Biology
WAEC 2017
(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) above
(d) Outline the proce-dure used for testing for starch in a leaf
Explanation
(a). Characteristic of Enzymes;
- They are biological catalystsialter/speed up the rate of biological reactions
- remain chemically unchanged at the end of a reaction
- their actions are reversible
- they are specific in action/act on specific substrates
- enzymes are required in small amount
- are protein in nature
- they act best at optimum temperature/high temperature/denatures them/ low temperature inactivates them
- specific/sensitive to pH
- actions retarded by poisons/inhibitors
- some required co-enzymes to function.
(b)i. Digestive enzymes produced in the duodenum of humans
- Amylase
- Trypsin/chymotrypsin
- Lipase
ii. Substrates for each enzyme
- Amylase = starch
- Trypsin/chymotrypsin =protein
- Lipase = fats and oil
iii. Product of enzyme activity
- Amylase = maltose
- Trypsin/chymotrypsin = peptones/polypeptides/peptide
- Lipase =glycerol and fatty acid
(c)i. Importance of chlorophyll in plants
Absorbs/traps sunlight; for photosynthesis
ii. Macro-elements required for the formation of chlorophyll
iii. Deficiency symptoms of each macro-element in (c)ii
Nitrogen
- Chlorosis/yellowing of leaves
- Stunted growth
- Poor flower/fruit development
MagnesiuM
- Poor growth
- Chlorosis/yellowing of leaves
Iron
- Poor/stunted growth
- Chlorosis/yellowing of leaves
(d) Procedure for test for starch
- Detach/pluck off/take leaf to be tested from plant after 4 to 6 hours of exposure to sun to enable it to form starch
- Put leaf in boiling water for about 30 seconds to kill the cells
- Put boiled leaf in 70% warm alcohol/ethylated spirit in water bath to decolorise the leaf Rinse decolorised/brittle leaf in running cold water to soften the leaf tissues/remove alcohol
- Spread out on white tiles/watch glass and add a few drops of iodine solution
- Allow to stand for a few minutes
- It turns blue-balck showing/indicating presence of starch.
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