Transport In Plants Flashcards
What does xylem tissue transport?
Water and dissolved minerals
What are the main components of xylem tissue?
Xylem vessels, fibres, and parenchyma cells
What happens to xylem cells as they become lignified?
Cells die and contents and end walls decay, forming xylem vessels
Describe the structure of xylem vessels.
Continuous, hollow tubes with no end walls or contents
Why is there less resistance to the flow of water in xylem vessels?
Due to lack of contents and more space
What is the role of lignin in xylem vessels?
Increases cell wall rigidity and strengthens it
How does lignin affect the xylem vessel walls?
- Prevents collapse under tension
- Waterproofs the wall
- Reduces lateral flow of water
- Improves adhesion of water molecules
What pattern does lignification occur in xylem vessels?
Spiral pattern
What is the advantage of the spiral pattern in xylem vessels?
Allows the tubes to remain flexible
What are bordered pits in xylem vessels?
Pores in walls of vessels
What is the function of bordered pits?
- Allow water to divert into other tubes if one gets blocked
- Allow lateral movement of water between vessels
Why is a narrow lumen beneficial in xylem vessels?
Increases capillary rise and makes capillary action more effective
What is the function of phloem?
Transports sugars (sucrose) up and down the plant
- Phloem is essential for the distribution of nutrients throughout the plant.
What are the main components of phloem?
sieve tube elements and companion cells
What is the structure of sieve tube elements?
Thin layer of cytoplasm
- This structure allows for less resistance and more space for transport.
What is the significance of sieve plates?
Allows continuous transport
- Sieve plates are crucial for the bi-directional flow of sucrose.
True or False: Sieve tube elements have a large nucleus.
False
Most organelles, including the nucleus, are absent in sieve tube elements.
What is the role of companion cells?
Provides large amounts of ATP for active processes
Companion cells are vital for loading sucrose into sieve tubes.
Fill in the blank: Sucrose is transported as _______ dissolved in water.
sap
This sap is essential for the transport of nutrients within the plant.
What structures connect sieve tube elements to allow sucrose transport?
Plasmodesmata
Plasmodesmata facilitate the transport of molecules such as proteins and ATP.
What type of flow does phloem allow?
Bi-directional flow
This means sucrose can move both up and down the plant.
What is a key characteristic of sieve tube elements that aids in transport?
Less resistance for transport
The thin layer of cytoplasm contributes to this characteristic.
What is the function of the nucleus in companion cells?
Controls the functions of companion cell and sieve tube elements
The nucleus is essential for maintaining the activity of these cells.
Why do companion cells respire
This is necessary to generate ATP for active transport processes.
True or False: Sieve tube elements are living cells.
True
Despite lacking many organelles, sieve tube elements are still classified as living.
What is water potential?
The potential energy of water in a system compared to pure water
Water potential determines the direction of water movement in plants.
What happens to a plant cell when water enters it?
The cell becomes turgid
Turgidity is a state where the cell is firm due to water uptake.
What is the water potential of a concentrated solution?
Very low
Concentrated solutions have lower water potential compared to dilute solutions.
What occurs when water leaves a plant cell?
The cell becomes plasmolysed
Plasmolysis occurs when the cell membrane pulls away from the cell wall.
How does water enter root hair cells?
Through osmosis
Water moves from an area of higher water potential in the soil to lower potential in the root hair cells.
What are root hair cells adapted for?
They increase surface area for osmosis and mineral uptake
Adaptations include hair-like projections and thin cell walls.
What is the function of mitochondria in root hair cells?
To provide energy for active transport of minerals
Energy from mitochondria is crucial for mineral uptake against the concentration gradient.
What is the apoplast pathway?
Water travels through cell walls in gaps
This pathway does not involve crossing cell membranes.
What is the symplast pathway?
Water crosses cell surface membranes and moves through plasmodesmata
This pathway allows for direct movement within the cytoplasm of connected cells.
What is the vacuolar pathway?
Water moves through vacuoles as well as the cytoplasm
Similar to the symplast pathway but includes vacuole movement.
Fill in the blank: Water moves into the root hair cell via osmosis across the cell surface, down the _______.
water potential gradient
This movement is driven by differences in water potential.
What is the Casparian Strip?
A strip of waterproof material called suberin in the cell walls of the endodermis.
How are minerals transported into the xylem?
Minerals must be actively transported from the cytoplasm into the xylem through carrier proteins.
What is the relationship between water potential and osmosis in the xylem?
Water potential is lowest in the xylem, causing osmosis of water from the root hair cell to the endodermis.
What pathway is blocked by the Casparian Strip?
The apoplast pathway.
After the Casparian Strip blocks the apoplast pathway, what pathway must water take?
The symplast pathway.
What effect does the active transport of minerals have on water potential in the xylem?
It lowers the water potential in the xylem.
Where does water move from during osmosis into the xylem?
From the cells of the endodermis and cortex.
Fill in the blank: Water moves from soil into root hair cells across cell surface membrane through _______.
aquaporins
What are the two pathways water can take to move across the soil cortex?
- Apoplast pathway
- Symplast pathway
True or False: The Casparian Strip allows water to flow freely through the apoplast pathway.
False
What is the primary function of the Casparian Strip in water movement?
To force water to enter the symplast pathway.
What links the cytoplasm in neighboring cells for water movement?
Plasmodesmata.
What causes the water potential to be most negative in the xylem?
The active transport of minerals into the xylem.
What happens to water potential as minerals are actively transported into the xylem?
It decreases, causing water to move into the xylem.
Transpiration
The loss of water by evaporation out of plant leaves via the stomata
- happens at the same time as gas exchange
3 ways water is helped move up the xylem vessels from the root
Root Pressure
- the push from the water entering the vessels in the roots (doesn’t move water far)
Capillary Action
- adhesion of water molecules to lignin in narrow vessels and pull water up the sides of the vessel
Transpiration Pull
- most of the driving force
Evidence for cohesion-tension theory
Changes on the diameter of trees
- when transpiration is at its highest rate in the day, the tension in the xylem vessels is also highest
- this causes the tree to shift in diameter
if xylem is broken, air is drawn in rather than water leaking out
- if a xylem vessel breaks, pressure is lost
- this means that the cohesive forces (H bonds) break, and water cannot be pulled up so air is pulled out
Factors affecting transpiration rate
- number of leaves
- number & size of stomata
- waxy cuticle present
- light
- temperature
- humidity
- wind
- water availability
Xerophytes
A plant that is adapted to reduce water loss through transpiration so that it can survive in very dry, arid conditions
Xerophyte adaptations
- epidermis covered in hairs
- thick waxy cuticle
- small leaves/needles
- sunken stomata in pits
- curled leaves
- small air spaces in mesophyll
- stomata shut in day, open at night
Hydrophyte
A plant that is adapted to living in water or where the ground is very wet
Hydrophyte adaptations
- many large air spaces in the leaf - keeps leaf afloat
- stomata are on the upper epidermis- exposed to air for gas exchange
- leaf stem has many large air spaces- helps with buoyancy, but also allows oxygen to diffuse quickly to the roots for aerobic respiration.
Translocation
Movement of assimilates (sucrose/amino acids) by mass flow
- from source to sink
Source
Produces/releases sucrose (& amino acids)
- leaves
- storage organ e.g. root
Sink
Stores/uses sucrose
- leaf
Why is sucrose transported around a plant, not glucose
- sucrose is a disaccharide and non reducing sugar
- less reactive than glucose
- soluble
Process of translocation
active loading of sucrose at source
1. H+ actively transported from companion cell into sink cell
2. A proton gradient develops between sink cell and companion cell
3. H+ rapidly diffuse down electrochemical gradient into companion cell
4. Sucrose moves with H+ through specialised co-transporter proteins
5. Sucrose is using energy of proton gradient to move rapidly into companion cells
6. Sucrose DIFFUSES into sieve tube elements
- Sucrose lowers WP in sieve tubes (high in solutes)
- High hydrostatic pressure develops at the source
- At the sink, sucrose is unloaded, leaving a relatively high WP (low solutes) at sink in sieve tubes. Water flows out of sieve tubes by osmosis leading to a lower hydrostatic pressure
What gradient exists between source and sink
A hydrostatic pressure gradient exists between source and sink
Sucrose and assimilates move by mass flow dissolved in cell sap from source to sink
