Bio past paper Essay
Bio past paper
In an experiment to study the effect of pH on enzyme activity, five test-tubes containing equal volumes of an enzyme solution each at a different pH were prepared. A 1 cm3 cube of coagulated (clotted) egg white was then added to each tube. The tubes were allowed to stand at a room temperature of 25 oC. The time taken for the disappearance of the cube in each tube was recorded as follows .
A sample of bean extract was refrigerated at 4 C and then allowed to warm to room temperature. If the experiment was repeated using this sample, would the catalase activity be different from that of the previous experiment ? Explain your answer.
One day, when Keith and Jane walked past a fresh fruit juice shop, Keith noticed that some pears were cut into pieces and stored in a tank of water before use.
(a) Keith thought that the shopkeeper stored the cut pears in water in order to extract more juice. Explain the biological principle behind Keith’s idea.
(3 marks) Jane disagreed with Keith because she found that the shopkeeper also stored whole pears in water tanks. Explain why this observation provides Jane with evidence to oppose Keith’s idea. (2 marks)
(c) Suggest one possible hygienic problem of storing the cut pears in water tanks. (1 mark)
A student carried out an investigation to compare the activity of three brands of yeast. He added a mixture of fixed amounts of dough and yeast into a measuring cylinder and recorded the volume of the mixture. After putting the measuring cylinder in a water bath at 30oC for one hour, the volume of the mixture was recorded again. The diagram below shows his set-up:
(a) The results of the investigation are shown in the table below. Complete the table by finding out the percentage change in the volume of mixture for brand C.