This investigation is carried out with pondweed under a lamp. Fig. 1 shows an aquatic plant in a funnel with a test tube collecting gas. As light intensity ...
Question 1 Report
This investigation is carried out with pondweed under a lamp. Fig. 1 shows an aquatic plant in a funnel with a test tube collecting gas. As light intensity increases, more oxygen is produced by photosynthesis in leaf cells. Oxygen diffuses from the cells into surrounding water and forms bubbles that rise into the test tube. A student moves the lamp closer in equal steps, keeping the temperature controlled with a water bath.
(a) Identify the gas collected in the test tube. [1]
(b) Explain why oxygen leaves the pondweed cells. [2]
(c) Record one variable, other than lamp distance, that must be controlled. [1]
(d) Which measurement could the student use to compare oxygen production over five minutes? [1]
(e) Use the figure to explain why the test tube is filled with water at the start. [1]
(f) Suggest why the rate may stop increasing when the lamp is very close. [1]
Answer Details
(a) Oxygen [1] (b) Oxygen concentration becomes higher in photosynthesising leaf cells than in surrounding water [1]; oxygen diffuses down its concentration gradient [1] (c) Any one: temperature; species/length of pondweed; time; carbon dioxide concentration [1] (d) Volume of gas collected / number of bubbles [1] (e) It prevents trapped air from being measured / allows collected gas to displace water [1] (f) Another factor becomes limiting, for example carbon dioxide concentration or temperature [1]
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