Question

How do fish and underwater plants breathe?

Answer 1

Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes.

Complete answer:
When the water moves through the gills, the dissolved oxygen from the water passes through the thin walls of gills and blood vessels, and enters the blood. Apart from this, the waste carbon dioxide present in the blood passes into the water, thus helping fish to breathe underwater.

Plants and algae perform photosynthesis, which converts atmospheric carbon dioxide and water to sugar using the energy from the sun. This process produces oxygen as a by-product and this by-product of green life is thought to have given rise to the current atmospheric oxygen levels of around 20%.

Aquatic respiration is the process whereby an aquatic organism exchanges respiratory gases with water, obtaining oxygen from oxygen dissolved in water and excreting carbon dioxide and some other metabolic waste products into the water. Dolphins and whales are similar to humans in many ways: They give birth to live babies instead of laying eggs, are warm-blooded and have lungs for breathing air.

Note: Plants give out carbon dioxide not only at night but during the day too. It happens because of the process of respiration in which plants take in oxygen and give out carbon dioxide. As soon as the sun rises another process called photosynthesis starts, in which carbon dioxide is taken in and oxygen is given out.