2. what effect does amount of water have on plant growth?
independent variable:
dependent variable:
3. does a student's bedtime effect a student's energy level?
independent variable:
dependent variable:
4. what effect does exercise have on strength?
independent variable:
dependent variable:
5. does a person's height effect their ability to play basketball?
independent variable:
dependent variable:

2. It's a dependent variable,  3. Dependent variable,  4. Dependent variable,  5. Independent variable

Explanation:

As it's seen that plants and grow without the water which is their prime source of development and tissue takes nutrients from the soil and hence necessary for the growth even cactus needs small quantities of moisture or water but the water itself depends on the availability of rain. A student bedtime behavior is affected by his/her energy levels of the body if he is tired will fall to sleep soon. Thus dependent Similarly, exercise tones up the body muscles and which in turn leads to better performance of daily activities. A person's height and basketball ability are different as one gradually develops a good height due to the stretching exercise of the muscles and hence independent ability.

And a) oxygen i believe