IB Biology SL

Revision Notes

6.2.3 The Blood System: Double Circulation

Double Circulation

The need for a circulatory system

  • All organisms need to exchange materials with their environments
    • Small animals with large surface area to volume ratios (or relatively inactive animals like jellyfish) can rely on diffusion alone to exchange oxygen, carbon dioxide and nutrients with their environment
    • Larger animals have smaller surface area to volume ratios, so diffusion alone is insufficient for exchange of materials between cells further from the surface of the organism with the environment
  • Circulatory systems are systems which carry around fluids containing materials needed by the organism, as well as waste materials that need to be removed

Humans have a closed double circulatory system

  • It is a closed circulatory system because blood is pumped around the body and is always contained within a network of blood vessels
  • It is a double circulatory system because in one complete circuit of the body, blood passes through the heart (the pump) twice
  • In the pulmonary circulatory system
    • the right side of the heart pumps blood deoxygenated blood to the lungs for gas exchange
    • Pressure of the blood is lower in the pulmonary system, this prevents damage to the lungs
  • In the systemic circulatory system
    • Blood returns to the left side of the heart from the lungs
    • The left ventricle then pumps the oxygenated blood (at high pressure) around the body

The double circulatory system in mammals, IGCSE & GCSE Biology revision notes

The double circulatory system in mammals

Main circulatory system structures table1. Closed Double Circulatory System Table, downloadable AS & A Level Biology revision notes

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