2. Blood is in direct contact with the tissue cells. 3. Exchange of materials occurs directly between blood and tissue cells. 4. Blood flow is very slow. 5.
Blood has a very low pressure. 6. The system is less efficient as the blood flow cannot be regulated. 7.
Respiratory pigment, if present, is dissolved in the plasma, no red corpuscles are present. 8. Occurs in arthropods and most molluscs.
1. Blood flows in closed tubes, the blood vessels, with definite walls. 2. Blood does not come in direct contact with the tissue cells. 3. Exchanged of material between tissue cells and blood occurs via tissue fluid.
4. Blood flow is quite rapid 5. Blood has a high pressure 6. The system is more efficient as the blood flow can be regulated 7.
Respiratory pigment is present, and may be dissolved in the plasma but is usually held in red blood corpuscles. 8. Occurs in annelids and vertebrates.