GCE A-L Biology paper 2 Question 5 answer for june 2016

GCE A-L Biology paper 2 Question 5 answer for June 2016 available here in edunonia your number one site for educational resources, past papers and proposed answers to past questions.

June 2016 biology P2 Q5

5(a)(i): What is accommodation with respect to vision?

(ii): How are far and near objects focused by the eye?

(b)(i): List the differences of photosensitive cells found in the retina of the eye?

(ii): How are synapses important in the transmission of impulses in mammals?

Answers to the above questions

5a(i): It is a reflex mechanism in which light rays from a far object are brought to focus on the retina

It is the ability of the eye lens to change its focal length that is becoming thin or thick so as to focus distance or far objects on the retina

5a(ii): For far objects

• Parallel light ray from distant onject reach the eye
• The conea reflects the light rays
• The circular muscle of the ciliary body relax, while the redial ciliary muscle contract
• The suspensory ligaments are pulled tight (tension) hence pulling on the edge of the elastic lens
• This causes the lens to become less convex and thinner
• The refractive index of the lens is reduced or the focal length is increased
• Light is focused on the fovea of the retina, and the person sees the distant object clearly

See lesson notes on Enzymes

For near objects

• Divergent light rays from an objects reach the eye
• Conea refract the light rays
• The ciliary muscle of the ciliary body contracts, while the redial ciliary muscle relax
• The suspensory ligaments become relaxed(slack)
• The elastic lense become more convex that is bulges(fatter)
• The refractive index of the eye is increased or its focal length reduces
• Light ray from the near objects is focused on the fovea of the retina and the person sees the near objects clearly

(5b) Differences between photoreceptors cells of the retina

RODS	CONES
1) Outer segment is rod-shaped	1) Outer segments is a cone shape
2) More numerous	2) Fewer
3) Evenly distributed at the retinal periphery	3)Packed at the fovea
4)Give poor visual acuity	4) Gives a good visual acuity
5)Sensitive to low light intensity	5) Sensitive to high light intensity
6)Mostly used for night vision	6) Mostly used for daily vision
7)Cannot distinguish colour	7)Sensitive to colour
8)contain the visual pigment Rhodopsin	8)Contain the visual pigments Iodopsin
9)Rod of one kind only	9) Cones exist three types
10) Synaptic convergence	10) No synaptic convergence
11 Fat regeneration of pigments	11) Slow regeneration of pigments

5b (ii) Importance of synapses in nervous system of mammals

1. It enable transmision of electrical impulses between neurones
2. Ensures the nerve impulses is unidirectional passing from the pre-synaptic memmbrane to the post-synaptic memmbrane
3. It also provide a mechanism for filtering out non essential information
4. Enables information from different parts of the nervous system to converge and be inter grated
5. Protects the nervous syste from over stimulation which may lead to fatique
6. It helps in enabling cordination during conditional reflex
7. Controls muscle contraction
8. Controls two or more neurone