Final answer:
The test variable or independent variable in an experiment seeking to determine how light affects the 2) rate of photosynthesis is light. This is because the experiment is designed to manipulate light levels to observe changes in the rate of photosynthesis, making it the variable that is intentionally changed.
Step-by-step explanation:
Identifying the Independent Variable in a Photosynthesis Experiment:
The student's question is about determining the test variable or independent variable in an experiment that explores the effect of light on the rate of photosynthesis. In scientific experiments, the independent variable is the one that is manipulated by researchers in order to examine its effect on another variable. In this case, the independent variable is light because it is the factor that the student is changing to see how it affects the rate of photosynthesis, which is the dependent variable. The rate of photosynthesis will vary based on the different amounts or intensities of light, and this variation is what the student is aiming to measure.
Other variables that must be controlled in the experiment may include factors such as the amount of water, the type of soil, and the consistent temperature. Ensuring that these factors remain constant is critical to isolate the effects of the independent variable on the dependent variable and to avoid confounding results.