Theory question 102
Food Substances and Enzymes(a) State four characteristics of enzymes. (b)(i) List two digestive enzymes produced in the duodenum of humans. (ii) Name the substrate that each enzyme listed in 2(b)(i) acts on. (iii) State the products of each enzyme activity in 2(b)(ii). (c)(i) State one way in which chlorophyll is important in plants. (ii) Name two macroelements that are required for the formation of chlorophyll in plants. (iii) State one deficiency symptom of each macroelement named in 2(c)(ii). (d) Outline the procedure used for testing for starch in a leaf.
Show the model answer
(a) Any four: they are proteins; they are specific (each acts on one substrate); they speed up reactions (biological catalysts) and are not used up; they work best at an optimum temperature and are destroyed (denatured) by high heat; they work best at an optimum pH; many reactions are reversible; needed in small amounts; slowed by inhibitors.
(b) Enzymes in the duodenum (from pancreatic juice), any two, with substrate and products: amylase – starch → maltose; trypsin – proteins → peptides (polypeptides); lipase – fats and oils → fatty acids and glycerol.
(c)(i) Chlorophyll traps (absorbs) light energy for photosynthesis.
(ii) Magnesium and nitrogen.
(iii) Magnesium deficiency: yellowing between the veins of older leaves (chlorosis). Nitrogen deficiency: general yellowing of leaves and stunted growth.
(d) Pick a leaf that has been in sunlight; boil it in water for about a minute to kill it and break the cell membranes; put it in alcohol (ethanol) in a test tube heated in a water bath to remove the chlorophyll; dip it in warm water to soften it; spread it on a white tile and add iodine solution; a blue-black colour shows starch is present.
For the starch test, keep the steps in order and say why each step is done.