Transport in plants - Spec.

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  • Created by: rachel
  • Created on: 15-03-13 16:33
Explain the need for transport systems in multicellular plants in terms of size & surface area:volume ratio.
Need-take substances from & return wastes to environ. Every cell needs H2O & nutrients. Large plants epithelial cells could gain all needed by diffusion as are close to supply. Many cells inside plant further from supply, & wouldnt receive water ect.
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Describe the distribution of Xylem & Phloem in the roots.
In roots, xylem is arranged in an X shape, with the phloem found between the arms of the xylem.
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Describe the distribution of Xylem & Phloem in the stem.
In the stem, vascular bundles are found around outside of stem in ring shape. Xylem is on inside with phloem on the outside & they are separated by layer of cambium (a layer of meristem cells that can divide ro produce new xylem & phloem).
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Describe the distribution of Xylem & Phloem in the leaves.
The xylem is on top of the phloem in the 'veins' of the leaf.
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Describe the structure of xylem vessels.
Long thick walls. Cells die & end walls & contents break down leaving long column dead cells. vessel is always open. Patterned cell walls. Pits like pores in walls are left where lignification hasn't been complete.
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Describe the function of Xylem vessels.
Waterproofed walls - lignin. Lignin strengthens walls & prevents collapse, keeping vessels open. Thickening of lignin forms patterns on cell walls - prevents vessel from becoming too rigid & allows flexibility- stem/branch. pits - allow H2O to leave.
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Describe the structure & function of sieve tube elements.
Very little cytoplasm & no nucleus. Lined up end to end to form tube in which sugars are transported. At intervals, there are sieve plates - cross walls which are perforated, which are at intervals down tube. Have v. thin walls & are 5/6 sided.
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Describe the structure & function of companion cells.
Between sieve tubes. Dense cytoplasm, lg nucleus & mitochondria -> ATP for active processes. Use ATP to load sucrose into phloem. Many plasmodesmata between comp. cells & they sieve tube (gaps in cell walls allowing flow of minerals to others & commu
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Define the term transpiration.
The loss of water vapour from aerial parts of a plant due to evaporation via stomata.
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Explain why transpiration is a consequence of gaseous exchange.
Stomata are open to allow gaseous exchange for photosynthesis. Water vapour leaves leaf down water vapour potential gradient. Higher temperatures during day cause some water vapour loss through surface of leaf all the time.
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How do you reduce transpiration from a plant?
Thick waxy cuticle-waterproofs leaf preventing H2O loss through epidermis. Stomata on underside of leaf-reduce evaporation due to direct heating. Stomata close at night- no light, no photosynth. so no need for g.e. Deciduous- loose leaves-conservatio
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Name the factors that effect transpiration rate.
No. leaves, no size & position of stomata, presence of cuticle, light, temp, humidity, wind, water availability.
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Describe the effect of the number of leaves on transpiration rate.
more leaves = large surface area which water can be lost from.
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Describe the effect of the number, size & position of stomata on transpiration rate.
If leaves have many, large stomata water vapour is lost more quickly. If stomata are on lower surface, water loss is slower. If there are more stomata, more water vapour can be lost through them.
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Describe the effect of the presence of a waxy cuticle on transpiration rate.
a waxy cuticle prevents water loss from leaf surface.
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Describe the effect of the presence of light on transpiration rate.
In light, the stomata open to allow gaseous exchange for photosynthesis, so when it is very light, more will occur & when its dark, little/none will occur.
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Describe the effect of the presence of temperature on transpiration rate.
Higher temperatures will increase the rate of water loss, evaporation, diffusion (as water molecules have more kinetic energy) & will decrease the relative water vapour potential in the air, causing rapid diffusion of molecules out of the leaf.
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Describe the effect of the presence of relative humidity on transpiration rate.
high relative humidity in the air will decrease the rate of water loss. This is because there will be a smaller water potential gradient between air spaces in the leaf & the air outside.
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Describe the effect of the presence of air-movement/wind on transpiration rate.
Air moving outside the leaf will carry water vapour away from the leaf. This will maintain a high water potential gradient.
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Describe the effect of the presence of water availability on transpiration rate.
If there is little water in the soil, plants cannot replace the water lost, so water loss has to be reduced by closing the stomata or shedding leaves in winter.
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Describe the first 5 steps of how a potometer is used to estimate transpiration rates (step by step).
1- cut healthy shoot underwater to stop air entering xylem. 2- cut shoot at slant to > sa. 3-esure apparatus is full of H2O & only a desired air bubble. 4- insert shoot into apparatus under H2O. 5- remove photometer from H2O & ensure air-tight (shoot
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Describe the remaining 5 steps of how a potometer is used to estimate transpiration rates (there are 10 steps in total)
6 - dry leaves. 7 - keep conditions constant to allow shoot to acclimatise. 8 - shut screw clip. 9 - keep scale fixed & record position of air bubble. 10. Start timing & measure distance moved of air bubble per unit of time.
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Explain why the potometer only gives an estimate of transpiration.
It measures water uptake & not all the water taken up is lost as some water is used in photosynthesis & making cells turgid.
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Explain, in terms of water potential, the movement of water between plant cells.
Water passes from the cell with the higher (less negative) water potential to the cell with the lower (more negative) water potential.
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Explain, in terms of water potential, the movement of water between plant cells & their environment.
Water moves down the water potential gradient. If the water potential inside the cell is greater then the water outside the cell, water will move out of the cell by osmosis & vice versa.
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Describe the pathway by which water is transported from the root cortex to the air surrounding the leaves, with reference to the casparian *****, apoplast pathway, symplast pathway, xylem & stomata.
H2O -> root hair cells (os)& minerals actively pumped from root cortex into xylem. Symplast pathway =H2O enters cytoplasm & travels through plasmodes. Casparian ***** blocks apoplast pathway so uses symplast. H2O at top of xylem & leaves leaf by stom
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Explain the first step of the mechanism by which water is transported from the root cortex to the air surrounding the leaves, with reference to adhesion & cohesion & the transpiration stream.
1. water moves into xylem down pater potential gradient as there is high hydrostatic pressure at the bottom of xylem & transpiration at the top of the plant creating low hydrostatic pressure at top of xylem.
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Explain the second step of the mechanism by which water is transported from the root cortex to the air surrounding the leaves, with reference to adhesion & cohesion & the transpiration stream.
2. Water is under tension & is pulled up in a continuous column due to cohesion between water molecules. This is helped by adhesion of water molecules to xylem & capillary action.
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Explain the third & final step of the mechanism by which water is transported from the root cortex to the air surrounding the leaves, with reference to adhesion & cohesion & the transpiration stream.
3. Water moves up the xylem by mass flow from higher hydrostatic pressure to lower hydrostatic pressure down the hydrostatic pressure gradient.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves when the leaves are hairy.
Hairy leaves reduce evaporation through leaf surface & trap water vapour which creates high water potential outside the stomata reducing the water potential gradient.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves when the stomata are found in pits.
The pits trap water vapour which creates a high water potential outside the stomata reducing the water potential gradient.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves when they are rolled.
Rolled leaves reduce the exposed surface area for evaporation & trap water vapour which creates a high water potential outside the stomata reducing the water potential gradient.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves by having a high solute concentration in cells.
This reduces the water potential inside leaf cells.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves when they have a thick waxy cuticle.
A thicker cuticle which is waterproof reduces exposed surface area for evaporation.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves when they have small leaves/needles.
It gives the plant a smaller surface area for evaporation.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves when they have fewer stomata.
Fewer stomata reduces diffusion of water vapour.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves when the stomata close during the day.
When the stomata close in the day, this reduces the diffusion of water vapour.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves when most of the stomata are on the lower surface of the leaf.
Less exposure.
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Describe how xerophytes are adapted to reduce water loss by transpiration in their leaves when there's more densely packed spongy mesophyll.
This gives a smaller surface area for evaporation.
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Explain translocation as an energy-requiring process transporting assimilates, especially sucrose, between sources (leaves) and sinks (roots & meristem).
Source- where sugars are loaded into phloem. sink- where unloaded. Sugar made in leaves (source) and transported to roots (sink). in early spring, leaves need energy to grow, so sugars transported from roots to leaves (source to sink).
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Describe the first & second step of the mechanism of the transport of phloem involving active loading at the source & removed at the sink.
1. Active transport of H+ ions out of companion cells using ATP & creates a H+ ion gradient. 2.facilitated diffusion of H+ ions back into companion cells is caused by step 1.
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Describe the third & fourth step of the mechanism of the transport of phloem involving active loading at the source & removed at the sink.
3. sucrose moves in with the H+ ions through a co-transport protein. 4. Sucrose diffuses through the plasmodesmata from companion cell into sieve tube element.
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Describe the fifth & sixth step of the mechanism of the transport of phloem involving active loading at the source & removed at the sink.
5.The entry of sucrose into the sieve tube elements reduces the water potential. 6. Water follows by osmosis & creates the hydrostatic pressure in the sieve tube element.
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Describe the seventh & eighth step of the mechanism of the transport of phloem involving active loading at the source & removed at the sink.
7. Water moves down the sieve tube element from higher hydrostatic pressure at the source to lower hydrostatic pressure at the sink. 8. Sucrose moves, via either diffusion or active transport, from the sieve tubes to the surrounding cells.
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Describe the ninth & tenth step of the mechanism of the transport of phloem involving active loading at the source & removed at the sink.
9. This increases the water potential in the sieve tube element so water molecules then move into surrounding cells by osmosis. 10. Hydrostatic pressure is then reduced at sink.
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Give some evidence for the mechanism of transport in phloem involving: Active loading at the source and removal at the sink,
Ringing a tree to remove the phloem results in sugars collecting above the ring An aphid feeding on a plant stem can be used to show that the mouthparts are taking food from the phloem.
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Give some evidence against the mechanism of transport in phloem involving: Active loading at the source and removal at the sink.
Not all solutes in the phloem sap move at the same rate Sucrose is moved to all parts of the plant at the same rate, rather than more quickly to areas with a low concentration The role of sieve plates is unclear
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Other cards in this set

Card 2

Front

Describe the distribution of Xylem & Phloem in the roots.

Back

In roots, xylem is arranged in an X shape, with the phloem found between the arms of the xylem.

Card 3

Front

Describe the distribution of Xylem & Phloem in the stem.

Back

Preview of the front of card 3

Card 4

Front

Describe the distribution of Xylem & Phloem in the leaves.

Back

Preview of the front of card 4

Card 5

Front

Describe the structure of xylem vessels.

Back

Preview of the front of card 5
View more cards

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