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Leaving certificate biology
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Unit 1Ecology theory5 Topics|1 Quiz
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Nutrient recycling4 Topics|1 Quiz
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Ecological relationships and population dynamics2 Topics
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Human impact on the ecosystem2 Topics
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Study of a grassland ecosystem3 Topics
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Responses in the Flowering Plant4 Topics|1 Quiz
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Unit 3Sexual reproduction in the flowering plant1 Topic
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The human reproductive system3 Topics
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The menstrual cycle2 Topics
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Pregnancy2 Topics
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The circulatory system4 Topics
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Blood5 Topics
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The heart5 Topics
Lesson 11, Topic 1
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Open and closed circulatory systems
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Not all animals have a circulatory system
Some small organisms like this flatworm do not need a circulatory system to transport substances around their bodies
Due to their large surface area relative to their volume they can exchange materials with their surroundings by diffusion

Open circulatory systems
In an open circulatory system, blood is pumped by the heart into open ended blood vessels.
The blood then passes back into blood vessels. This blood lacks red blood cells.
Examples: insects

Closed circulatory systems
In a closed circulatory system blood is always enclosed in blood vessels.
Examples: Vertebrates and worms

Double circulatory system
Humans have a double circulatory system.
It is comprised of a pulmonary and systemic circuit
Tap each circuit to see the direction of blood flow
The heart is divided by a wall into a left and right hand side.
This allows for the separation of oxygenated and deoxygenated blood

Advantages of a double circulatory system
Oxygenated and deoxygenated blood does not mix
Oxygen an nutrients can be pumped around body faster
Blood pressure is maintained
Pulmonary, systemic and portal system
In general blood flows from artery to capillary to vein as in the pulmonary and systemic systems
Pulmonary system:
Heart → pulmonary artery → arterioles → capillaries (in lungs) →venules → pulmonary vein → heart
Systemic system:
Heart → aorta → arterioles → capillaries (in body) →venules → veins → vena cava → heart
The portal system is an exception to this
Portal system