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 transport materials to where they are needed inside their tissues
    • Small organisms (or relatively inactive animals like jellyfish) can rely on diffusion alone to transport oxygen, carbon dioxide and nutrients around their bodies
    • Larger organisms have more layers of cells, so diffusion alone is insufficient for transport of materials between cells further from the exchange surface of the organism
  • Circulatory systems are systems which transport fluids containing materials needed by the organism, as well as waste materials that need to be removed
    • Circulatory systems ensure that fluids containing these substances reach all of the cells in an organism quickly enough to supply their needs and remove waste

Humans have a closed, double circulatory system

  • A closed circulatory system is one in which blood is contained within a network of blood vessels
    • As opposed to an open circulatory system in which the fluid fills the body cavity e.g. as in insects
  • A double circulatory system passes through the heart twice for every one complete circuit of the body, with blood passing through two separate circuits known as pulmonary and systemic circulation
    • In the pulmonary circulatory system
      • The right side of the heart pumps deoxygenated blood to the lungs for gas exchange
      • Blood pressure is lower in the pulmonary system; this prevents damage to the lungs
    • In the systemic circulatory system
      • Oxygenated 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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Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. With 10 years of teaching experience across the 3 key science disciplines, Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.

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