Mass transport plants
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- Created by: Hindleyc
- Created on: 17-06-18 20:51
What is the Xylem?
Tissue that transports water in the stem and leaves of the plant
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What are the roots like?
Highly branched penetrate deep into soil absorbing water and anchoring plant down
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What does the Xylem being arranged as X shape allow
to resist forces exerted when penetrating soil
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What is Xylem surrounded by?
Cortex cells that are a thick layer of packing cells often containing starch
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What is the endodermis ?
Controls if water gets into xylem
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What is epidermis?
Single layer of cells often with long extensions called root hairs to inc SA
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Endodermis?
Single layer of tightly packed cells containing waterproof layer called casparian ***** that prevents movement of water between cells- polysaccharide Suberin
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What is only way for water to move?
Through whole cells
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What is Xylem tissue?
Dead cells joined together to form long empty tubes
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How does water move?
Only up
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What it like?
Waterproof- lignin so no leaks- rings initially that inc in number that are strong, dead cells and empty- no organelles making uninterrupted columns with end walls broken down
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What do they form , what can't occur what stop them collapsing
Continuous pipes, no osmosis in xylem vessels as dead, strong lignin walls stop them collapsing
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What is the Apoplast?
Movement of water along cell walls and through spaces b/w cells from root hairs through cortex cells through to endodermis pathway of least resistance 80-90% until casparian *****
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What is symplast ?
Cytoplasm of root hair cells is lower in W.P than soil h2o so h2o enters by O and W.P gradient from soil thru to cortex to xylem in centre. h2o moves from cell 2 cell through plasmodesmata (pores in adjacent cell walls) through CSM into cytoplasm
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What does this way provide?
More resistance so less h2o molecules pass this way
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Steps of water movement
High W.P in soil so ions and minerals transported into root hair lowering W.P so water moves through epidermis and cortex by Appoplast (stopped at *****)/symplast . Endodermis AT ions into xylem to lower W.P
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What does this do?
stops water uncontrollably moving- block though cell wall where most water comes rom in order to remove pathogens etc- only way through is whole cells
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Whats cohesion?
Water is a polar molecule therefore H bonds between molecules makes them sticky
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What is tension?
Pulling effect caused by sun (evaporation of first water molecule ) stretching column of water creating a tension and pulling water up xylem
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Steps?
Sun causes water molecule to evaporate from stomata reducing W.P in sub stomatal air space. h2o molecule from next cell moves along by osmosis into sub0-stomatal air space reducing water potential in that cell so next h2o molecules follow
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Next?
. W.P now higher in xylem so water in X moves into Spongy cells and h2o molecules move up by tension/cohesion along W.P gradient. Then h2o moves into X from roots due to AT of ions pumped into X reducing W.P in X so water will move across root
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What is Transpiration?
Loss of water from the plant by evaporation
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What do Mesophyll cells in a leaf have? what does some water do? what happens if stomata open
Moist cell walls- some water evaporates into air spaces. If S open and h2o vapour conc is lower outside than inside then water will diffuse out
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How can plants reduce rate of T?
Close stomata
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What does this mean though?
Have to balance need fro CO2 with water loss as plants get their co2 through S for p/s
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Where are stomata generally found? what does this avoid?
On the underside of leaf. Excess water loss from evaporation
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What is the transpiration stream?
Movement of water up a plant as a consequence of evaporation from the leaves
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What is the role of transpiration?
Delivers water to all parts of plant (although most h2o leaves plant), distributes mineral ions throughout plant, cools plant by evaporation from leaves
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Why is water important ?
Lack of it means more may be lost than replaced so cells lose water and become placid which may lead to wilting and death
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What does Temperature do?
Inc kinetic energy of H2O molecules leading to increased evaporation from spongy cells and inc diffusion out of leaf inc rate of transpiration
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What does light do?
Increases transpiration as stimulates stomata to open for photosynthesis enabling more water vapour to diffuse out of the leaf and also heats up leaf which increases rate of evaporation and diffusion
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What do air movements do?
water diffuses out of the leaf through stomata down concentration gradient . In still air diffusion is slow. Water vapour tends to accumulate in shells of decreasing concentration around each stomata and if disturbed water vapour conc increases
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Inc air movement...
Inc transpiration
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What does humidity do?
If H is high then there is lower water vapour conc gradient from air spaces out of stomata so as H increases T decreases
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Perfect conditions transpiration ?
High Temp, High air movement , High light, Low humidity
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Other cards in this set
Card 2
Front
What are the roots like?
Back
Highly branched penetrate deep into soil absorbing water and anchoring plant down
Card 3
Front
What does the Xylem being arranged as X shape allow
Back
Card 4
Front
What is Xylem surrounded by?
Back
Card 5
Front
What is the endodermis ?
Back
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