Xylem and phloem structure Flashcards
What is the structure of the xylem?
- Vessels to carry the water and dissolved mineral ions
- Fibres to help support the plant
- Living parenchyma cells which act as packing tissue to separate and support the vessels
What is the function of lignin in xylem?
It develops the walls of the cell walls, making them waterproof and it kills the cells.
It strengthens the vessel walls prevents the vessel from collapsing to keep the vessel open even at times when water may be in short supply.
What patterns can the lignin make?
Spiral, angular or reticulate
What are bordered pits?
They are areas where the lignification was incomplete, so there were gaps in the walls. The bordered pits in 2 adjacent vessels are aligned to allow water to leave one vessel and pass through the next vessel.
What are the xylem adaptations?
- It has dead cell aligned from end to end as a continuous column
- Tube is narrow, so the water columns doesn’t break easily and capillary action can be effective
- Bordered pits so water moved from cell to cell
- Ligninified cells for strength
How is the flow of water not stopped?
No cross walls
No cell content like nucleus or cytoplasm
Lignified walls preventing collapse
What is the function of phloem?
Transports sugar dissolved in water in sap and assimilates like amino acids
What is the structure of phloem tissue?
Sieve tubes made of sieve tube element
Companion cells
What is the function of the sieve tubes?
The perforations in the sieve tubes allow for sap to go from 1 cell to the next
Sieve tube elements are lined up end to end to form sieve tubes
What is the structure of sieve tubes?
Contain little to no cytoplasm so there is space for mass flow to occur
Where were companion cells?
Small cells between the sieve tubes
What was the structure of companion cells?
Large nucleus, dense cytoplasm and many mitochondria for the production of ATP in active processes.
What was the function of companion cells?
Carry out the metabolic reactions needed to load the assimilates actively into the tubes
In what direction does the xylems contents flow?
Only up
In what direction does the phloems contents flow?
Up and down
