Question

what is the principle in exchange of gases in hydra and planarians​

Answer 1

All living things obtain the energy they need by metabolizing energy-rich compounds, such as carbohydrates and fats. In the majority of organisms, this metabolism takes place by respiration, a process that requires oxygen .
In the process, carbon dioxide gas is produced and must be removed from the body.

Answer 2

Answer:

Gas exchange in Hydra and Planaria:

Explanation:

Hydra:

Hydra is a genus of small, fresh-water organisms of the phylum Cnidaria and class Hydrozoa. They are habituated to the temperate and tropical regions.

The cells of Hydra are made up of two layers that form their body. The body of Hydra will be in direct contact with the water.

Thus the exchange of gases takes place directly between the cells of hydra and the environment. This process of exchange of gas is known as diffusion.

Planarians:

Planarians are one type of flatworms and they live in both salt water and fresh water rivers and ponds.

Planarians are capable of regenerating their lost body parts.

As their body is so thin, oxygen and carbon dioxide exchange take place through its skin into the environment and this is known as diffusion.