General exam questions

Question 1

Explain the advantage of presenting results as a ratio (2)

Answer 1

Allows comparison

Number/sample size may vary

Question 2

Why did the scientists carry out a control experiment? (1)

Answer 2

To compare

Question 3

A statistical test showed that the difference between the two frequencies of the t allele was significant at the P=0.05 level.

Use the terms probability and chance to help explain what this means. (2)

Answer 3

There is a 0.05 probability

That the differences in results are due to chance.

Question 4

Scientists investigated the effect of the number of feather mites on breeding success.

State a null hypothesis that would be appropriate for this investigation. (1)

Answer 4

There is no correlation between the number of feather mites and breeding success.

Question 5

Scientists investigated the effect of the number of feather mites on breeding success.

The correlation coefficient that they obtained had a negative value. What does a negative value indicate about these data? (1)

Answer 5

• Negative correlation between number of feather mites and breeding success
• As number of feather mites increases, breeding success decreases.

Question 6

Scientists investigated the effect of iron deficiency on the production of triose phosphate in sugar beet plants.

Explain why it was important to grow the plants under the same conditions up to ten days before the experiment. (1)

Answer 6

So any difference is due to iron deficiency (variable being investigated).

Question 7

Scientists investigated the effect of iron deficiency on the production of triose phosphate in sugar beet plants.

The plants were left in the dark for 6 hours before the experiment. Explain why. (1)

Answer 7

Amount of triose phosphate will be similar at start.

Question 8

When analysing their results, the scientists used the percentage of lizards infected at each site, rather than the number of lizards infected. Explain why. (2)

Answer 8

Allows comparison

Number/sample size varies

Question 9

Calculate the percentage difference in the average life expectancy for females compared with males in the USA in 2010.
Males = 80
Females = 84

Answer 9

Percentage difference = difference in values
________________ x 100
smaller value
84-80 = 4
4/80 = 0.05 x 100 = 5%

Question 10

A student investigated the effect of different wavelengths of light on the rate of photosynthesis.

Other than temperature and pH, give 2 factors which should be kept constant during this investigation. (2)

Answer 10

1. Intensity of light;
2. Amount/number/mass/species of
   algae/photosynthesising cells;
3. Carbon dioxide (concentration/partial
   pressure);
4. Time;