Plant Transport Flashcards
Function of the xylem
Transports water and inorganic ions around the plant. Water is needed for photosynthesis and turgidity
What are inorganic ions
Nitrate ions for proteins, magnesium ions for chlorophyll, potassium ions for stomatal opening and closing.
What direction does the xylem travel?
Root to leaf
Where does the the phloem travel?
Leaf to root mostly but it is also bi-directional
What does phloem do?
Transport sucrose and other organic solutes. For example amino acids, sucrose, fatty acids and glycerol. These are all linked to photosynthesis.
What is the apoplast pathway?
It Moves along the cell walls and 80% of water uses this pathway
What is the symplast pathway?
It goes through the cytoplasm and plasmodesmata
What is the vacuolar pathway?
It goes through the vacuoles and cytoplasm
Describe the conditions at a root hair cell?
There is a high water content in the soil and lots of aquaporins through which osmosis can occur. There is also a large surface area created by the root hairs on the root and lots of mitochondria for active transport of nutrients
How does water enter a root hair cells by osmosis?
The high solute concentration in the vacuole of the cells and the high water content in the soil means that water enters the root hair cells by osmosis from high water potential to low water potential.
When do ions get actively transported into the root?
In a drought or when the water is frozen
How can the water potential gradient be increased?
Ions can be actively transported into the root hair cell to lower the water potential and increase the water potential gradient.
How many ways does the water move through the root ?
3
What is the casparian strip?
The strip of suberin in the cell walls of the endodermis that surrounds the endodermal cell. It prevents water and minerals from seeping between cells so that in order to get to the vascular cylinder, water and minerals must pass through the cell membrane.
Where do the three pathways reach up to?
The apoplast and vacuolar pathways stop after the endodermis
What does the casparian strip do?
It prevents movement through the apoplast pathway . Therefore the only water that moves through the endodermis is via the symplast pathway as there are no longer any vacuoles
How does the water enter the xylem?
Via the apoplast pathway as there is no cellular contents in the xylem….?
What is root pressure?
The greater force of water flow into and up the xylem (positive hydrostatic pressure)
How does root pressure happen?
Solutes ( nitrate ions / ammonium ions) diffuse with the concentration gradient through the apoplast pathway. They are then actively transported (selective ion uptake) into the endodermis to set up a steeper water potential gradient. Therefore more water flows into the endodermis and through the xylem, causing a propulsion called root pressure.
Why is a continuous flow of water able to move through the xylem?
It is made of dead cells aligned end to end, no end walls , no cell contents including the nucleus or cytoplasm. Lignin thickening also prevents Walls from collapsing and is waterproof. Pits in the lignified walls allow water to move sideways from one vessel to another
How is the transfer of water between cells the facilitated with the xylem?
Tracheids are a semi-living tissue that have tapered ends which fit together and pits which allow transfer of water between cells. They also conduct water but are not as well adapted as the vessels for the function.
Other xylem structures
The xylem also contains fibres for support - DO NOT transport water - and parenchyma cells for packing tissue
What 4 types of structure are phloem made out of ?
Phloem cells, companion cells, fibres for support and parenchyma cells for packing tissue
What additional feature do phloem have in them?
Sieve plates
What what do companion cells do in phloem tissue? Describe one
They have lots of mitochondria in which produces ATP which then goes into the sieve tube part of the phloem tissue. Also dense cytoplasm
What is the pericycle ?
Layer just inside the endodermis. It retains the capacity to divide and form branch roots
What does the thin layer of cytoplasm in the sieve tube element of the phloem tissue do?
It means there is less resistance and more ease of transport
What does the sieve plate do?
Connect elements and let’s through
What do the plasmodesmata linking cytoplasms of companion cell and sieve tube elements do?
Allow movement of fluid from companion cells to sieve tube for transport
Describe a sieve tube element.
It is clear of most organelles with a thin layer of cytoplasm . as a result Transport flow is less restricted
Why do plants need a transport system?
Because they are large and multicellular. Therefore diffusion alone is too slow and inefficient so a transport system is used to take minerals from cells to exchange surfaces and the environment.
How are animal and plant transport system similar?
They are both closed systems
How do the systems in plants differ from those in animals?
Xylem and phloem are used, not arteries and veins. Water not blood. The heart is used to move substances rather than hydrostatic pressure and evaporation. There are valves and pigments used in animal Systems, not in plants
What are the main water conducting tubes in plants?
The vessel elements in the xylem tissue
What four types of cells do xylem tissue consist of?
Parenchyma, fibre, vessel, tracheids
Where can one find spiral lignin?
In the the hollow lumens of the vessels and tracheids in xylem tissue
What do tracheids and vessels have in common?
They allow water and dissolved nutrients and minerals to pass throughout the plant. They also give support for the plant due to their strength from the lignin in the cell walls. The water and minerals go in and out of the tube through the pits on the side of the tubes. Tracheids are more primitive than vessels and are the only transport cells found in coniferous trees such as Pine.
How does waterlogged soil affect the root pressure in a plant?
It means there is less oxygen in the soil and less oxygen supplied to the endodermal cells. Less aerobic respiration will occur and less ATP will be produced. Fewer mineral ions will be actively transported into the endodermal cells. The water potential gradient will not be a steep. Less water will enter the endodermal cell and xylem vessel. Root pressure will be reduced.
Explain the effect a respiratory inhibitor would have on root pressure
Less aerobic respiration will occur and less ATP will be produced. Fewer mineral ions will be actively transported into the endodermal cells. The water potential gradient will not be a steep. Less water will enter the endodermal cell and xylem vessel. Root pressure will be reduced.
Summary of cohesion tension Theory
Water travels up the xylem to the leaves and is lost as part of transpiration. This loss of water means that more water moves via osmosis into the leaf. As water molecules leave the xylem they pull up the water molecules behind them . this pulling force is known as the transpiration pull. It occurs because water molecules have large piece of forces between them. In addition, the water molecules form adhesive forces with the hydrophilic lining of the xylem vessels.
What is a potometer used to measure?
The rate of transpiration by measuring Water uptake. It doesn’t measure the rate of transpiration exactly however as this relies on water lost not water uptake . and this is not the case as some water is lost through photosynthesis not transpiration. So it is an overestimate
How is water uptake distributed between transpiration and photosynthesis/turgid cells?
10% of water uptake is lost through photosynthesis and turgid cells. 90% is lost through transpiration
How does an increase of temperature have an effect on transpiration?
There will be an increase in transpiration because the kinetic energy of water molecules will increase and the rate of evaporation from the mesophyll cells will increase.
How does an increase of humidity have an effect on transpiration?
There will be a decrease in transpiration as there will be a smaller water potential gradient between the air space in the leaf and the air outside.
How does an increase in air movement have an effect on transpiration?
There will be an increase in transpiration as the wind will remove water vapour which has just evaporated from the stomata. This will increase the water potential gradient between the air spaces and the external atmosphere.
How does an increase in light intensity have an effect on transpiration?
There will be an increase in transpiration as the rate of photosynthesis will increase meaning more stomata open and consequently water is lost and more water is required.
How to increase accuracy in a potometer experiment?
Use a tube with smaller graduations and measure for a longer distance
How to increase validity in a potometer experiment?
Ensure all control variables were controlled between each incremental change in the independent variable
Why is the potometer not a true measure of transpiration?
Some of the water taken up will be used by the plant for photosynthesis and maintaining cell turgor
How to increase reliability in a potometer experiment?
Repeat the experiment three times and calculate a mean
How to comment on the reliability of the data in a potometer experiment?
Use range bars - a large range bar means it is less reliable as there is a greater spread around the mean. If the Range bars overlap , this is unreliable data as results are overlapping in this dataset. Use standard deviation - if it is a large number, the data is less reliable.
Independent variables of a potometer experiment
Humidity, light intensity, temperature, wind speed, number of leaves, surface area of leaf, age of leaf, species of plant
Dependent variables in potometer experiment
Distance moved by bubble per unit of time, mass of potometer and shoot
What do we mean as the source in mass flow Theory?
Any area where sucrose is produced in a plant
What do we mean as the sink in mass flow Theory?
Any area where sucrose is taken to usually to be used in respiration, growth or storage
What is mass flow Theory?
An idea to explain how sucrose is transported in plants.
How do we know that the flow in the phloem is bi-directional ?
Carbon dioxide labelled With radioactive Carbon 14 is supplied to an illuminated plant. The radioactive carbon is fixed into the sucrose through supply in carbon dioxide. Aphids can be used to collect the phloem sap and then it is analysed using radioisotope labelling. A high concentration of Carbon 14 is found above the source and another fairly high concentration is found below the Source at another sink
What is the evidence against mass flow hypothesis?
sieve plates, with small pores would obstruct mass flow so why are they there? Sucrose and amino acids have been observed moving at different rates in different directions in the same tissue. Why are there companion cells in the middle of the stem not just at the source and sink?
What are some other theories instead of mass flow hypothesis?
Some scientists have observed protein filaments passing through the sieve pores and suggest that different solutes are transported along different filaments.
How do we know that the phloem transports sugars such as sucrose?
We can use the stylet of an aphid to penetrate the stem of a plant and and collect fluid from the phloem more easily. The rate of Transport in the phloem is about 10000 times faster than it would be through diffusion alone
How do we know that the phloem transport sugar from source to sink?
Since the phloem is in the bark of trees and the xylem is in the wood, experiments have been done where a ring of bark is cut away and the area above the ring has been forced to collect the sugar. This has meant no further growth occurred below the Ring and a bulge appeared where sugar collected above the ring….?
Translocation
The process of moving photosynthetic products EG sucrose or amino acids from source to sink.
