8.3 Transportation
Water movement through the plant
● Class work
● Homework
● Video
Students book pg 1, 2, 3
Learning Objective
● To recall that water movement through a plant
begins with water loss from the leaves
● To understand that water is lost from leaves via the
stomata, through which the exchange of gases
between the leaf and the atmosphere also occurs
● To describe how the leaf surface most involved in
water loss can be identified
● To understand how environmental conditions can
affect water movement through plants
Key term
Wilting To wilt means to lose freshness or to become flaccid wilting occurs if water
loss exceeds water uptake, the tissues become limp and the plant is no longer
supported.
Turgid swollen and distended or congested.
Key term
Transpiration: Transpiration is the process of water movement
through a plant and its evaporation from aerial parts, such as
leaves, stems and flowers.
Active transport: Active Transport is defined as a process that
involves the movement of molecules from a region of lower
concentration to a region of higher concentration against a
gradient or an obstacle with the use of external energy.
TASK: Draw and label the diagram of Potometer
Key term
Transpiration stream: the transpiration stream is the uninterrupted
stream of water and solutes which is taken up by the roots and transported
via the xylem to the leaves.
Potometer:
A potometer' (from Greek Poto = drunken, and meter = measure),
sometimes known as transpirometer, is a device used for measuring
the rate of water uptake of a leafy shoot which is almost equal to the
water lost through transpiration.
Water uptake
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Transpiration is a side-effect of
how leaves are adapted to
maximise gas-exchange for
photosynthesis
Plants contain tiny pores
(openings) called stomata that
allow for gas exchange
○ Stomata are typically found
on plant leaves but can be
found on some stems
Role of Stomata in transpiration
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Stomata are formed by two kidney-shaped guard cells which open and close the
stomatal pore
○ Stomata can be opened or closed depending on the conditions the plant is in
The role of stomata and guard cells is to control gas exchange and water loss
Guard cells have cell walls with unevenly distributed cellulose – the inner wall is thicker
and the outer wall is thinner to aid opening and closing of the stomata
When the availability of water is high, guard cells become turgid as a result of osmosis
○ This causes the stomatal pore to open which allows gases to diffuse in and out of
the leaf
○ Water is consequently lost via transpiration
When less water is available, the guard cells lose water by osmosis and become
flaccid, pulling them together
Role of Stomata in transpiration
Path of water movement to the leaf from the toots
Atmospheric conditions may affect transpiration
• Wind moves humid air away from the leaf surface and increases
transpiration
• High temperatures increase the water-holding capacity of the air
and increase transpiration
• Low humidity increases the water potential gradient betv.een leaf
and atmosphere and increases transpiration
• High light intensity causes stomata to open (to allow photosynthesis)
which allows transpiration to occur
Translocation
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The transport of the soluble products of photosynthesis (mainly
sucrose) in the plant is called translocation
○ Translocation is an active process that requires energy
Sucrose (and amino acids) are transported around the plant in the
phloem tubes
In general, translocation happens between where the substances are
made (sources) and where they are used or stored (sinks).
Plenary Past paper question - CW
Reference
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Cambridge biology students book by marry john