Single and Double Circulatory Systems

Question 1

Single circulatory system

Answer 1

Single circulatory system (fish): One in which blood flows through heart once for each circuit of the body. Heart -> gills -> body -> heart…
Disadvantages:
- Blood pressure drops as blood passes through tiny capillaries of the gills.
- Blood has low pressure as it flows back towards the body – flows slowly.
- The rate at which O2 and nutrients are delivered to respiring tissues and waste is removed, is limited.
Fish are not as metabolically active as mammals, as they don’t maintain their body temp. Therefore, less energy is needed, so a single circulatory system is sufficient.

Question 2

Double circulatory system

Answer 2

Double circulatory system (mammals): One in which blood flows through the heart twice for each circuit of the body. Heart -> body -> heart -> lungs -> heart…
2 separate circuits:
1. Pulmonary circulation – carries blood to the lungs to pick up oxygen.
2. Systemic circulation – carries O2 and nutrients around the body to tissues.
Advantages:
- Blood pressure mustn’t be high in pulmonary circulation, as it may damage capillaries in the lungs.
- The heart can increase pressure after blood has passed through the lungs, so blood is under higher pressure and flows faster through the body – faster delivery of O2 to respiring tissues.
- The systemic circulation can carry blood at higher pressure than the pulmonary circulation.
Mammals are very metabolically active (maintaining temp increases activity). Supplying the energy needed for activity and heat to keep the body warm requires energy from food released in aerobic respiration. To release enough energy cells, need good supply of O2 and nutrients and good removal of waste products.