O-LevelBiologyCoordination & Response5090/21 · May/June 2021 · Q218 Marks

A person visits an eye doctor to have an eye test. On the wall of the doctor's room is a diagram of an eye. X layer Y choroid layer contains melanin in its cells

(a)(i)Name the part labelled X.[1]
(a)(ii)Describe one way in which the structure of X is related to its function.[2]
(a)(iii)Name layer Y.[1]
(b)(i)Name structure Z.[1]
(b)(ii)Layer Y does not contain blood vessels. Explain how the blood vessels in the choroid layer are important for layer Y.[4]
(c)When the bright light is shone into the eye there is a pupil reflex which causes the pupil to become smaller. Explain how named parts of the eye and of the nervous system are involved in this pupil reflex.[4]
(d)(i)Complete the genetic diagram to show the possible genotypes and phenotypes of the children. genotypes of parents gametes possible genotypes of children possible phenotypes of children[4]
(d)(ii)State the probability of these two people having a child who does not produce melanin.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[1] lens;
[1] transparent / spherical / curved sides ;
[1] allows light to pass through / to focus / refract light ;
[1] flexible / elastic / can change shape AW ;
[1] accommodation / focus objects;
[1] retina;
[1] macula / yellow spot / fovea;
[1] bring glucose / amino acids / minerals / vitamins;
[1] for energy / repair of cells ;
[1] bring oxygen ;
[1] for (aerobic) respiration;
[1] take urea / carbon dioxide away;
[1] diffusion;
[1] capillaries / veins / arteries mentioned in correct context ;
[1] bring white blood cells ;
[1] to fight infection;
[1] retina / rods detect extra light (intensity);
[1] impulse + to CNS / brain ;
[1] via optic nerve / sensory neurone ;
[1] back to eye / iris / effector / muscle + motor neurone ;
[1] radial muscles relax ;
[1] circular muscles contract ;
[1] iris becomes bigger / elongates ;
[1] reflex arc;
[1] parental genotypes = Aa + Aa;
[1] gametes a and A;
[1] offspring genotypes AA, Aa, Aa and aa ;
[1] correctly linked phenotypes: AA & Aa = produce melanin, aa don't produce melanin ;
[1] 25% / 1/4 / 0.25 / 1 in 4 / 1:3;

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