31 Turn over 9 The diagram shows the structure of a rod cell. outer segment inner segment mitochondria nucleus synaptic vesicles Golgi apparatus endoplasmic reticulum (a) (i) How many of the labelled organelles have a double membrane? (1) A 0 B 1 C 2 D 3 (ii) Which of the following statements about the effect of light on rod cells are correct? (1) 1. rhodopsin breaks down into opsin and trans-retinal 2. voltage-gated sodium channels open in the membrane 3. more neurotransmitter is released from the presynaptic terminal A 1 only B 1 and 2 C 1 and 3 D 2 and 3 32 *(b) Graph 1 shows the distribution of photoreceptors across the retina. Graph 2 shows the sensitivity of rod cells and cone cells to light of different wavelengths. 70 0 50 100 150 200 70 60 50 40 30 20 10 0 10 20 30 40 50 60 Cell density / ´103 mm –2 Angle from fovea in degrees Key Rod cells Cone cells Graph 1 Percentage retinal response (%) Wavelength of light / nm 380 450 500 600 650 700 750 550 Blue Cones Rods Green Cones Red Cones Graph 2 33 Turn over Students investigated the ability to detect beams of light of different colours and intensities. A student covered one eye and a bright red light (wavelength 670 nm) was placed at different angles in the field of vision of the other eye. The student stated if they could detect the red light. This was repeated with a dim red light. This was then repeated with a bright green light and a dim green light (wavelength 525 nm). The table shows the results of this investigation. Angle from fovea in degrees Light detected (Yes/No) Bright light Red Dim light Red Bright light Green Dim light Green 60 N N Y Y 30 N N Y Y 15 N N Y Y 10 N N Y Y 5 Y N Y N 0 Y N Y N 5 Y N Y N 10 N N Y Y 15 N N N N 30 N N Y Y 60 N N Y Y Analyse the data to explain the results of this investigation. 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(Total for Question 9 = 8 marks) TOTAL FOR PAPER = 90 MARKS 35 BLANK PAGE 36 BLANK PAGE