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Plants and animals are both able to sense and respond to light - NSC Life Sciences - Question 4 - 2016 - Paper 1
Question 4
Plants and animals are both able to sense and respond to light. Explain how plant stems respond to unilateral light and describe the path taken by light through the... show full transcript
Worked Solution & Example Answer:Plants and animals are both able to sense and respond to light - NSC Life Sciences - Question 4 - 2016 - Paper 1
Step 1
Explain how plant stems respond to unilateral light
Answer
Plant stems respond to unilateral light through a process known as positive phototropism. When light is directed from one side, auxins, which are plant hormones produced in the tip of the stem, are redistributed.
- Auxins move away from the light source, concentrating on the darker side where they promote cell division and elongation, stimulating growth.
- Conversely, on the side exposed to the light, lower auxin concentrations inhibit growth.
- This uneven growth causes the stem to bend toward the light source, enabling the plant to optimize its light absorption.
Step 2
Describe the path taken by light through the human eye until it is converted into an impulse
Answer
Light enters the human eye through the cornea, which refracts the light.
- After passing through the cornea, light travels through the aqueous humour and reaches the pupil.
- The size of the pupil is adjusted by the iris to regulate the amount of light entering the eye.
- The light then passes through the lens, which refracts the light again before it enters the vitreous humour, filling the eye.
- The light rays continue their journey until they reach the retina at the back of the eye, where photoreceptors, known as rods and cones, convert the light stimulus into a nerve impulse.