Answer:
This process is called cellular respiration.
Step-by-step explanation:
Human- We get oxygen by breathing in fresh air, and we remove carbon dioxide from the body by breathing out stale air.
Flatworm- In order to breathe, they must be able to pass oxygen and carbon dioxide in and out of their bodies through their skin by diffusion. In order for this to work, even the largest flatworms are extremely thin.
Fern- Plants release oxygen during the day in the presence of natural light through the process of photosynthesis. While at night, the plants uptake oxygen and release carbon dioxide.