Transport in Plants Detailed Summary

another summary for plants from the old OCR bio spec.

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  • Created by: amehlia
  • Created on: 10-04-16 12:22
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Amelia Kirk
Transport in Plants Summary
Need of a transport system
every cell of multicellular plants needs regular supply of water & nutrients
epithelial cells can use simple diffusion, but cells not exposed to external environment within
the plant cannot
plants can obtain water from the roots, but not sugars, and the leaves can produce sugars,
but not obtain water from the air
the transport system in plants moves these substances in the vascular tissue: water moves
up in the xylem and sugars move up and down in the phloem
Vascular tissues
distributed through the plant
xylem and phloem found together in vascular bundles containing other types of tissue to give
the plant strength & support
Vascular Bundle in the Young Root
Xylem arranged in X shape, phloem
Vascular Bundle in the Stem
Xylem arranged on inside of vascular bundle,
phloem arranged on outside. In between each is a
layer of cambium (meristem cells dividing to produce
new xylem & phloem).
Vascular Bundle in the Leaf
Xylem on top of phloem within central
Xylem & Phloem
vessels : long
thick cell walls
covered in lignin
causing cells to die, end walls and
contents are lost/decay, tubes are narrow

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ATP for active processes,
they carry out the metabolic processes needed by
sieve tube elements (using ATP to load sucrose into
sieve tubes), cytoplasm of companion cells & sieve
tube elements are linked through many
plasmodesmata , gaps in cell walls
Plant cells and water
apoplast pathway: water passes through spaces between cells, water does not pass through
plasma membranes
symplast pathway: water enters cell through plasma membrane, then passes through
plasmodesmata from one cell to another (plasmodesmata are gaps in cell wall that contain…read more

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transpiration: loss of water through the leaves in plants as a result of gaseous exchange (the
stomata are open allowing water vapour to leave the plant), water leaves xylem & moves in
mesophyll cells (via osmosis), water evaporates from surface of mesophyll cells forming water
vapour which then passes through air spaces increasing the water potential inside the leaf,
water molecules move to lower water potential through stomata
transpiration stream: water lost through transpiration at leaves is replaced by water at the
roots which…read more

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Reducing water loss:
plants need to take in carbon dioxide for photosynthesis & remove oxygen (a waste product)
so stomata must be on during the day allowing water loss
to reduce water loss plants have certain adaptations: waxy cuticle on top leaf, stomata on
underside of leaf, stomata close at night, deciduous plants lose leaves in wither
Xerophytes have further adaptations:
smaller leaves: shaped like needles, reduces total surface area, less water lost by
transpiration (example: pine tree)
dense spongy mesophyll: reduces cell surface area…read more

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Along phloem:
water entering phloem at source, leaving at sink, moving down hydrostatic pressure gradient
produces flow of water along phloem
carries sucrose & other assimilates - MASS FLOW
mass flow can occur up/down in same phloem tube at different times…read more


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