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Module 2: Exchange and Transport
1.2.3 Transport in Plants
(a) explain the need for transport systems in multicellular plants in terms of size and surface area: volume ratio
Multicellular plants have a small surface area: volume ratio so diffusion would be too slow to provide necessary
substances like water, minerals…

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Module 2: Exchange and Transport




(c) describe, with the aid of diagrams and photographs, the structure and function of xylem vessels, sieve tube
elements and companion cells
Xylem Phloem (Sieve tube elements/companion cells)
Transports water and minerals from roots to Transports dissolved
leaves substances sucrose(sugars)
Dead cells Living cells
Long…

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Module 2: Exchange and Transport
the leaf than in the air outside water moves out of the leaf down the water potential gradient when the stomata
is open.


(f) describe the factors that affect transpiration rate
Light The lighter it is the faster the transpiration rate. When it is light,…

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Module 2: Exchange and Transport
























A Apoplast Water moves through the spaces between
Pathway cellulose cell walls
Water doesn't pass through any plasma
membranes meaning that dissolved mineral ions
and salts can be carried within the water

B Symplast Water enters the cell cytoplasm through the
Pathway plasma membrane then…

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Module 2: Exchange and Transport
1. Water enters from the soil to the root hair and epidermis
through osmosis from a higher water potential (soil) to
the most negative water potential (xylem)
2. Water enters the cortex by the apoplast pathway
between cell walls , the symplast pathway through
plasmodesmata…

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Module 2: Exchange and Transport
Thicker waxy cuticle This reduces water loss as it is waterproof and so reduces the need to take
up water
Closing stomata at low levels On a warm day, there is more transpiration through the stomata creating a
of water steep water potential gradient .…

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Module 2: Exchange and Transport
4. As the concentration of sucrose molecules builds inside the companion cells, they diffuse into the sieve tube
element through the numerous plasmodesmata .

Movement of Sucrose Along the Phloem:
At the Active transport is used to actively load the sucrose into the sieve tubes…

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