3.3 Transport in plants Flashcards
Explain why lignin is essential in the wall of a xylem vessel
Structure
-to prevent collapse/keep open
Waterproofing
- Kills cell contents to create a hollow space for a continuous flow of water
- prevent lateral flow of water
What does the xylem transport?
Water and minerals
What does the phloem transport?
Sugars and amino acids
What is the name for the cells in the xylem which transport water?
Xylem vessel
How is the xylem adapted for its function?
- Lignified]in patterns to allow the xylem to bend and stretch
- Dead cells end to end form a continuous column
- narrow tubes so that the water column doesn’t break
- bordered pits allow water to move to adjacent vessels and water to move to the living parts of the plants
What are the components of the phloem?
Sieve tubes
- Sieve tube elements (+ sieve plates)
- Companion cells
What are sieve tube elements and how are they adapted for their function?
Elongated cells which contain no nucleus and very little cytoplasm, to allow the mass flow of sap in the phloem.
Adaptions
- no nucleus/very little cytoplasm
- contain sieve plates at either end with perforations that let the sap through while keeping the phloem open
- sieve plates can block to prevent spread of disease through a plant (using callose)
What is the function of companion cells?
They contain large amounts of mitochondria to enable them to produce the large amounts of ATP necessary for the active loading of hydrogen ions out of the companion cells and sucrose in.
How does sucrose move from the cells surrounding the phloem into the phloem?
The companion cells use active transport to move hydrogen ions out of the companion cells. This creates a concentration gradient.
The hydrogen ions then move down the concentration gradient in cotransport with sucrose molecules.
The sucrose then diffuses into phloem via plasmodesmata.
How is sucrose transported from the source to the sink?
The sucrose lowers the water potential at the sink, causing water to flow by osmosis into the sieve tube element, and raise the hydrostatic pressure
The sap moves down the sieve tube from higher hydrostatic pressure at the source to lower hydrostatic pressure at the sink.
How does sucrose leave the phloem and move into the sink?
It diffuses out via the plasmodesmata, or removed via active transport.
This reduces the hydrostatic pressure causing more sucrose to move down.
How does water move from the roots to the xylem?
Water diffuses into the root hair cells and moves down the water potential gradient to the endodermis.
This is done either through the apoplast, symplast or vacuolar pathway.
The apoplast pathway cannot go past the endodermis due to the casparian strip.
Mineral ions are loaded into the endodermis to decrease the water potential.
What happens in the apoplast, symplast and vacuolar pathway?
Apoplast: Water passes through the spaces in the cell walls and between cells
Symplast: water travels through the cell cytoplasm and passes through the plasmodesmata from one cell to the next
Vacuolar: Water can pass through the vacuoles aswell as the cytoplasm
