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Excretion

Respiration and photosynthesis

Excretion is the removal of the following substances:

Plants respire during the day and night, but they only
photosynthesise during the day when it is light:

• toxic materials
• waste products of metabolism
• excess substances from organisms

Remember the equations for aerobic respiration and
photosynthesis:

Excretion is not the same as egestion - which is the passing
out of undigested food through the anus as faeces
...
Carbon dioxide
is a waste product of aerobic
respiration in plant cells
...


In terms of reactants and products, they are the reverse of each
other
...
Excess
carbon dioxide and oxygen
are excreted from the plant
through the stomata in the
leaves
...
Photosynthesis doesn’t occur at night
...

If there is enough light during
the day, then:

Excretion &
Gas Exchange
in Plants

The leaf
The structure of the leaf is adapted for gas exchange
...
There are tiny pores, called
stomata, in the surface of the leaf
...


The role of stomata
The stomata control gas exchange in the leaf
...

In the light, the guard cells absorb water by osmosis, become
turgid and the stoma opens
...

Diffusion of carbon dioxide, oxygen and water vapour into (or
out of) the leaf is greatest when the stomata are open

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