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

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.

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,

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emerald ash borer

the emerald ash borer is a green buprestid or jewel beetle native to north-eastern asia that feeds on ash species. females lay eggs in bark crevices on ash trees, and larvae feed underneath the bark of ash trees to emerge as adults in one to two years. hope this !

can you make it bigger i can't see it