1.2.2 double and single circulatory system


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Single circulatory system Fish

  • Blood passes around the body ONCE for every complete circuit
  • O2 is picked up at the gills and sent around the whole body in just once circuit

Double circulatory system Mammals

  • Blood passes around the body TWICE for every complete circuit
  • The right side of the heart takes blood to the lungs, where it picks up O2
  • The blood goes to the left side of the heart where it is pumped around the body
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Multicellular animals need transport systems:

  • Because of their large size, so they have a low Surface area to volume ratio.
  • They need constant supply of oxygen and glucose
  • Theyre always active and need replacing constantly.
  • Circulatory system: The two linked loops
  • Pulmonary systems: Sends blood to lungs
  • Systemic system: sends blood to the whole body


  • Heart can give blood that extra push it needs. Therefore blood travels around body faster, and cells can take in the gases and nutrients in faster.
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