Summary notes for A-level Biology OCR B (Advancing Biology). Chapter 6 - Transport systems in mammals (2.2.2 on specification). In-depth detailed notes covering all required content.
Once organisms reach a certain size, diffusion is no longer sufficient to
Transport provide all body cells with the oxygen and nutrients they need.
systems in
mammals This is when a mass transport system is needed. In mammals this is
the circulatory system.
Unicellular organisms don't need a specialist transport system because
they have a high surface area : volume ratio. These cells use diffusion,
osmosis and active transport.
Mass transport = a system that transports all substances in the same
direction at the same speed.
A good transport system in humans has:
Large surface area
Pump to move substances
Fluid to suspend substances so they can be moved
Human circulatory system
Double circulation:
Pulmonary circuit – between the lungs and the heart
Systemic circuit – between the body and the heart.
Advantages
o Blood pressure maintained
o Oxygenated and deoxygenated blood does not mix
o Delivery of O and nutrients to tissues is more efficient
2
Closed system:
The blood in the human circulatory system always moves within
blood vessels, and can be maintained at pressure.
Advantages
o Blood pressure maintained
o Pressures can differ in pulmonary and systemic
systems
o Blood supply to organs can be varied due to functions
Blood vessels
Arteries:
Take blood away from the heart under high pressure
Narrow lumen
Thick wall, large amounts of smooth muscle and elastic fibres
Stretches during ventricular systole and recoils during diastole
Inner endothelium lining smooth to reduce friction
Veins:
Return blood to the heart
Thin walls, small amount of muscle and elastic tissue
Contain semilunar valves which prevent backflow
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