Transcript AS Level Biology

AS Level Biology
Lesson 2
Gas exchange and respiration
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If cells are to stay active, grow and
divide they need energy.
This energy comes from the oxidation
of organic molecules such as glucose
in respiration.
All respiration involves oxidation
reactions, all cells must have a
constant supply of oxygen.
Respiration
A series of oxidation reactions taking
place in all living cells. It results in the
release of energy from organic
compounds such as glucose.
Gas exchange
…..is not the same as respiration!
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Process by which oxygen gets into
cells and carbon dioxide is removed.
Respiration creates the constant
demand for oxygen and a constant
release of carbon dioxide.
Gas exchange surfaces
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Special surfaces the animals and
plants have evolved to promote the
exchange of gases.
allow the diffusion of gas into and out
of cells
These surfaces include mesophyll
layers in leaves, skin in earthworms,
gills in fish and lungs in mammals.)
Features of gas exchange
surfaces
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Have a large surface area relative to the
volume of the organism.
They are thin, so have a short diffusion
pathway.
They have a moist surface where gases can
dissolve first before they diffuse in our out.
They are able to maintain the diffusion
gradient down which the gases can diffuse.
Gas exchange in humans
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Humans have a high metabolic rate so
require a fast rate of gas exchange.
To help with this there are two key feature
that have evolved in the human system:
A blood transport system with red cells
containing haemoglobin
A means of ventilation to get the gases to
and from the gas exchange surface.