3.3. Transport in plants Flashcards
What is a dicotyledonous plant?
A plant with two seed leaves ans a branching pattern of veins in the leaves.
What is the meristem?
A layer of dividing cells.
What is the phloem?
Transports dissolved assimilates.
What is the vascular tissue?
Consists of cells specialised for transporting fluids by mass flow.
What is the xylem?
Transports water and minerals.
Why do plants need a transport system?
Plants need a transport system to move:
- water and minerals from the roots up to the leaves.
- Sugars from the leaves to the rest of the plant.
What does the plants vascular tissue consist of?
- Xylem tissue- transports water and soluble mineral ions up the xylem.
- Phloem tissue- transports assimilates, such as sugars up and down the phloem.
What may the vascular bundle contain to provide strength and support for the plant?
Collenchyma and sclerenchyma.
What does the vascular bundle look like in the root of a plant?
The vascular bundle is found in the centre of the root. There is a central core of xylem in the shape of an X. The phloem is found in between the arms of the X-shaped xylem tissue. This arrangement provides strength to withstand the pulling forces to which roots are exposed to.
What is found around the vascular bundle in the roots?
Around the vascular bundle is a special sheath of cells called the endodermis. The endodermis has a key role of getting water into the xylem vessels.
Just inside the endodermis is a layer of meristem cells called the pericycle.
What does the vascular bundle look like in the stem?
The vascular bundle is found near the outside of the edge of the stem.The xylem is found towards the inside of each vascular bundle and the phloem towards the outside. In between the xylem and the phloem, is a layer of cambium (a layer of meristem that divides into new xylem and phloem).
How may the vascular bundles look different in the stems of woody and non-woody plants?
In non-woody plants, the bundles are separate and discreet. In woody plants, the bundles are separate in young stems, but become a continuous ring in older stems.
What does the vascular bundle look like in the leaf?
The vascular bundle form the midrib and veins of a leaf. A dicotyledonous leaf has a branching network of veins that get smaller as they spread away from the midrib. Within each vein, the xylem is located on top of the phloem.
What does the dissection of plant material to examine the distribution if vascular tissues require?
Staining the tissues.
What is a companion cell?
The cells that help to load sucrose into the sieve tubes.
What are the sieve tube elements?
They make up the tube in the phloem tissue the carry sap up and down the plant. The sieve tube elements are separated by the sieve tube plates.
What do xylem tissues consist of?
- Vessels to carry water and dissolved minerals.
- Fibres to support the plant.
- Living parenchyma cells which act as packing tissue to separate the support the vessels.
How do xylem vessels form?
As xylem vessels develop, lignin impregnates the walls of the cells, making the walls waterproof. This kills the cells. The end walls and contents of the cells decay, leaving a long column of dead cells with no contents.
What does the lignin provide the xylem vessel?
Strengthens the vessel and prevents the vessels from collapsing. This keeps the vessel open at all times when water may be in short supply.
How does the lignin strengthen the xylem?
The lignin thickening forms a pattern in the cell wall. These may be spiral, angular or reticulate. This prevents the vessel from being too rigid and allows some flexibility of the stem to branch.
Where in the xylem vessel may lignification not be complete?
In some places, lignification is not complete, leaving gaps in the cell wall. These gaps from bordered pits. The bordered put in two adjacent vessels the aligned to allow water to leave one vessel and pass into the next vessel.
How are xylem vessels adapted to their function?
- They are made from dead cells aligned end to end to form a continuous column.
- The tubes are narrow, so that the water column does not break easily and capillary action can be effective.
- bordered pits in the lignified walls allow water to move sideways from one vessel to another.
- Lignin deposited in the walls in spiral, annular or reticulate patterns allow xylem to stretch as the plant grows, and enables stem the branch.
Why isn’t the flow of water impeded in the xylem vessel?
- There are no cross-walls.
- There are no cell contents, nucleus or cytoplasm.
- Lignin thickening prevents walls from collapsing.
What does the phloem transport?
Assimilates (mainly sucrose and amino acids).
What is the phloem made up of?
Phloem tissue consists of sieve tubes- made up of sieve tube elements - and companion cells.
What is the structure of a phloem vessel?
Elongated sieve tube elements are lined up end to end to form sieve tubes. They contain no nucleus and very little cytoplasm, leaving space for mass flow of sap to occur. At the ends of the sieve tube elements are proliferated cross-walls called sieve plates. The sieve tubes are usually 5/6 sided.
What is the function of the sieve plates?
They serve as a mechanism to block the sieve tubes after injury or infection. The pores in the sieve plate rapidly become blocked with the deposition of callose. This prevents the loss of sap and inhibits the transport of pathogens around the plant.
What are companion cells and where can they be found?
In between sieve tubes are companion cells. they each have a large nucleus and dense cytoplasm. They have numerous mitochondria and produce ATP needed for active processes. The companion cells carry out metabolic needed to load assimilates into the sieve tubes.
What are plasmodesmata?
Gaps in the cell wall containing cytoplasm the connects two cell walls.
Are cellulose cell walls permeable to water?
Cellulose cell walls are fully permeable to water.
How can water move across plant cells?
Water can pass across the cell wall and through the partially permeable plasma membrane into the cell cytoplasm or even into the vacuole.
What is it called when the cytoplasm of one cell is connected to another?
A cytoplasmic bridge or a plasmodesmata.
What is a cytoplasmic bridge?
Cell junctions at which cytoplasm of one cell is connected so that of another through a gap in their cell walls. These junctions are also called plasmodesmata.
How many possible pathways are there for water to travel through a plant?
3.
What are the 3 pathways water can take through a plant?
- The apoplast pathway.
- The symplast pathway.
- The vacuolar pathway.
What is the apoplast pathway?
Water passes through the spaces in the cell walls and between cells. It does not pass through any plasma membranes into the cells. This means the water moves by mass flow not osmosis. Dissolved mineral ions ans salts can be carried with the water.
What is the symplast pathway?
Water enters the cytoplasm through the plasma membrane. It can then pass through the plasmodesmata from one cell to the next.
What is the vacuolar pathway?
This is similar to the symplast pathway, but the water is not confined the the cytoplasm of the cells. It is able to enter the vacuoles instead.
What causes a plant to take up water?
A plant will take up water by osmosis. This is because the water potential in the cell is more negative than the water potential of the water- water molecules will move down the water-potential gradient into the cell.
Why wont a plant cell carry on absorbing water till in bursts?
Because it has a strong cellulose cell wall it will not burst. Instead once the cell in full of water, it is described as being turgid. The water inside the cell starts to exert a pressure on the cell wall, called the partial pressure, as the pressure potential builds up, in reduces the influx of water.
What will happen if you put a plant in a salt solution with a very low water potential?
The plant will loose water by osmosis. As water loss continues, the cytoplasm and vacuole shrink. Eventually, the cytoplasm no longer pushes against the cell wall. If the cell continuous to loose water, the plasma membrane will loose contact with the cell- known as plasmolysis. This tissue in now flaccid.
What can we call this process?
Plasmolysis.
What is a potometer?
A device That can measure the rate of water uptake as a leafy stem respires.
