20 6 Acetylcholine is a neurotransmitter released by neurones in the autonomic nervous system. (a) (i) Which of the following substances bind to acetylcholine receptors? (1) 1. cobra venom 2. nicotine 3. lidocaine A 1 and 2 B 1 and 3 C 1, 2 and 3 D 2 and 3 (ii) Which row is correct for acetylcholine? (1) Type of neurone that releases acetylcholine Effect of acetylcholine A parasympathetic neurone increases heart rate B parasympathetic neurone decreases heart rate C sympathetic neurone increases heart rate D sympathetic neurone decreases heart rate Turn over 21 (iii) Describe the events that lead to the release of acetylcholine at a synapse. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 22 (b) Capsaicin is a substance found in chilli plants that makes them taste ‘hot.’ Capsaicin binds to temperature receptor proteins called TPV receptors. This stimulates impulses along sensory neurones that send impulses to the brain. The effect of capsaicin on the depolarisation of the membrane of a sensory neurone was investigated. The potential difference across the membrane was measured at two places on the sensory neurone after adding capsaicin. The results for a high concentration and a low concentration of capsaicin are shown in the diagram. Low concentration of capsaicin capsaicin TPV receptor potential difference / mV potential difference / mV receptor cell sensory neurone time time High concentration of capsaicin time potential difference / mV potential difference / mV capsaicin TPV receptor receptor cell sensory neurone time Turn over 23 (i) Explain the effect of capsaicin on the depolarisation of the sensory neurone. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 24 *(ii) Capsaicin affects sweat production. It has been suggested that capsaicin could be used to lower the temperature of people with fevers. The effect of three different doses of capsaicin on sweat production was investigated. Five students took one 10 mg tablet of capsaicin each day, for one week. The mass of sweat produced from a 10 cm2 area of skin was measured one hour after taking each tablet of capsaicin. The mean mass of sweat per square centimetre of skin for the group of students was calculated for each day. This was repeated with different groups of students taking 50 mg of capsaicin and taking 100 mg of capsaicin. Most of the students who were given 100 mg of capsaicin reported a burning sensation and redness of the skin. The results are shown in the graph. Error bars represent standard deviations. Key 10 mg capsaicin 50 mg capsaicin 100 mg capsaicin Time / days 7 6 5 4 3 2 1 0 60 50 40 30 20 10 0 Mean mass of sweat produced / mg cm−2 Turn over 25 Analyse the data to discuss the use of capsaicin to lower the temperature of people with fevers. 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(Total for Question 6 = 14 marks)