QUESTION 26 (7 marks)
Scientists investigating the impact of ocean temperature on the evolution of marine organisms compiled the data shown.
30
35
Cretaceous | Paleogene | Neogene |
25
30
20 Body length (cm)
Temperature (°C) 25
15
10
20
5
15
0
100
80
60
40
20
0
Time (millions of years ago)
Key Body length Ocean temperature
a) Identify the abiotic changes that occurred at the boundary of the Cretaceous and Paleogene periods. Refer to the data in your response.
[2 marks]
b) Identify a relationship between ocean temperature and body length.
[1 mark]
c) Use the principles of natural selection to provide a possible explanation for the trend in body length over geological time.
[3 marks]
d) Identify the type of phenotypic selection that has occurred.
[1 mark]
QCAA guide · typeset solution
QCAA sample response and mark allocation
26a) | At the end of the Cretaceous period, the ocean temperature dropped from ~21 oC to ~16 oC and then rose again to ~24 oC at the beginning of the Paleogene period. | • identifies the changes [1 mark] • provides appropriate data [1 mark] |
26b) | As ocean temperature decreases, body length increases. | • identifies that as ocean temperature decreases, body length increases [1 mark] |
26c) | Larger body size provided a selective advantage to marine organisms. Organisms with larger bodies were more likely to survive until reproductive age, when they could pass on the advantageous alleles to their offspring. This caused the allele/s for increased body size to become more common in the population over time. | • explains the observed trends, referring to - phenotypic variation [1 mark] - differential survival and reproduction [1 mark] - change over time [1 mark] |
26d) | Directional selection | • identifies directional selection [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.