Exchanging Materials in Plants
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All living things need to exchange materials
Plants need to obtain
certain materials for
healthy growth, including:
 sunlight
 water
 mineral ions
 oxygen
 carbon dioxide.
Where do plants get these nutrients?
Like all organisms, plants have to get materials for growth
from their environment. Plants must then transport the
nutrients to the part of the plant that needs them.
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How are plants adapted for transport?
The cell and tissue structures in different parts of the plant
are adapted to allow transportation of essential materials.
Leaves are entry and
exit points for the gases
needed by plants.
Stems connect the roots to
the leaves, flowers and fruits.
They contain cells specially
adapted for transportation of
water, minerals and sugars.
Roots absorb water and
minerals from the soil.
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Roots and uptake
Roots are adapted to obtain water and mineral ions.
 Roots are long and thin, and divide into many branches.
This root network covers a large area in the soil.
 Near the growing tips of roots are root hair cells. These
have projections that reach out between soil particles to
increase the surface area for absorption.
soil
root
hair cell
mineral ions
and water
molecules
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Which cells transport nutrients?
Plants contain two types of cell adapted for transportation.
Xylem cells transport water
and minerals up the stem from
the roots to the shoots and
leaves. This transport occurs
in one direction only.
Phloem cells transport sugars
produced in the leaves up
and down the stem to growing
and storage tissues.
Both phloem and xylem form continuous systems
connecting roots, stems and leaves.
The phloem and xylem are arranged as vascular bundles.
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Transporting water, mineral ions and sugar
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Demonstrate water movement
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Exchange of gases in plants
Plants use carbon dioxide and produce oxygen during
photosynthesis. These gases move in and out of the leaves
of plants by diffusion through the stomata.
When the concentration of
carbon dioxide inside the
plant is low, it will diffuse in
from the air, through pores in
the leaves into the plant cells.
If the concentration of
oxygen is high inside the
plant, it will diffuse from the
plant cells through the pores
and into the air.
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Adaptations for gas exchange
Leaves are adapted to increase the rate of diffusion of
gases, and to reduce the rate of water loss by evaporation:
A flat leaf shape increases
the surface area for diffusion.
A waterproof waxy
cuticle
reduces
water loss.
Internal air spaces allow
the gases to reach cells.
Thin leaves
minimize
the diffusion
distance for
gases.
Guard cells control the opening and closing of the stomata
to regulate how much water is lost through these holes.
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How do gases enter and leave plants?
Stomata are small holes, or pores, that can be found on
the underside of leaves. A single hole is called a stoma.
Each stoma is surrounded by two guard cells.
When guard cells gain
water, they curve outwards.
This opens the stoma,
allowing carbon dioxide in
and oxygen out.
Losing water causes the guard
cells to come closer together,
closing the stoma. This stops
the movement of gases, but
also prevents water loss.
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Water and gas exchange in plants
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What is transpiration?
Transpiration is the loss of water from the leaves of a plant.
Most of this occurs from the underside of a leaf, where the
water vapour can leave through open stomata.
In hot, dry and windy conditions, evaporation
of water from plant leaves is more rapid.
This loss of water at the leaf will cause
more water to be taken up by the roots.
However, if it cannot be replaced, the
stomata will close to prevent wilting.
Transpiration rates also vary naturally in
response to environmental factors such as
temperature and humidity.
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Transpiration rates
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Why does transpiration vary?
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Transpiration – true or false?
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Glossary
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Anagrams
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Multiple-choice quiz
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