……………………………………………………………………………… 187 Topic 11 Human Evolution ………………………………………………..………………………………………………… 213 Topic 12 Human Impact on the Environment …………………………………….………………………………. 243 Assessment Test Three – Practice Paper …………………………………….…………………………………………… 299 Assessment Trial Exam – Practice Paper 1 ………………………………….…………………………………………… 303 Assessment Trial Exam – Practice Paper 2 ………………………………………………………….…………………… 315 Glossary ………………………………………………………………………………………………………………………………… 327
ABOUT THE BOOK ABOUT THE BOOK This book is based on the National Curriculum and Policy Statement (CAPS) for the subject Life Sciences. CAPS was introduced at Grade 10 level in 2012, Grade 11 in 2013, and implemented in Grade 12 in 2014. The Grade 12 book is part of a series for Life Sciences. Topics to be Studied and Assessed in Grade 12 Strand One Life at Molecular, Cellular and Tissue Level • DNA: The Code of Life • RNA and Protein Synthesis • Meiosis • Genetics and Inheritance Strand Two Life Processes in Plants and Animals • Reproduction in Vertebrates (other than humans) • Human Reproduction • Human Nervous System • Sense Receptors • Human Endocrine Glands • Homeostasis • Hormones and Plant Defence Mechanisms Strand Three Diversity, Change and Continuity • Darwinism and Natural Selection • Human Evolution Strand Four Environmental Studies • Human Impact on the Environment (Revision of Grade 11 Content and activities) Term-by-Term Arrangement of the Topics The topics listed above will NOT be studied in the exact sequence as listed. For example: • In term one, topics from Strand One and Two are included • In the same way, in term two, topics from Strand One and Two are included • In term 3, topics from Strands Two and Three will be studied • In term 4, topics from Strands Three and Four will be studied Grade 12 - CAPS i
ABOUT THE BOOK The complete re-arrangement of topics is shown in Table 0.1 below. Table 0.1. Term-by term arrangement of topics that will be studied and assessed in Grade 12 TERMS STRAND TOPIC From Strand One Topic 1 The Nucleic Acids and Protein Synthesis TERM ONE From Strand One Topic 2 Meiosis Topic 3 Reproduction in Vertebrates: From Strand Two Diversity of Reproductive Strategies Topic 4 Human Reproduction From Strand One Topic 5 Genetics and Inheritance TERM TWO From Strand Two Topic 6 Nervous System and Sense Organs Life Processes in Plants and Animals Topic 7 Human Endocrine Glands From Strand Two Topic 8 Homeostasis Topic 9 Plant Responses to the Environment Topic 10 Evolution by Natural Selection • Genetics and Inheritance TERM THREE (Revision of earlier work, especially those aspects related, natural selection, mutations, mitochondrial DNA and genetic engineering) • Artificial Selection and Natural Selection From Strand Three • Darwin’s Theory • Speciation • Mechanisms of Reproductive Isolation • Evolution in Present Times Topic 11 Human Evolution • Evidence of common ancestors for living hominids • ‘Out of Africa’ Hypothesis From Strand Three Topic 11 Human Evolution - continued TERM FOUR • Importance of the Cradle of Humankind • Alternatives to Evolution From Strand Four Topic 12 Human Impact on the Environment (Grade 11) (Revision of Grade 11 Content and Activities) Note that Topic 12 (Human Impact on the Environment) is a repetition of work studied in Grade 11. This topic will be assessed again in the Grade 12 examinations. ii UNDERSTANDING LIFE SCIENCES
ABOUT THE BOOK Structure of the Book This textbook is structured in the same sequence as indicated in Table 0.1 on Page ii. At the beginning of each topic, a flow chart indicates the relationship between the different sub-sections within the topic. In these topics you will learn specific content and apply the skills and behaviour learned when studying the Orientation to the Life Sciences in Grade 10. In some cases, there are further flow charts to indicate how the different aspects of the topic are linked together. Such mind mapping serves as advance organisers and should go a long way towards enabling you to see the ‘bigger picture’ and in preparing you for what is to come in each topic. Icons used in this Book For each activity in the book, special icons are used to indicate how the activity should be conducted. Work on your own Work in pairs Work as a group Undertake an excursion In addition, the following icon is used to indicate a reference to a web-site link. This will allow you to obtain additional information about the topic being dealt with. Grade 12 - CAPS iii
ASSESSMENT ASSESSMENT Assessment Requirements for Grade 12 You will be assessed both informally as well as formally in the subject Life Sciences. Informal or Daily Assessment During the course of the year, your teacher will ask you to carry out a number of small activities to find out whether you understand the content being taught and whether you are developing the skills that you should develop. These activities may be in the form of written homework or classwork exercises and practical work. In addition, the teacher may ask you questions or may observe you while you are working with others. The results of this informal or daily assessment are not formally recorded, unless your teacher wishes to do so. Also, these results are not taken into account for promotion and certification purposes. What, then, is the purpose of this informal assessment? Your teacher will use the answers to the written exercises, the way you carry out the practical activities and interact with your classmates and him/her to provide you with valuable information with regard to the progress you are making in your study of Life Sciences. When this information is given to you, it helps you to learn from your performance and make changes to the way in which you study/learn. Formal Assessment In addition to activities given to you as part of Informal Assessment, you will also be required to do tasks that make up a Formal Programme of Assessment for the year. Examples of formal assessment tasks include tests, examinations, practical activities, projects, oral presentations and demonstrations. Your efforts in tasks such as these will be marked, formally recorded and used by your teacher for progression, promotion and certification purposes. The number and nature of tasks for the Formal Programme of Assessment for Grade 12 Life Sciences is shown in Table 0.2. Note the following with regard to the assessment tasks conducted throughout the year, which is also referred to as school-based assessment: • There will be three tests in all, one in each of the first three terms, each carrying a minimum of 50 marks. • There will be one mid-year examination (2 ½ hours, 150 marks) in the second term; this may be replaced by a control test. • There will be one trial examination: two papers, each of 2 ½ hours duration and each carrying 150 marks. • Three practical tasks will be selected, one in the first term, one in the second term and one in either the third or fourth term. • Selection of the practical activities will be done in such a way as to ensure that the full range of scientific skills, listed earlier, are assessed. • One project/assignment will be given. It may be given at any time, but its assessment mark will be used for the third term. The project/assignment will carry 100 marks. Field work activities are one type of project/assignment. iv UNDERSTANDING LIFE SCIENCES
ASSESSMENT The project is a long-term assignment in which you are required to carry out an investigation by literature research, interviews and/or practical activity. The results of the research are usually written up in the form of a report which may sometimes be supported by a model or poster. You may be required to formally present your research findings to a large audience (other learners in the class or school). Since you are required to spend a lot of time in doing the research, your teacher will give you details of the project well in advance. The research topic and other relevant details are likely to be given in the first term, for submission and assessment of the project in the third term. Examples of research projects given in the Learner’s Book include the following: o The major phases in hominid evolution (Activity 11.6) o Disorders caused by under-secretion and over-secretion of one hormone (Activity 7.5) Your teacher will help you with following details regarding the project: o Explanation of exactly what is required o Development of a time plan o Planning the structure of the project o Preparing to collect information/data o Carrying out the research itself o Writing up the report o Presentation of the report. Table 0.2 The number and nature of tasks for the Formal Programme of Assessment in Grade 12 ASSESSMENT TASKS CONDUCTED THROUGHOUT THE YEAR TRIAL: YEAR-END INTERNAL EXAMINATIONS Term 1 Term 2 Term 3 and Term 4 2 written examinations • One test • One test • Based on work covered in first, • One test • One selected • One control test or • One selected practical task second and third terms practical task mid-year examination (will not be included in year • Will test content knowledge, • One selected mark) concepts, skills as well as practical task • One project/assignment, e.g. practical work Field work on environmental • Each paper will carry 150 marks studies and will be of 2 ½ hours duration 33.3% 33.3% 33.3% 100% Converted to 50% Converted to 50% • The marks for all the 4 tests (or 3 tests and June examination), 3 practical tasks, assignment/project will be added and then converted to 50%. • This 50% will be added to the 50% for the trial examinations to give 100%, which will form the mark for the formal, school-based assessment or year mark. Grade 12 - CAPS v
150) will then be added together to the 100 marks for the school-based assessment to give 400 marks or 100%, which will form the basis for promotion and certification. • Each of the two written papers will be of 2 ½ hours duration. • Tables 0.3, 0.4 and 0.5 list the topics, the time that should be spent in teaching and learning of each topic and the weighting and marks for each of these topics in the examination papers. Table 0 .3 Expected time to be spent in teaching each topic Expected time to be Term Topic spent in teaching • DNA: the code of life 2 ½ weeks • Meiosis 2 weeks 1 • Reproduction in vertebrates ½ week • Human reproduction 3 weeks • Responding to the environment (humans) 4 weeks 2 • Genetics and Inheritance 4 weeks • Responding to the environment (plants) 1 week 3 • Human Endocrine System 1 ½ weeks • Homeostasis in humans 1 week • Evolution through natural selection 2 weeks • Human evolution 1 week • Human evolution- continued 3 weeks • Human Impact on the Environment: Current crises 4 for human survival: problems to be solved within 2 ½ weeks the next generation (Review and revision of Grade 11 work) Total 28 weeks vi UNDERSTANDING LIFE SCIENCES
ASSESSMENT Table 0.4 Weighting for each topic in the year–end Paper 1 examination paper Expected time to Weighting in the examination Term Topic be spent in paper (Paper 1) teaching % Marks • Meiosis 1 week 7 11 • Reproduction in vertebrates ½ week 4 6 1 • Human Reproduction 3 weeks 21 31 • Responding to the Environment 4 weeks 27 40 2 (Humans) • Human Endocrine System 1 ½ weeks 10 15 3 • Homeostasis in Humans 1 7 11 • Responding to the Environment 1 7 11 (Plants) • Human Impact on the Environment 2 ½ weeks 17 25 4 (Grade 11 Work) Total 14 ½ weeks 100% 150 Table 0.5 Weighting for each topic in the year–end Paper 2 examination paper Expected time to Weighting in the examination Term Topic be spent in paper (Paper 2) teaching % Marks • DNA: Code of Life 2 ½ weeks 19 27 1 • Meiosis 1 week 7 12 2 • Genetics and Inheritance 4 weeks 30 45 3 • Evolution through Natural Selection 2 weeks 15 23 4 • Human Evolution 4 weeks 29 43 Total 13 ½ weeks 100% 150 The weighting given per topic serves only as a guideline. In other words, the number of marks allocated for each topic in the examination papers may not be exactly the same as those shown in the tables above. Moderation of Assessment In order to ensure that the school-based assessment tasks and the marks each learner has been awarded for them are fair, valid and reliable, the tasks as well as learners’ marks will be moderated at four levels viz. at school level, by the subject advisor, by the province and at national level. Moderation at school level will be on-going. It is meant to ensure that the activities meet the requirements in terms of difficulty, content and skills. It is also meant to ensure that the marks allocated to each learner are a true reflection of their performances. Moderation by the subject advisor is also an on-going process. In addition to serving the same purpose as school based moderation, moderation by subject advisors is meant to determine whether the prescribed number of assessments has been complied with and whether the assessments in different schools are comparable. Grade 12 - CAPS vii
ASSESSMENT Moderation by the province is once-off. It is meant to determine whether the required quality of school based assessment is being met within the Department of Basic Education as a whole. At national level, school-based assessment marks will be moderated statistically to ensure comparability across schools, districts and provinces. Interpretation of Results In order to arrive at the final percentage you obtained for Life Sciences your marks for the assessment tasks carried out throughout the year (out of 25) will be added to the examination marks (out of 75). How your performance in percentages should be interpreted is shown in the table below: Table 0.6 The interpretation of your performance in terms of codes and descriptions of competence Percentage Description of competence Rating Code 80-100 Outstanding achievement 7 70-79 Meritorious achievement 6 60-69 Substantial achievement 5 50-59 Adequate achievement 4 40-49 Moderate achievement 3 30-39 Elementary achievement 2 0-29 Not achieved 1 viii UNDERSTANDING LIFE SCIENCES
DNA- THE CODE OF LIFE 1 DNA – The Code of Life Grade 12 - CAPS 1
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Introduction Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) are the two nucleic acids we are going to study. Activity 1.1 is meant to help you review some aspects of the structure of plant and animal cells that we studied in Grade 10. This will help you to understand the structure of DNA and RNA and their roles in the synthesis (manufacture) of proteins. Activity 1.1 Some Basic Information Classwork/Homework Study the following diagram showing part of the contents of a plant or animal cell and answer the questions set. DID YOU KNOW? • The length of DNA in a human cell totals about 3 metres • All your DNA could fit into a cube about the size of an ice cube • If all the DNA strands in a human body were strung together, it would stretch from earth to the Sun and 1. Write down the letter and name of the part for each of the following: back—70 times! 1.1 The part that unwinds to become chromosomes • The distance from the 1.2 The site of protein synthesis Earth to the Sun is 150 1.3 The part in which DNA will be found (6) million km 2. What do A, B, C and D together make up? (1) 3. What are its TWO main functions? (2) 4. Make an outline drawing of a plant or animal cell. Copy the above parts into your drawing. Add to your drawing the organelle that is referred to as the “power house” of the cell. Label all the parts and include a caption for your NEW WORDS drawing. (9) [18] to check in the glossary DNA Activity 1.1 above would have reminded you that the nucleus has four basic parts as RNA follows: Protein synthesis • A nuclear membrane which is double and continuous with the endoplasmic Chromosome reticulum. It contains pores on its wall. Nuclear membrane • The nucleoplasm or nuclear sap which contains free nucleotide bases. Chromatin • A nucleolus which manufactures and contains ribosomal RNA. Nucleolus • The chromatin network which contains DNA. The chromatin network later unwinds to form chromosomes. 2 UNDERSTANDING LIFE SCIENCES
DNA- THE CODE OF LIFE Structure of Nucleic Acids P • Both DNA and RNA are referred to as nucleic acids • Both types of nucleic acids are made up of a number of smaller units or NB monomers called nucleotides S • Each nucleotide is made up of: o A nitrogenous base (NB) o A sugar portion (S) - deoxyribose in DNA; ribose in RNA Fig 1.1 Structure of a o A phosphate portion (P) single nucleotide DNA (Deoxyribonucleic acid) Location of DNA The DNA within the nucleus is called nuclear DNA. Together with proteins, it makes up the chromosomes which in turn go to make up the chromatin network. Types of DNA Small amounts of DNA are also found outside the nucleus (extra-nuclear DNA) such • Nuclear DNA in the as within chloroplasts (called chloroplastic DNA) and mitochondria (called nucleus mitochondrial DNA or mtDNA). Mitochondrial DNA is particularly important in • Mitochondrial DNA helping us trace our ancestors. We will look at how this is done later when we study (mtDNA) in the mutations. mitochondrion • Chloroplastic DNA in the chloroplast NEW WORDS to check in the glossary Nucleotide Nuclear DNA Extra-nuclear DNA Mutation Fig. 1.2 The location of nuclear DNA Grade 12 - CAPS 3
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Functions of DNA • Nuclear DNA controls the synthesis (manufacture) of proteins Examples of some proteins synthesized by the cell include myosin found in muscles, collagen found in white connective tissue, bone tissue and some fish scales, keratin found in horns, nails and hair and legumin found in seeds of leguminous plants. NEW WORDS to check in the glossary Since enzymes are specialised proteins, DNA also controls the synthesis of enzymes. Enzymes control all the metabolic activities within the cell e.g. Deoxyribose cellular respiration. We can summarise the first function of DNA and say that it Complementary base pairs controls the structure and functioning of cells and thus the organism as a whole Double helix by controlling the manufacture of proteins, including enzymes. Adenine Guanine Chloroplastic DNA and mtDNA control protein synthesis within these organelles Cytosine themselves. Thymine Weak hydrogen bonds • Nuclear DNA also transmits hereditary characteristics from parents to offspring DNA is passed down from existing cells to new cells during reproduction. In this way the characteristics of parents are passed onto their offspring. Structure of DNA • DNA is made up of a number of smaller units or monomers called nucleotides. • As indicated in Figure 1.1, each nucleotide is made up of: o A sugar molecule o A phosphate portion o A nitrogenous base • The sugar molecule in DNA is deoxyribose • There are 2 groups of nitrogenous bases: purines and pyrimidines • The purines are adenine and guanine whilst the pyrimidines are cytosine and thymine. • The sugar molecule of one nucleotide becomes attached to the phosphate ion of another by sugar-phosphate bonds, thus forming a long chain. • Another chain of nucleotides comes to lie next to this one in such a manner that: Fig. 1.3 o Cytosine pairs off with guanine. A portion of DNA to o Adenine pairs off with thymine. show pairing of bases • Since cytosine only pairs with guanine and adenine only with thymine, these are called KEY complementary base pairs. • The nitrogenous bases are held together by P – phosphate S - sugar weak hydrogen bonds so that a double stranded structure results. A - adenine C - cytosine • This ladder-like DNA molecule twists so that T - thymine one strand coils around the other forming a G – guanine double helix Fig. 1.4 A portion of DNA to show its double helix structure 4 UNDERSTANDING LIFE SCIENCES
DNA- THE CODE OF LIFE Genes and Non-coding DNA NEW WORDS • Small sections of DNA may carry the genetic code for the formation of a to check in the glossary particular trait or charactertistic. They may also carry the code for a particular protein. Such small portions of DNA are called genes. (We will learn more about genes when we study genetics). Gene • Every small portion of DNA does not carry a code for proteins or some other Non-coding DNA characteristic. In fact, most sections of DNA do not carry any codes at all. Such portions of DNA are called non-coding DNA. Brief History of the Discovery of DNA No one has actually seen DNA (or RNA). Our knowledge of the structure of DNA comes from a theoretical model put forward by the scientists Watson and Crick. In other words, what we have studied so far is a theory of what DNA looks like. James Watson and Francis Crick teamed up and carried out their research at Cambridge University. At King’s College London, two other scientists, Rosalind Franklin and her assistant Maurice Wilkins were also working on researching the structure of DNA. Rosalind Franklin realised that DNA was some sort of double helix from X-ray diffraction pictures she took. Maurice Wilkins disliked Rosalind Franklin. He showed these X-ray diffraction pictures to James Watson. This helped Watson in his own research, especially about the helical structure of DNA. Watson and Crick continued their research and found that DNA contained similar amounts of adenine and thymine, and also similar amounts of cytosine and guanine. The similar amounts of adenine and thymine and also of cytosine and guanine gave them the idea of complementary base-pairing i.e. that cytosine always pairs with guanine and adenine always pairs with thymine. Another significant aspect of their findings was that the complementary pairing of bases allows DNA to make exact copies of itself (See DNA replication later). In 1953 Watson and Crick put forward their model of DNA which indicated that it was a double-helix with complementary base-pairs. Rosalind Franklin died of cancer in 1958. In 1962 James Watson and Francis Crick, as well as Maurice Wilkins who provided important X-ray diffraction pictures, were awarded the Nobel Prize for their work. If Rosalind Franklin was still alive, it is likely that she, and not Maurice Wilkins, would have been the third person to share the Nobel Prize with Watson and Crick. Fig. 1.5 James Watson and Francis Crick with their model of DNA Fig. 1.6 Recipients of the Nobel Prize Grade 12 - CAPS 5
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Activity 1.2 Extracting DNA Practical Work What you need • an onion • 3 g (about 1 tablespoon) table salt • grater • cold water (100 ml - about half a • scalpel (or knife) cup) in a large beaker or jar • filter funnel • ice (in a large container into which the large beaker or jar fits) • filter paper (or blotting paper) • hot water (600 ml – about 3 cups) • small beaker (50 ml) or small poured into a large shallow bottle onto which the funnel fits • 10 ml (about 2 tablespoons) container dish-washing liquid • methylated spirits • meat tenderizer What you should do The diagrams on the pages that follow will help you to follow the steps) (a) Preparing a solution to break down the onion cells 1. Add the dish-washing liquid and salt to the beaker of cold water and mix. ° The dish-washing liquid breaks down the cell membranes. ° Remember the DNA is not visible, so the salt combines with the nucleic acids to form tiny crystals, which we will be able to see later. 2. Place the methylated spirits in one corner of the container of ice for use later. (b) Breaking up the cells to get to the DNA 3. Remove the brown papery leaves of the onion. 4. Grate the onion into small pieces. ° Grating the onion into small portions breaks up the cells so that the dish-washing liquid, salt and meat tenderizer (see later) can get to the DNA and act on them. 5. Add the onion pieces into the salt and dish-washing solution prepared earlier. 6. Place the beaker (or jar) containing the above in hot water for about 15 minutes. ° Heat makes the process of breaking up the cells take place faster. 7. Then place the beaker in a large container of ice for about 5 minutes. 6 UNDERSTANDING LIFE SCIENCES
DNA- THE CODE OF LIFE (c) Separating the DNA from the rest of the cells 8. Use the filter paper (or blotting paper) and funnel to filter the mixture, allowing the filtrate to collect into a small beaker or small bottle. 9. Stop when you have about 10 -15 ml (about 2-3 tablespoons). ° The larger particles of the onion cells, such as the cell walls, are left behind in the filter paper. The smaller particles, including the DNA and proteins pass through the filter paper into the beaker or small bottle. (d) Unwrapping the nucleic acids from its histone proteins 10. Add about a teaspoon tip of meat tenderizer to the filtrate. ° DNA strands are tightly wrapped around proteins called histones. This allows them to fit into the nucleus as an entangled mass called the chromatin network, even though the strands are extremely long. ° The meat tenderizer contains the enzyme protease which breaks down the histones. ° The DNA strands break very easily, so you need to work very carefully. (e) Causing the nucleic acids to settle out of solution 11. Carefully pour about 1 teaspoon (5 ml) of the ice cold methylated spirits along the walls of the inside of the bottle or beaker containing the onion extract. It will run down and make contact with the extract. ° DNA does not dissolve in methylated spirits. ° It forms a milky white cloud in the methylated spirits above the layer of water. Follow-up questions 1. Is the DNA you extracted most likely to be nuclear DNA, mitochondrial DNA or chloroplastic DNA. Give a reason for your answer. (2) 2. What precaution must you take in carrying out stages (d) and (e)? Why? (2) 3. Write down numbers 3.1 to 3.4 in your work book and next to each, write down sentences or phrases which best complete the functions of the substances indicated in the table below. (4) Substance Functions Table salt 3.1 Dish-washing liquid 3.2 Meat tenderizer 3.3 Methylated spirits 3.4 [8] Grade 12 - CAPS 7
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Activity 1.3 Structure of DNA Classwork/Homework 1. Give the correct biological term for each of the following descriptions. Write down only the correct term next to the relevant question number. 1.1 Nucleic acid that is a constituent of chromosomes 1.2 Segment of a chromosome that controls each characteristic 1.3 Tangled network of chromosomes located within the nucleus 1.4 Type of DNA that only occurs in the nucleus 1.5 Type of DNA that occurs only in the mitochondria 1.6 Natural shape of a DNA molecule 1.7 Building blocks consisting of sugar, phosphate and nitrogen base 1.8 Bonds by which base pairs are linked in DNA 1.9 The base that pairs off with adenine in DNA 1.10 The base that pairs off with guanine (10) 2. For each of the questions 2.1 to 2.6 choose an answer from the list below: • Weak Hydrogen Bonds • Deoxyribose • Ribose • Nucleotides • Phosphate • Cytosine • Double Helix • Thymine 2.1. The monomers of nucleic acids. 2.2. How are the two strands of DNA held together? 2.3. Region of nucleotide to which the nitrogen base is attached in DNA. 2.4. The three parts that make up a cytosine nucleotide in RNA. 2.5. The term used to describe the natural shape of DNA. 2.6. The nitrogen base to which guanine bonds. (8) 3. The following diagram is a schematic representation of a segment of a DNA molecule. Answer the questions set on it. 3.1 Where do we usually find this molecule in a living cell? (1) 3.2 Of what biological significance is this molecule? (2) 3.3 Identify the parts numbered 1 and 2. (2) 3.4 Identify the nitrogenous bases 3 and 4. (2) [25] 8 UNDERSTANDING LIFE SCIENCES
DNA- THE CODE OF LIFE Activity 1.4 Model of DNA Practical Work What you should do You must plan and construct a three-dimensional model of DNA, showing its helical structure and correct base-pairing. You may use any material of your choice to construct your model. How you should go about it 1. Plan your model on paper. Your construction should show at least five complementary base pairs. 2. Discuss your ideas with your partner and then with your class teacher. 3. Once approved by the teacher, you may go ahead and complete the model. All the parts must be labelled and there must be a caption. What you should hand in • Your model • Your plans and any other supporting documents you wish to hand in. RNA (Ribonucleic acid) Types of RNA Location of RNA • Ribosomal RNA (rRNA) • Messenger RNA (mRNA) • Transfer RNA (tRNA) There are three types of RNA: • Ribosomal RNA (rRNA) found in the ribosomes in the cytoplasm of the cell • Messenger RNA (mRNA) which is found in the nucleus of the cell but later moves out of the nucleus and attches to the ribosomes in the cytoplasm • Transfer RNA (tRNA) found in the cytoplasm of the cell Functions of RNA All three types play important roles in protein synthesis (See protein synthesis later). Structure of RNA KEY Ribonucleic Acid (RNA) is similar to DNA except that: P – phosphate • It is a single-stranded structure S - sugar • It is not coiled A - adenine • The sugar in it is ribose (not deoxyribose) C - cytosine • Thymine has been replaced by uracil U - uracil G – guanine • The chains are shorter Fig. 1.7 Structure of RNA Grade 12 - CAPS 9
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Comparison of DNA and RNA Similarities between DNA and RNA • Both contain sugar alternating with phosphate • Both contain the nitrogenous bases adenine, guanine and cytosine • Both play a role in protein synthesis Differences between DNA and RNA DNA RNA Found in the nucleus only Found in the nucleus and the cytoplasm Long molecule Short molecule Double stranded molecule Single stranded molecule Contains the sugar, deoxyribose Contains the sugar, ribose Contains the nitrogenous base, Contains the nitrogenous base, uracil thymine Activity 1.5 Structure of RNA and DNA Classwork/Homework 1. Study the following diagram and answer the questions set. 1.1 Identify the nucleic acid shown here. (1) 1.2 Give TWO reasons for your answer in 1.1 (2) 1.3 Name the THREE different types of this nucleic acid found in a cell. (3) BASES OF DNA 1.4 Why are there no hydrogen bonds present? (1) • Adenine • Guanine 1.5 Name the type of sugar represented by the letter S. • Cytosine (1) • Thymine 2. State whether each of the phrases in Column I applies to A only, B only, A and B, or none of the items in Column II. Column I Column II BASES OF RNA 2.1 Found as a constituent of DNA A. Ribose B. Uracil • Adenine 2.2 Ribosomes present A. Plant cell • Guanine B. Animal cell • Cytosine 2.3 Contains RNA A. Ribosomes • Uracil B. Nucleolus 2.4 Carries genetic material A. Chromosome B. Ribosome 2.5 Nitrogenous base found in DNA A. Uracil B. Adenine (10) [18] 10 UNDERSTANDING LIFE SCIENCES
DNA- THE CODE OF LIFE DNA Replication What is DNA replication? The process by which DNA makes an identical copy of itself is called DNA replication. When does it occur? Fig. 1.8 The Cell Cycle In Grade 10, we learned about the cell cycle. We learned that, in preparation for mitosis, DNA needs to make an exact copy of itself. You will learn later that DNA replication also occurs before meiosis begins. In summary then, we can say that NEW WORDS DNA replication occurs just before cell division (mitosis and meiosis). It occurs to check in the glossary during interphase. Cell cycle Why does it occur? Mitosis Meiosis DNA replication As a result of DNA replication, each and every chromosome within the cell is able to Interphase make an identical copy of itself. This increases the number of chromosomes so that Template they can be shared between the cells resulting from cell division. It enables the Complementary strand nucleus of the cell to split into two in such a way that each new cell produced has the same number of chromosomes. In mitosis, it allows for the resulting cells to be identical to each other and to that of the parent from which they arose because of the identical copies made of the chromosomes. How does it occur? 1 - unwinds DNA replication takes place as follows: 1 • Double helix DNA unwinds 2 - unzips • Weak hydrogen bonds between nitrogenous bases break 3 - template 2 • and the two DNA strands unzip /separate 3 - template 3 • Each original DNA strand serves as a template to form a new strand • by attaching to free nucleotides from the nucleoplasm 4 • to form complementary strands (A to T and C to G) • Each DNA molecule now consists of 1 original strand and 1 new strand 4 – complementary 5 • The result is two genetically identical DNA molecules strands form • The entire process is controlled by enzymes Fig. 1.9 The process of DNA replication 5- two identical strands Grade 12 - CAPS 11
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL DNA ‘Fingerprinting’/ DNA Profiling Advantages of DNA fingerprints over ordinary fingerprints Every person, excepting identical twins, has his/her own unique fingerprint. Since the 1930’s this knowledge has been used by detectives in tracking down suspects of crime. Although it is still useful, ordinary fingerprinting has some disadvantages. Since fingerprints are found only at the tips of fingers, and because fingerprints can be altered by plastic surgery, it is sometimes difficult to use them in identifying suspects of crime. Fig. 1.10 Ordinary Like fingerprints, every person, excepting identical twins, has his/her own unique fingerprints DNA. However, every cell within a person’s body has DNA and this DNA is identical in all cells of that person’s body. It cannot be altered by any known treatment. Therefore, DNA ‘fingerprinting’ is rapidly becoming the main method for identifying and distinguishing among individual human beings. Recently the term DNA profile has been preferred over the term DNA ‘fingerprint’ to avoid confusion with the traditional skin fingerprints. What is a DNA profile? DNA fingerprints are not really “fingerprints”. They are actually a pattern of black bars left on X-ray film when an extract of DNA is put through a special biotechnical process. DNA profiling is a method of identifying an individual by comparing his/her DNA profile with another known DNA fingerprint. Fig. 1.11 Diagrammatic How is a DNA profile made? representation of a DNA profile A DNA profile is made by first extracting a DNA sample from body tissue or fluid such as hair, blood, or saliva. The sample is then broken up into small pieces. These small segments of DNA are marked with radioactive probes and exposed on X-ray film. The pattern of black bars left behind on the X-ray film is the DNA profile. If the DNA profiles produced from two different samples match, the two samples probably came from the same person. NEW WORDS What are the uses of DNA Profiles? to check in the glossary DNA profiles were originally used to identify the presence of genetic diseases. Fingerprints Today, it is used for the diagnosis of inherited disorders, developing cures for DNA ‘fingerprint’ inherited disorders, as biological evidence in criminal cases and for identification of DNA profiling relatives. Inherited disorder Forensic science Diagnosis of Inherited Disorders DNA profiling is used to diagnose inherited disorders such as cystic fibrosis, haemophilia and sickle cell anaemia in new-born and unborn children. Early detection of such disorders helps medical staff and parents to prepare themselves for proper treatment of the child. Also, genetic counsellors can help couples who would like to have children, understand the risk of having an affected child. 12 UNDERSTANDING LIFE SCIENCES
DNA- THE CODE OF LIFE Developing Cures for Inherited Disorders DNA profiling allows researchers to look for patterns in large groups of people with and without the disorder. This work is a necessary first step in designing an eventual genetic cure for these disorders. Biological Evidence Police laboratories throughout the world are now using DNA profiles from biological evidence left at the scenes of crimes, to track down criminals. If a DNA profile obtained from biological evidence such as blood, semen stains, hair, or items of clothing matches that obtained from a suspect, then we can safely say that the evidence came from the suspect. This is called forensic science. Identification of Relatives DNA profiles are also useful in establishing relationships amongst individuals. For example, it can be used to: • Establish whether a particular person is the father of a child or not • Trace siblings (brothers and sisters) who have been separated at birth • Identify people who have died and where their bodies cannot be recognised Some debates around DNA profiling DNA profiling is generally accepted as being extremely reliable. However, DNA testing is sometimes controversial because of the following reasons: Fig. 1.12 Studying a DNA profile • Since only a small piece of DNA is analysed, a DNA profile may not be unique to an individual. • DNA profiling performed in private laboratories may not follow uniform testing standards and quality controls. • Since human beings must interpret the test, human error could lead to false results. • DNA profiling is expensive; suspects who are unable to provide their own DNA experts may not be able to adequately defend themselves against charges based on DNA evidence. • DNA analysis might reveal personal information such as the presence of HIV/AIDS and this could be used against the person because of prejudice against persons with the disease. Type the following link into your internet browser for an interesting interactive exercise on DNA profiling as used in forensic science. http://www.biotechnologyonline.gov.au/popups/int_dnaprofiling.html CASE STUDY – DNA profiling Activity 1.6 Classwork/Homework A man was stabbed with a knife. The victim managed to scratch the attacker before he ran away. The skin tissue found underneath the victim’s fingernails was analysed for DNA. This is shown as “DNA from crime scene” in the DNA images shown on the next page. DNA from seven suspects was also analysed. These are shown as A, B, C, D, E, F and G. Which of the suspects was the attacker? How do you know? Grade 12 - CAPS 13
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL DNA from crime scene A B C D E F G DNA from suspects Protein Synthesis Introduction • Amino acids are the basic building blocks or monomers that make up proteins. • When amino acids combine, water is released and the process is called dehydration synthesis. • When two amino acids combine, the product formed is a dipeptide. When three or more amino acids combine, a polypeptide is formed (‘di’ means two, and ‘poly’ means many). Proteins are really long chains of polypeptides. NEW WORDS to check in the glossary Amino acid Protein Dipeptide Polypeptide Dehydration synthesis Fig. 1.13 Dipeptide and polypeptide formation • There are just twenty different amino acids from which all proteins are made. • Some of these amino acids are used more than once so that typical proteins form long chains of 300 or more amino acids. • The sequence in which the amino acids are going to combine is determined by the sequence of the nitrogenous bases in DNA. • The sequence in which the amino acids are attached to each other determines which protein is going to be formed. • In other words, the sequence of bases in the DNA determines which protein is going to be formed. 14 UNDERSTANDING LIFE SCIENCES
DNA- THE CODE OF LIFE The Process of Protein Synthesis Protein synthesis takes place in three stages as follows: • Transcription - formation of messenger RNA (mRNA) NEW WORDS o DNA double helix unwinds to check in the glossary o Weak hydrogen bonds of DNA break o forming two single strands of DNA Nucleus o One strand acts as a template Nuclear pore o to form a complementary strand which is mRNA Transcription Translation o using free RNA nucleotides from the nucleoplasm Codon o This process is called transcription Anticodon o Three adjacent bases on mRNA make up a codon mRNA o which codes for an amino acid tRNA Ribosome • Movement of mRNA out of the nucleus o mRNA moves out of the nucleus o through the nuclear pore o into the cytoplasm o where it attaches to the ribosome • Translation – using information from mRNA to form a protein o According to the codons of mRNA o tRNA molecules with matching/complementary anticodons o bring the required amino acids to the ribosome o The amino acids link together by a peptide bond o to form the required protein o This process is called translation TRANSCRIPTION TRANSLATION Fig. 1.14 Events in protein synthesis Grade 12 - CAPS 15
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL The Genetic Code DID YOU KNOW? • The sequence of nitrogenous bases on DNA determines the sequence of bases on mRNA. • Normally DNA forms • The sequence of bases on mRNA determines the order in which the tRNAs are mRNA. The process is called transcription. going to be attached to mRNA. • The sequence of tRNAs determine the order in which the amino acids are going • When the HI Virus attacks to combine. its host cell, the RNA of • The sequence in which the amino acids combine determines which protein is the virus forms DNA by a process called reverse going to be formed. transcription. • We therefore say that DNA carries the genetic code to determine which protein is going to be formed. • This is why the HI Virus is called a retro-virus. Protein Synthesis Activity 1.7 1. Give the correct biological term for each of the following: Classwork/Homework 1.1 Portion of DNA which carries the genetic code for the formation of a particular protein by specifying its amino acid sequence 1.2 The triplet of three consecutive bases on mRNA 1.3 The inorganic substance that is removed when amino acids combine during dehydration synthesis 1.4 The site of protein synthesis 1.5 The triplet of bases on tRNA 1.6 Special name given to viruses like HIV which make DNA from RNA 1.7 That part of protein synthesis from the time amino acids are arranged in a particular sequence to the time dehydration synthesis takes place (7) 2. Study the diagram below which shows the process of protein synthesis and answer the following questions. D A F B C E amino acids 16 UNDERSTANDING LIFE SCIENCES
DNA- THE CODE OF LIFE 2.1 Provide labels for structures A, B and D respectively. (3) 2.2 State ONE function of molecule D. (1) 2.3 Which stage of protein synthesis takes place at F? (1) 2.4 Identify organelle C. (1) 2.5 Name and describe the stage of protein synthesis that takes place at organelle C. (7) 2.6 Write down the codon of anticodon E from top to bottom. (1) 3. The table below shows the DNA base triplets that code for different amino acids. Base triplet in Amino acid DNA template GAA Leu (leucine) GTA His (histidine) TTT Lys (lysine) GGG Pro (proline) CGA Ala (alanine) ACC Trp (tryptophan) AAA Phe (phenylalanine) CCT Gly (glycine) The following is a part of a sequence of amino acids that forms a particular protein molecule: Ala His Trp Leu Lys 3.1 Name the process by which mRNA is formed from a DNA template. (1) 3.2 How many mRNA codons would be involved in forming the portion of protein shown above? (1) 3.3 Write down the sequence of the first THREE mRNA codons (from left to right) for this portion of the protein. (3) 4. The first 7 triplets of nitrogenous bases that form part of the gene coding for one chain of the haemoglobin protein that makes up red blood corpuscles in humans is shown below. DNA CAC GTG GAC TGA GGA CTC CTC TEMPLATE BASE TRIPLET 1 2 3 4 5 6 7 NUMBER 4.1 How many of the following are coded for in the DNA template sequence above: (a) Nitrogenous bases (1) (b) Different types of t-RNA molecules that are required to form the polypeptide from this piece of DNA (1) (c) Amino acids (1) Grade 12 - CAPS 17
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL 4.2 Write down the mRNA sequence from triplet number 4 to triplet number 6 for the DNA template above. (3) 4.3 Using the table below, determine the amino acid sequence coded by triplet number 4 to triplet number 6. Anticodons on tRNA Amino acid coded coding for the amino for acid CUC Glutamate GUG Histidine GGA Proline GAC Leucine UGA Threonine CAC Valine (3) th 4.4 If the T in the 6 triplet of bases changed to A in the DNA template above: (a) Write down the new amino acid (using the table th above) that this 6 triplet now codes for (1) (b) State the type of gene mutation that has occurred (1) 4.5 The change of T to A, referred to in QUESTION 4.4, is the mutation that causes sickle cell anaemia. It is characterised by the red blood corpuscles changing shape from biconcave to sickle-shaped with a much smaller surface area than normal red blood corpuscles. Explain how this may possibly affect the person suffering from sickle cell anaemia. (3) [40] 18 UNDERSTANDING LIFE SCIENCES
MEIOSIS l 2 CELL DIVISION - Meiosis Grade 12 - CAPS 19
XY chromosomes (in males). Fig. 2.1 All 22 pairs of autosomes and 1 pair of sex chromosomes in a human male 20 UNDERSTANDING LIFE SCIENCES
MEIOSIS • Since there are really two sets of 23 different kinds of chromosomes in each somatic cell, we say that the cells have a diploid (2n) number of chromosomes, and in humans the diploid or 2n number is 46. • Sex cells or gametes of humans have just one set of 23 different chromosomes, we say that the sex cells or gametes have a haploid (n) number of chromosomes and in humans the haploid number is 23. • Note that the two chromosomes making up each pair of autosomes are identical. One member of each pair is of maternal origin (comes from our mothers) and the other is of paternal origin (comes from our fathers). • A pair of identical chromosomes, one of maternal origin and the other of paternal origin, is called a homologous pair of chromosomes. • Just prior to cell division (after DNA replication), the chromosomes appear double, each being made up of two chromatids being held together by a centromere. Fig 2.2 Chromosomes before replication Meiosis Introduction • Meiosis is the division of one cell into four cells each of which has half the chromosome number as the parent cell. Furthermore, each of the four cells is genetically different from each other. • Meiosis usually occurs during gametogenesis, a process during which gametes are formed. • In plants meiosis occurs in the anther to produce pollen grains and in the ovary to produce the ovule. • In humans meiosis occurs in the testes to produce sperms and in the ovary to produce an ovum. • In some lower organisms, meiosis occurs immediately after fertilization. Fig 2.3 Chromosomes Importance in Maintaining the Chromosome Number after replication • As seen earlier in Table 2.1, each species has a characteristic number of chromosomes that has to be maintained from one generation to the next. • Meiosis allows for diploid cells in the sex organs to form haploid gametes. This NEW WORDS is known as the halving effect. to check in the glossary • When two haploid gametes fuse, they form a diploid zygote. This is known as the doubling effect. Gametogenesis • In this way, the halving effect of meiosis overcomes the doubling effect of Homologous fusion, thus maintaining a constant chromosome number from one generation Chromosome to the next. This can be seen clearly by studying the life cycles of different Chromatid organisms. Centromere Grade 12 - CAPS 21
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Meiosis and Life Cycles Meiosis during Gamete Formation i.e. before Fertilisation Adult Adult Growth in number of male (2n) female (2n) cells (2n) • In most plants and animals (Kingdoms Plantae and Animalia), including humans, meiosis takes place when gametes are formed (i.e. before fertilisation). MEIOSIS • These gametes therefore have half the chromosome MITOSIS number or one set of chromosomes (the haploid number or n) compared to the adult. • The fusion of the gametes results in the diploid Sperm Egg cell (n) cell (n) chromosome number being restored in the zygote which Zygote undergoes mitosis to produce a multicellular adult. (2n) Fig. 2.4 Life cycle of most plants and animals, including humans Meiosis after Fertilisation Filament MITOSIS • In some algae (Kingdom Protista), for example (n) Spirogyra, and in some fungi, for example, Rhizopus the adults are haploid giving rise to haploid gametes, which on fertilisation result in a diploid zygote. MEIOSIS • Meiosis occurs in the zygote or zygospore (i.e. after Female Male fertilisation) to halve the chromosome number so that Gamete (n) gamete (n) the new offspring also have the haploid number of Zygospore (2n) chromosomes. Zygote (2n) Fig.2.5 The life cycle of some algae and fungi The Place of Meiosis in the Moss and the Fern Sporophyte MEIOSIS • Mosses and ferns show an alternation of generations (2n) whereby a haploid gametophyte (gamete producing) generation alternates with a diploid sporophyte Spores (n) (spore producing) generation. MITOSIS • The haploid gametophyte produces haploid gametes Gametophyte (n) by mitosis. • The diploid sporophyte produces haploid spores by Zygote meiosis. (2n) Sperm Egg cell (n) cell (n) • It is the halving effect of of meiosis that allows for such an alternation of generations. Fig.2.6 The life cycle of moss and fern 22 UNDERSTANDING LIFE SCIENCES
MEIOSIS Meiosis - Introduction Activity 2.1 Classwork/Homework 1. Give the correct biological term for each of the following: 1.1 The type of cell division that results in halving of the chromosome number. 1.2 Cell division producing identical cells 1.3 Cell division producing daughter cells that are dissimilar 1.4 The two strands that make up a chromosome 1.5 Process by which a single stranded chromosome becomes double stranded 1.6 Chromosomes that are identical in shape and appearance that code for the same set of characteristics 1.7 Chromosome condition describing the presence of two sets of chromosomes in each cell 1.8 Chromosome condition describing the presence of a single set of chromosomes in each cell 1.9 Process by which gametes are produced by meiosis 1.10 The haploid generation in the life cycle of mosses and ferns 1.11 The diploid generation in the life cycle of mosses and ferns (11) 2. The diagram in Figure 2.7 represents the life cycle of humans. Which ONE of the following combinations of terms correctly matches the numbered boxes? 1 2 3 A mitosis fetilisation meiosis B meiosis mitosis fertilisation C fertilisation meiosis mitosis D mitosis meiosis fertilisation (2) 3. The number of chromosomes in a fertilised human egg cell is … A. the same as in a sperm B. twice the number as in a sperm Fig. 2.7 Life cycle of humans C. twice the number as in a skin cell D. half as many as in an unfertilized egg (2) [15] How Meiosis takes place Phases of Meiosis • Interphase occurs Meiosis is the division of one cell into four cells each of which only has half the before meiosis chromosome number as the parent cell and each of the four cells is genetically different from each other and the parent cell. • The phases of meiosis are: In meiosis, the nucleus undergoes two divisions viz. the first division (Meiosis I) and ° Prophase I & 2 the second division (Meiosis II). Although meiosis is a continuous process, the ° Metaphase I & 2 various events in this process are often divided and described under different ° Anaphase I & 2 phases for convenience (prophase, metaphase, anaphase and telophase). You will ° Telophase I & 2 remember from your knowledge of the cell cycle that DNA replication takes place before meiosis begins during a stage called interphase. • The ‘word’ IPMAT will help you remember the In the drawings that follow, the nucleus is greatly enlarged compared to the rest of names of the phases in the cell so that changes within the nucleus can be clearly shown. order Grade 12 - CAPS 23
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Interphase • In preparation for the first nuclear division, DNA replicates so that the genetic material is doubled in the chromatin network. chromatin • Single stranded chromosomes become double stranded. network (DNA replicates and doubles itself) MEIOSIS 1 Prophase I nuclear membrane • Nuclear membrane begins to disappear. a pair of • Chromatin network unwinds to form distinct chromosomes. homologous • Each chromosome is made up of two identical chromatids chromosomes (because of DNA replication in Interphase I). each with two • The chromosomes come together in homologous pairs i.e. two chromatids identical chromosomes, one of maternal origin and one of paternal origin. a chromosome • Crossing-over takes place between chromatids of homologous with two chromosomes leading to the exchange of genetic material. (We chromatids will explain how crossing-over takes place a little later). • Centrosome splits into two centrioles which start moving to opposite poles. centriole Metaphase 1 spindle thread chromosomes along the • Spindle threads form between the centrioles. equator in • The chromosomes become arranged along the equator in homologous homologous pairs, attached to spindle threads. pairs 24 UNDERSTANDING LIFE SCIENCES
MEIOSIS Anaphase 1 centriole • Spindle threads contract. spindle thread • The two chromosomes of each homologous pair (each with two chromatids) are pulled to the opposite poles. whole chromosome pulled to one pole the other whole chromosome goes to the other pole Telophase 1 • Two groups of chromosomes appear forming a nucleus at each pole. • The cytoplasm divides to form two new cells. • Thus we have a nucleus in each cell within which there is two cells half the number of chromosomes as the original. formed with • The two new cells (A and B) are also genetically different genetically because of crossing-over. different nuclei nucleus MEIOSIS II Cell A centriole Prophase 2 spindle thread two • In cell A (and the same applies to cell B). chromatids nucleolus disappearing • Each chromosome is visible as two chromatids. centromere • Centrosome splits into centrioles which move to opposite poles. nuclear • Nuclear membrane begins to disappear. membrane begins to disappear Grade 12 - CAPS 25
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Cell A Metaphase 2 • The chromosomes become arranged along the equator singly single • attached to the spindle threads chromosome arranged along the equator Anaphase 2 Cell A spindle thread contracts • The chromosomes split and the two chromatids making up each chromosome chromatids are • are pulled towards opposite poles pulled towards • when the spindle threads contract. opposite poles when the Each chromatid is really a single-stranded chromosome since centromere splits DNA replication took place in Interphase 1. Cell A nucleolus re- Telophase 2 appears nuclear membrane • Two groups of chromosomes occur - one at each end of re-appears the cell forming two new nuclei. • The cytoplasm of cell A divides to form two new cells. two genetically • In the same way cell B also divides to form two new cells. different nuclei with • In total there are now four new cells. half of the original • The nucleus in each of these four cells has half the chromosome number number of chromosomes we originally started with in the first division. • The four cells are genetically different because of crossing-over. 26 UNDERSTANDING LIFE SCIENCES
MEIOSIS Note that: Meiosis I and Meiosis II • Each of the two cells formed during the first division of meiosis undergoes the second division, which is similar to mitosis. • In meiosis I the • In meiosis II, each phase name ends with a “2” to indicate that we are chromosomes are double describing the second division. stranded in all phases • Note, however, that there is no Interphase 2 in meiosis II because DNA • In meiosis II the chromosomes are single replication already took place before meiosis I. The chromosomes are still double stranded at the start of meiosis II. stranded in all phases • The names of the phases of meiosis, in order, can be learnt using the ‘word’ IPMAT as follows: LETTER NAME OF PHASE EVENT I Interphase I for inter/in between: a part of the cycle of the cell that occurs between two cell divisions. P Prophase P for preparation: the chromosomes prepare for meiosis by untangling and becoming clearly visible. Crossing over also takes place. M Metaphase M for middle: the chromosomes move to the ‘middle’ /equator. A Anaphase A for apart: the chromosomes/chromatids move apart/move to the poles. T Telophase T for terminal/end: the final phase of meiosis I/meiosis II. Phases of Meiosis Activity 2.2 Classwork/Homework 1. Give the correct biological term for each of the following descriptions. Write down only the correct term next to the relevant question number. 1.1 Phase in meiosis in which crossing-over occurs 1.2 Phase in meiosis in which four cells are formed having half the chromosome complement as the original cell 1.3 Phase in meiosis in which chromatids are pulled apart 1.4 Phase in meiosis in which two cells are formed having half the NEW WORDS chromosome complement as the original to check in the glossary 1.5 Phase in meiosis in which chromosomes line up at the equator in pairs 1.6 Phase during which DNA replication takes place DNA replication 1.7 Phase in meiosis in which chromosomes are arranged singly at the Centrosome equator Centrioles 1.8 Phase in meiosis in which chromosomes are pulled apart Spindle threads (8) 2. Which of the following is TRUE about Anaphase I of meiosis? Chromosome Chromatid A. Chromosomes arranged at equator Crossing-over B. Centromere splits C. Chromosomes are pulled to the poles Interphase Prophase D. Chromatids of a chromosome separate and move to the poles Metaphase (2) Anaphase Telophase [10] Grade 12 - CAPS 27
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL The Process of Crossing-over Fig. 2.8 A homologous pair of Fig. 2.9 Chromatids intertwining Fig, 2.10 A pair of homologous chromosomes before crossing-over chromosomes after crossing-over ° It takes place in Prophase 1 of ° One chromatid of each ° The chromosomes separate in meiosis. chromosome overlaps with a such a way that each has one ° Homologous chromosomes chromatid of its homologue (or original chromatid and one come to lie close together. homologous partner). chromatid with some genetic ° Homologous chromosomes ° The points of crossing-over are material from its homologous (consisting of 4 chromatids in called chiasmata (singular partner. total) involved in crossing over chiasma). is referred to as a bivalent. • Crossing-over results in an exchange of genetic material so that each chromosome has genetic material from both parents. • The cells (usually gametes) produced will therefore be different from each other. • This, therefore results in variation in the offspring. Differences between Meiosis I and Meiosis II Table 2.2. Differences between Meiosis I and Meiosis II Meiosis I Meiosis II NEW WORDS to check in the glossary Chromosomes double stranded in all Chromosomes single stranded in all phases phases Crossing-over Crossing-over takes place in No crossing-over Bivalent Prophase 1 Chiasmata Chromosomes arranged along the Chromosomes arranged along the equator in homologous pairs in equator singly in Metaphase 2 Metaphase 1 Whole chromosomes are pulled to Chromatids are pulled to opposite poles opposite poles in Anaphase 1 in Anaphase 2 Chromosome number is halved during Chromosome number does not change meiosis I during meiosis II Results in two cells Results in four cells 28 UNDERSTANDING LIFE SCIENCES
MEIOSIS Why the Cells Produced by Meiosis are Different • The cells (usually gametes) produced during meiosis are always different from each other for two reasons: ° Firstly, crossing-over during the Prophase 1 results in the exchange of Variation due to genetic material. meiosis ° Secondly, during Metaphase 1, the chromosomes arrange themselves along • Crossing over the equator of the cell randomly. This means that all the chromosomes of • Random arrangement maternal origin are not necessarily on one side with all those of paternal of chromosomes in origin on the other. So when the chromosomes separate during Anaphase 1, metaphase I & II there is no definite pattern in the way the chromosomes move to the Variation due to other opposite poles. In Metaphase II also, the chromatids of a single chromosome factors may occupy two possible positions. • Mutations • If all the sperm cells produced by the male parent are different from each • Random Mating other and all the egg cells produced by the female parent are also different • Random fertilisation from each other, then quite obviously, the offspring produced by the same parents will also be different (except in the case of identical twins). The Importance of Meiosis • Leads to the formation of haploid gametes in some organisms and haploid spores in other organisms • The halving effect of meiosis neutralises the doubling effect of fertilisation, thus maintaining a constant chromosome number from one generation to the next. • Crossing over introduces genetic variation. Genetic variation results in offspring that are better adapted to a particular environment ensuring a better chance of survival. Differences between Mitosis and Meiosis In Grade 10, we studied the process of mitosis and now you studied meiosis. Study the table below for a better understanding of the differences between the two processes. Table 2.3. Differences between mitosis and meiosis Mitosis Meiosis Usually occurs to form more somatic cells Usually occurs to form sex cells/gametes One nuclear division Two nuclear divisions Two cells formed have the same number Four cells formed have half the of chromosomes as the parent cell number of chromosomes as the parent cell Two cells formed are genetically Four cells formed are genetically identical to each other and to the parent different from each other and from the parent During prophase the chromosomes are During prophase I the chromosomes not in pairs come together in homologous pairs Crossing-over takes place during first No crossing-over prophase I During metaphase the chromosome splits During metaphase I, whole and chromatids are pulled towards chromosomes are pulled towards opposite poles opposite poles. The chromosome does not split Grade 12 - CAPS 29
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Similarities between Mitosis and Meiosis In both mitosis and meiosis: • DNA replication takes place • The nucleus divides • The cytoplasm divides • New cells are formed Activity 2.3 The Process of Meiosis Classwork/Homework 1. Study the diagrams alongside showing two stages of meiosis. 1.1 Name the phase of meiosis represented by diagrams I and II. (2) 1.2 State ONE visible reason in diagram I which indicates that meiosis is taking place. (2) 1.3 How many chromosomes would be present in each daughter cell at the end of meiosis? (1) 1.4 The chromosomes labelled A are not identical. Describe the process that leads to them being different. (5) 1.5 Name the phase of meiosis that occurs after the phase represented by: (a) Diagram I (b) Diagram II (2) 1.6 State ONE difference between the events that occur in the two phases mentioned in 1.5. (2) (14) DIAGRAM I 2. Tabulate FOUR differences between the processes of mitosis and meiosis. (8) 3. Tabulate FOUR differences between meiosis I and meiosis II. (8) 4. The diagram below represents a process taking place during meiosis. C D A B DIAGRAM II Diagram representing a process taking place during meiosis 4.1 Provide labels for parts A, B, C and D. (4) 4.2 Name the process in meiosis that is illustrated in the diagram above. (1) 4.3 State ONE importance of the process named in Question 4.2. (2) 4.4 Draw a diagram of the structure labelled A to show its appearance immediately after the process named in Question 4.2. (2) (9) [39] 30 UNDERSTANDING LIFE SCIENCES
MEIOSIS Practical Investigation of Meiosis Activity 2.4 Practical Work What you need • The micrographs shown on the next page What you should do Examine the micrographs which show the various stages of meiosis. Note that the micrographs are not in the correct sequence in which they occur when the process of meiosis takes place. Answer the following questions: 1. State TWO places each where this process will take place in: a. Plants (2) b. Animals (2) 2. Write down the numbers 2.1 to 2.8 and next to each, the answer that will best complete the table below. Micrograph Name of Phase Reason for Identification C 2.1 2.2 D 2.3 2.4 G 2.5 2.6 H 2.7 2.8 (12) 3. State ONE reason why you would identify: 3.1 Micrograph A as Telophase 3.2 Micrograph B as Metaphase 3.3 Micrograph E as Prophase 2 (3) 4. List TWO reasons why meiosis is regarded as being very important, (2) 5. If the original cell undergoing meiosis had 14 chromosomes, how many chromosomes will be present in each cell in micrograph H? (1) 6. Explain your answer to question 5 above. (1) 7. Make a fully labelled drawing of the cell shown in micrograph F if the cell undergoing meiosis had 6 chromosomes at the beginning and this stage was in its first division. (7) [30] Grade 12 - CAPS 31
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL A B C D E F G H Fig. 2.11 Micrographs showing various phases of meiosis 32 UNDERSTANDING LIFE SCIENCES
MEIOSIS Consequences of Abnormal Meiosis Down syndrome or Down’s syndrome? Non-disjunction of chromosomes Down syndrome is named after Dr. John Langdon Down who first described • Sometimes, the following mistakes may occur during the process of meiosis: the characteristic ° During Anaphase 1, one or more homologous pairs of chromosomes may not features of Trisomy-21. separate. The term ‘Down ° During Anaphase 2, the sister chromatids of one or more chromosomes may syndrome’ IS NOW used as opposed to ‘Down's not separate. syndrome’ because Dr. Down did not have Down • This is referred to as non-disjunction. syndrome, and he did • As a result of non-disjunction, gametes forming from meiosis may have one extra not own Down syndrome. chromosome, one less chromosome, no chromosomes or an extra set of chromosomes. • Such an abnormal gamete may fuse with a normal gamete or another abnormal gamete, leading to different genetic disorders. • Non-disjunction may lead to two general conditions; aneuploidy or polyploidy. Aneuploidy • In aneuploidy, one gamete receives two copies of the same chromosome, while the other gamete receives no copy. • If fertilisation occurs with either of these gametes by a normal gamete, the zygote will have an abnormal number of chromosomes i.e. either one less or one extra chromosome. • If the zygote has one extra chromosome, we say it is trisomic for that chromosome. • If the zygote has one chromosome short, we say it is monosomic for that chromosome. • Down syndrome is an example of the result of aneuploidy. This has been dealt with in more detail below. Fig.2.12. An 8 year old boy with Down syndrome Down syndrome • It is the result of an extra chromosome number 21. Since the cells are trisomic for chromosome 21, Down syndrome is also called trisomy 21. • In meiosis 1, the chromosome pair 21 may not separate or, • in meiosis II, the chromatids of chromosome 21 may not separate. • Some gametes will therefore have an extra copy (2 copies) of chromosome number 21 • If a gamete with 2 copies of chromosome 21 fuses with a normal gamete with • 1 copy of chromosome 21, • the resulting zygote will have 3 copies of chromosome number 21 (47 chromosomes instead of 46) resulting in Down syndrome. • Individuals with Down syndrome are characterised by mental retardation, hearing loss, heart defects, decreased muscle tone, upwardly slanting eyes, a small mouth and nose, abnormal ear shape and a depressed nasal bridge. • There is no cure for Down syndrome. Only the symptoms are treated. • To detect the occurrence of Down syndrome in unborn babies, foetal cells are removed from the uterus of the pregnant mother by amniocentesis and analysed. • The karyotype resulting from such an analysis is then examined to determine if Fig.2.13. Karyotype of an there is an abnormal number of chromosomes individual with Down syndrome Grade 12 - CAPS 33
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL Polyploidy • Most animals and plants contain cells that are diploid i.e. each cell has two complete sets of chromosomes. Different types of Ploidy • When there is non-disjunction of all the chromosomes during meiosis, a gamete may end up with no chromosomes or an extra set of chromosomes (gamete will • Haploid – contains 1 set of chromosomes be diploid instead of haploid). • Diploid – contains 2 sets • If an abnormal, diploid gamete fuses with a normal haploid gamete, the zygote of chromosomes will be triploid (3n). • Triploid – contains 3 sets • If an abnormal diploid gamete fuses with another abnormal diploid gamete, the of chromosomes zygote will be tetraploid (4n). • Tetraploid – contains 4 • If a plant or animal has more than two complete sets of chromosomes, we say it sets of chromosomes is polyploid, and the condition is known as polyploidy. • Aneuploid – contains one • Polyploidy is very common in plants, especially in angiosperms. Polyploidy is extra or one less chromosome rare in animals. It is found in some insects, fishes, amphibians, and reptiles. • Polyploid – contains more Until recently, no polyploid mammal was known. However, in 1999 a polyploid than two sets of rat (4n) was found in Argentina. chromosomes • Scientists use polyploidy as one of the explanations for the production of new species. Advantages of Polyploidy in Agriculture • Polyploid plants not only have larger cells but the plants themselves are often larger. This has led to the deliberate creation of polyploid varieties of such plants as watermelons, marigolds, and snapdragons. • Polyploid individuals can also be created in plant breeding laboratories by treating dividing cells with colchicine. This drug prevents the formation of a spindle during mitosis. As a result, the duplicated chromosomes fail to separate in mitosis. In this way, scientists have produced plants with larger flowers, fruits and storage organs. Fig. 2.14 Polyploid rat Fig. 2.16 Larger flower of NEW WORDS Fig. 2.15 Larger fruit of polyploid plant on the right to check in the glossary polyploid strawberry plant on Non-disjunction the right Aneuploidy Monosomic Trisomic Down syndrome Amniocentesis Karyotype Polyploidy Fig. 2.17 Larger leaves of polyploid plant on the right 34 UNDERSTANDING LIFE SCIENCES
MEIOSIS Meiosis and Abnormal Meiosis Activity 2.5 1. The diagram alongside represents an animal cell in a phase of meiosis. Classwork/Homework 1.1 State whether the phase of meiosis shown above is meiosis I or meiosis II. (1) 1.2 Give ONE visible reason for your answer in Question 1.1. (1) 1.3 Identify the parts labelled A and B. (2) 1.4 How many chromosomes: 1.4.1 Were present in the parent cell before meiosis began? (1) 1.4.2 Will be present in each cell at the end of meiosis? (1) 1.5 State ONE place in a human female where meiosis would take place. (1) 1.6 Could the cell represented in the diagram be that of a human? (1) A 1.7 Explain your answer to Question 1.6. (2) 1.8 Give TWO reasons why meiosis is biologically important. (2) 1.9 Give the term for the situation when some of the chromosomes do not separate correctly during the phase shown in the diagram. (1) (13) 2. State the significance of meiosis in the life cycle of: 2.1 A human 2.2 The alga Spirogyra or the fungus Rhizopus 2.3 The moss or the fern 3x2 (6) B 3. The diagrams below represent cells from the same organism. One diagram represents a stage in mitosis while the other shows a stage in meiosis. Diagram I Diagram II 3.1 Are these diagrams representative of a plant or an animal cell? (1) 3.2 Give ONE observable reasons for your answer. (1) 3.3 Provide labels for the parts indicated by letters A, B. C. F, G, I, L and M. (8) 3.4 Which diagram (I or II) represents mitosis? Give a reason for your answer. (2) 3.5 Which diagram (I or II) represents meiosis? Give a reason for your answer. (2) 3.6 Explain the significance of the nuclear division represented by: 3.6.1 Diagram I (2) 3.6.2 Diagram II (2) (18) Grade 12 - CAPS 35
LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL 4. The Klinefelter syndrome is a genetic disorder in which males usually inherit one extra X chromosomes - their genotype is usually XXY. In severe cases, they have relatively high-pitched voices, feminine body contours as well as breast enlargement, and comparatively little facial and body hair. They are usually sterile, and their testes and prostate gland are small. Explain how abnormal meiosis during sperm formation can lead to the Klinefelter syndrome. (5) 5. The table below shows how the risk of having a child with Down syndrome changes with the age of the mother. Age of Risk of having a child Mother with Down syndrome 20 1 in 1,500 25 1 in 1,300 30 1 in 900 35 1 in 350 40 1 in 100 45 1 in 30 5.1 State the relationship between the age of the mother and the risk of having a child with Down syndrome. (2) 5.2 How many times greater is the risk of having a child with Down syndrome when the mother is 40 compared to when she is 30 years old? (2) 5.3 Why is Down syndrome also known as trisomy-21? (2) (6) [48] 36 UNDERSTANDING LIFE SCIENCES
REPRODUCTION IN VERTEBRATES 3 REPRODUCTION IN VERTEBRATES Diversity of Reproductive Strategies Grade 12 - CAPS 37
LIFE PROCESSES IN PLANTS AND ANIMALS Diversity of Reproductive Strategies Introduction Different groups in the animal kingdom have different strategies to maximize reproductive success in different environments. Let us now look at a few of the strategies used by vertebrates. External and Internal Fertilisation External Fertilisation During external fertilisation, the sperm cell fertilises the egg cell outside the body of the female. During external fertilisation, it is not necessary for the two parents to make physical contact. Water is always required for external fertilisation for two reasons. Firstly, it prevents the eggs from drying out. Secondly, water must be present to allow the sperms to swim towards the eggs. Frogs, starfish and trout are examples of animals that undergo external fertilisation. Fig. 3.1 Male and female The disadvantage of external fertilisation is that a large amount of sperm may not frog swim together to increase reach the egg cells. To compensate for this, organisms with external fertilisation chances of sperms and eggs meeting after release (external produce a large number of sperm to ensure that at least some do reach the egg cells. fertilisation) Internal Fertilisation During internal fertilisation, the male deposits its sperm cells inside the NEW WORDS reproductive organs of the female and fertilisation occurs inside the female’s to check in the glossary reproductive organs. Internal fertilisation is an adaptation that allows terrestrial animals to reproduce in a dry environment. Internal fertilisation External fertilisation Birds and mammals are examples of animals that undergo internal fertilisation. Ovipary Ovovivipary Because internal fertilisation is more certain than external fertilisation, organisms Vivipary with internal fertilisation produce a smaller quantity of sperm. Predators Invertebrates [Note that the following section deals with reproductive strategies amongst vertebrates. For completeness sake, however, some of the examples given in the text that follows are, in fact, invertebrates]. Ovipary, Ovovivipary and Vivipary Ovipary This refers to a method of reproduction in which eggs are laid and development of these eggs takes place outside the mother's body. These eggs may have been fertilised internally before being laid or they may be fertilised after thay are laid. Each egg eventually hatches into a young animal. Most invertebrates (e.g. snails) and many vertebrates (e.g. frogs) reproduce in this way. Fig. 3.2 An oviparous reptile The disadvantage of ovipary is that the eggs may be preyed upon by predators. The chances of this happening are reduced if the eggs are protected by the parents. 38 UNDERSTANDING LIFE SCIENCES
Related Publications
List of Life Sciences essays for Grade 10, 11 and 12 (South Africa)
Life Sciences essays for Grade 1 0, 11 and 12 (South Africa):
Table of Contents
List of Life Sciences essays for Grade 10, 11 and 12
NEPHRON ESSAY
Essay Question: Write a short essay explaining the homeostatic functioning of the nephron if a person is suffering from dehydration
Life Sciences essays for Grade 10, 11 and 12
When the water content of the body drops below normal, the following happens
- the osmotic potential of the blood increases √
- which stimulates the osmoreceptors in the hypothalamus √
- which produces ADH
- to transmit impulses to the pituitary gland (hypophysis) √
- to release more ADH √ in to the blood
- ADH is transported by bloodstream to the kidney √ where this hormone increases the permeability √ of the walls of the distal convoluted tubule and collecting duct √
- more water √ is re-absorbed from the filtrate √
- and small amount of concentrated urine √ is excreted
- the adrenal gland √ secrete aldosterone √ which cause sodium ions √ to be actively √ pumped out of the filtrate √ in the ascending limb of loop of Henle √ in to the tissue fluid of the kidney medulla √
- this creates a low water potential √ and water moves by passive osmosis √ from the collecting tubule √ in to the tissue fluid of the medulla √ from where it is absorbed in to the blood capillaries √
ECOUTOURISM ESSAY
Essay Question: Write a mini essay on ecotourism in South Africa using the following guideline
- Brief explanation of what ecotourism entails,
- Long term sustainability and Possible threat to Ecotourism
- Ecotourism is mainly inclined to promote environmental awareness and instil asense of appreciation of natural formations and beauty.
- It makes people respect the existence of other living organisms (fauna and flora) that shares the resources of the planet earth
- Its main clients are people who are interested in preserving the environment.
- A potential ecotourist prefers to spend his/her holidays in a natural environment to experience and be part of the environment
- They like to visit and spend time in quiet natural settings such as unspoiled beaches, river mouths, waterfalls, wet lands with lush green forests, gorges,mountains etc.
- Always prefer to use eco-friendly mode of transport to cause less pollution and damage to fauna and flora
- Encourages people to consume naturally grown, fresh produce from the area
- Greater emphasis is placed on the well-being of local people and constantly look for ways and means to contribute towards the local economy
- Eco-friendly accommodation is provided for visitors to minimise the possible human impact on the surrounding area
- Renewable energy is utilised wherever possible
Long term sustainability
Educate the local population about the importance of conserving the natural resources.
- The involvement of the local community should be prioritised.•
- Active participation generates income for local communities. e.g. selling composts, organic food products.
- Job creation alleviates poverty. e.g. tour guides, security personnel, and creating opportunities to sell and exhibit art work.
- Ownership of the concept leads to proper caring and protection of the fauna and flora. e.g. prevention of poaching, illegal smuggling of exotic animals and plants, discourages over exploitation of natural resources.
- Part of the income generated can be utilised for conservation and rehabilitation projects.
- Cementing strong partnership with the private and public sector could provide more management and financial support
Possible threats to ecotourism
- Poaching / illegal hunting
- Crime and violence against tourists
- Illegal trade of exotic plants and animals
- Illegal occupation of land and the establishment of squatter camps
- Natural disasters. e.g. wild fires, droughts, floods, etc.
- Deforestation• Extension of farming lands
- Illegal dumping of waste
- Illegal developments e.g. hotels and golf estates, airports, stadia. etc.
- Building of dams in an ecologically sensitive area
- Miningo Exploitation of tourists
Free Grade 10 Online Lessons, Classes, Past Exams Papers and Notes
- Accounting Grade 10 past papers, online lessons, and revision notes
- Economics Grade 10 past papers, online lessons, and revision notes
- Mathematics Grade 10 past papers, online lessons, and revision notes
- Technical Mathematics Grade 10 past papers, online lessons, and revision notes
- Physical Science Grade 10 past papers, online lessons, and revision notes
- Life Sciences Grade 10 past papers, online lessons, and revision notes
- Technical Sciences Grade 10 past papers, online lessons, and revision notes
- Mathematics Literacy Grade 10 past papers, online lessons, and revision notes
- Biology Grade 10 past papers, online lessons, and revision notes
- Life Orientation Grade 10 past papers, online lessons, and revision notes
- Religion Studies Grade 10 past papers, online lessons, and revision notes
- Business Studies Grade 10 past papers, online lessons, and revision notes
- Consumer Studies Grade 10 past papers, online lessons, and revision notes
- Tshivenda Home Language Grade 10 past papers, online lessons, and revision notes
- IsiXhosa Home Language Grade 10 past papers, online lessons, and revision notes
- IsiZulu Home Language Grade 10 past papers, online lessons, and revision notes
- Sepedi Home Language Grade 10 past papers, online lessons, and revision notes
- Sesotho Home Language Grade 12 past papers, online lessons, and revision notes
- Setswana Home Language Grade 10 past papers, online lessons, and revision notes
- Seswati Home Language Grade 10 past papers, online lessons, and revision notes
- Afrikaans Home Language Grade 10 past papers, online lessons, and revision notes
- English Home Language Grade 10 past papers, online lessons, and revision notes
- Xitsonga Home Language Grade 10 past papers, online lessons, and revision notes
- Tourism and Hospitality Studies Grade 10 past papers, online lessons, and revision notes
- Computer Applications Technology Grade 10 past papers, online lessons, and revision notes
- Civil Technology Grade 10 past papers, online lessons, and revision notes
- Electrical Technology Grade 10 past papers, online lessons, and revision notes
- Engineering Graphics and Designs Grade 10 past papers, online lessons, and revision notes
- Information Technology Grade 10 past papers, online lessons, and revision notes
- Mechanical Technology Grade 10 past papers, online lessons, and revision notes
- Agricultural Sciences Grade 10 past papers and revision notes
- Agricultural Technology Grade 10 past papers, online lessons, and revision notes
- Agricultural Management Practices Grade 10 past papers, online lessons, and revision notes
- Dance Studies Grade 10 past papers, online lessons, and revision notes
- Design Grade 10 past papers, online lessons, and revision notes
- Dramatic Arts Grade 10 past papers, online lessons, and revision notes
- Music Visual Arts Grade 10 past papers, online lessons, and revision notes
- Geography Grade 10 past papers, online lessons, and revision notes
Did You See These?
- Latest Life Sciences Grade 12 2022 Term 3 September Exam Question Papers with Memorandum
- Life Sciences Grade 12 November 2021 Examination Final Question Papers with Memos to revise with
- Why is DNA replication important? CAPS (South Africa)
- Differences between DNA and RNA: South African Curriculum CAPS (South Africa)
1 thought on “List of Life Sciences essays for Grade 10, 11 and 12 (South Africa)”
I will appreciate
Leave a Comment Cancel reply
You must enable JavaScript in order to use this site.
By the end of the course, the learner should be able to: 1. communicate biological information in a precise, clear and logical manner 2. develop an understanding of interrelationships between plants and animals and between humans and their environment 3. apply the knowledge gained to improve and maintain the health of the individual, family and the community 4. relate and apply relevant ...
On this page you will find Life Sciences Grade 12 Essays and Topics Guide for Term 1, Term 2, Term 3, and Term 4. View all #Life-Sciences-Grade12 Study Resources. We have compiled great resources for Life Sciences Grade 12 students in one place. Find all Question Papers, Notes, Previous Tests, Annual Teaching Plans, and CAPS Documents.
Welcome to the GRADE 12 LIFE SCIENCES Past Exam Paper Page. Here, you'll find a comprehensive range of grade 12 past year exam papers and memos, ranging from 2024 to as far back as 2009. Our collection will help you prepare for your upcoming exams by familiarizing yourself with the exam format and identifying areas for improvement.
grade 12 life sciences grade12 essay questions 2018 life sciences grade 12 compilation of posdible essays compiled by :tlhako josias year : 2018 facebook page :lifescience/grade12/ whatsapp no : 062-634-use this document as your guideline on essay questions life science made easy for all grade 12
STUDY NOTES. LESSON PLANS 2021. Life Sciences Essay (Gr 10-12) Life Sc. Revision (Gr 12) Life Science Resource. Click on button below to download Zip File. (D.O.E papers from 2012 to 2017 supplementary and Final Exam) Exam papers grade 12 Life Science and study notes.
hormone essay (paper 1) 16 process of pregnancy and developmentof 17 zygote (paper 1) genetic variation (paper 2) 18 mutations and genetic disorders leading 19. compiled by sbumkansi and solly makhongla |life science grade 12. stem cells essay (paper2) 20 hearing, human eye ,balance and 21 equilibrium (paper 1) hearing and reflex action (paper ...
Exam papers and study material for grade 10,11 and 12
January 27, 2024 by Modern Classroom. On this page you will be able to download Life Sciences Grade 12 Paper 1 P1 and Paper 2 P2 Term 3 September 2022 trial exam question papers with the memos. There is no better way to do your revisions and exam preparations than to use the previous papers. Modern Classroom aims to provide the ….
Grade-12-Life-Sciences-Exploring-Essays - Free download as PDF File (.pdf), Text File (.txt) or read online for free. This document provides a table of contents and summaries for various life science topics that could be included in essays for Grade 12. The topics covered include water quality, eutrophication, threats to biodiversity, DNA replication, meiosis, reproduction in vertebrates, the ...
GRADE - 12 LIFE SCIENCES MARCH 2020 Downloaded from Stanmorephysics.com. 2 ... o Writing essays in Life Sciences NB: The document comprises of paper 1 and paper 2 topics Downloaded from Stanmorephysics.com. 3 ... 12 3.11 DEVELOPMENT OF FOETUS
LIFE SCIENCES STUDY GUIDES AND NOTES GRADE 12. Dear Grade 12 learner. This Mind the Gap study guide helps you to prepare for the end-of-year CAPS Life Sciences Grade 12 exam. The study guide does NOT cover the entire CAPS curriculum, but it does focus on core content of each knowledge area and points out where you can earn easy marks.
Life Sciences . Grade 12 . Life Sciences telematics resource Grade 12 2021 . 2 . FOREWORD . Life Sciences is the scientific study of living things from molecular level to their interactions with one another and their environments. To be successful in the subject you need to
This guides the philosophy underlying the teaching and assessment of the subject in Grade 12. Provide clarity on the depth and scope of the content to be assessed in the Grade 12 National Senior Certificate (NSC) Examination in Life Sciences. Assist teachers to adequately prepare learners for the examinations.
Life Science Paper 1 Essays Grade 12 P. L. Zulu Life Sciences Key Points P. L. Zulu,2020 Life Sciences, Grade 12 Gonasagaren S. Pillay,Prithum Preethlall,Bridget Farham,Annemarie Gebhardt,2014-06-26 Why I Write George Orwell,2021-01-01 George Orwell set out 'to make political writing into an art', and to a wide extent this aim shaped the ...
LIFE Sciences Essays Grade 10-12. essays that are most likely to come. Subject. Life Sciences. 999+ Documents. Students shared 1986 documents in this course. Degree FET. School Germiston High School. Academic year: 2020/2021. Uploaded by: Anonymous Student.
Grade 12 Life Science Essays. Package deal • 21 items • 2019. Grade 12 life science essay which are easy to read and are in bullet form. (0) R150,00. 2x sold. + learn more.
This document contains essays and study materials for Life Sciences for grades 10-12 in South Africa. It includes sample essays on topics like meiosis, genetic variation, speciation, evolution, homeostasis, and more. It also provides study tips and time management advice for the grade 11 end of year exam. The document is intended to help students prepare for the National Senior Certificate ...
Life Sciences Essays Document Grade 10-12 - Free download as PDF File (.pdf), Text File (.txt) or read online for free. The document provides a clear structure on how to write the essays. This document has been created from information available from the internet and it is not meant for any business purposes (FREE SUPPLY) but to help South African Life sciences Learners by gathering all the ...
ABOUT THE BOOK ABOUT THE BOOK This book is based on the National Curriculum and Policy Statement (CAPS) for the subject Life Sciences. CAPS was introduced at Grade 10 level in 2012, Grade 11 in 2013, and implemented in Grade 12 in 2014. The Grade 12 book is part of a series for Life Sciences.
Table of Contents. List of Life Sciences essays for Grade 10, 11 and 12. Essay Question: Write a short essay explaining the homeostatic functioning of the nephron if a person is suffering from dehydration. Essay Question: Write a mini essay on ecotourism in South Africa using the following guideline. Ecotourism.
Institution. 12. A comprehensive guide to writing an IEB Life Sciences Essay. Includes the ideal planning format, general structural notes, tips and the official IEB memorandum. Applicable to all IEB Grade 12s. Makes reference to 3 videos, all linked in the notes. Credit to Hanette Bouwer.
Grade 12 life science essay which are easy to read and are in bullet form. [Show more] 21 items . Hearing and reflex action Essay (0) R80. 1x sold. Easy to read summarized essays for Grade 12 Learners studying Life Sciences.
Summaries are in bullet form for easy understanding .
OpenStax offers free college textbooks for all types of students, making education accessible & affordable for everyone. Browse our list of available subjects!
grade 12. life sciences grade12 essay questions 2018 life sciences grade 12 compilation of posdible essays compiled by :tlhako josias year : 2018 facebook page :lifescience/grade12/ whatsapp no : 062-634-use this document as your guideline on essay questions life science made easy for all. grade 12. table of content topic name page number water ...
- business plan
- course work
- research paper
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
IMAGES
VIDEO
COMMENTS
Preowned sailboats for sale under 25 feet preowned sailboats for sale by owner.
Outer Banks of North Carolina, North Carolina. Asking $19,500. 47' Beneteau Oceanis 46. Daytona Beach, Florida. Asking $185,000. 38' sabre 38 MKI. Tarpon Springs, Florida. Asking $75,000. 39' CE Ryder Southern Cross 39 - for Sale by Auction.
Find Catalina 25 boats for sale in your area & across the world on YachtWorld. Offering the best selection of Catalina boats to choose from.
Catalina 22 Sport. Catalina 22 is a very popular choice for smaller sailboats that can be trailered easily. The Catalina 22 sport is the updated version that has some added features. This sailboat is perfect for the weekend sailing excursion. Features: Retractable keel made of lead.
Find Daysailer boats for sale in your area & across the world on YachtWorld. Offering the best selection of boats to choose from. ... All 25 miles 50 miles 100 miles 200 miles 300 miles 500 miles 1000 miles 2000 miles 5000 miles. ... larger than a dinghy. Widely used for recreation, it's ideal for beginners who are learning how to sail ...
For Sale: 1982 Nonsuch 26-Foot Classic Sailboat - Hull #42 Step aboard one of the strongest and most reliable sailboats ever built by Hinterhoeller Yachts. ... The self-bailing cockpit of the Harbor 25 is eight feet in length and comfortably seats six adults, the halyards are internal, and they are led aft to the cockpit for easy sail ...
New Haven, Indiana. Year 1995. Make Sweetwater. Model SW2019ES. Category Pontoon. Length -. Posted 6 Days Ago. 1995 Sweetwater Pontoon - 20 ft with Mariner 25 HP (2 stroke) outboard motor - Binimi Top - Good Condition for year - TRAILER IS NOT INCLUDED - $3299 - GREAT FOR Pond or River CALL 260-749-8909.
Sail boats for sale. Sailboats are available in a variety of models and rigs, including racing boats, sloops, schooners, catamarans, trimarans, sailing cruisers, and others. ... Tout 25 km 50 km 100 km 200 km 300 km 500 km 1000 km 2000 km 5000 km. ... Used. Length. to. ft. m. Price. to. USD. Year. to. Class. Power. Power-all-power. All power ...
Catalina 25 boats for sale 4 Boats Available. Currency $ - USD - US Dollar Sort Sort Order List View Gallery View Submit. Advertisement. Save This Boat. Catalina 25 . Pigeon, Michigan. 1979. $8,500 Seller Pop 80. Contact. 941-265-2874. ×. In-Stock. Save This Boat. Catalina 25 . Gilford, New Hampshire. 1987. $7,000 Seller Fay ...
The starting price is $20,000, the most expensive is $98,000, and the average price of $54,998. Related boats include the following models: 28, 35 and 28 Express. Boat Trader works with thousands of boat dealers and brokers to bring you one of the largest collections of Carolina Classic 25 boats on the market.
Find sailboats for sale near you, including boat prices, photos, and more. Locate boat dealers and find your boat at Boat Trader! ... Zip Only 10 miles 25 miles 50 miles 75 miles 100 miles 200 miles 300 miles 500 miles 1000 miles. from. Use My Location. ... Keyword. Apply. Length. to. ft. Year. to. Price. to. Price Drop. info. Boat Type. Power ...
1984 Catalina 25. $6,500. Melvern Lake, Kansas , KS 66510 | Private Seller. <. 1. >. Find Catalina 25 boats for sale near you, including boat prices, photos, and more. Locate Catalina boat dealers and find your boat at Boat Trader!
2024. Request Price. The Balance 580 was designed for sailors with speed in their hearts but luxury on their minds. With her powerful 2,255-square foot-sail plan the 580 ghosts along in 5 knots of wind while others are burning diesel. But when It's blowing, furl in her headsails, reef her down, and fly.
Find Sail Catamaran boats for sale in your area & across the world on YachtWorld. ... Tout 25 km 50 km 100 km 200 km 300 km 500 km 1000 km 2000 km 5000 km. from your location. Condition. All. ... and the average length overall (LOA) is 45 feet. Listings range in size from 30 feet long to 80 feet long, with an average sail area of 1,323 square ...
Trailer preowned sailboats for sale by owner. Trailer used sailboats for sale by owner. Home. Register & Post. View All Sailboats. Search. ... 25' Catalina 25' Rocky Fork Lake East Shore Marina, Ohio Asking $7,500. ... 28.58' Ericson 29 foot sloop Madison County FL, Florida Asking $3,000. 30' S2 9.1 Mamaroneck, New York
These sailboats have a minimum total sail area of 143 square feet, a maximum total sail area of 2,249 square feet and an average of 817 square feet. Boat Trader currently has 1,038 cruiser sailboats for sale, including 302 new vessels and 736 used and custom yachts listed by both private sellers and professional dealerships mainly in United States.
The Transpac Yacht Club, which organises the biennial race, proposed a new class to a few local naval architects, including teams from Alan Andrews Yacht Design, Nelson Marek and Reichel/Pugh.... 15.85 m (52 ft 0 in) [ edit on Wikidata] The Transpac 52 (TP52) is a class of yacht used for competitive 52 Super Series yacht racing, and the Audi ...
25' Catalina 25' Rocky Fork Lake East Shore Marina, Ohio Asking $7,500. ... 28.58' Ericson 29 foot sloop Madison County FL, Florida Asking $3,000. 30' S2 9.1 Mamaroneck, New York Asking $5,000. ... Show all sailboats for sale under: 15 20 25 30 35 40 45 50 55 60 70 80 (feet LOA) | Multihulls: ...
Houses and apartments for sale Kazan': Real estate listings Kazan' for the purchase and sale by owners of houses, apartments or land.
Find Sail boats for sale in United States. Offering the best selection of boats to choose from. ... All 25 miles 50 miles 100 miles 200 miles 300 miles 500 miles 1000 miles 2000 miles 5000 miles. from your location. Region. Region-all. All Regions. Region-greatlakes.
Real Estate Catalog of Kazan: current offers of property from owners and developers ⏩️ Buying real estate in Kazan without intermediaries ️ Current prices, verified owners and developers with reviews on the property search site 👉 GEOLN.COM
Find sailboats for sale near you by owner, including boat prices, photos, and more. Locate boat dealers and find your boat at Boat Trader! ... Zip Only 10 miles 25 miles 50 miles 75 miles 100 miles 200 miles 300 miles 500 miles 1000 miles. from. Use My Location. ... Keyword. Apply. Length. to. ft. Year. to. Price. to. Price Drop. info. Boat ...
For sale, Property, Tatarstan: Buying a home has never been easier and faster thanks to Realigro.com ... Tatarstan, Kazan, Borovoe Matushino, Laishevskiy rayon 25 km. 11,019,000.00USD For sale Villa 500 m². This fully decorated luxurious country residence in geographically unique location of republic of Tatarstan, in the prestigious area of ...
Find Chris-craft 25 Sportster boats for sale in your area & across the world on YachtWorld. Offering the best selection of chris-craft boats to choose from.