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Learn about variation in plants and animals, the differences between inherited and environmental variations, and the processes of asexual and sexual reproduction. Understand why organisms have traits similar to their parents and where chromosomes and genes are found in the body.
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At the end of this unit you should: • Be able to describe what is meant by variation and describe variation in plants and animals. • Understand the differences between inherited and environmental variations. • Know that asexual reproduction results in new individuals that are genetically identical to the parent. • Identify that sexual reproduction results in new individuals that are not genetically identical to the parent. • Understand why plants and animals have features similar to their parents. • Know where chromosomes and genes are found in the body.
asexual characteristics chromosome clones DNA environmental fertilised fuse gamete genes genetic germinate inherited offspring reproduction sexual traits variation zygote
LIGHTBULB QUESTION Yes. Examples: different hair colour, type and thickness; different colour of eyes. Why? Example: hair or eye colour is a characteristic that is found on genes that we inherit from our parents. So having different parents means we will inherit different genes and different characteristics.
(a) Copy and fill in Table 04.01.02 by writing ‘Yes’ under the correct heading for each variation – inherited, environmental or both. Explain your choice in the last column. Use Table 04.01.01 as a guide.
(b) Compare the physical appearance of the following pairs. How are they different? How are they similar? (i) A snail and a robin Different: a snail does not have legs, they do not fly, and they have a shell. A robin has two legs, wings, can fly and does not have a shell. Similar: They both carry out the seven characteristics of life. Both move, they take in food, excrete, take in oxygen and let out carbon dioxide, release energy at cells, respond to senses, make new cells and reproduce.
(b) Compare the physical appearance of the following pairs. How are they different? How are they similar? (ii) A beech tree and a dandelion Different: Grow to different heights, have different types of leaves and different depth of roots. A beech tree has a bark and the dandelion has a non-woody stem. Similar: They both carry out the seven characteristics of life. Both move when they grow towards the sunlight or extend roots towards water, they make food, they excrete oxygen and take in carbon dioxide, release energy at cells, respond to senses, make new cells and reproduce.
Investigation 04.01.01: Showing how asexual reproduction happens in a potato Equipment: A large see-through glass jar, a potato or a sweet potato and some water. Instructions: Design an investigation to show asexual reproduction in a plant, using either a potato or a sweet potato. Write down your observations as the potato grows.
1. What predictions can you make about what will happen? • The potato will develop new shoots over a few days.
2. What conclusions can you draw from the fact that the • potato grows? • That it reproduces asexually.
3. If you placed the potato in soil and not a glass jar, • would new potatoes grow? • Yes, as asexual reproduction would still take place. The glass jar just allows us to see the new shoots develop.
(a) What is reproduction? Name two types of reproduction. Reproduction is the process of making new individuals or offspring. Asexual, sexual, budding (asexual) or production by spores (sexual).
(b) How many parents are involved in asexual reproduction? One.
(c) There is a risk that at some point an organism that reproduces asexually could become extinct. Can you explain this possibility? Asexual reproduction involves one parent only. If that parent dies and there have been no other offspring or seedlings, then that species will become extinct.
(d) Why is the process of asexual reproduction an advantage to a plant? The plant does not have to produce flowers to attract animals to pollinate it, nor does it have to produce or disperse any seeds in order to reproduce.
(e) Explain briefly what a clone is. Producing an exact genetic copy of the parent.
(a) What is another name for the sex cells in plants and animals? Gametes.
(b) Name the specific sex cells in plants and animals. Plants: female – egg cell; male – pollen cell. Animals: female – egg cell; male – sperm cell.
(c) Describe what fertilisation means in plants and animals. The fusing of the sex cells or gametes together to form a zygote.
(e) What are the advantages of new cells produced from sexual reproduction? The variation within the organisms will help them to survive if their environment changes, and it can help to prevent extinction.
LIGHTBULB QUESTION Hair and eye colour comes from the genes we inherit from our parents.
Inheritance: The passing on of characteristics from generation to generation. Characteristic: A distinguishing feature or quality that helps us to tell organisms apart.
(a) What would it mean if someone said to you that you had ‘inherited your straight blonde hair from your mum’? That the gene for straight blonde hair was passed on to you from your mother.
(b) What is a meant by a ‘characteristic’? Give two examples for humans and two for plants. A characteristic is feature that is passed on or inherited from your parents. Humans: eye colour, hair colour. Plants: The height of the plant, whether the plant has deep or shallow roots, whether the plant has broad or narrow leaves, whether the leaves have netted veins or veins in parallel.
(c) Where are genes located in the body? On chromosomes, in the nucleus of cells in the body. (d) What do genes control? Genes control and determine all of our characteristics or features. (e) What are chromosomes made up of? DNA and protein.
Investigation 04.01.02: Investigating the DNA in fruit Instructions: Stage 1: Prepare the fruit pulp (i) If using kiwi, peel away skin. Using a pestle and mortar crush a small section of the fruit into a pulp. (You should have a fairly smooth pulp.) Note: Crush up the pulp very well to extract more of the DNA.
Investigation 04.01.02: Investigating the DNA in fruit Stage 2: Prepare the water mixture (i) Measure 100 ml of distilled water using graduated cylinder and add to a beaker. (ii) Add to the water 10 ml washing up liquid and, using the spatula, 3 g of salt. (iii) Dissolve the salt by mixing the mixture slowly Note: Mix slowly to dissolve the salt, and avoid making any bubbles with the washing-up liquid.
Investigation 04.01.02: Investigating the DNA in fruit Stage 3: Heat the mixture Slowly mix the pulp into the water mixture. (ii) Place the beaker with the pulp mixture into a water bath at 60°c for approximately 15 minutes but not any longer. Stage 4: Filter the mixture and collect the filtrate Place the sieve over the empty beaker. (ii) Remove the beaker from the water bath and pour the pulp mixture through the sieve into the empty beaker. You can throw away the pulp and keep the liquid as this has the DNA.
Investigation 04.01.02: Investigating the DNA in fruit Stage 5: Add the ethanol (i) Pour approximately one third of the new liquid into the boiling tube. (ii) Tilt the boiling tube and gently and slowly let the ice-cold ethanol dribble down the side of the tube so a layer sits on top of the liquid. (iii) Add enough until there is a layer of ethanol on top of the liquid.
Investigation 04.01.02: Investigating the DNA in fruit Stage 6: Remove the DNA (i) Hold the boiling tube at eye level or place in test tube rack. (ii) Look at where the ethanol and liquid meet. You should start to see a stringy material forming between the two layers. This is the DNA. Use a cocktail stick or a paper clip folded into a hook lift out the strands of DNA.
Investigation 04.01.02: Investigating the DNA in fruit How to see the DNA 1. Place DNA sample onto centre of slide. 2. Gently and at an angle place a cover slip on top. 3. Adjust the stage on the microscope to a low level. 4. Place slide on the stage. 5. View DNA by starting with the low power lens and then changing powers.
1. What predictions can you make about what will happen? • The salt helps to clump the DNA together and protect it.
2. Why did you not heat the mixture for longer than fifteen minutes? • The DNA molecules would be destroyed were the mixture heated for longer than this.
3. What shape are you expecting the DNA to be? • A double helix shape.
4. Why would the DNA strand you are looking for be considered delicate? • The DNA strand is delicate as the proteins and membranes that protected it have been destroyed.
(a) How many chromosomes are in a human body cell? Forty-six or twenty-three pairs.
(b) Draw a diagram showing where you got your chromosomes from. A chromosome mix from mum and dad, which should be replicated by the students.
(c) Look again at Table 04.01.03 on inherited characteristics. Did you inherit any of these characteristics from your parents, grandparents or great-grandparents? You may need to ask at home!
Copy and Complete In this unit I learned that the differences between organisms is known as variation. In animals these differences are passed on from the parent to the baby and in plants to the young seedling. Reproduction is where new cells or individuals are made. There are two types of reproduction: asexual and sexual. Asexual reproduction only needs oneparent. Each cell is identical to the parent. Sexual reproduction needs twoparents, and the sex cells fuse together to produce a fertilizedegg. The new cell is different to the parents. The sex cells are called the gametes.
Copy and Complete The plant gametes are the egg and pollen; the human gametes are the eggand sperm. The fertilised egg is called the zygote. In humans, every body cell has 46 chromosomes, except the sex cells, which have 23. They carry the genes that give us our characteristics. Characteristics are controlled by the genes. The chromosomes are made of DNA and protein. They are inherited from our parents and are found on chromosomesinside the nucleus of a cell. When sexual reproduction happens the sex cells fuse together to form 46chromosomes and this means that there is a mix of genes. We can therefore say that our characteristics have been passed on to us.
1. How do plants show variation? There are numerous answers. For example: they are different heights, have different types of flowers, different colours, depth of roots, shape of leaves; they flower at different times of the year, have a different number of petals on the flowers; some grow fruit; some have a bark while others have a soft stem.
3. Raspberry and strawberry plants are able to produce many plants from one parent. What advantages does this give the plant? They do not have to rely on pollination. If one plant dies there are many more that will grow.
4. What disadvantages, if any, would there be in plants or animals being exactly the same as the parent? If disease was to strike a plant, it would kill all the plants as they would have the same genetic make-up. Therefore the chances of extinction are greater.
5. Sexual reproduction leads to variation among organisms. List the advantages of variation. Each individual is unique, individuals can adapt to environments that might change, and this will help against extinction, and if disease strikes it may not affect all individuals as they have a different make-up.
6. Write down three examples of both inherited and environmental characteristics of plants and animals.
7. Explain the difference between asexual and sexual reproduction. You must use all the words in the following list. The words can be used more than once. fertilisation sex cells gametes inherit exact copy clone identical genetically different genes Asexual reproduction involves one parent and no sex cells. There are two cells produced that have identical genes that they inheritfrom the parent and are now exact copies of the parent. This can also be referred to as a clone of the parent. Sexual reproduction involves two parents and need sex cells or gametes to fuse together during fertilisation. The cells are not identical to the parents they are genetically different as they have a mix of genes from both parents.
8. Which of the statements in Table 04.01.05 are true and which are false? Chromosomes are found on the genes False Genes are not passed on from our parents False The nucleus is found in cells True Genes are found on chromosomes True Genes are made of DNA False There are 23 chromosomes in every cell in your body False There are 46 pairs of chromosomes in cellsFalse
9. State how many chromosomes a newborn baby would have in (i) a muscle cell; (ii) a cheek cell. Muscle cell: 46 or 23 pairs Cheek cell: 46 or 23 pairs
