I have researched and thought further into my ideas:

What types of soil affect the growth of one type of seed:

Independent variable: the two or three different soils the plants are put in.

Controlled variable: the amount of water and light, same type of plants/seeds, same amount of soil for each plant/seed, same temperature and same planting pots.

Dependent variable: the growth and structure of the plants.

Does the colour of light have an affect on the growth rate of a plant?:

Independent variable: the different colours of light subjected to the plant.

Controlled variable: the same plants, the plants are put into the same environment, everything else that is done to the plants, like watering, are done at the same time.

Dependent variable: the height or structure of the plant after the period of time for the experiment.

Does the amount of light have an affect on the growth of plants?

Independent variable: the different amount of light that the plant is subjected to.

Controlled variable: the same plants, the same time they are watered and the same things are done to both of the plants.

Dependent variable: the height and growth of the plants a certain period of time.

Here are some independent, dependent and controlled variables that I have thought of for the different ideas for my project. However, think some of the ideas I have researched and thought of are either too simple or cannot be done without the proper equipment needed which I have.

I will be back on later, to decide which one I have decided to do for my project.

BYE.