Science Biology Tma C

IGCSE Science Suggested Answers to Biology Tutor-Marked Assignment C

Question 1

A student measured the time taken for a reaction to finish at a range of different temperatures. He also measured the pH of his solutions to see if they varied. At 10OC the reaction took 1 minute 35 seconds. At 15OC it took 65 seconds, at 20OC 42 seconds, and at 25OC half a minute. The pH was exactly 7 for the 10OC result, 7.2 for the next, 7.1 for the third and 7.4 for the last (pH has no units).

Record these results in a suitable table.

Answer:

Temperature (OC)

Time (s)

pH

10

95

7.0

15

65

7.2

20

42

7.1

25

30

7.4

Recorded as a table (1), all lines drawn (1), numbers correct (1), units in heading (1), no units after figures (1), all times converted to seconds (1), all readings given same number of decimal places (1)

(7 marks)

IGCSE Science Biology TMA C

2

Question 2

In a classic experiment carried out by the biologist Hopkins in the 20th century, 20 young rats were divided into two groups. One group was fed on a diet of pure carbohydrate, lipid and protein; the other was fed the same diet, but with some added milk. The rats were weighed every day. After 18 days the diets of the two groups were swapped over. Here are the results of the experiment in the form of a graph:

Average mass of rats

Time in days

Diet switched

Rats with milk

IGCSE Science Suggested Answers to Biology Tutor-Marked Assignment C

3

(a) Why did Hopkins use two sets of rats? (2 marks)

(b) Explain why 20 rats were used, rather than just 2. (2 marks)

(c) Name two types of nutrient that were missing from the diet of only one of the groups. (2 marks)

(d) Suggest why Hopkins used young rats, rather than adult rats, for his investigation. (2 marks)

(e) Explain the importance of switching