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| Closed Circulatory System in Humans |
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| The closed circulatory system can be represented as follows. |
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| Diagram showing inter-relationship between artery, vein and capillary |
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| The closed blood vascular system is a very well developed system |
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| This is so because, |
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| a) The organisms have a thick body wall to prevent the evaporation of water, so exchange of materials between the body cells and the environment by diffusion is not possible. |
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| b) The organisms have higher metabolic rate and need a greater supply of nutrients and oxygen. They also need a more quick removal of wastes and carbon dioxide. |
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| c) External changes of temperature. |
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