How does a single-celled organism breathe? ​

Cellular respiration takes place in each and every living cell. The mechanism of 'breathing' in unicellular organisms is different from multi-cellular organisms. Single celled organisms like Amoeba, Paramoecium etc. respire within their cell. Instead of the actual process of breathing, oxygen simply enters in their bodies by simple diffusion.

Explanation:

the sphincter muscles at the end of the digestive tract is the anus.

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands