Transport in Plants Flashcards
Why do plants need a transport system?
Get water from the roots to the leaves
Move sugars from leaves to the rest of the plant
What is the function of the xylem?
Carry water up the plant
Provide structure
What happens to xylem cells as they mature which impacts their function?
They become lignified
What does lignin do to the xylem?
Kills the cells
Makes them waterproof
Strengthens the vessel
What is the function of the cambium?
Contains meristem cells which can divide and specialise to form new xylem and phloem cells
Give ways in which xylem is adapted to its function
Made from dead cells aligned end to end
tubes are narrow so capillary action can be effective
Bordered pits allow water to move from one vessel to another
Lignin deposited in a spiral allows the xylem to stretch as the plant grows despite being dead
What are the two types of cells that make up the phloem?
sieve tube elements
Companion cells
What is the function of the phloem?
Transport assimilates (mostly sucrose and amino acids)
How are sieve tube elements specialised to carry out their function?
Lined up end to end to make a long tube
contain no nucleus and little cytoplasm, leaving more space for mass flow to occur
What is the function of the companion cells?
To carry out metabolic processes needed to actively load assimilates into the sieve tube elements
They are needed because the little cytoplasm in the sieve tube elements means that they can’t do this themselves.
How are companion cells adapted to their function?
They have a large nucleus
Dense cytoplasm
This is because they need to carry out metabolic reactions for not only themselves but the sieve tube elements also
What is a plasmodesma?
A gap in the cell wall of a cell where it connects to another cell
describe what the 3 pathways in which water can move are and how they work?
Apoplast pathway - Moves in the spaces between cells
Symplast pathway - Moves between the plasmodesmata of cells through the cytoplasm
Vacuolar pathway - Moves through the vacuoles of cells also
Where will water move in a water potential gradient?
To the area with he lowest water potential
What will happen if you put plant cells in distilled water and why does this happen?
The plant cells will take up water by osmosis and swell
This because the solutes in the plant cell cause the water potential to be lower than that of the distilled water
Water moves to the area of lowest water potential
What will happen if you put plant cells in a salt solution and why?
A salt solution will have a very low water potential
Water will move out of the plant cell into the solution down a water potential gradient
Water will move to the area of lowest water potential
Cells will shrink
What is the name of the condition whereby the plasma membrane comes away from the cell wall?
Plasmolysis
What is Transpiration?
The loss of water vapour from the upper parts of the plant- particularly the leaves
Describe the pathway of water leaving the leaf
Water enters leaf through xylem and moves by osmosis into the spongy mesophyll
Water evaporates from the cell walls of the spongy mesophyll
Water vapour moves by diffusion out of the leaf through he open stomata. This requires a water potential gradient between the leaf and the surroundings
Why is transpiration essential for a plant to survive?
As water vapour is lost it draws water up the stem as a transpiration stream, this movement:
Transports useful mineral
Maintains cell turgidity
Supplies water for growth, cell elongation and photosynthesis
Supplies water that can evaporate to cool the plant
Give 5 environmental factors that affect rate of transpiration
Light intensity Temperature Humidity Wind Water availability
What type of cells is the epidermis of a root made of?
Root hair cells
Where does water move from and to in the root?
Water moves from the soil into the epidermis of the root hair cells
Moves across the root cortex to the endodermis of the vascular bundle
Why can water only move through the apoplast pathway as far as the endodermis?
Because the Casparian strip blocks the apoplast pathway
Describe how the endodermis and Casparian strip act to move water into the medulla and xylem
Casparian strip blocks the apoplast pathway between the cortex and medulla
Ensures that mineral ions (especially nitrates) pass through the plasma membrane into the cytoplasm
Mineral ions are actively transported into the medulla and xylem
This creates a water potential gradient so water moves by osmosis into the medulla
The Casparian strip then blocks it from moving back out
What are the 3 processes that ensure mass flow occurs?
Root pressure
Transpiration pull
Capillary action
Describe what root pressure is.
As water moves into the roots and xylem it causes an increase in pressure
This pressure forces water up the xylem
This can push water a few meters up a stem but can’t account for tall trees
Describe the process of transpiration pull
Water is lost from the top of the plant by transpiration
Hydrogen bonds cause cohesion between water molecules
Water moves up to the leaves to replace lost water and other molecules are pulled up with it
Describe the process of capillary action
The high surface tension of water causes it to stick to the sides of the xylem vessels. This is called adhesion
Because the xylem vessels are very narrow, this can pull water up the xylem.
What is the term given to plants that are adapted to survive in arid conditions?
Xerophytes
Give an example of a Xerophyte
Marram grass
What are the adaptions of marram grass that make it a xerophyte?
Rolled leaf - increases humidity next to the stomata
Thick waxy cuticle - reduces evaporation
Stomata are on the inside of the rolled leaf - protected by the enclosed space
Hairs surround stomata - reduce air movement maintaining a water potential gradient
Dense spongy mesophyll - fewer air spaces so slower evaporation of water
What type of plant are cacti?
Succulents
Give some adaptions of cacti to reduce water loss
Leaves are reduced to spines to reduce transpiration
Stem is green to perform photosynthesis (no leaves)
roots are shallow and very widespread to increase water uptake in a rain event
What is the name given to plants that can live in water?
Hydrophytes
Give some adaptions of hydrophytes
Large air spaces to keep the leaf afloat so the leaves can perform photosynthesis
Stomata on the upper epidermis to allow gaseous exchange
Stem has large air spaces to keep it afloat but also so oxygen can quickly diffuse all the way to the roots.
Where does translocation occur?
In the phloem
What is translocation?
The movement of assimilates throughout the plant
What are assimilates?
Substances made by the plant from substances absorbed from the environment.
e.g Sugars and amino acids
What is a source? (Translocation)
Somewhere where assimilates are loaded into the phloem
What is a sink?
A part of the plant where assimilates leave the phloem
Describe the process of active loading
H+ ions are actively transported out of the companion cells
A concentration gradient is formed
H+ ions diffuse back into the host cell through co-transporter proteins
These proteins only allow H+ back in that is attached to sucrose molecules
Sucrose can then diffuse into the sieve tube elements through the plasmodesmata
By what process does the sucrose move in the phloem?
Mass flow
Describe the process of mass flow
Flow is caused by a difference in hydrostatic pressure between the two ends of phloem
Water enters the tube at the source increasing hydrostatic pressure and leaves at the sink which reduces the pressure.
Therefore mass flow always goes from source to sink
Why does water enter the phloem at the source?
Because the assimilates cause the solution inside the phloem to have a low water potential
Thus, water moves in via osmosis
