How is oxygen transported in different circulatory systems?

Oxygen is transported in the circulatory system through red blood cells, specifically bound to haemoglobin.

In more detail, oxygen is primarily transported in the body through the circulatory system, which is composed of the heart, blood vessels, and blood. The blood, specifically the red blood cells, play a crucial role in oxygen transport. Red blood cells contain a protein called haemoglobin, which binds to oxygen molecules and carries them from the lungs to the rest of the body.

The process begins in the lungs, where oxygen is inhaled into the alveoli, tiny air sacs where gas exchange occurs. Oxygen diffuses across the thin walls of the alveoli and into the capillaries, where it binds to haemoglobin in the red blood cells. Each haemoglobin molecule can bind up to four oxygen molecules, forming oxyhaemoglobin. This bright red, oxygen-rich blood is then pumped by the heart through the arteries and delivered to the body's tissues.

In the tissues, oxygen is released from the haemoglobin due to the lower oxygen concentration and higher carbon dioxide concentration. The now oxygen-poor, dark red blood returns to the heart through the veins and is pumped back to the lungs, where the process begins again.

In some organisms with different circulatory systems, such as insects, oxygen is transported directly to the tissues through a network of tubes called tracheae, bypassing the need for blood-based transport. In fish, oxygen is extracted from water through gills and transported in the blood bound to haemoglobin, similar to humans.

In all cases, the key to oxygen transport is the principle of diffusion: oxygen moves from areas of high concentration (the lungs or gills) to areas of low concentration (the body's tissues), facilitated by specialised structures and proteins.