Transport In Plants Flashcards
Need for water
Mineral ions and sugars are transported
Raw material for photosynthesis
Cooling effect, via transpiration
Turgor pressure
Water potential
Is the tendency for water molecules to move within and between cells.
Highest water potential is zero
Presence of solute lowers water potential
Root hair cell adaptations
Very thin permeable cellulose cell wall that are permeable to water and minerals
Microscopic
Large SA;V
concentration of solutes in cytoplasm of root hair cells maintains water potential gradient between soil water and cell
3 water pathways, and what they mean
Symplast- through the cytoplasm and plasmodesmata
Vacuolar- through vacuoles
Apoplast- through the cell walls
What is the Casparian strip
Impermeable layer of Suberin, waxy material.
Continuous cylinder of endodermal cells which surround the central vascular tissue, xylem and phloem
Forces water in the apoplast pathway into symplast pathway
Use of the casparian strip
- when water reaches the endodermis of the root it’s path is blocked
- endodermis has impermeable layer called caspairan strip
- in order to cross the endodermis the water is moved into the apoplast pathway. Water now moves through the cell surface membrane and into the cytoplasm
- this is a selectively permeable plasma membrane, this removes toxins
3 processes to move the water up the stem
Root pressure, active process
Transpiration pull
Capillary action
( all happens due to gas exchange at the top of the plant)
Define transpiration
The loss of water vapour from the stems and leaves of a plant as a result of evaporation from cell surfaces inside the leaf and diffusion down a concentration gradient out through the stomata
How is water transported up the stem to the leaves
- Water is lost from the leaves as water vapour, through the stomata
- this creates a low hydrostatic pressure at the top of the plant compared to the higher hydrostatic pressure at the bottom.
- due to the pressure gradient a transpiration stream/tension is created causing the water in the xylem to be drawn up into the leaves
- water sticks to the walls of the xylem vessel due to adhesion and water molecules stuck to each other due to hydrogen bonds allowing the water to move against gravity upwards.
Evidence for the cohesion tension theory
Tree rings- when transpiration is at its highest tree diameter decreases due to the tension in the xylem vessels being higher.
Broken xylem vessel- when a vessel breaks air is drawn in stead of water leaking out
Factors affecting the rate of transpiration
Light intensity - required for photosynthesis therefore stomata open for gas exchange, open stomata increase the rate of transpiration
Relative humidity - if volume of water in the air is high this reduces the conc gradient between the inside of the leaf and the outside air meaning transpiration rate decreases
Soil water availability -
Air movement - sweeps water molecues off leaf surface maintaining conc graidents
Temperature - increases KE of water particles meaning they move out of the leaf at a faster rate ( if temp gets too high stomata close to prevent excess water loss)
What is the gap between the companion cell and the phloem sieve tube called
Plasmodesmata
Function / adaptations of xylem
- transports dissolved minerals and water around the plant
Lignified cell walls - add strength to withstand the hydrostatic pressure of transpiration pull so that the vessels do not collapse
No end plates - allows the mass flow of water to cohesive and adhesive, these forces are not impeded (continuous forces)
Cells are dead - cells do not need the minerals that are being transported
Bordered pits - allows movement of water into the phloem
Small diameter- helps prevent colum from breakig and assists with capillary action
Function / adaptations of phloem
Transports assimilates from source to sink, Assimilates are disolved in water to form sap
No vacuole or nucleus - to maximise space for assimilates
Sieve tube elements line up end to end to form a continous tube
Sieve plates with sieve pores - allow phloem content to flow through whilst removing preventing movement of unwated stubstances. Can also become signified to prevent spread of disease
Companion cells linked by plasmodesmata ( channels through the cell wall which allow sucrose to enter)
Celluose cell wall - withstands hydrostatic pressure
What is facilitated diffusion
Diffusion that takes place through the use of protein channels
effect temperature has on sugar transportation
Higher temp means cells have more KE.
Higher KE means rate of photosynthesis is higher meaning more ATP is available for companion cells to facilitate diffusion of h+ ions and sucrose
Structures and function of companion cells
Have role in loading and unloading sugars from phloem
Large number of mitochondria
Plasmodesmata - link to sieve tube elements which allow organic compounds to move from the companion cells to seive tube
Charged particles are move out of companion cells by ————
Active transport
How are guard cells adapted to their function
Unevenly thickened cell wall ( side beside pore thicker )
Meaning cell is able to bend and change shape
Contains lots of transporter proteins in plasma membrane
Presence of chloroplasts to provide energy
Why is lignin essential for xylem vessels
Provides strength and support Prevent collapse Transpiration produces tension To waterproof the cell, adhesion of water So cell dies to create a hollow tube Spiral allows flexibility
Why is cartilage essential
support to keep airway open
Provides strength to prevent collapse during inspiration as the volume of thorax increases meaning the pressure in the tranche drops
Need for transport system in plants
Metabolic demands- glucose and oxygen made in the plant must be transported to other areas that do not photosynthesise
Size- increasing transport distances
SA:V - relatively small SA:V despite adaptions such as leaves, this means they cannot rely on diffusion alone to supply cells with everything they need
Plants need to take carbon dioxide and nutrients in
Waste products generated need to be released
Structure of the stem
Vascular bundles around the edge to give strength and support
Structure of root
Vascular bundles are in the middle to help the plant withstand the tugging strains that result as the steams and leaves are blown in the wind
Structure/function of dicot leaf
Midrib is the main vein carrying the vascular tissue through the organ.
It also helps to support the structure of the leaf
Many small branching veins spread through the lead functioning both in transport and support
Movement of water into the root, due to root hair cells
Microscopic size means they can penetrate easily between soil particles
Each microscopic hair has a large SA:V
Each hair has a thin surface layer, giving a short distance for diffusion and osmosis to take place
Concentration of solutes in cytoplasm maintains water potential gradient
Symplast pathway
Continuous cytoplasm of living plant cells that is connected through plasmodesmata
Root hair cell has high water potential than the next cell along so water moves along my osmosis
Apoplast pathway
Through cell walls and intracellular spaces
Water fills the spaces between the loose open network of fibres in the cellulose cell wall
As more water molecules move into the xylem more are pulled through the apoplast due to cohesion forces, creating a tension and a continuous flow of water
Sources of assimilates
Green leaves and green stems
Storage organs such as tubers and tap roots that are unloading their stores at the begging of growth periods
Food stores seeds when they germinate
Sinks of a plant
Any part of the plant that is removing sucrose from the phloem for :
Roots that add growing
Meristem that are actively diving
Metabolic activity
Translocation process
- h+ ions move from the companion cell into the source cell from an area of high conc to low conc
- h+ ions and sucrose molecules bind to the transporter protein and are transported across into the companion cell via active transport
- sucrose diffuses into the phloem tube down the conc gradient
- this causes water to rush in from the xylem tube as the additional sucrose lowers water potential
- this mean hydrostatic pressure outside the source is higher than at the sink causes sucrose to move towards the sink
- sucrose is in high conc in the phloem tube and low in the companion cell meaning the sucrose diffuses in (unloading)
How water is transported into the roots
Mineral ions enter via active transport decreasing the water potential.
Water then moves in by osmosis
Travels to the casperian strip,which forces water into the symplast pathway
Dissolved nitrates travel into the xylem decreasing water potential, water follows
Structure of phloem tubes
Sieve tubes are elongated cells that line up to form tubes with thin cytoplasm and perforated cross walls / sieve plates
They form the phloem and allow the flow of sap
Why transpiration is unavoidable during the day
Stomata are open allowing gaseous exchange
Photosynthesis occurs
Higher temperature during the day causes greater evaporation
2 types of cell that can be found in the phloem tissue
Sieve tube elements
Sieve tube plates
Companion cells
Parenchyma
Why may plant need lenticels (area found on trunk that allow diffusion)
No leaves in winter for diffusion of o2 into the plant
Stomata closed at night
Location where growth occurs in plants
Cambium, situated between phloem and xylem
Apex of root/shoot
Meristem
Bud
When does leaf/stem growth occur
Mitotic division in the cambium
Source of plant
Any part of the plant that loads sucrose into the phloem
Name one other part of the lead which water may be lost
Epidermis/ cuticle
