Suggest a suitable word for each of the following statements.

(a) Chemicals added to food to prevent the growth of microorganisms.

(b) Nitrogen-fixing microorganisms present in the root nodules of legumes.

(c) The agent spreads pathogens from one place to another.

(d) Chemicals which kill or stop the growth of pathogens.

(a) Preservatives:

1. Preservatives are the chemicals added to food.
2. They prevent microbial infection without altering the taste or appearance.

(b) Rhizobium:

1. Rhizobium is a nitrogen-fixing bacteria that fix the atmospheric nitrogen into that form (i.e. nitrates, nitrates) that is usable for plants.
2. It is the genus of Gram-negative soil bacteria and it forms a symbiotic association with the leguminous plants.

(c) Carrier/Vector:

1. Carrier or vectors are the agents of transmission of disease.
2. The carrier is asymptomatic and transmits the diseases to other organisms.
3. For example, mosquitoes are vectors for many diseases such as malaria, dengue, and West Nile fever.

(d) Antibiotics:

1. Antibiotics are antimicrobial agents for inhibiting or killing the growth of microbes.
2. They are produced mostly by bacteria.