DP Biology (last assessment 2024)

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Question 23M.3.HL.TZ2.8

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Date May 2023 Marks available [Maximum mark: 6] Reference code 23M.3.HL.TZ2.8
Level HL Paper 3 Time zone TZ2
Command term Explain, Identify, Suggest Question number 8 Adapted from N/A
8.
[Maximum mark: 6]
23M.3.HL.TZ2.8

Breeding plumage can be an important signal for mate selection in birds. Breeding plumage in red knots (Calidris canutus) includes a rusty red colour. Red knots have six recognized subspecies, each with different migratory routes.

The scatter graph shows the overall migration distance and the breeding plumage colouration for different subspecies of red knots. The darkest plumage colouration is 6.

[Source: Used with permission of The Royal Society (U.K.), from Phil. Trans. R. Soc. B, Buehler, D.M. and Piersma, T, 363, 2008;
permission conveyed through Copyright Clearance Center, Inc.]

(a.i)

Identify the relationship between migration distance and plumage colouration.

[1]

Markscheme
  1. the longer the migration, the lighter the colour / vice versa;
  2. too much variation so it is not possible to see a relationship;
Examiners report

Most could identify the relationship between distance and colouration but ignored that a mathematical correlation would be difficult to establish due to the logarithmic x-axis, the relative units of the y-axis, and the limited number of points. They should realize that a trend line doesn't always indicate correlation.

(a.ii)

Suggest two reasons, other than mate selection, for variation in plumage colouration in red knots.

[2]

Markscheme
  1. camouflage to avoid predators (in different migratory routes);
  2. different diets (in different migratory routes);
  3. less migratory distance leaves more energy to produce pigments (in plumage);
  4. geographic isolation (due to different migratory routes) leads to different gene pools;
(b)

Explain the evolution of behaviour by natural selection.

[3]

Markscheme
  1. behavioral variations within the population have a genetic basis;
  2. selection pressure creates competition;
  3. individuals that are best adapted to the environment have greater chances of survival;
  4. adapted organisms have greater chances of reproduction/produce more offspring;
  5. advantageous alleles/behaviour is inherited by offspring;
  6. (the frequency of) the favourable alleles/behaviour increases in the population;

Do not accept “genes” instead of alleles

Examiners report

Most correctly explained natural selection mainly mentioning survival advantage but it was difficult for many to add substance to their explanation, especially in terms of alleles and populations.

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