Asexual and Sexual Reproduction

1. 1 State [1 mark]

   State what is meant by asexual reproduction.

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   Model answer

   Reproduction by one parent, with no gametes, which produces genetically identical offspring.

   Mark scheme

   • One parent, identical offspring — 1 mark
2. 2 Give [2 marks]

   Give two advantages of asexual reproduction.

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   Model answer

   Any two from: only one parent is needed; many offspring are made quickly; the offspring are well adapted to the same environment; it uses less energy.

   Mark scheme

   • First — 1 mark
   • Second — 1 mark
3. 3 Explain [3 marks]

   Explain why a population of genetically identical organisms is at risk from a new disease.

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   Model answer

   All of the individuals have the same genes, so they all have the same susceptibility to the pathogen. If none of them is resistant, the disease can affect all of them, and the whole population could die.

   Mark scheme

   • All have the same genes — 1 mark
   • None may be resistant — 1 mark
   • The whole population could be killed — 1 mark
4. 4 Calculate [3 marks]

   A bacterium divides every 30 minutes. Calculate the number of bacteria that would be produced from one cell after 4 hours, if none die.

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   Model answer

   4 hours is 240 minutes, so there are 240 ÷ 30 = 8 divisions. 2 to the power 8 is 256 bacteria.

   Mark scheme

   • 8 divisions — 1 mark
   • 2 to the power 8 — 1 mark
   • 256 — 1 mark
5. 5 Explain [3 marks]

   Explain why an organism that reproduces sexually is more likely to survive a change in the environment than one that only reproduces asexually.

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   Model answer

   Sexual reproduction produces offspring that are genetically different. If there is an environmental pressure, some of them are likely to have variants that help them to survive. The survivors reproduce, so the species survives. Clones would all have the same genes, and the whole population could die.

   Mark scheme

   • Offspring are genetically different — 1 mark
   • Some are likely to survive — 1 mark
   • Clones would all be affected in the same way — 1 mark
6. 6 Evaluate [6 marks]

   Aphids reproduce asexually in the summer and sexually in the autumn. Evaluate the advantages to the aphids of using both methods of reproduction.

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   Model answer

   In the summer the conditions are good, with plenty of food. Asexual reproduction is fast, and makes many offspring without the need for a mate, so the population grows very quickly and takes advantage of the food. The offspring are clones of well-adapted parents, which will do well in the same conditions. In the autumn the conditions are going to change, as the winter approaches. Sexual reproduction produces variation, so some of the eggs are likely to survive the cold or other pressures, such as a different host plant or predators. It is slower and uses more energy, but this is not a problem when the population is not growing. By using both methods, the aphids get the benefit of speed in the summer, and variation for the winter.

   Mark scheme

   • Summer: good conditions, so fast growth — 1 mark
   • Asexual: many offspring, no mate needed — 1 mark
   • Clones are well adapted — 1 mark
   • Autumn: conditions change — 1 mark
   • Sexual: variation, so some survive — 1 mark
   • A reasoned conclusion on using both methods — 1 mark

Quick check

1. 1

   Which type of cell division is used in asexual reproduction?

   1. AMeiosis
   2. BMitosis
   3. CFertilisation
   4. DDifferentiation
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   B: Mitosis

   Mitosis.

2. 2

   How are the offspring of asexual reproduction related to the parent?

   1. AThey are completely different
   2. BThey have half of the genes
   3. CThey are genetically identical
   4. DThey have extra chromosomes
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   C: They are genetically identical

   They are genetically identical clones.

3. 3

   Which is an advantage of sexual reproduction?

   1. AIt produces variation
   2. BIt is very fast
   3. CIt needs only one parent
   4. DIt uses little energy
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   A: It produces variation

   It produces variation.

4. 4

   Which is an advantage of asexual reproduction?

   1. AIt gives variation
   2. BIt makes the offspring different
   3. CIt helps evolution
   4. DIt makes many offspring fast, without a mate
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   D: It makes many offspring fast, without a mate

   It can make many offspring quickly, with no mate.

5. 5

   Why were the potatoes in Ireland all affected by blight?

   1. AThey were all different
   2. BThey were genetically identical
   3. CThey had too much water
   4. DThey were all very old
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   B: They were genetically identical

   They were genetically identical, so none was resistant.

6. 6

   A bacterium divides every 20 minutes. How many bacteria are there after 1 hour, from one cell?

   1. A3
   2. B6
   3. C8
   4. D20
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   C: 8

   3 divisions gives \(2^3 = 8\).

7. 7

   Which organism uses both asexual and sexual reproduction?

   1. AA strawberry plant
   2. BA human
   3. CA mouse
   4. DAn elephant
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   A: A strawberry plant

   A strawberry plant makes runners and seeds.

8. 8

   How many babies are usually born at one time to a human?

   1. AFive
   2. BFour
   3. CTwo
   4. DOne
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   D: One

   Usually one.

9. 9

   A population of clones is in an environment that suddenly gets hotter. What is most likely to happen?

   1. ASome will adapt quickly
   2. BThey could all be affected in the same way
   3. CThey will become different
   4. DThey will reproduce sexually
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   B: They could all be affected in the same way

   All the clones have the same tolerance, so if it is not high enough, they will all die.