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Elodea is a plant that lives in water. Like all plants, elodea can make its own food through
process called photosynthesis. Oxygen gas is also produced during photosynthesis.
Photosynthesis can only happen in the presence of light. To measure the rate of
photosynthesis, a piece of elodea can be placed in an inverted test tube filled with a
sodium bicarbonate solution. Oxygen gas produced by photosynthesis will collect at the
top of the test tube.
A student has designed an experiment using elodea plants. The experimental setup is
shown in Figure 1-4
Which of the setups would serve as the control of the experiment?
Bucket
Lamp
Flashlight High
Natural
Elodea
Sodium
bicarbonate
solution

Respuesta :

The controlled variable is kept constant during the whole experiment in all the different study groups. In this experiment, Sodium  bicarbonate  solution is the controlled variable.

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During an experiment, the controlled variables are kept constant in the control groups and the experimental groups. Unlike the independent variable, the controlled variables do not influence the results. These variables do not affect the response of the dependent variable.  

In this experiment,

  • The independent variable → presence/absence of light reaching the plant. The researcher regulates the amount of light by using different elements such as the bucket, lamp, flashlight, and natural light.
  • The dependent variable → oxygen production through which the researcher measures the photosynthesis rate.
  • The controlled variableSodium  bicarbonate  solution. It provides carbon dioxyde, and must be constant in the four scenarios to avoid an effect on the results.      

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