O-LevelBiologyEcology & Environment5090/21 · Oct/Nov 2020 · Q210 Marks

Corals are a collection of small animals living together in the sea. Their skeletons produce coral reefs. The cells of these animals contain microscopic, green, plant-like organisms called algae.

(a)Suggest the name of the process by which the algae make their food and explain your answer. process explanation[2]
(b)The corals and the algae depend on each other to survive. Suggest • how the algae benefit from the corals • how the corals benefit from the algae.[5]
(c)An increase in the average temperature of the sea over the last 20 years has caused the algae to manufacture chemicals that are poisonous to the corals. Suggest and explain the long-term effect on the corals and on the algae of this rise in temperature.[3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.

[1] photosynthesis ;
[1] green / plant + chlorophyll / chloroplasts;
[1] algae benefit: gain carbon dioxide ;
[1] protected / sheltered / habitat ;
[1] coral benefit: gain oxygen ;
[1] corals feed on + glucose / carbohydrate / protein / food + produced by algae ;
[1] algae or coral: respiration + gas produced or required;
[1] photosynthesis + gas produced or required ;
[1] coral dies / killed / decreases / extinction AW ;
[1] algae die / killed / decrease / extinction AW ;
[1] algae no longer + protected / cells to live in / get CO2;
[1] coral / algae decompose ;

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