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Date	November 2021	Marks available	2	Reference code	21N.2.SL.TZ0.1
Level	Standard Level	Paper	Paper 2	Time zone	Time zone 0
Command term	Explain	Question number	1	Adapted from	N/A

Question

Figure 1(a): Savanna food chain

[Source: Djsudermann, 2019. [Elephants in the Savannah] [image online] Available at: https://pixabay.com/photos/
elephant-trees-savannah-sky-animal-4121954/ [Accessed 29 September 2020]. Source adapted.
designerpoint, 2012. Lion-wildcat-safari-africa-515030. [image online] Available at: https://pixabay.com/photos/
lion-wildcat-safari-africa-515030/ [Accessed 3 September 2020].]

Figure 1(b): Biting flies in the savanna

Biting flies bite and drink the blood of zebras. They commonly carry diseases that can be fatal to zebras.

[Source: [Tsetse fly] 2006. [image online] Available at: https://commons.wikimedia.org/wiki/File:Tsetse_fly.png [Accessed 22
May 2020]. Source adapted.

Wellcome Material: Tropical Medicine, 2014. Illustration of ‘Tabinus socius’. [image online] Available at:
https://commons.wikimedia.org/wiki/File:Illustration_of_%27Tabinus_socius%27;_Tropical_Medicine_Wellcome_
L0025345.jpg. Second report of the Wellcome Research Laboratories at the Gordon Memorial College, Khartoum
/ Andrew Balfour. https://wellcomecollection.org/works/ez3txjfg. Attribution 4.0 International (CC BY 4.0)
https://creativecommons.org/licenses/by/4.0/deed.en [Accessed 22 May 2020]. Source adapted.]

State the trophic level of the zebra.

[1]

a.i.

State how you could determine gross secondary productivity of the zebra.

[1]

a.ii.

Explain how the second law of thermodynamics applies to this food chain.

[2]

a.iii.

State the type of relationship that exists between biting flies and the zebra.

[1]

Zebra stripes may reduce the ability of the biting flies to land on the zebra. Describe how natural selection may have led to the evolution of zebra stripes in response to biting flies.

[3]

Markscheme

primary consumer/herbivore/second trophic level;

a.i.

measure the mass of food that the zebra eats and measure the mass of the fecal loss;
GSP is the difference between food consumed & fecal loss/GSP = food eaten − fecal loss;

a.ii.

second law of thermodynamics states that the entropy/disorder of a system increases over time / conversions/transformations in energy aren’t 100 % efficient;
available energy is lost to environment between trophic levels;
energy is lost as heat from cell respiration;
often only 10 % of available energy is passed on / 90 % lost between trophic levels / ecological efficiency is limited;
not all parts of the grass/zebra are consumed/absorbed;

a.iii.

parasitism / predation / carnivory / disease vector;

there was variation in the population / more or less stripes;
that variation arose randomly/through mutation;
biting flies are an environmental pressure / cause disease / natural selection;
having more stripes is advantageous where flies are present / zebras with stripes are less prone to disease / are better adapted to survive (survival of fittest);
striped individuals have a reproductive advantage;
their offspring inherited the advantageous traits / stripes;

Note: Award [2 max] if not related to biting flies.