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3

Respiration

BIOLOGY 2

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3Energy Release

Every cell needs energy to keep it alive. This energy comes from glucose. This sugar is broken down by a series of reactions called respiration.

These reactions are speeded up by enzymes acting as biological catalysts.

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3Aerobic respiration

This is the usual type of respiration seen in humans - it uses oxygen. The reactions of respiration take place in tiny structures called mitochondria (singular: mitochondrion) and they are referred to as the ‘power-houses’ of the cell because they produce the cell’s energy.

Mitochondrion

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3Anaerobic Respiration

Respiration can happen without oxygen.

This process is called anaerobic respiration.

Only a portion of the energy contained in

the glucose is released.

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3Anaerobic respiration

in yeast cellsWhen yeast respires without the presence of oxygen (anaerobic respiration) it produces ethanol (alcohol). This process is called fermentation.

Glucose CO2+ ethanol +H2O +EGNI

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3Anaerobic respiration in the

musclesWhen muscles work hard and the oxygen level decreases in the cells, they can respire anaerobically for a

short time to enable them to keep going:

glucose lactic acid + energy

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3Disadvantages of Anaerobic Respiration

• It doesn’t release all the energy trapped in the glucose.

• Ethanol is toxic to cells.

• Lactic acid builds up in muscle cells and causes cramp.

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3Oxygen Debt

During physical exercise, acid lactic builds up in the muscles and it needs to be broken down. The body needs oxygen to do this

and so we breathe deeper and quicker. In a way, we are paying this oxygen back. The name given to the

‘loan’ is oxygen debt.

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O2O2

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3Practical Work

Energy release from respiring seeds.

The peas in the three flasks below have

been treated differently:

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3Flasks of peas

A B Cthermos flask

metal case

fresh

pea s

eeds

boile

d p

ea s

eeds

boile

d p

ea s

eeds

in

dis

infe

ctant

temperature probes

datalogging interface

computer

time

tem

pera

ture

clock12

6

9 3

12

457

8

1011

A computer can be used to prove that respiring peas release energy in the form of heat.

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3

0

5

10

15

20

25

30

35

1 2 3 4 5 6

Time/ Days

Tem

pera

ture

/

°C

Results

fresh pea seeds

boiled pea seeds

boiled pea seeds in disinfectant

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3Question

Why do the boiled peas that haven’t

been disinfected cause a temperature

increase?