s3chapter5 (1).doc - Ch 5 Metabolism and enzymes Suggested...

This preview shows page 1 - 4 out of 8 pages.

Ch 5 Metabolism and enzymes Suggested answers Ch 5 Metabolism and enzymes Think about… (Ch 5, p.2) 1. Enzymes are proteins that act as biological catalysts to speed up metabolic reactions. 2. Enzymes catalyse the breakdown of cellulose fibres of the jeans so that the jeans become soft. 3. This reduces the overall cost of stonewashing, such as water, electricity, wages etc. Quick Practice (Ch 5, p.9) A (3) is incorrect. The active site of an enzyme has a specific shape. Only the substrate that fits exactly into the active site can bind to the enzyme. Quick Practice (Ch 5, p.21) 1. D A is incorrect. Most enzymes are inactive, but not denatured, at 0 o C. B is incorrect. 37 o C is the body temperature of humans but the optimum temperature of most human enzymes is 40 to 45 o C rather than 37 o C. C is incorrect. Enzymes are not living thing. They are denatured, rather than killed, by high temperatures. 2. D High temperatures, extreme pHs and inhibitors that bind permanently to the enzymes can cause the active sites of enzymes to change shape, so that the active sites no longer fit the substrates. Quick Practice (Ch 5, p.28) A Enzyme P works well in moderate temperatures which do not cause damage to the clothes. It can tolerate in a slightly alkaline medium of the detergent. B is incorrect. Enzyme Q works well only in high temperatures, which can cause damage to the clothes. C is incorrect. Enzyme R works well only in acidic medium, while the washing powder solution is alkaline. D is incorrect. Enzyme S works well only in extremely high temperatures, which can cause damage to the clothes. 1
Ch 5 Metabolism and enzymes Suggested answers Section exercise (Ch 5, p.31) 1. (a) catabolism (b) anabolism (c) respiration (d) photosynthesis 2. T 3. F 4. T 5. F 6. F 7. T 8. F 9. F 10. (a) The activation energy of the reaction catalysed by enzymes is lower than the uncatalysed reaction. (b) It is because enzymes speed up chemical reactions taking place in an organism. 11. (a) C: enzyme D: product X: enzyme-substrate complex (b) lock-and-key hypothesis (c) Both the active site of the enzyme and the key have a specific shape. In order to open a lock, the key with a specific shape must fit into the lock. Similarly, each enzyme can act only on substrates that fit into its active site. (d) formation of protein or starch 12. B The enzyme is denatured upon heating. It loses its activity permanently. 13. C 14. D 15. (a) protease (b) pectinase (c) cellulose (d) protease and amylase 2
Ch 5 Metabolism and enzymes Suggested answers Revision exercise (Ch 5, p.33) 1. A The graph represents an anabolic process as the higher energy level of product indicates an increased energy level, i.e. energy is absorbed during the reaction. 2. B The activation energy of the reaction catalysed by the enzyme is lower than the uncatalysed reaction. The energy levels of products are the same in catalysed and uncatalysed reactions.

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture