Photosynthesis and cellular respiration have a unique relationship in that the products of one process are the reactants of the other. For example the products of photosynthesis are reactants of cellular respiration. Select ALL of the molecules that are
produced in photosynthesis and then used in cellular respiration.

a. decomposes use carbon from dead organisms as fuel for cellular respiration, returning carbon dioxide back into the atmosphere.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.