A scientist grew bacteria on gel in her lab. She wanted to find out if bacteria would grow faster on gel A or gel B.
she placed a few bacteria on gel A and a few on gel B.
After 24 hours, she observed how many bacteria were present.
Identify the independent and dependent variables.

The independent variable is type of gel and the dependent variable is the number of bacteria.

Explanation:

An experiment generally tests how one variable is affected by another. The affected variable is called the dependent variable. In the plant experiment shown above, the dependent variable is plant growth. The variable that affects the dependent variable is called the independent variable. In the plant experiment, the independent variable could be fertilizer—some plants will get fertilizer, others will not. The scientists change the amount of the independent variable (the fertilizer) to observe the effects on the dependent variable (plant growth). An experiment needs to be run simultaneously in which no fertilizer is given to the plant. This would be known as a control experiment. In any experiment, other factors that might affect the dependent variable must be controlled. In the plant experiment, what factors do you think should be controlled? (Hint: What other factors might affect plant growth?)

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