can form in the body during respiration, and are chemically reactive, which means that they can chemically modify (and thus render useless) other biological molecules.

Peroxides

Explanation:

Peroxides are group of compounds that have the structure R-O-O-R. Peroxides have two oxygen atoms linked together by single covalent bond.

Hydrogen peroxide is most common peroxide and toxic byproduct of respiration. Hydrogen peroxide is involved in producing oxidative stress and thus producing damage to cellular components.

Peroxidases are enzymes that are found in wide range of organisms from bacteria to plants and animals. Most of these enzymes breakdown invloved in breakdown of hydrogen peroxide. Peroxidases act as antioxidant to reduce oxidative stress by cleavenging hydrogen peroxide radicles.

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