Question on: JAMB Biology - 2024

Gaseous exchange occurs directly through the plasma membrane in single-celled organisms and simple multicellular organisms.

• Paramecium: is a single-celled organism, and therefore it relies on diffusion across its plasma membrane for gas exchange.
• Hydra: While multicellular, it has a simple body plan where all cells are close to the external environment, and gas exchange occurs directly via diffusion.
• Flatworms and Earthworms: have more complex body plans and specialized respiratory structures (or, in the case of earthworms, their skin) for gas exchange, rather than relying solely on the plasma membrane.