12   4 The photograph shows a plant called lantana (Lantana camara). (Source: © Peter Vrabel/Alamy Stock Photo) The leaves of lantana contain chemicals known to have antimicrobial properties. The antimicrobial activity of lantana leaf extracts prepared using three different solvents, A, B and C, was compared. Fresh lantana leaves were dried and powdered. The dried leaf material was mixed with the solvent and then the extract was purified and dried. The mass of extract obtained from 5 g of powdered leaf, using each solvent, was measured. Solvent used Mean mass of extract ± SD / µg A 501.3 ± 3.5 B 721.3 ± 1.5 C 245.6 ± 4.0 (a) The mass of dried and powdered lantana leaves is 10.5% of the mass of fresh leaves. Calculate the mass of fresh leaves needed to produce 1 mg of extract using solvent A. Give your answer to three significant figures. (2) .............................................................. g Turn over 13   (b) The antimicrobial properties of the extracts produced using these solvents are shown in the table. Solvent used to prepare extract Dry mass of extract / µg Bacteria tested Klebsiella pneumoniae (Gram negative) Micrococcus luteus (Gram positive) Mean diameter of the zone of inhibition / mm A 5.0 8.3 7.1 10.0 10.5 7.0 B 5.0 14.5 12.2 10.0 18.1 18.0 (i) Deduce the effect of using different solvents on the effectiveness of the extracts against these two bacteria. 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(Total for Question 4 = 8 marks) Turn over 15   5 Habituation is a learning response observed in many types of animal. (a) Explain the importance of the habituation response in an animal. 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(b) The ‘light-off jump’ assay can be used to study habituation in fruit flies. When the light is turned off the flies jump into the air and attempt to fly away. The strength of this response can be measured by recording the noise made by the flies. In one experiment, fruit flies with reduced expression of a protein called synapsin were compared with a control group. Synapsin is a protein that inhibits the binding of presynaptic vesicles to the cell membrane. The results of this experiment are shown in the graph. 100 90 80 70 60 50 40 30 20 10 0 Number of times light was turned off 80 70 60 50 40 30 20 10 0 Mean percentage of maximum jump response (%) reduced synapsin normal synapsin 16   (i) State two variables associated with the light-off stimulus that need to be controlled in this experiment. 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(ii) Determine the effect of reduced synapsin on the habituation of fruit flies in this experiment. 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Turn over 17   (iii) Explain how reduced expression of synapsin could produce these results. 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(c) Scientists are using fruit fly habituation to investigate the role of genes associated with human autism spectrum disorders (ASD). Before they can do this, the scientists first identify genes linked to human ASD. Describe how genes linked to human ASD could be identified. 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(Total for Question 5 = 12 marks)