General Science - Biology MCQs

a. They give out oxygen

b. They give out carbon dioxide

c. The give out oxygen and carbon dioxide simultaneously

d. They take oxygen and give out carbon dioxide

ANSWER: See Answer

 

Oxygen is a natural element which no animal can live without. Fish and other aquatic animals depend on oxygen gas dissolved in water as much as people depend on oxygen gas in air. Many people are surprised to learn that fish and other aquatic organisms don’t use oxygen from water molecules (H2O). This is because the single oxygen molecule (O) is bound to the two hydrogen molecules (H2) and is not useable in this form. Instead, aquatic organisms depend on dissolved oxygen gas (O2), a colorless, tasteless and odorless substance that enters the water from plants and the atmosphere.