4   2 The human circulatory system is composed of the heart and blood vessels. (a) The graph shows pressure changes in the aorta, left atrium and left ventricle during the cardiac cycle. 20 15 10 5 0 –5 Blood pressure / kPa 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Time / s Left ventricle Left atrium Aorta Q R S P (i) At which part of the graph is the left atrioventricular valve starting to close? (1) A P B Q C R D S (ii) At which part of the graph is a semilunar valve opening? (1) A P B Q C R D S Turn over 5   (iii) Describe what happens during diastole. (2) ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... (b) The photograph shows a cross‑section of part of a human aorta, as viewed under a light microscope. The diameter of the lumen can be reduced to maintain blood pressure in the aorta. X Y Magnification ×18 © JOSE CALVO/SCIENCE PHOTO LIBRARY (i) Calculate the diameter of the lumen along the line XY. Give your answer to two significant figures. (2) Answer .............................................................. mm 6   (ii) State the feature of the wall of the aorta that causes a reduction in the diameter of the lumen. (1) ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... (Total for Question 2 = 7 marks) Turn over 7   3 Starch and amylase are molecules found in some cells. (a) Amylase is a biological catalyst. State what is meant by the term biological catalyst. (2) ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... (b) The hydrolysis of starch by amylase was investigated. The diagram shows the hydrolysis of starch into maltose. substrate product enzyme (amylase) 8   The concentration of maltose in the solution was measured at regular intervals. The graph shows the results of this investigation. 300 250 200 150 100 50 0 Concentration of maltose / mg dm–3 0 10 20 30 5 15 25 Time / minutes (i) Which of the following shows the type of molecules in this reaction? (1) A B C D (ii) Which of the following is the type of bond that is broken when starch is hydrolysed by amylase? (1) A glycosidic B hydrogen C ionic D peptide Substrate Product Polypeptide Disaccharide Polysaccharide Disaccharide Polypeptide Monosaccharide Polysaccharide Monosaccharide Turn over 9   (iii) Which of the following shows the correct unit for the rate of this reaction? (1) A mg dm3 min1 B mg dm–3 min1 C mg dm3 min–1 D mg dm–3 min–1 (c) Explain how the structure of starch makes it a good storage molecule. (2) ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... 10   (d) The diagram shows part of another molecule. OH H O H H H H H2COH OH OH H O O O H H OH H H O H H O H OH H H2COH OH H O H2COH The enzyme amylase cannot hydrolyse this molecule. Deduce why amylase cannot hydrolyse this molecule. 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(Total for Question 3 = 9 marks) Turn over 11   BLANK PAGE