573136
Description
Mind Map by m.c.ridley, updated more than 1 year ago
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Created by m.c.ridley
about 10 years ago
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Plant transport: F211: 1.2.3
- Transpiration
- Constant evaporation of water from aerial parts of a plant.
Transpiration stream = constant flow of water from roots to shoots.
- Rate = lower in afternoon - plant is wilting; stomata may be closed; more humid (humidity decreases
the water VAPOUR potential gradient). However, it is unavoidable during daylight since stomata
need to be open to allow for gas exchange for photosynthesis. Rate = fastest in WARM and WINDY
conditions (WARM = photosynthesis faster so more need for water; WINDY = maintains a high
water VAPOUR potential gradient.
- Contributes to water movement up stem in: a) leaf - water loss in leaf is
replaced by apoplast/symplast/vacuolar pathway down a water potential
gradient; b) xylem - loss of water at the top of the leaf means hydrostatic
pressure is less at the top of the stem, therefore water moves down a
pressure gradient; there is cohesion/adhesion of water molecule. [cohesion
= attraction with other water molecules; adhesion to sides of xylem].
- Potometer = estimate of transpiration rate since it measures uptake of water NOT loss. To use a
potometer, you need to use a healthy shoot; cut the shoot 2cm from the bottom (to ensure no air in xylem);
watertight seals (to ensure water uptake is accurate); use dry leaves (so evaporation from stomata not
affected). Repeats = reliability.
- Constant flow of water from roots to leaves =
transpiration stream. Achieved by a) water
moving from a higher water potential to a lower
water potential; b) high hydrostatic pressure at
bottom of xylem; c) transpiration at the leaves
(i.e. giving a lower hydrostatic pressure here); d)
water under tension; e) cohesion between water
molecules; f) adhesion between water and
xylem
- Constant evaporation of water from aerial parts of a plant.
Transpiration stream = constant flow of water from roots to shoots.
- Phloem = sieve tubes and companion cells. Moves SUCROSE from
sources (where sucrose is loaded) to sinks (where sucrose is
deposited). Leaves = sources; DEVELOPING buds/GROWING tips
= sinks.
- Sieve tubes = living; moves sucrose in
BOTH directions (unlike xylem with
water); no lignin; no bordered pits (but
does have PLASMODESMATA to allow
sucrose to move from companion cell to
sieve tube).Cross walls allow sap to
flow.
- Companion cells - contain
mitochondria to produce ATP
required for active transport.
Contain plasmodesmata to
allow communication between
companion cells and sieve
tubes.
- Loading assimilates (sucrose) into phloem is the role of the companion cell. It involves a) active
transport of H+ out of the companion cell. b) This creates a H+ concentratio gradient so H+
diffuses back into the companion cell. c) As it does this, sucrose moves in with the H+. d)
Sucrose then diffuses via the plasmodesmata into the sieve tube element
- Evidence for = companion cells have lots of mitochondria. Evidence against = role of sieve plates unclear
- Evidence for = companion cells have lots of mitochondria. Evidence against = role of sieve plates unclear
- Loading assimilates (sucrose) into phloem is the role of the companion cell. It involves a) active
transport of H+ out of the companion cell. b) This creates a H+ concentratio gradient so H+
diffuses back into the companion cell. c) As it does this, sucrose moves in with the H+. d)
Sucrose then diffuses via the plasmodesmata into the sieve tube element
- Sieve tubes = living; moves sucrose in
BOTH directions (unlike xylem with
water); no lignin; no bordered pits (but
does have PLASMODESMATA to allow
sucrose to move from companion cell to
sieve tube).Cross walls allow sap to
flow.
- Xerophytes = plants
which survive hot,
dry conditions
- Have a thick cuticle for
waterproofing; rolled
leaves (to trap water
VAPOUR - this reduces
the water potential
gradient meaning water
is less likely to
evaporate); reduced
SA (so less water
evaporation); hairs (to
trap water VAPOUR);
fewer stomatal pores
(so less water
evaporation)
- Have a thick cuticle for
waterproofing; rolled
leaves (to trap water
VAPOUR - this reduces
the water potential
gradient meaning water
is less likely to
evaporate); reduced
SA (so less water
evaporation); hairs (to
trap water VAPOUR);
fewer stomatal pores
(so less water
evaporation)
- Uptake of minerals from the soil is by active uptake. A consequence of this is that the water
potential in the root is lower than the soil. Water is able to move in by osmosis from a high water
potential to a lower one down a water potential gradient. Once in, water moves by the
APOPLAST (in between cells - can also carry minerals with it); SYMPLAST (through the
cytoplasm - using plasmodesmata to get from one cell to the next) and VACUOLAR (through the
vacuoles).
- CASPARIAN STRIP blocks the APOPLAST pathway so the water potential in the
xylem is lowered meaning water will enter by OSMOSIS from higher water potential
to lower water potential.
- CASPARIAN STRIP blocks the APOPLAST pathway so the water potential in the
xylem is lowered meaning water will enter by OSMOSIS from higher water potential
to lower water potential.
- Plants need transport systems due to low SA: vol rations. They are XYLEM and PHLOEM
- Xylem = water/minerals up a plant to leaves for photosynthesis. Made
of continuous column of DEAD cells; contains BORDERED PITS (to
allow water to move in/out and supply water to other parts of the plant)
and LIGNIN (strength - stops it collapsing; flexibility - stops stem from
breaking; c) waterproofing (to reduce water loss).
- Xylem = water/minerals up a plant to leaves for photosynthesis. Made
of continuous column of DEAD cells; contains BORDERED PITS (to
allow water to move in/out and supply water to other parts of the plant)
and LIGNIN (strength - stops it collapsing; flexibility - stops stem from
breaking; c) waterproofing (to reduce water loss).
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