32 10 The retina of the human eye contains rod cells. These cells detect light energy as photons. The light energy is converted to a nerve impulse that is interpreted by the brain. (a) A current is produced by a rod cell when ions move through the cell surface membrane of a rod cell. The graph shows the effect of increasing light intensity on the current produced by a rod cell. 10 000 1000 100 30 20 10 0 Light intensity / photons Current / pA Turn over 33 Explain the effect of increasing light intensity on the current produced by a rod cell. (5) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 34 (b) (i) The transmission of an impulse between a neurone in the optic nerve and a cell in the brain involves ions and neurotransmitter molecules. Describe how these ions and neurotransmitter molecules are involved in the transmission of an impulse. 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Turn over 35 (ii) The diagram shows a human brain. T W V U Which label on the diagram identifies the area of the brain where an image is interpreted? (1) A T B U C V D W 36 (c) In one experiment, Hubel and Wiesel kept the right eye of a kitten closed during the critical period. They then studied the effect of this on the visual region of the brain of this kitten. Describe the differences in the visual region of this kitten compared with the visual region of a kitten that had both eyes open during the critical period. 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(Total for Question 10 = 12 marks) TOTAL FOR PAPER = 100 MARKS