Chaoter 9 ~ Transport In Plants Flashcards
Why are transport systems in multicellular plants needed?
To meet high, metabolic demands, oxygen and glucose is needed to be transported and waste products need to be removed hormones which are made in one part of the body also need to be transported
To overcome low surface area to volume ratio
To allow diffusion across large distance
What are dicotyledonous plants
Plants which produce seeds containing two cotyledons Which act as a food stores for developing embryos and form first leaves when seed germinate they also contain vascular bundles
Herbaceous dicots
Xylem and phloem
How is the xylem and phloem arranged together?
In a vascular bundle within the leaves, stems, roots and herbaceous dicots
In the stems, how are the vascular bundles?
Check textbook
In the roots, how are the vascular bundles?
Check textbook
In the leaves, how are the vascular bundles?
Check textbook
How can you observe xylem vessels in living plants, stems?
Vessels can be clearly stained in transverse and long, usual sections of plants, stems, and roots on prepared slides
1. In one specimen, make clean transverse, cut across the stem with a sharp blade on a white tile
2. Observe and draw the position of this xylem vessel, which should show up as coloured spots.
3.in another specimen, make careful, longitudinal, cut through a region, where you expect there to be xylem vessels
4. Observe and draw the design vessels which may show up as coloured lines.
Explain the structure and function of the xylem
It is a nonliving vessel
It transports water and mineral irons from the roots to the rest of the plant
It is made up of dead hollow cells with no end walls, long hollow structure
It provides support as it is lignified which provides mechanical strength
Transport from the roots to the shoots and leaves
It contains xylem parenchyma which stores food containing tannin
The cell wall contains pits which allow water mineral irons to move into and out of the cell
Explain the structure and function of phloem
It is a living tissue which transports food in the form of organic solute around the plants
It can go in both directions and essentially goes from source to sink
It is made up of two types of cells to sieve tube element and companion cells
The sieve tube element is a living cell joined end to end to form sieve tube plates which allow solute to move. It contains lots of holes and no organelles which creates more space for solute to be transported
The companion cells are linked to the tube elements by plasmodesmata. It contains a nucleus and is packed with mitochondria which provides lots of energy for active loading of sucrose
It is not lignified
What is plasmodesmata
Microscopic channels through the cellulose cell wall, which link the cytoplasm of adjacent cells. They maintain nucleus and organelles.
How are root hair cells adapted as exchange surfaces
The microscopic size which means they can penetrate easily
They have a large surface area to volume ratio
They have a thin surface layer which allows diffusion and osmosis take place quickly
What are the two ways that water moves across the root to the xylem
The symplast pathway
The apoplast pathway
Explain the symplast pathway
Water moves through cytoplasm connected to plasmodesmata via osmosis. The root has a high WP
What is the main pathway?
Apoplast as it provides least resistance however water by passes cell membrane which controls substances going in and out of cell and prevents toxic substances
What is the apoplast pathway
Water moves through cell walls and diffuses Due to high hydrostatic pressure
What interrupts water moving across apoplast pathway
Casparian strip
What is the casparian strip?
A band of waxy cuticle called Suberin which forms a waterproof layer
water can-no longer more and is pushed into cytoplasm where it goes through symplast pathway
How does carbon dioxide move from the air into the leaf and oxygen move out of the leaf by diffusion through?
Stomata, which can be open and closed by guard cells
What is the loss of water vapour called?
Transpiration
What is the transpiration stream?
Refers to the movement of water from the roots to the leaves
How does the transpiration stream work?
Transpiration stream:
moves water up from roots to leaves
1) water molecules evaporate from surface Of mesophyl into leaf and out of stomata into air via diffusion
2) loss of water by evaporation ↓ water potential So water mores into cell via osmosis along sympast + apoplast pathways
3) repeated across leaf to xyIem.
4) water molecules form hydrogen bonds with carbohydrates -adhesion. And water molecules form hydrogen bonds with each other + stick togeter - cohesion. This results in cohesion adhesion theory. water can rise up narrow tube against force of gravity and is drawn up xylem in a continuous Stream to replace water lost by evaporation (transpiration pull)
5) This moves water across cell.
Cohesion tension theory
Water molecules form hydrogen bonds with each other and they stick to each other this is cohesion
Water molecules from hydrogen bonds with carbohydrates, which is adhesion
The combined effects cause water exhibiting a capillary action water rises up a narrow tube against gravity and is drawn up the xylem
What are the evidence for the cohesion tension theory?
There are changes in the diameters of trees
When xylem. vessel is broken, it is drawn out to the xylem. rather than water being leaked
If the xylem vessel is broken and air is pulled in plant can no longer move water up the stem as the continuous stream of water molecules held together by cohesive forces has been broken
What are the four factors affecting transpiration?
Light humidity, temperature and air movement and soil water availability
How does temperature affect transpiration?
Increasing the temperature increases the kinetic energy and evaporation
How does light intensity affect transpiration?
Increase on the light increases the amount of stomata which is open
How does wind and humidity increase transpiration?
They decrease the water vapour potential gradient between the inside of the leaf and outside air which increases the rate of transpiration,
What is translocation?
It is the energy requiring process transporting assimilates (sucrose) from source to sink
What are the products of photosynthesis, which are transported known as
Assimilates
What is the main assimilate transported around the plant?
At the source, sucrose lowers the water potential and water enters via osmosis increasing hydrostatic pressure
At the sink , respiring cells is used up and therefore has a more positive water potential and water leaves via osmosis decreasing hydrostatic pressure
Explain mass flow hypothesis, including points about source and the sink
At the source
Active transport is used to actively low solute into tubes of phloem at source
This lowers the water potential inside the sieve tube so water enters via osmosis from xylem and companion cells
This increases the hydro static pressure inside the tube at source
At the sink
Solutes removed from phloem are used up
This increases water potential inside sieve tubes so water leaves via osmosis
This low is a hydrostatic pressure
This process results in the pressure gradient which pushes solute along
Explain active loading
① companion cell, ATP actively transports H+ ions out of cell into tissUe
② set up concentration gradient, moves H+ ions in surrounding tissue than in companion cell
③ H+ binds to co- transporter protein In companion cell and re enter cell
④ sucrose binds to co-transporter protein, movement of H+ is used to
Move sucrose into cel then transport out Of sieve tube
Evidence for mass flow hypothesis
Advances in microscope allows us to see the adaptations of companion cells for active transport
If the mitochondria of a companion cell is poison translocation stops
The flow of sugars in the flame is about 10 times faster than it would be by diffusion alone suggesting an active process is driving mass flow
If it can be used to demonstrate the translocation of organic solutes in phloem
What are xerophytes
Plants adapted to live in regions where water is scarce
How to xerophytes conserve water
Waxy layer on epidermis which reduces evaporation from the surface as water cannot easily pass through
Sunken stomata, they have stomata which are sunken in pits which sheltered the stomata from the wind producing water potential gradient between the inside of the leaves and the outside
Hairs on epidermis which trap water vapour and reduce water potential gradient between the inside and outside of leaf
Spines of leaves which reduce surface area for water loss
Rolled leaves as curled leaves, trap water vapour reducing the water potential gradient for transpiration. It also reduces surface area of the leaf for water loss.
Closure of stomata during conditions where there are high temperatures or light intensity this reduces transpiration
What are hydrophyte?
They live in water
Adaptations of hydrophyte
Stomata on upper surface this maximises gasket change
Spaces which help the plant to float and store oxygen for aerobic respiration
Flexible leaves and stems which prevent damage from water current
Wide flat leaves which spread across the surface area to capture as much light
