Transport Flashcards
Why do plants need a transport system?
They have a small surface area to volume ratio, have high demands for water and sugar and need transport systems to allow them grow
What are xylem vessels?
These are tubes which carry water up the plant
What does lignin do within the xylem?
Xylem cells are lignified which makes them waterproof. However lignin also causes the cells to die which causes the components of the cell to decay creating a long column with no contents. Lignin strengthens the vessels walls to prevent them from collapsing. Also forms patterns in the wall which prevent rigidity and allow for some flexibility of the stem/branch.
What happens to parts of the xylem which aren’t lignified?
Bordered pits are created. When 2 adjacent pits align it allows for water to leave 1 xylem vessel and pass onto the next allowing the flow of water.
How is the flow of water not impeded in the xylem?
There are no cross walls, no cell contents, lignin prevent collapsing
What is the phloem?
This is a tissue used to transport assimilates like sucrose and amino acids around the plant
What does the phloem consist of?
Consists of sieve tubes which are made from companion cells and sieve tube elements
What are sieve tube elements?
They are lined end to end to form sieve tubes, contain no nucleus and little cytoplasm which allows space for the mass flow of sap
What are sieve plates?
They are perforated cross walls at the end of sieve plates which allow movement of sap from one sieve tube element to the next.
What are companion cells?
These are small cells in between the sieve tubes which contain many mitochondria to produce ATP for active transport
What is the apoplast pathway?
Water passes through spaces in the cell wall and between cells by mass flow.
What is the symplast pathway?
Water enters the cell through the plasma membrane
What is the vacuolar pathway?
Water enters through the cytoplasm as well as the vacuoles of the cell.
What is transpiration?
Transpiration is the loss of water vapour from upper parts of the plant usually out the stomata
Why is transpiration important?
It maintains cell turgidity, transports useful minerals up the plant and supplies water for growth.
How does light intensity affect the transpiration rate?
Stomata are usually only ope during the light to allow for more gas exchange so more light means more transpiration
How does temperature affect the transpiration rate?
A higher temperature increases the rate of evaporation and therefore increases the rate of transpiration as the molecules have increased levels of kinetic energy. Temperature also decreases water vapour potential in the air so there is more diffusion of water molecules out of the leaf
How does air movement affect the transpiration rate?
air moving outside the leaf carries water vapour away so maintains a water vapour potential gradient
How does water availability affect the transpiration rate?
if there is little water in the soil then the plant is unable to replace any lost water and the stomata closes and the leaves wilt.
What is the transpiration stream?
This is the continuous flow of water
How does cohesion and adhesion allow for the transport of water through the xylem?
Cohesion - water is a polar molecule which allows for the formation of hydrogen bonds which creates cohesion between water molecules. So water travels up the xylem as a continouos water column. Pull is created when water evaporates causing water to be pulled up the xylem, narrows xylem.
Adhesion - when water sticks to other molecules by forming hydrogen bonds with surfaces so water adheres to the xylem walls
