Final answer:
In the experiment on radish seedlings, the dependent variable is the height of the plants, which is influenced by the independent variable, the color of the light under which they are grown.
Step-by-step explanation:
In the experiment where 20 radish seedlings were grown under different colors of light and their heights were measured once per week for 8 weeks, the dependent variable is the height of the plants. This is the outcome that is being observed and measured, and it depends on the conditions set by the experiment. The independent variable, which is what the experimenters change or manipulate, would be the color of the light (red, blue, green, and white light) under which the plants are grown.
It is essential to keep other factors constant in the experiment, such as the amount of water, nutrients, and the temperature, to ensure that any changes in the height of the plants can be attributed to the color of the light, which is the variable being tested. The control group in such an experiment could be the plants grown under white light, assuming white light represents the standard or normal lighting conditions for plant growth.