7.4 Transport Of Water Flashcards
What is the battery of water as it is transported through the plant?
- transpiration of water vapour through open stomata into air(mainly from underside of leaf)
- Evaporation of water into leaf air spaces.
- water moves from xylem to leaf cells.
- Water moves xylem
- Water enters xylem
- Water uptake near roots.
Water always moves from
Region of higher water potential to region of lower water potential
How does the movement of water through the plant happen?
The movement of water through the plant is driven by evaporation of water from the leaves.
The energy of the Sun causes water to evaporate from the leaves, a process called transpiration. This reduces the water potential in the leaves and set up a water potential gradient throughout the plant. water moves down this gradient from the soil into the plant. water then move across the root into the xylem tissue in the centre of the root, once inside the xylem, the water moves upwards through the root to the stem and from there into the leaves
Describe how transpiration takes place in a dicotyledonous plant
The cells inside the leaf(mesophyll cells) how many air spaces around them. The walls of the mesophyll cells are wet and some of this water evaporates into air spaces so the air inside the leaf is usually saturated with water vapour.
The air inside the leaf has direct contact with the air outside the leaf through stomata. There is usually a water potential gradient between the air inside the leaf and the air outside the leaf. Water vapour will diffuse out of the leaf down this gradient.
When does most of transpiration take place and why?
Most of the transpiration takes place during the day because stomata open during the day and close at night.
What is transpiration?
The loss of water vapour from a plants to its environment
What is mesophyll?
The region of a leaf between the upper and lower epidermis
In dicotyledonous plants, the massive field has two layers which are
An upper palisade layer and a lower mesophyll layer.
The palisade mesophyll cells are column shaped and form. The main photosynthetic layer whereas the spongy mesophyll has large airspaces between the cells for gas exchange
What is stoma(plural: stomata)
A pore in the epidermis of a leaf bounded by two guard cells and needed for efficient gas exchange
What is a xerophyte?
A plant adapted to survive in conditions where water is in short supply
What is a cuticle?
A layer covering and secreted by the epidermis; in plants it is made of a fatty substance called cutin which helps to provide protection against water loss and infection
Water constantly moves out of the xylem vessels through the
Unlignified parts of the cell wall
What is symplast pathway?
The living system of interconnected protoplasts extending through a plant used as a transport pathway for the movement of water and solutes, individual protoplasts are connected via plasmodesmata
What is apoplast pathway?
The non living system of interconnected cell walls extending throughout a plant used as a transport pathway for the movement of water and mineral ions
In symplast pathway, water moves
From cells to cells via the plasmodesmata
In apoplast pathway, water moves through
The cell walls
What are xylem vessel elements?
Xylem contains more than one type of cells however the ones of particular importance in transport are xylem vessel elements
What are xylem vessel elements?
Xylem contains more than one type of cells however the ones of particular importance in transport are xylem vessel elements
Keyword: what is a xylem vessel element?
A dead lignified cell found in xylem specialised for transporting water and for support; the ends of the cells break down and join with neighbouring elements to firm long tubes called xylem vessel
How does each vessel element begins life?
It begins life as a normal plant cell, but later substance collagen is laid down in the walls. As lignin build up around the cell, the contents of the cell die leaving a completely empty space or lumen inside
Lenin is a very hard strong substance which is
Waterproof
How does the xylem vessel element form a long tube?
The xylem vessel elements are quite elongated and they lineup and to end. End of the elements, then breakdown completely to form a continuous tube running through the plant.
Many of the xylem vessel tubes are found in
The xylem
When the cell walls lignified what happens to the part which had plasmodesmata?
No lignin is laid down. These non-lignified areas appear as gaps in the thick walls of the xylem vessels and are called pits. Pits are not open pores; they still have the original unthickened cell wall containing cellulose. The pits in one cell link with those in the neighbouring cells just like the plasmodesmata did.
When the cell walls lignified what happens to the part which had plasmodesmata?
No lignin is laid down. These non-lignified areas appear as gaps in the thick walls of the xylem vessels and are called pits. Pits are not open pores; they still have the original unthickened cell wall containing cellulose. The pits in one cell link with those in the neighbouring cells just like the plasmodesmata did.
Why are the pits in xylem vessels necessary?
Because it allows water to move in and out of the vessels despite the waterproof lignin
How can xylem provide support?
Because of the strength of lignin which is hard to compress or stretch.
How can xylem provide support?
Because of the strength of lignin which is hard to compress or stretch.
What causes water to move up the Xylem vessels?
The removal of water from Xylem vessels in the leaf creates attention in the water left in the asylum vessels.(the water potential at the top of the Salim vessel becomes lower than the water potential at the bottom). The tension causes water to move up the xylem vessels
What causes water to move up the Xylem vessels?
The removal of water from Xylem vessels in the leaf creates attention in the water left in the asylum vessels.(the water potential at the top of the Salim vessel becomes lower than the water potential at the bottom). The tension causes water to move up the xylem vessels
If you suck hard on a straw, it’s walls make collapse inwards as a result of high tension you are creating. Why does this not happen in xylem vessels?
Because of the strong lignified walls
Tension or sucking is actually _________.
A negative pressure, it is like pulling on the water
The moment of water and mineral ions up through xylem vessels is by
Mass flow
What does mass flow mean? And how is it different from diffusion?
This means that all the water molecules plus any dissolved solute move together at the same speed like water in a river. This is different from diffusion where the different types of molecule or iron move a different speeds and directions according to their own diffusion gradients.
What is cohesion?
The attraction of water molecules to each other by hydrogen bonding
What is adhesion?
The attraction of water molecules to the cellulose and lignin in the words of the xylem vessels which are hydrophilic
Cohesion and adhesion help
To keep the water in a xylem vessel moving as a continuous column
Why is it an advantage that the cells in xylem vessels are dead and empty
Because it means there is no protoplasm to get in the way of transport
What is an air lock?
When an herbal forms in the column of water in a vessel, the water stops moving upward.
What prevents air locks from happening?
The small diameter of xylem vessels
How is an airlock bypassed?
The pits in the vessel walls allow water to move out from one vessel to a neighbouring vessel
Why can air bubbles not pass through pits?
Because there is a cellulose cell wall in the pit.
Why are pits important?
Because they allow water to move in and out of xylem vessels from and to surrounding living cells
What is the benefit of root hair?
They increase the surface area for absorption of water and mineral ions
After entering the root hair water crosses the cortex of the root and enters the xylem in the centre of the route. Why does water do that?
Because the water potential inside the Xylem vessels is lower than the water potential in the root hairs
After entering the root hair water crosses the cortex of the root and enters the xylem in the centre of the route. Why does water do that?
Because the water potential inside the Xylem vessels is lower than the water potential in the root hairs
describe how water travels in apoplast pathway?
Water can soak into the cell walls and can move across the root from cell wall to cell wall without ever entering the cytoplasm of the cells
describe how water travels in apoplast pathway?
Water can soak into the cell walls and can move across the root from cell wall to cell wall without ever entering the cytoplasm of the cells
Describe how water travels in a symplast pathway
The water will move into the cytoplasm or vacuole of a cortex cell by osmosis and then into neighbouring cells through interconnecting plasmodesmata
What happens when the water reaches endodermis in roots?
The apoplast pathway is blocked
What happens when the water reaches endodermis in roots?
The apoplast pathway is blocked
Why is the apoplast pathway blocked when it reaches endodermis
The cells in the ender dermis have a thick waterproof waxy band of suberin in their cell walls. This band is called the Casparian strip and it goes right round the cell. The only way for water coming across the cortex to cross the endodermis is through the unthickened parts of the wall into the cytoplasm of the endodermis cells
Why is the apoplast pathway blocked when it reaches endodermis
The cells in the ender dermis have a thick waterproof waxy band of suberin in their cell walls. This band is called the Casparian strip and it goes right round the cell. The only way for water coming across the cortex to cross the endodermis is through the unthickened parts of the wall into the cytoplasm of the endodermis cells
What happens as the endodermis cells get older?
The Suberin deposits become more extensive except in passage cells
What is the cell in which water can enter?
Passage cells
What is the cell in which water can enter?
Passage cells
What is the benefit of suberin on endodermis cells?
It gives a plant control over what mineral ions pass into its xylem vessels as everything has to cross cell surface membrane
What happens once the water gets across endodermis?
Water continues to move down the water potential gradient towards the xylem vessels through either the symplast or apoplast pathways. Water moves into the xylem vessels through the pits or non lignified regions of their walls.
What is the tip of the root covered by?
Tough protective root cap that is not permeable to water
What are root hairs?
They are extensions of some of the epidermal cells of the root.
What is the benefit of the large number of very fine root hairs?
Provide a large surface area in contact with the soil surrounding the root does increasing the rate at which water can be absorbed.
What are assimilates?
Are the chemical compounds made by the plant itself as a result of assimilation
What are assimilates?
Are the chemical compounds made by the plant itself as a result of assimilation
What is assimilation ?
Assimilation in plants is the range of processes by which the plant converts its in organic nutrients into organic compounds
What is assimilation ?
Assimilation in plants is the range of processes by which the plant converts its in organic nutrients into organic compounds
What is an example of assimilation?
Photosynthesis
During photosynthesis inorganic carbon dioxide and water are converted using energy to organic solute like sugars
Use of nitrates obtained from the soil to make amino acids
What is an example of assimilation?
Photosynthesis
During photosynthesis inorganic carbon dioxide and water are converted using energy to organic solute like sugars
Use of nitrates obtained from the soil to help make amino acids
Assimilate are transported from______ to______
Source,sink
What is source in plants?
A site in plant which provides food for another part of the plant, sink
Source is the place where the assimilate is located
What is sink in plants?
A site in plant which receives food from another part of the plant,the source
Sink is the place assimilates has to be moved to and is the needed for growth and development or for storage
What are some common sources in plants?
Leaves and storage organs such as tubers
What are common sinks in plants?
Buds, flowers fruits, roots and storage organs
Assimilates implants are transported using
Phloem
Phloem tissue is made up of several types of cell. The two most important type for transport are.
Sieve tube elements and companion cells
What is the difference between xylem vessels and sieve tubes
Sieve tubes are made of living cells
What is a sieve tube element?
A cell found in phloem tissue with non-thickened cellulose walls, very little cytoplasm, no nucleus and end walls perforated to form sieve plates, through which sap containing sucrose is transported
What is companion cell?
Cell with an unthickened cellulose wall and dense cytoplasm that is found in close association with a phloem sieve tube element to which it is directly linked via many plasmodesmata.
The companion cell and the sieve tube element form
A functional unit
The companion cell and the sieve tube element form
A functional unit
Sieve tube elements have
No nucleus, tonoplast or ribosomes
Sieve tube elements are_____ in shape
Elongated
What is a sieve tube?
Tube formed from sieve tube elements lined up end to end
The amount of cytoplasm is so reduced in a sieve tube element that it
Only forms a thin layer lining inside of the cell wall
Where the end walls of 2 see tube elements is met
A sieve plate is formed
What is a sieve plate formed of?
The cell walls of both cells, perforated by large pores. These pores are easily visible with a good light microscope.
What is a sieve plate formed of?
The cell walls of both cells, perforated by large pores. These pores are easily visible with a good light microscope.
What is the difference between a normal plant cell and a companion cell?
A companion cell has a small vacuole
The number of mitochondria and ribosomes is greater than normal and the cells are metabolically more active
Phloem sap moves by
Mass flow
Mass flow on average moves organic solutes at the speed of
About 1 m/h
Mass flow on average moves organic solutes at the speed of
About 1 m/h
On average mass flow is________ faster than diffusion
10,000
On average mass flow is________ faster than diffusion
10,000
What does it mean that the moment in xylem vessels is passive?
It requires no energy input from the plant (only the sun)
What does it mean that phloem transport is an active process?
To create a differences needed for mass flow in phloem, the plant has to use energy.
What does it mean that phloem transport is an active process?
To create a differences needed for mass flow in phloem, the plant has to use energy.
How is the pressure difference in phloem produced?
Active loading (moving) of sucrose into the sieve tube elements at the source. Loading a high concentration of sucrose into a sieve tube element greatly decreases the water potential of the sap inside it. Therefore, water enters the sieve tube element, moving down a water potential gradient by osmosis. This causes a buildup of pressure inside the sieve tube element. This pressure is referred to as hydrostatic pressure.
What happens after hydrostatic pressure takes place in sieve tube
A pressure difference is therefore created between the source and the sink. This pressure difference causes a mass flow of water and dissolved solutes through the sieve tube from a high-pressure area to a low pressure area.
What happens at the sink in sieve tube element?
Sucrose is removed causing the water to follow by osmosis. The loss of water from the tube reduces pressure inside the tube thus maintaining hydro static pressure gradient
Sugars are made in leaf mesophyll cells, some of the sugars are used to make sucrose which is then dissolved in solution. How how is the sucrose transported to the phloem tissue?
Through symplast pathway or apoplast pathway
Sugars are made in leaf mesophyll cells, some of the sugars are used to make sucrose which is then dissolved in solution. How how is the sucrose transported to the phloem tissue?
Through symplast pathway or apoplast pathway
how is sucrose loaded into the sieve tubes?
Hydrogen ions(protons, H+) are pumped out of the companion cell into its cell wall by proton pump using ATP as an energy source. The proton pump creates a large excess of hydrogen ions in the apoplast pathway outside the companion cell. The hydrogen ions can move back into the cell by passive diffusion down their concentration gradient through a protein which acts as a carrier for both hydrogen ion and sucrose molecule at the same time. because it carries two substances at the same time it is called transporter the transporter will only work if both a hydrogen ion and a sucrose molecule move through it together. Sucrose molecules are carried through this co-transporter molecule into the companioncell against the concentration gradient for sucrose but down the concentration gradient for hydrogen ions. Once inside the companion cell the sucrose molecules can move by diffusion into the sieve tube
