PLANT TRANSPORT OCR BIOLOGY A LEVEL

A level ocr biology plant transport 3.1.3

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  • Created by: Davina1st
  • Created on: 26-03-21 19:52
What are the main reasons why a multicellular plant needs a specialised transport system?
High metabolic demand, size, SA:V ratio is different in plants (stem is thick but leaves are small and flat).
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What is a dicotyledonous plant? (Dicots)
They make seeds that contain two cotyledons (organs that act as food stores for developing embryo of plant)
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What is a vascular bundle?
Made up of xylem and phloem, the transport system of vessels in a plant.
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Where are the vascular bundles found in a stem and why?
Around the edge to give it strength and support
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Where are the vascular bundles found in a root and why?
In the middle, to help the plant withstand the tugging strains that result as the stems and leaves are blown in the wind.
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Where is the vascular bundles found in a leaf and why?
The midrib of the leaf is the main vessel carrying vascular tissue. It helps to support the structure of the tissue, branching veins spread through the leaf for functioning.
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Describe the structure of the xylem
Long hollow tubes of dead cells, made by several columns of cells fused together. Spirals of lignin around the lumen of the xylem. Have no cytoplasm, no end walls, do not resist water flow and have pits in the side walls.
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What is the function of the xylem?
Transports water and mineral ions up the stem, from roots to leaves.
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What s the structure of the phloem?
Companion cells attached to side of sieve tubes. No nucleus, and sieve plates have holes connecting to cytoplasm. Not lignified.
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What is the function of the phloem?
Moves dissolved substances e.g. sugars from the leaves which were made during photosynthesis.
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How are root hair cells adapted to carry out their function?
Microscopic size - penetrate between soil particles, large SA:V for efficient exchange, thin surface layer for quick diffusion.
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How is a water potential gradient maintained the root hair cell and water in the soil?
The cytoplasm in the root hair cell has a lower water potential than the soil so that water moves into the cell.
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What are roles of water in plants?
Raw material for photosynthesis, mineral ions for photosynthesis transported in aq solutions. Turgor pressure=cell expansion so plant roots can go through concrete. Turgor pressure=result of osmosis=hydrostatic skeleton to support stem and leaves.
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Describe how water moves via the apoplast pathway
Movement of wate through cell walls, as water moves into xylem, cohesion pulls water in=tension=continuous flow of water and little to no resistance
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What does the casparian ***** do?
It is a thick wax which forces any water travelling by the apoplast pathway into the endodermal cell to move by the symplast pathway.
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Describe how water moves via the symplast pathway
Moves through the continuous cytoplasm that are connected by the plasmodesmata by osmosis. Root hair cell has a higher water potential than the next cell along. result of water diffusing in from soil=more dilute cytoplasm.
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What is root pressure?
The result of active umping of minerals into the xylem to produce a movement of water by osmosis. Occurs inside the vascular bundles.
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Evidence for the role of active transport in root pressure
Root pressure increase with rise in temp shows chemical reactions are involved, if levels of O2 decrease rootpressure decreases. Cyanide affects mitochondria and prevents atp production, if applied to root cells= no energy supply root pressure disapp
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What is transpiration?
The loss of water from the leaf, involving the stomata and air spaces.
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What is the role of the stomata in transpiration?
Water vapour passes out of the underside of the leaf, through gaps in stomata. Gaps are produced by movement of guard cells.
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Why do stomatal pores open?
For gaseous exchange, to let CO2 in and O2 out. Water inside the leaf accumulate in air spaces which are surrounded by spongey mesophyll cells. This area has a high conc of water so loses it to the atmosphere around the leaf.
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When is transpiration speeded up?
On hot days-more kinetic energy/evaporation, on windy days-more mass movement, during daylight hours-more stomata open, reduced humidity-increased water vapour gradient.
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When carrying out a potometer experiment, why is the shoot cut underwater?
To prevent an air bubble travelling up the xylem which could create an air lock.
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When carrying out a potometer experiment, why are all joints smeared with Vaseline?
Reduce leakage of water
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When carrying out a potometer experiment, why is the plant cut with a razor and at an angle?
A clean cut using a razor ensures the water can enter freely at the base of the xylem. Angle means there is a larger SA for water uptake.
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When carrying out a potometer experiment, what is the function of the reservoir?
As you open the tap the column of the water pushes the air bubble back to reset the experiment and allow for repeats.
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What is some evidence for the cohesion-tension theory?
A broken xylem vessel sucks air in not water leaking out. After air is sucked in, no more water gets sucked in as the cohesion force has been broke. When transpiration rate is highest, diameter of tree is smallest due to suction.
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What is the cohesion tension theory?
Model of water moving from soil in a continuous stream up the xylem and across the leaf
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Describe the mechanism for stomata opening
Uneven thickness of cell wall means cell bends and stomata open, K+ moves in and lowers the water potential, so water moves in by osmosis and the cell swells (increased turgor pressure)
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Describe the mechanism for stomata closing
Potassium ions move out, higher water potential, water moves out by osmosis and the cell shrinks (decreased turgor pressure)
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What is a xerophyte?
Plants that live in dry habits, so they have adapted to minimise water loss.
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Give 3 adaptions of xerophytes and how it reduces water loss
Thick waxy cuticle=impermeable reduces transpiration through cuticle. Fewer stomata=reduced water loss less stomata can open. Hairy leaves create a still microclimate of humid air, reducing water vapour potential grad. Marram Grass
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What is a hydrophyte?
A plant adapted to live in water/permanently saturated soil.
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Give 3 adaptions of a hydrophyte
Wide flat leaves-capture as much light as possible and increase transpiration. Small roots-as water readily available for uptake. Very thin/no waxy cuticle-water lost by transpiration very easily.
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Describe transpiration stream briefly
Water evaporates from mesophyll cells and out of stomata, loss of water=lower potential so water moves into cell. Repeated across leaf, water moves into xylem, H bond=cohesion and adhesion =transpirational pull and continuous flow of water.
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What is the transpirational pull?
Tension in the xylem from cohesive and adhesive forces helps to move water up the plant.
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What is translocation?
The movement of organic solutes around a plant in the phloem
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What is a source and what is a sink?
Source- where the sugars are loaded into the phloem/where they are produced. Sink- where the sugars are offloaded from the phloem.
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What is an assimilate?
The products of photosynthesis that are transported. Mainly sucrose
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Give 3 of the main sources of assimilates in a plant
Green leaves and stems, storage organs such as tubers and tap roots that are unloading their stores at the beginning of a growth period, food stores in seeds when they germinate.
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Give three of the main sinks in a plant
Roots that are growing/actively absorbing minerals, meristems that are actively dividing any part of the plant that are laying down food stores, such as developing seeds, fruits or storage organs.
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Describe how a movement of water by mass flow is created during translocation
Sugars loaded from source cells to companion cells, then move into sieve tubes by active transport. Water potential in phloem decreases so water moves in by osmosis, from xylem. Build up of water+solutes in phloem=pressure=mass flow to low pressure.
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When sucrose is loaded into the phloem, it can be by the symplast pathway. Describe this and if it is passive/active?
Passive, the sucrose from the source moves through cytoplasm of mesophyll cells and on into sieve tubes by diffusion through the plasmodesmata. Sucrose ends up in sieve and water follows by osmosis=pressure of water and sucrose moves by mass flow.
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What is the role of H+ in loading sugars into the phloem via the apoplast route?
H+ ions are actively pumped out of the companion cell into the surrounding tissue using ATP. The h ions return to the companion cell down a conc grad via a co-transport protein. Sucrose is transported which increase the conc of it in companion cells.
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How are companion cells adapted to help with loading via the apoplast route?
Many infoldings in cell membranes to increase SA for active transport of sucrose into cell cytoplasm. Lots of mitochondria to supply ATP needed for transport pumps.
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Explain how mass flow works by creating pressure differences?
build up of sucrose in compan cell=water moving in by osmosis=turgor pressure. Water carry assimilate moves into sieve tube=reduced companion cell pressure and moves up/down plant by mass flow to areas of low pressure (sink).
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How does the sink retain a lower concentration than the phloem? (When the sucrose leaves the plant by diffusion)
The sucrose rapidly moves on into other cells or is converted into another substance so that a conc grad of sucrose is maintained between the contents of the phloem and the surrounding cells.
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What is some evidence for translocation?
Microscopy allows us to see adaptions of companion cell, if mitochondria is poisoned translocation stops, flow of sugars is 10,000 times faster than diffusion alone=suggesting active transport is involved.
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How can aphids be used as evidence for translocation?
From aphid studies, its been show there is positive pressure in the phloem that forces sap out. The pressure and flow rate in phloe is therefore lower closer to sink rather than source. Conc of sucrose in phloem sap is higher near to source not sink.
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Other cards in this set

Card 2

Front

What is a dicotyledonous plant? (Dicots)

Back

They make seeds that contain two cotyledons (organs that act as food stores for developing embryo of plant)

Card 3

Front

What is a vascular bundle?

Back

Preview of the front of card 3

Card 4

Front

Where are the vascular bundles found in a stem and why?

Back

Preview of the front of card 4

Card 5

Front

Where are the vascular bundles found in a root and why?

Back

Preview of the front of card 5
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