The oxygen consumed in the oxidation of an organic compound by microorganisms in the aquatic ecosystem is called __________.

Oxygen used by microbes to break down organic matter in water is the biochemical oxygen demand.

Dissolved oxygen is simply the oxygen already present in the water, not the amount consumed.

Chemical oxygen demand measures oxygen needed to oxidise wastes chemically, not by microbes.

Theoretical oxygen demand is a calculated value from the chemical formula, not a measured microbial use.

A high biochemical oxygen demand signals heavy organic pollution and low water quality.

Clean rivers show low biochemical oxygen demand while sewage-laden water shows very high values.