IB ESS Unit 2: Ecosystems & Ecology (id: 08cf6c086)

本题目来源于试卷: IB ESS Unit 2: Ecosystems & Ecology，类别为 IB环境系统与社会

[单选题]
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Which of the following is not a method of keeping a controlled variable at a constant value throughout this particular experiment?

A. Placing the tube containing Elodea in a water bath
B. Using the same volume of sodium hydrogen carbonate solution for each trial.
C. Placing the Elodea at a constant distance from the same light source for each trial.
D. Using the same concentration of sodium hydrogen carbonate solution for each trial.


参考答案:  A


本题详细解析:
Since the experiment is about testing the temperature; the ted:n . tgkxabh9e0uvd. gvt5wb 9a17*tmperature would be the independent variable, not the controlled variable. A water bath wo n kw0tgtb5ue v.d*t xb9hvad9g7a.:1uld be used in this experiment to set up different increments of the independent variable.
When investigating the effect of temperature on photosynthesis, the other limiting factors (concentration of carbon dioxide and light intensity) must be controlled. The light intensity can be controlled by placing the test tube containing the Elodea at a constant distance from the same light source for each trial (option C) to make sure that the light intensity is the same for all trials.
Using the same volume and concentration of sodium hydrogen carbonate solution (option B and option D) ensures that the source of carbon dioxide is controlled, and it is not a limiting factor.

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