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Respiration and Gas exchange
Aerobic and anaerobic respiration
AEROBIC RESPIRATION
Mammals and birds need energy to maintain a constant body temperature
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Aerobic respiration needs oxygen
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Note that respiration is different to breathing
(ventilation)
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ANAEROBIC RESPIRATION
Anaerobic respiration happens in muscles during hard exercise:
glucose → lactic acid

C6H12O6 → 2C3H6O3

Glucose is not completely broken down, so much less energy is released than during aerobic respiration
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The lactic acid needs to be oxidised to
carbon dioxide and water later
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This is why we keep on breathing deeply for a few minutes after we have finished exercising
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Anaerobic respiration in yeast is used
during brewing and bread-making:
glucose → ethanol + carbon dioxide

C6H12O6 → 2C2H5OH + 2C02

Ethanol is the alcohol found in alcoholic drinks like beer and wine
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AEROBIC VS ANAEROBIC
Oxygen
Glucose break down
End product(s)
Energy Released

1

AEROBIC
Needed
Complete
Carbon dioxide and water
Relatively large amount

ANAEROBIC
Not Needed
Incomplete
Animal cells: lactic acid
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In terms of gas exchange
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The cells in the spongy mesophyll (lower layer) are loosely
packed, and covered by a thin film of water
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Most of
these are in the lower epidermis, away from the brightest sunlight
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Each stoma can be open or closed, depending on how turgid
its guard cells are
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In the dark, the guard cells lose water, become flaccid and the stoma closes
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Pleural membranes surround each lung
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The bronchi split into smaller and smaller tubes called bronchioles
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There is a muscular diaphragm below the lungs
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the internal intercostal muscles relax and the external intercostal muscles contract, pulling the
ribcage upwards and outwards
2
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lung volume increases and the air pressure inside decreases
4
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the external intercostal muscles relax and the internal intercostal muscles contract, pulling the
ribcage downwards and inwards
2
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lung volume decreases and the air pressure inside increases
4
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Some of the features of
alveoli include:





thin walls (just one cell thick)
large surface area
moist surface
many blood capillaries

EFFECTS OF EXCERSICE ON BREATHING
During exercise there is an increase in physical activity and muscle cells respire more than they do when the body is
at rest
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35 to 7
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During exercise, the concentration of carbon dioxide
in the blood and respiring tissues increases
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