Biology 14.4 Rods and Cones Questions

2b) Cells of the same type as cells 6 and 7 are found in large numbers in the fovea. This results in colour vision with high visual acuity. Explain what causes vision using the fovea i) to be in colour ii) to have high visual acuity

2b) i) 3 different types of cone cells; type 6 and 7 are sensitive to different wavelengths ii) impulses run along separate bipolar cells. Each receptor cell connects to separate neurone.

1. When a person looks directly at an object, its image is focused on the fovea a) when the image is focused on the fovea, the person sees the object in colour. Explain why. (3) Vision using the fovea has HIGH VISUAL ACUITY but LOW SENSITIVITY to light compared with vision using other parts of the retina b) i) Explain why vision using the fovea has high visual acuity b)ii) Explain why vision using other parts of the retina has high sensitivity to light

a) Colour detected by cone cells - Fovea contains cone cells - Different types of cone cells sensitive to different wavelengths b)i) Each cone is connected to a separate neurone b)ii) Many rods in other parts of the retina - Rhodopsin is pigment in rod cells - sensitive to light - Rods connected in groups - Summation - enough light above threshold.

2. The diagram shows part of the retina in a human eye. a) explain each of the follow observation i) When light falls on cells 1 and 2, only one spot of light is seen. But, when light falls on cells 2 and 3, two spots of light are seen. ii) When one unit of light energy falls on cell 3, no light is seen. But, when one unit of light energy falls on cell 3, one unit falls on cell 4 and one unit falls on cell 5, light is seen.

a)i) 1 and 2 share neurone/ 2 and 3 have separate neurones a)ii) 1 unit is sub-threshold/3 units above threshold/ give sufficient depolarisation; No impulses/no action potential