Unit 1 Section 5 Transport System - Circulatory System

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  • Circulatory System
    • why do multicellular organisms need a transport
      • well single celled organisms can get all the substances they need by diffusion across their outer membranes
      • multicellular organisms find it slightly difficult to get all their substances as they are relatively big and have a low surface area to volume ratio
      • a lot of the multicellular organisms are very active
        • meaning that they have a large number of cells that are all respiring very quickly so they need a constant supply of glucose and oxygen
          • to make sure every cell has a good supply they need a transport system
            • in mammals transport system is uses blood to carry glucose and oxygen around the body, this is known as the circulatory system
              • it also carries hormones antibodies and waste such as CO2
    • Single and Double circulatory system
      • Single
        • in a single circulatory system, blood only passes through the heart once for each complete circuit of the body
          • fish have a single circulatory system. the heart pumps blood to the gills and then on through the rest of the bodyin a single circuit
      • Double
        • in a double circulatory system, the blood passes through the heart twice for each complete circuit of the body
          • mammals have a double circulatory system. the heart is divided down the middle, so its really like two hearts joined together.
            • the right side of the heart pumps blood to the lungs to pick up oxygen
              • from the lungs it travels to the left side of the heart, which pumps it to the rest of the body
                • when blood returns to the heart, it enters the right side again
    • closed and open circulatory systems
      • Closed circulatory system
        • in a closed circulatory system the blood is enclosed inside blood vessels
          • fish have a closed circulatory system
            • the heart pumps blood into arteries, which branch into millions of capillaries
              • substances like oxygen and glucose diffuse from the blood in the capillaries into the body cells, but the blood stays inside the blood vessels as it circulates
                • veins take blood back to the heart
      • Open circulatory system
        • in an open circulatory system, blood isn't enclosed in blood vessels all the time, instead it flows freely through the body cavity
          • Insects have an open circulatory system
            • the heart is segmented, it contracts in a wave, starting from the back, pumping blood into a single main artery
            • the artery opens up into the body cavity. the blood flows around the insect's organs, gradually making its way back to the heart segments through a series of valves


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