Eyes

Question 1

Explain what causes vision using the fovea.

(i) to be in colour;
(ii) to have high visual acuity.

Answer 1

(Three) different types of (cone) cells / types 6 and 7 sensitive to different wavelengths / different frequencies / different colours
Impulses along separate neurone from each receptor cell / each receptor cell connects to separate neurone;

Question 2

Nocturnal mammals are active at night. Describe how the number and distribution of rods and cones across the retina would differ in a nocturnal mammal from the number and distribution in a human. Explain your answer.

Answer 2

more rods and no / fewer cones present;
rods at the fovea / rods not mainly at periphery;
rods have high sensitivity / show retinal convergence / converse for cones;
rhodopsin ‘bleached’ at low light intensities / iodopsin ‘bleached’; at high light intensities;

Question 3

(a) When the image is focused on the fovea, the person sees the object in colour. Explain why.

Answer 3

Colour detected by cone cells;
Fovea contains (only / mainly) cone cells;
Three types of cone / cells described / each sensitive to different wavelength / to red or green or blue;

Question 4

Explain why vision using the fovea has high visual acuity.

Answer 4

Each receptor (in fovea)/each cone connected to separate neurone / rods/cells in other parts share a neurone;

Question 5

Explain why vision using other parts of the retina has high sensitivity to light.

Answer 5

Many rods in other parts of retina;
Rhodopsin / pigment in receptors / rod cells very sensitive to light/ works in low light;
Receptors / rods connected in groups to ganglion cell / neurone; Summation;
Description of summation, eg if enough light above threshold
hits any cells in the group, then get nerve impulses to brain/along optic nerve;