Natural Selection

1. 1 State [2 marks]

   State two things that organisms in a habitat may compete for.

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   Model answer

   Any two from: food, water, light, space, mates, shelter.

   Mark scheme

   • First — 1 mark
   • Second — 1 mark
2. 2 Define [2 marks]

   Define the term adaptation.

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   Model answer

   A feature of an organism that helps it to survive and reproduce in its environment.

   Mark scheme

   • A feature of an organism — 1 mark
   • Helps survival / reproduction in its environment — 1 mark
3. 3 Describe [3 marks]

   Describe what happened to the proportions of dark and pale peppered moths during the Industrial Revolution.

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   Model answer

   The proportion of dark moths increased, from about 2% in 1848 to about 98% in 1895, and the proportion of pale moths fell from about 98% to about 2%.

   Mark scheme

   • Dark moths increased — 1 mark
   • Pale moths decreased — 1 mark
   • Figures to support — 1 mark
4. 4 Explain [4 marks]

   Explain why dark peppered moths became more common in industrial areas.

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   Model answer

   Soot from factories made the tree trunks dark. Dark moths were better camouflaged, so birds were less likely to eat them. They were more likely to survive and reproduce, and passed on the allele for dark colour to their offspring. So the proportion of dark moths increased.

   Mark scheme

   • Soot blackened the trees — 1 mark
   • Dark moths were camouflaged and less likely to be eaten — 1 mark
   • They survived and reproduced — 1 mark
   • Passed on the allele for dark colour — 1 mark
5. 5 Explain [4 marks]

   A giraffe's neck is long. Use Darwin's theory to explain how this may have evolved.

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   Model answer

   There was variation in neck length in the ancestors of giraffes. Those with longer necks could reach leaves higher up in the trees, and so had more food and were more likely to survive and reproduce. They passed on the alleles for long necks to their offspring, so over many generations the average neck length increased.

   Mark scheme

   • Variation in neck length — 1 mark
   • Longer necks could reach more food and survive — 1 mark
   • Passed on the alleles — 1 mark
   • The average length increased over generations — 1 mark
6. 6 Evaluate [6 marks]

   A student says: "The giraffe grew a longer neck because it needed to reach the leaves, and its babies inherited the longer neck." Explain why this idea is incorrect, and give the correct explanation.

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   Model answer

   This is Lamarck's idea, that a characteristic acquired during a lifetime is passed on. It is wrong because stretching a neck does not change the genes in the gametes, so the babies would not inherit a longer neck. A giraffe cannot change its genes because it needs to. The correct explanation is natural selection. There was variation in neck length because of different alleles. Giraffes with longer necks could reach more food, so they survived and reproduced more, and passed on their alleles. Over many generations, the alleles for long necks became more common in the population.

   Mark scheme

   • Describes the incorrect idea — 1 mark
   • Acquired characteristics are not inherited — 1 mark
   • Variation due to alleles — 1 mark
   • Longer necks survive and breed more — 1 mark
   • Pass on alleles — 1 mark
   • Proportion increases over generations — 1 mark

Quick check

1. 1

   What does natural selection act on?

   1. AA single organism
   2. BThe environment
   3. CVariation in a population
   4. DAcquired characteristics
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   C: Variation in a population

   Natural selection acts on the variation that is already present in a population.

2. 2

   Which is the correct first step of natural selection?

   1. AReproduction
   2. BVariation
   3. CCompetition
   4. DSurvival
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   B: Variation

   Variation between individuals is needed, so some are better suited than others.

3. 3

   Why do dark peppered moths survive better in sooty areas?

   1. AThey are larger
   2. BThey fly faster
   3. CThey do not reproduce
   4. DThey are camouflaged on dark trees
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   D: They are camouflaged on dark trees

   They are camouflaged against the dark trees, so birds are less likely to see them.

4. 4

   What is an adaptation?

   1. AA feature that helps an organism survive in its environment
   2. BA change in the weather
   3. CA type of mutation
   4. DA kind of fossil
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   A: A feature that helps an organism survive in its environment

   An adaptation is a feature that helps an organism to survive and reproduce in its environment.

5. 5

   Which of these is an example of a behavioural adaptation?

   1. AThick fur
   2. BSharp claws
   3. CMigration of birds
   4. DWebbed feet
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   C: Migration of birds

   Migration is something an organism does, so it is a behavioural adaptation.

6. 6

   What does it mean to say that an adaptation is inherited?

   1. AIt develops during a lifetime
   2. BIt is controlled by alleles passed to offspring
   3. CIt is caused by the environment
   4. DIt is not passed on
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   B: It is controlled by alleles passed to offspring

   It is controlled by alleles that are passed from parents to offspring.

7. 7

   Which idea is Lamarck's?

   1. AAcquired characteristics are inherited
   2. BVariation is caused by mutation
   3. CSpecies compete
   4. DNatural selection
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   A: Acquired characteristics are inherited

   Lamarck suggested that features acquired during a lifetime are passed to offspring, which is not supported by evidence.

8. 8

   How can a new species form?

   1. ABy acquired characteristics
   2. BBy individuals changing during their life
   3. CBy a change in the weather
   4. DBy isolation and different selection until they cannot interbreed
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   D: By isolation and different selection until they cannot interbreed

   If groups are isolated and different characteristics are selected in each, they can become unable to interbreed.

9. 9

   In an exam answer, which statement about natural selection is best?

   1. AGiraffes grow longer necks because they need to reach food
   2. BGiraffes with longer necks survive and reproduce more
   3. CGiraffes stretch their necks and pass this to their young
   4. DAll giraffes change in the same way
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   B: Giraffes with longer necks survive and reproduce more

   Selection acts on variation that is already there. Organisms do not change because they need to.