ideas, anyone?

I've been thinking about my ideas, and so far i've only come up with a few and all have something to do with plants 0_o

- does the amount of sunlight affect the rate of growth?
independent: the hours of exposure to sunlight
dependent: the rate of growth, and the colour of the leaves

- Does the amount of water given plants affect their growth?
independent: the amount of water given to the plant
dependent: the growth rate, and leaf colour

- what liquids will a plant grow best with?
independent: the type and amount of liquid given to the plant
dependent: the growth rate, and health of the plant

- in what kind of material to seeds grow best in (sand, dirt, clay, etc)
independent: the type of material in which the plant grows
dependent: the growth rate (of it grows at all)