1. a) Saliva amylase breaks down starch into maltose.
b)(ii) The rate of reactions in sets P and Q are slow because enzymes are less active at low temperatures. The rate of reaction in set R is the highest because it is in its optimum temperature of enzme activity. Starch is hydrolysed very quickly. There is no breakdown of starch in set S as enzymes are denatured after they have been boiled.
c) The reaction in set R will stop as salivary amylase is not active in acidic medium.
d) Increase the temperature to 40oC.
e)(i) Wash the clothes in water of temperatures between 37oC and 40oC.
(ii) A temperature range of between 37oC and 40oC is an optimum temperature for enzymes to break down stains.
2. a) To study the effect of pH on enzyme activity.
b) A: Clear solution
B: Cloudy suspension
C: Cloudy suspension
D: Clear solution
c) In test tube A, enzyme pepsin breaks down albumen because pepsin works effectively in an acidic medium. Neutral medium is not suitable for the action of pepsin as shown in test tube B. There is no breakdown of proteins in test tube C as there are no enzymes present.
d) It is because a temperature of 37oC is an optimum temperature for enzyme activity.
e) There is no albumen/substrate, so no reaction takes place.
Section B
3a)
| Characteristic | Explanation |
| Enzymes are biological catalysts and enzyme reactions are reversible | .Enzymes speeds up the rate of metabolism in the body. · Metabolic reactions are reversible · Enzymes remain unchanged at the end of reaction |
| Enzyme action is highly specific | · Acts on specific substrate only · Has an active site which is complimentary to certain substrate molecule only · Acts on ‘lock and key hypothesis’ |
| Enzymes are sensitive to pH | · Normally function best at neutral eg amylase · Some enzymes work best in acidic condition. For example, pepsin · Some enzymes work best in alkaline condition. For example, trypsin. |
| Enzymes are sensitive to temperature | · Work best at temperatures between 35oC and 40oC. · Enzymes are inactive at low temperatures. · They are denatured at high temperatures. |
b)
Acidity or alkalinity of solutions affect rate of reaction.
Each enzyme has an optimum pH so as to function at its maximum rate.
For example, pepsin at pH 3, salivary amylase at pH 7, trypsin at pH 8.5
Change in pH alters the charges on the active sites of an enzyme.
Alterations in the ionic charges also changes configuration of substrate.
Excess hydrogen ions attach to active sites of enzymes when pH is low.
Substrate is not able to bind to form enzyme-substrate complex.
Free hydroxyl ions attach to active sites when pH is high.
Extreme changes in pH alter the structures of enzymes and substrates.
4a) An enzyme has a specific three-dimension shape. As it is a protein molecule, the polypeptide chain fold to form an active site. Active site of enzyme complements the structure of the substrate it acts on. Substrate molecule fits into active site of enzyme like a key fits into a lock. Substrate is represented by the key while the lock represents the enzyme. When substrate fits into active site of enzyme, an enzyme-substrate complex is formed. Hydrogen and ionic bonds hold the enzyme-substrate complex. Reaction takes place to convert the substrate into products. The products have different shapes. The product then leaves the active sites.
b)Food processing industry
In meat industry, protease is used to tenderise meat.
In fish industry, protease is used to remove the skin of fish.
In dairy industry, lipase is used for ripening of cheese, rennin coagulates milk in the making of cheese, lactase is used to hydrolyse lactose.
In baking industry, amylase is used to breakdown starch in the making of bread, glucose oxidase is used for the stability of bread dough.
In brewing industry,zymase is used to hydrolyse sugar into ethanol.
In seaweed products, cellulase is used to hydrolyse cellulose to extract agar-agar from seaweeds.
Medical field
Trypsin is used to remove blood clots and clean wounds.
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