People have a very small surface area to volume ratio. They need a transport system to carry sugar and oxygen for cellular respiration, and waste products such as lactic acid and carbon dioxide must me removed
- Singular circulatory system – found in cold blooded animals usually because of their size, passes by the heart once and goes in one direction
- Double circulatory system – found in warm blooded animals, passes by the heart twice in dual directions.
Double circulatory system:
- Warm blooded animals need to maintain a constant body temperature, requiring a lot of energy, requiring a very efficient system for oxygen transport
- Cold blooded animals don’t need as much energy to keep body temperature constant. Therefore, a single circulatory system is efficient enough for a cold blooded animal