The independent variable should be the plants you used.
Abiotic
An ecosystem involves both the biological (plants, animals, human beings) and non-biological (land, water, soil, and atmosphere) community which interacts as a system. More importantly, the living things are very dependent on the abiotic community since it cannot survive by itself. Every animal, plant and human needs the primary physiological needs of water, food and shelter provided by the abiotic system. <span>
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Biotic factors:
Plants
Microorganisms
Macroorganisms
I believe it is (B) It is not used up
Hope this helps!
- Rainbow :3