2017年5月IB生物SL真题下载-Paper2
1. Native oyster populations are decreasing where rivers meet the ocean along the northwest coast of North America. These oyster populations are being attacked by a gastropod.
It is known that oysters and gastropods have hard parts composed of calcium carbonate and that ocean acidification is increasing. Studies were carried out using juvenile oysters and gastropods to investigate the effects of acidification on the decrease in the population of oysters.
The first step was to raise oysters in two different mesocosms. One had seawater at a normal concentration of CO2 and the other had sea water with a high concentration of CO2. Gastropods were raised in two further mesocosms with normal and high CO2 concentrations respectively.
(a) Outline how acidified sea water could affect the shells of the oyster.
A juvenile gastropod will attack a juvenile oyster by using its tongue-like structure (radula) to drill a hole through the oyster shell. Once the hole has been drilled, the gastropod sucks out the soft fl esh. Researchers investigated the shell thickness at the site of the drill hole in relation to the size of the oyster. The results are seen in this graph.
(b) Outline the trends shown in the data in the graph.
Equal numbers of oysters raised in seawater with a normal CO2 concentration and in seawater with a high CO2 concentration were then presented together to the gastropod predators in seawater with a normal CO2 concentration. The same numbers of oysters from the two groups were also presented together to the gastropods in seawater with a high CO2 concentration. The bar charts show how many of the oysters were drilled by the gastropods and the mean size of drilled oysters.
(c) Estimate how much smaller drilled oysters raised in seawater at a high CO2 concentration were than drilled oysters raised in seawater at a normal CO2 concentration.
(d) (i) Deduce from the data in the bar charts which factors were and were not correlated significantly with the number of oysters drilled by the gastropods.
(ii) Suggest reasons for the differences in the numbers of oysters drilled, as shown in the bar charts.
(iii) The radula in a gastropod is hard but not made of calcium carbonate. Outline how this statement is supported by the drilling success of the gastropods in seawater with normal or high CO2 concentrations.
(e) Using all the data, evaluate how CO2 concentrations affect the development of oysters and their predation by gastropods.
2017年5月IB生物SL真题余下省略！
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