Activators and inhibitors regulate
oxygen consumption in cells
enzyme activity within metabolic pathways
the release of chlorophyll in plants

The correct answer would be "enzyme activity within a metabolic pathway".

Enzymes are biocatalysts which helps in escalating the rate of a biochemical reaction in an organism without getting consumed in the reaction.

These are usually protein in nature (except ribozyme) and are regulated with the help of allosteric regulation that is, binding of an effector molecule regulates the functioning of an enzyme.

The molecules which bind to the enzyme in order to activate the enzyme are termed as enzyme activators. For example,  fructose 2,6-bisphosphate activates phosphofructokinase 1.

In contrast, the molecules which inhibit the functioning of an enzyme are termed as enzyme inhibitors.