Science I need help since I’m not smart

Carbon dioxide

Explanation:

If you hold your breath for a while, you will struggle to breathe. That is because your cells are running out of oxygen because it is being formed into carbon dioxide. Of course, your body cannot survive if it has too much carbon dioxide circulating through it, so you breathe it out.

a community that experiences major changes undergoes progress

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.