Page 143 - Biology Form Two

Biology for Secondary Schools

Gas exchange in plants Lenticels
These are porous tissues in the bark of
Task 6.5
woody plants, consisting of cells with
Search the library and internet sources large intercellular spaces. They allow
for information on gas exchange in gases to pass between the atmosphere
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plants. Then, summarise your findings. and the organs' interior tissues. On stems
and roots, lenticels appear as elevated
Gas exchange in plants is the process circular, oval or elongated patches.
whereby oxygen gas leaves and carbon
dioxide gas enters the plant during Breathing roots
the day. During the night, oxygen gas These are specialized roots developed
enters and carbon dioxide gas leaves in some plant species that grow in
the plant. Gas exchange mostly takes waterlogged or strongly compacted

place through the stomata on the leaves soils, e.g. mangroves. Breathing roots
and lenticels on the stem. In plants such are also called pneumatophores. These
as mangrove, gas exchange is carried specialized aerial roots protrude from the
through breathing roots, also called trunk and branches of mangrove trees.
pneumatophores, which usually project Mechanism of gas exchange in plants
above the water surface.
Gas exchange in leaves
Parts of the plant responsible for gas Atmospheric air moves in and out
exchange
of the leaf through the stomata. Gas
Stomata exchange mostly takes place in the air
Gases diffuse into the intercellular spaces within the spongy mesophyll of
spaces of the leaf through pores, which the leaf, as shown in Figure 6.8. The
are normally on the underside of the spongy mesophyll is a suitable site for
leaf. These pores are called stomata gas exchange because it has numerous
(singular: stoma). Stomata refer to the air spaces between the cells due to their
pores, together with a pair of specialized loose arrangement.
guard cells which surround them, found
on the aerial parts of plants that enable
gas exchange.

Student’s Book - Form Two 137

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BIOLOGY FORM 2 NEW.indd 137 05/10/2024 15:36:44
BIOLOGY FORM 2 NEW.indd 137