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Natural Science 2. Secondary Education
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Circulatory systems

• They are present in most animals and consist of
• A circulating liquid, like blood, that
  transports substances throughout the organism.
• Vessels, which the liquid travels through.
• A pumping mechanism, the heart, which moves the
  liquid.

Heart
Blood vessels Arteries Veins Capillaries
An example of a closed circulatory system, that
of a mammal.
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Animals with open circulatory systems

• Found in arthropods and molluscs.
• The circulating liquid leaves the vessels to
  bathe the organisms tissues with oxygen and
  nutrients. Once substances have been exchanged
  with the tissues, the liquid is drawn back to the
  vessels.

A hole-filled heart pumps the circulating liquid.
The circulating liquid is transported through the
vessels to the tissues, where substances are
exchanged.
The open circulatory system of an arthropod
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Animals with closed circulatory systems

• Found in vertebrates and some invertebrates,
  such as annelids.
• The circulating liquid is only found inside the
  vessels. The exchange of substances takes place
  through the walls of the smallest vessels, called
  capillaries.
• There are two types
• Single
• Double

The circulating liquid stays inside the vessels.
Substances are interchanged in the capillaries.
A heart with no holes pumps the circulating
liquid.
The closed circulatory system of a fish
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Animals with single closed circulatory systems

• Found in some invertebrates and in fish.
• The heart pumps the circulating liquid, which
  travels to the respiratory organs, where it
  absobs oxygen. From there it travels throughout
  the rest of the body.
• After interchanging substances with the body,
  the blood goes back to the heart.

2 The blood goes to the gills, where oxygen is
absorbed.
3 The blood travels throughout the body
interchanging substances.
1 The heart pumps the blood.
4 The blood travels from the different organs
back to the heart.
The single closed circulatory system of a fish
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Animals with double closed circulatory systems

• Found in land vertebrates.
• The heart pumps the blood to the lungs in
  pulmonary circulation. The blood releases carbon
  dioxide and absorb oxygen.
• The blood then returns to the heart, where it is
  pumped to the organs. Substances are interchanged
  in the organs.
• The blood then travels from the different organs
  back to the heart.

2 The blood travels to the lungs, where it
absorbs oxygen, and returns to the heart.
1 The heart pumps the blood.
3 The heart pumps the blood again, which flows
to different organs.
The double closed circulatory sytem of a bird
4 The blood travels from the different organs
back to the heart.
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Natural Science 2. Secondary Education