Seconday 4 (MYE) - Essay (7)

7. Diagram 11 shows an experiment to test the action of a detergent with enzymes on oil residue on clothes. Three similar shirts P, Q and R with the same oil residue of equal size were washed at three different temperatures which are 15 °C, 65 °C and 35 °C, respectively.

Diagram 11 - Clothes with stains

(a) Explain your observations. ` [9 marks]

· At 15C – the low temperature did not promote rapid enzymatic reaction to break down the oil residue on clothes P [1]
· This is because the enzymes were inactive which caused low frequency of effective collision between the enzyme and its substrate to form an enzyme-substrate complex [1]
· Therefore, the rate of reaction was low [1]
· At 35C – the optimal temperature allowed rapid enzymatic reaction to break down the oil residue on clothes R [1]
· This is because the enzymes were actively moving to collide with its substrate to form an enzyme-substrate complex [1]
· Therefore, the rate of reaction was at optimal level [1]
· At 65C – the high temperature has denatured the enzymes [1]
· This caused the enzymatic reaction to stop and the oil residue on clothes Q was not greatly removed [1]
· Therefore, the rate of reaction was very low [1]


Diagram 12 - Graph

(b) Diagram 12 shows the effect of an increase in temperature on the reaction rate of an enzyme. Based on the above graph, explain why a rise in temperature increases the rate of reaction until it reaches the optimal temperature. [4 marks]

· At low temperature, the enzyme is inactive because due to the low kinetic energy of the enzyme and substrate molecules [1]
· As the temperature increases, the enzyme and substrate molecules are moving faster and the effective collision between the molecules becomes more frequent [1]
· This encourages the formation of enzyme-substrate complex which leads to the formation of products [1]
· At optimal temperature, the enzyme catalyses a reaction at the maximum rate [1]

(c) Explain what causes the decrease in the rate of reaction in Diagram 12 when the temperature exceeds the optimal temperature. [4 marks]

· Beyond the optimal temperature, any increase in temperature causes the rate of reaction to decrease sharply until it finally stops completely at about 60C [1]
· At high temperature, the chemical bonds holding the enzyme molecules in their precise configuration begin to break [1]
· This alters the 3D shape of the enzyme molecules and eventually destroys the active sites [1]
· This means that the substrate can no longer fit into the active sites of the enzyme as the enzyme has denatured [1]

(d) Enzymes are widely used in many industrial processes. State two enzymes that can be used in food production and their functions. [3 marks]

· Protease - Meat/Fish products [1]
· To tenderize meat/remove skin of fish [1]

· Cellulase – Seaweed products [1]
· To extract agar from seaweed [1]