Effects of climate change and predictionsEdexcel A-Level Biology A: Subtopic test

1. 1
   A student investigates the effect of temperature on the activity of catalase in a suspension of liver tissue. She keeps the pH constant using a buffer, mixes the enzyme with hydrogen peroxide at each temperature and measures the initial rate of oxygen production. At 20 °C the initial rate was 0.012 cm³ s⁻¹ and at 30 °C it was 0.030 cm³ s⁻¹. At 60 °C no oxygen was produced.

   (a)

   What is the Q10 for the reaction between 20 °C and 30 °C?

   [1 mark]

   • A0.4
   • B1.5
   • C2.5
   • D0.018

   (b)

   Why was no oxygen produced at 60 °C?

   [1 mark]

   • AHydrogen bonds in the tertiary structure broke, changing the shape of the active site so the substrate could no longer bind.
   • BThe kinetic energy of the hydrogen peroxide molecules fell, so there were no collisions with the enzyme.
   • CThe peptide bonds of the enzyme were hydrolysed, releasing free amino acids.
   • DAll of the hydrogen peroxide had been used up before the rate was measured.

   (c)

   Explain why the student measured the initial rate of the reaction rather than the rate after several minutes.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a woodland in the Netherlands, great tits time their breeding so that the chicks hatch when winter moth caterpillars are most abundant, because the chicks are fed mainly on caterpillars. Over 25 years the mean spring temperature has risen. The caterpillars now hatch from their eggs 14 days earlier than they did 25 years ago, whereas the date on which great tits lay their eggs has advanced by only 4 days.

   (a)

   Which effect of climate change does this woodland illustrate?

   [1 mark]

   • AA shift in species distribution towards cooler regions
   • BA loss of genetic variation in the caterpillars
   • CA change in rainfall pattern in the woodland
   • DA change in the timing of life cycles that has caused a mismatch between predator and prey

   (b)

   Which is the most likely reason that the caterpillars hatch earlier in warmer springs?

   [1 mark]

   • AWarmer conditions reduce the rate of enzyme-controlled reactions in the eggs, so the eggs hatch sooner.
   • BHigher temperatures increase the rate of enzyme-controlled reactions in the eggs, so development is faster.
   • CWarmer conditions cause mutations in the caterpillar eggs that make them hatch earlier.
   • DWarmer springs increase rainfall, which makes the eggs hatch earlier.

   (c)

   Predict, and explain, the effect of this change on the size of the great tit population.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates the effect of temperature on the development of brine shrimp. At each temperature she places 100 eggs in salt water of the same concentration in a thermostatically controlled water bath and counts the newly hatched shrimp every hour. Her results for the mean rate of hatching are: 15 °C, 0.5 % of eggs per hour; 20 °C, 0.9 % per hour; 25 °C, 1.6 % per hour; 30 °C, 1.3 % per hour.

   (a)

   Describe how the student should set up the investigation so that her results are valid.

   [3 marks]

   (b)

   Calculate the Q10 for the rate of hatching between 15 °C and 25 °C. Suggest an explanation for the lower rate at 30 °C than at 25 °C.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   On a mountain in northern Europe the mean annual temperature has risen by 1.2 °C over 50 years. Spring now begins earlier and summer rainfall has become less predictable. Surveys show that the range of an alpine butterfly has moved 150 m higher up the mountain since 1970 and that its main food plant now flowers 12 days earlier. A computer model, which extrapolates the current rate of change, predicts that the butterfly will have no suitable habitat on the mountain by 2060.

   (a)

   Explain how climate change may have caused the changes in the distribution of the butterfly and in the flowering time of its food plant.

   [6 marks]

   (b)

   Evaluate the reliability of the model's prediction that the butterfly will have no suitable habitat on the mountain by 2060.

   [6 marks]

   Total for question 4: 12 marks

End of questions