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Water Transport
Learning Objectives
1.
Describe how root hair cells are adapted to take up water by osmosis.
2.
Define osmosis as the movement f water molecules from an area of
higher concentration of water to an area of lower concentration of
water through a partially permeable membrane.
To reduce loss the leaf is coated in a wax cuticle to stop the water vapour
escaping through the epidermis.
Leaves usually
have fewer
stomata on
their top
surface to
reduce this
water loss.
The water inside a
leaf can escape
by diffusion.
Leaves have pores called stomata to allow carbon dioxide into the leaf.
These pores can allow water to leave the leaf, so the plant loses water.
Osmosis – the diffusion of water
• Osmosis is the movement of water from a
high water concentration (HWC) to a lower
water concentration (LWC) through a
partially permeable membrane.
How osmosis works
•
Which side of the container has more water molecules?
•
Where would you say is the higher water concentration?
•
Where is the lower water concentration?
•
Which way will the water molecules travel to make it equal water
concentrations on both sides?
• Water molecules
travelled to the side
of the container
where there was
more sugar, and so
less water.
• It was able to do this
because the
membrane in
between the two
sides is partially
permeable
Osmosis and plants
• Osmosis is important to plants. They gain
water by osmosis through their roots.
• Water moves into plant cells by osmosis,
making them turgid or stiff so that they are
able to hold the plant upright.
Plant cells are flaccid.
This means that they have
lost water by osmosis.
Plant cells are turgid. This
means that they have
gained water by osmosis.
The plant has become soft
and droopy.
The plant has become
firm, keeping it upright.
Roots
• Plants absorb water from the soil by osmosis.
• Root hair cells are adapted for this by having a large
surface area to speed up osmosis.
• The absorbed water is transported through the roots to
the rest of the plant where it is used for different
purposes:
–
–
–
–
used in photosynthesis
supports leaves and shoots by keeping the cells rigid
cools the leaves by evaporation
transports dissolved minerals around the plant
http://www.youtube.com/watch?v=2TtQQLC66RI
Water will
move into
the root hair
cells from a
HWC to a
LWC by
osmosis