OCR F211 Transport in Plants

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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 and sugars and to remove waste substances. Also multicellular plants are large so
have a greater demand for substances . Therefore plants need transport systems to move substances to and from
individual cells quickly.
(b)describe, with the aid of diagrams and photographs, the distribution of xylem and phloem tissue in roots,
stems and leaves of dicotyledonous plants
Vascular bundle found in the centre
Large central core of xylem X
Phloem between arms of xylem
Vascular bundles found near the
outer edge
Xylem found towards the inside of
each vascular bundles
Phloem found towards the outside of
each vascular bundles
Cambium found in between xylem
and phloem
Vascular bundle forms the midrib and
veins of a leaf found in the centre
Xylem found closer to the flatter
Phloem found closer to the bump

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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, the stomata open to
allow gaseous exchange for photosynthesis so water can easily diffuse out the leaves
Temperature The higher the temperature the faster the transpiration rate.…read more

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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 of the phloem at the
SOURCE source
This lowers the water potential inside the sieve tubes, so water enters the tubes by osmosis.…read more


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