Transport In Plants Flashcards
Why do plants need a transport system
Underground parts of plants do not photosynthesise- they need glucose transporting to them and need to remove waste, hormones need to be transported to where they will have an effect and mineral ions need to be transported as well
Why do single called plants have no transport system
They have a large SA:Vol ratio
How do large plants exchange gases
Through openings called lenticels
Oxygen enters for aerobic respiration
What is the food store in dicots
Cotyledons x2
What is the food stores in monocots
Endosperm
Describe the seeds of a dicotyledonous plant
They make seeds which consist of two cotyledons
What is a cotyledon
Organs that act as a food store for the developing embryo and form the first leaves
What is the name of the transport vessels that run through dicots
Vascular system
What does xylem transport
Water and mineral ions up the plant
What does the phloem transport
Sucrose and amino acids both up and down the plants
Where are meristematic cells found
At growing points in plant
Stem apex and root tip
What can cambium specialise into
Xylem and phloem cells
What are the microscopic channels in the cellulose cell wall of phloem called
Plasmodesmata
Describe the structure of phloem tissue and how this improves its function
Sieve tune elements are living cells that are joined end to end so diluted can be transported long distances
Sieve plates have perforations so solutes can pass from one sieve tube to another
Cytoplasm is pushed close to walls
Few organelles and no nucleus
How are companion cells specialised
They have many mitochondria to allow for more atp to be produced for use in active transport
What is source site
Where assimilated are loaded into the phloem
What is the sink place
Where assimilated are unloaded from the phloem
Describe the movement of sucrose and other assimilated down the phloem vessel
1) Hydrogen ions are actively transported using atp out of companion cells into source cell, creating a concentration gradient
2) h+ ions love by facilitated diffusion back into companion cell with sucrose and amino acids through co transport proteins
3) the sucrose diffuses from the companion cell through plasmodesmata into the phloem sieve tube element
4) causing the water potential to be lowered
5) water moves in by osmosis
6) creating a high hydrostatic pressure
7) water moves him from a high hydrostatic pressure to low (called mass flow)
8) sucrose and amino acids moves into companion and sink cell by diffusion
9) water leaves the phloem by osmosis (high to low WP)
What is the evidence for companion cells
1) companion cells become negatively charged compared to there surroundings (due to H+ ions)
2) ph inside the companion cells increased and outside decreased
3) when companion cells were treated with cyanide which stops aerobic respiration ph change did not occur
4) ultra structure shows many mitochondria intrinsic proteins and plasmodesmata
Explain aphid studies on the phloem
Aphids pierce plant tissue with mouth part
They reach the phloem
If aphid is anethetised sap continues to flow out of the stylet due to pressure from the phloem contents
This measures flow rate and concentration of sucrose
Shows that the conc of sucrose is higher near the source than the sink
Why do plants need water
Material used in photosynthesis
Mineral ions and products of photosynthesis are transported in aqueous solutions
Loss of water by evaporation helps plants keep cool
What are xylem vessels formed of
Dead hollow cells with lignified Walls
What does lignin do
- Gives strength to xylem vessel wall- helps prevent collapse of xylem
- lignin is waterproof which reduces the loss of water through wall
- lignin is a spiral shape- allows vessel to stretch
Xylem vessels have bordered pits- what does this allow
Bordered pits allow sideways movement of water into other vessels- allows them to bypass a blockage of air
What is transpiration
Evaporation of water and the loss of water from the aerial parts of a plant via the stomata
What is the transpiration stream
The movement of water up the xylem vessels from roots to leaves and then to the air surrounding the leaves
Name the three processes involved in transpiration
Evaporation
Diffusion
Osmosis
Describe the process of transpiration
1) water enters xylem by osmosis from a higher water potential in the soil to a lower WP in the roof cells (caused by active transport of ions into root cells and xylem)
2) causes a high hydrostatic pressure at bottom of xylem
3) transpiration of water from leaf mesophyll (water vapour diffuses from a high to a low concentration into the air surrounding the leaf) this creates a low hydrostatic pressure at the top of xylem
4) water is now under tension, cohesion between water molecules and adhesion of water molecules to xylem wall
5) causes water to move up by mass flow from high to low hydrostatic pressure
What is cohesion tension theory
As water is removed from xylem more water molecules are ‘pulled up’ to replace them - this is tension.
What can break cohesion in the xylem, how is the xylem adapted to overcome this
Air bubbles cause a blockage in xylem - this breaks cohesion and prevents continuous flow
Xylem has bordered pits which allows lateral movement of water up the xylem
How can you prevent air bubbles in the xylem
Cut flowers under water to prevent air bubbles , this stops blockage of xylem
Explain how guard cells can open
Large vacuoles take up water and become turgid, thicker inner cell walls and thinner outer cell walls forces them to bend outward and therefore open.
When do guard cells open and close
Open in light
Close in dark
Why do guard cells have lots of mitochondria
To create ATP for active transport of k+ ions
What happens when k+ ions are actively transported into guard cells
Decreases the water potential so water moves in by osmosis
Why do guard cells open, what happens
Open stomata to allow vital gas exchange- co2 must enter for photosynthesis to occur, as a result plants lose water vapour from stomata when open.
Describe root pressure
What is the evidence fo this
Water is moved by osmosis into xylem along a water potential gradient
If you cut a plant stem at soil level water will continue to come out of the cut stem for some time due to osmosis.
Where can you find the casparian strip
In the endodermis
Explain how a root hair cell is adapted
Cells have extended hairs
Increased SA to absorb water by osmosis and mineral ions by active transport
Thin cell wall for short pathway
Many mitochondria for ATP for active transport of mineral ions
Water can be moved into the roots by three ways, name and describe them:
Appoplastic pathway- water moves through cellulose cell walls and between cells ( when it reaches the casparian strip its waxy waterproof layer forces water into the symplastic pathway)
Symplastic pathway- water moves by osmosis through cytoplasm
Vascuolar pathway- uses cytoplasm and vacuoles
What is the advantages of a casparian strip
Forces water to travel across the cell surface membrane, this is selectively permeable and stops the toxic solutes from the soil reaching the xylem and other tissues of plant.
Why does water and minerals move into root hair cells
By osmosis
Higher water potential in soil water, lower water potential in root hair cells (due to mineral ions)
Minerals- active transport of mineral ions into root hair cells ( low conc of minerals in soil water) high conc in root hair cell / uses ATP
THIS GIVES A POSITIVE PRESSURE FORCING WATER UP THE XYLEM
What is the evidence for root pressure
If cyanide is applied to root hair cells- atp production stops- root pressure disappears
If levels of oxygen falls, root pressure falls as well ( this is because oxygen is used in atp production
Name and describe the five factors which affect transpiration rate
1) light intensity- more light more transpiration as light stimulates the stomata opening
2) temperature- higher temp higher transpiration- water molecules have more KE - increasing rate of evaporation
3) humidity- INCREASE humidity DECREASES transpiration- this is because the water vapour gradient becomes less steep
4) air movement (wind speed)- more windy= more transpiration- water vapour from outside is removed increasing steepness of water vapour gradient
5) soil water availability- less water available= transpiration rate decreases- very dry soil puts plant under water stress lowering rate
What is used to estimate the rate of transpiration
A potometer
How does a potometer calculate the rate of transpiration
By measuring the distance travelled by an air bubble in a capillary tube over a given time, the faster the bubble moves, the greater rate of water uptake and so the greater rate of transpiration.
Why is a potometer set up underwater
To avoid air bubbles in the xylem of the plant which can disrupt the transpiration stream
Describe the method you would use to estimate transpiration rate using a potometer
ENSURE IT IS AIRTIGHT AND WATER TIGHT
1) a single air bubble should be introduced into the capillary tubing
2) the tap on the reservoir is opened to add water to push the air bubble back to zero on the scale
3) a timer is started and a set time measured
4) the distance the air bubble has travelled along the scale is recorded
5) the experiment can be repeated ( call a mean/ discard anomalies…)
How are plants designed to reduce water loss
- waxy cuticle
- stomata on the underside of leaf
- stomata closed at night (no need for photosynthesis here)
- some plants evolved to close stomata at times where transpiration is at its highest (CAM plants)
What is a xerophyte
Plants which have structural and physiological adaptations that enable them to survive in extreme conditions (ie hot, dry)
Give a named example of a xerophyte
Cacti
Xerophytes have a thick waxy cuticle, why?
The waxy layer that covers the epidermis is waterproof to reduce evaporation of water, reducing loss of water
Xerophytes have a leaf surface overhead with hairs, why
To reduce the movement of air over the surface of the leaf, trapping a layer of water vapour between the hairs, reducing the steepness of the water vapour potential gradient
Xerophytes have sunken stomata, why
Traps water vapour, reducing steepness of water vapour potential gradient
Xerophytes have fewer air spaces inside the spongy mesophyll, why
To reduce the surface area for evaporation of water to form water vapour
Describe why CAM plants are xerophytes
They have evolved to close there stomata at times during the day where transpiration rate would be at its highest, the stomata instead opens at night and carbon dioxide enters and is stored in vacuoles to be released during the day for use in photosynthesis
What is a hydrophyte
Plants that live in water and need adaptations to survive growing in water/ soil saturated with water.
Name five adaptations of hydrophytes
- Many stomata on upper surface of leaves that are always open (maximise gas exchange)
- very thin or no waxy cuticle (no need to reduce transpiration)
- wide flat leaves (maximise light capture)
- small roots (water moves directly into stem and leaves)
- air sacs( allows plant to float)
Describe aerenchyma
Specialised packing tissue
Forms in leaves stems and roots
Many large air sacs
Internal pathway for movement of oxygen
Describe pneumatophores
Found in mangrove swamps where roots can become waterlogged
*These are aerial roots which grow upwards into the air
Have many lenticels to allow air into the plant *
