Fish:
- Fish have a single circulatory system, which means that blood passes through the heart only once during one complete circuit of the body.
- The heart of a fish consists of two chambers: an atrium and a ventricle.
- Deoxygenated blood from the body enters the heart through the atrium, and then flows into the ventricle.
- The ventricle then contracts and pumps the deoxygenated blood out to the gills, where it picks up oxygen.
- The oxygenated blood then flows back to the heart through the atrium and into the ventricle.
- Finally, the ventricle contracts once again and pumps the oxygenated blood out to the rest of the body.
Amphibians:
- Amphibians, such as frogs and salamanders, also have a single circulatory system.
- Their hearts consist of three chambers: two atria and one ventricle.
- Deoxygenated blood from the body enters the heart through the right atrium, and oxygenated blood from the lungs enters the heart through the left atrium.
- Both atria then contract and pump the blood into the ventricle.
- The ventricle then contracts and pumps the oxygenated blood out to the rest of the body, while the deoxygenated blood is pumped to the lungs.