Xylem and Phloem Flashcards
What does xylem transport and the direction?
Water and mineral ions from roots to leaves
What does phloem transport and the direction?
Assimilates (mainly sucrose and amino acids) around the plant
Why are xylem and phloem both tissues?
As they are made from different cell types
What structures make up xylem?
-Xylem Vessels
-Xylem Parenchyma
-Cell Walls
-Annular lignin
-Spiral lignin
-Bordered Pits
What are xylem vessels?
long empty tubes formed from cells called vessel elements
What are xylem parenchyma?
forms packing tissue to separate and with xylem fibres, support the xylem vessels
What is lignin (annular and spiral)?
It is formed by lignification-it waterproofs and strengthens the vessels so they can withstand pressure of water and help support the plant
What are bordered pits?
Allow water minerals to move between vessels and into surrounding cells
What are examples of the minerals that are transported?
Magnesium
NO3
Potassium
Phosphates
What is the first adaption of xylem?
Lignin is usually arranged in rings or spirals
Why is this adaptation useful?
Lignin is usually arranged in rings or spirals
To allow felxibility preventing the stem from breaking
-if it was continuous, stem would be rigid and unable to bend
What is the second adaptation of xylem?
Xylem die once formed (happens during lignification)
Why is this adaptation useful?
Xylem die once formed (happens during lignification)
So that xylem vessels form long tubes and there is nothing to disrupt or get in the way of the transpiration stream
What is the third adaptation of xylem?
No sieve plates inbetween vessel elements-the cell walls inbetween them decay away completly once the xylem vessel has formed
Why is this adaptation useful?
No sieve plates inbetween vessel elements …..
So there are no organelles/cytoplasm to get in the way of the transpiration stream
What is the fourth adaptation of xylem?
Xylem vessles have a larger diameter than phloem vessels
Why is this adaptation useful?
Xylem vessles have a larger diameter than phloem vessels
Plants need to transport more water than they do assimilates
What structures make up phloem?
-Sieve tube
-Sieve tube element
-Sieve plate
-Companion cell
-Phloem parenchyma
What are sieve tubes?
Don’t have lignin in their walls so they are thinner than xylem so don’t help to support the plant
What are sieve tube elements?
Elongated living cells that form sieve tubes
What are Phloem parenchyma?
Along with Phloem fibres and phloem parenchyma helps support the sieve tubes
What is the first adaptation of phloem?
There are sieve plates in between the sieve tube elements (they don’t decay away completely like in xylem)
Why is this adapatation useful?
There are sieve plates in between the sieve tube elements
To protect the plant-if a plant is attacked, enarby sieve plates can ‘close’ to protect adjacent cells and/or their assimilates
-also help to maintain pressure inside the sieve tube (important in trasnlocation)
What is the second adaptation of phloem?
Sieve plates have lots of pores in them
Why is this adapatation useful?
Sieve plates have lots of pores in them
To connect the cytop[lasm of adjacent cells which allows them to communicate with eachother (e.g. via hormones).
-also allow assimilates to pass through
What is the third adaptation of phloem?
Sieve tube elements have no nucleus, a thin layer of cytoplasm and a few organelles (e.g. mitochondria)
Why is this adapatation useful?
Sieve tube elements have no nucleus,thin cytoplasm & few organelles
To make it easier for the assimilates to pass through
What is the fourth adaptation of phloem?
Each sieve tube element is associated with a companion cell
Why is this adapatation useful?
Each sieve tube element is associated with a companion cell
-To carry out the living functions for the sieve tube element.
-CC also contain nuclues and many mitochondria to release energy for active transport/loading sucrose into sieve tubes during translocation
How are sieve tube elements and companion cells connected?
By plasmodesmata
