Fig. 1 illustrates a field station test on a pond snail. A student places one snail in a dark, airtight chamber of pond water. An oxygen probe records the c...
Question 1 Report
Fig. 1 illustrates a field station test on a pond snail. A student places one snail in a dark, airtight chamber of pond water. An oxygen probe records the concentration of dissolved oxygen in the water. The chamber is kept in a water bath at 18 degrees C so that temperature does not change. Before the cap is fitted, the oxygen concentration is 8.4 mg dm-3. After 12 minutes, it is 6.0 mg dm-3. The water has been filtered to remove small plants and algae. The student uses the result to investigate aerobic respiration in the animal's body cells, where glucose is used to release energy.
(a) Identify the gas whose concentration decreases in the chamber. [1]
(b) Calculate the mean decrease in oxygen concentration per minute. Give your answer in mg dm-3 min-1. [3]
(c) Explain why the chamber is kept in a water bath at a constant temperature. [2]
(d) Explain how the oxygen taken from the water is used by the snail's cells during aerobic respiration. [4]
Answer Details
(a) oxygen [1] (b) decrease in concentration = 8.4 - 6.0 = 2.4 mg dm^-3 [1]; time = 12 minutes [1]; 2.4 / 12 = 0.20 mg dm^-3 min^-1 [1] (c) temperature affects the rate of respiration / enzyme-controlled reactions [1]; keeping it constant makes this a fair test so any oxygen decrease can be attributed to respiration by the snail [1] (d) oxygen moves from the water into the snail / into its blood [1]; it is transported to body cells [1]; oxygen is used with glucose in aerobic respiration [1]; respiration releases energy for activities such as movement, growth or active transport [1]
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