Which best explains the importance of nitrogen in the cycling of energy and
matter?
a nitrogen increases protein production in plants.
b nitrogen decreases protein production in plants.
c nitrogen decreases the effectiveness of photosynthesis.
d nitrogen increases the effectiveness of photosynthesis.

The correct option is A.

Explanation:

Nitrogen is a gas that is present in high quantity in the atmosphere. This gas contribute significantly to the growth and development of plants and that of animals. Nitrogen in the atmosphere usually get incorporated into the soil via lightening and it is typically fixed by nitrogen fixing bacteria. This nitrogen is then used as part of the nutrients that plants need to grow and develop and it is also used in the production of protein in plant parts. Animals use these plants as source of proteins in their diets. Ultimately the waste products derived from protein is return to the soil where they are broken down by decomposers to nitrogen forms that plants can use. Thus, nitrogen increases the production of proteins in plants.

to this one it would be receptive field