<span>The word from the pick list that fits here is "enzyme". Enzymes are normally spcialised protein molecules and they act as catalyst ie agents to speed up a reaction in causing traits to develop in the genes of organisms in reaction to chemical stimulants.</span>
Plants need nitrogen in order to grow. Nitrogen is abundant in the earth's atmosphere, but plants cannot use it in that particular form (nitrogen gas). Certain bacteria which reside on some plant roots are able to change atmospheric nitrogen into a form that plants can use (ammonia).
This is because HIV weakens the immune system and so the body becomes more susceptible to infections or illnesses
