Download Plants do not have special respiratory or circulatory

Plants do not have special respiratory or
circulatory systems, and therefore must rely on
the direct exchange of gases with their
environment
The roots and rhizomes of plants depend on
gas exchange with the air and the soil
The surface of the root is covered with root hairs
Root hairs increase the surface area and also
provide a moist surface area for gas exchange
As long as the soil is aerated and contains
water , the oxygen will diffuse from the air
into the air spaces of the soil and then into
the moisture film surrounding the soil
particles and root hairs
The dissolved oxygen enters the root hairs
by diffusion and is then passed on to other
cells of the root
At the same time CO2 diffuses out of the
root hairs and into the soil
Gas Exchange in
Leaves
The main job of leaves in plants is photosynthesis
During photosynthesis, plants absorb CO2
and give off O2
During respiration plants absorb O2 and give
off CO2
During the day both process occur in the
leaves
Because gas exchange is constantly occurring, the leaf
has to protect itself against too much water loss,
therefore it is covered with a waxy waterproof coating
called the cuticle
The leaf also has tiny pores in it called stomata that
allow for the passage of gases in and out of the leaf
These stomata (singular stoma ) are bordered by a
pair of guard cells
The guard cells allow the pore to be opened to permit
for gas exchange or close to prevent water loss
Cross section of a leaf:
Gases are held in the intercellular air spaces and
can be used for either respiration ( O2 ) or
photosynthesis ( CO2 )
Every cell is close to air spaces so that the gases
can readily diffuse into the cells and be used for
either process
STOMATES & GUARD CELLS
Scattered about the lower epidermis are small
openings called stomata. It is through these holes
that carbon dioxide enters the leaf, & oxygen &
water vapor exit.
Each stoma is surrounded by a pair of guard
cells. When guard cells swell, the stomates open
when the guard cells shrink, the stomates are
closed. Plants respond to changes in temperature &
humidity by opening or closing their stomata (an
example of maintaining ... homeostasis).
Gas Exchange in Stems
Every stem contains pores
The green flexible stems of grasses and other
nonwoody stems photosynthesize and thus
contain stomata
Woody stems contain small white markings
called lenticels
Lenticels are normally found where stoma
were once situated when the stem was young
and capable of photosynthesis
O2 Diffuses into the stoma or lenticels and
enter the intercellular air spaces here every cell
in the stem is able to obtain gases they need
for photosynthesis or respiration
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