Transport tissues 3.3.2 Flashcards
(23 cards)
State the function of the xylem
The xylem transport water and mineral ions from the roots up to the leaves & other parts of the plant.
What does the xylem consist of?
Vessels for transport, fibres to support the plant & parenchyma cells which act as packing tissue to separate & support the vessels.
What do the xylem walls become impregnated with?
Lignin
What is the function of lignification/lignin?
It makes the xylem walls waterproof.
However it kills the cells but strengthens the walls and prevents them from collapsing.
Are xylem cells living or dead?
Dead, apart from the living parenchyma
What patterns form due to lignification?
Forms patterns which may be spiral, annular or reticulate (broken rings).
What is the purpose of the patterns within the xylem, formed by lignin?
They allow the xylem to stretch as the plant grows and enables the stem to bend.
What are the gaps known as, that are formed following the process of lignification?
Bordered pits
What is the purpose of bordered pits?
Allows water to move sideways from one vessel to another
What cell packs around xylem vessels?
Parenchyma
What does parenchyma contain?
Contains tannin deposits
What does tannin do?
It is a chemical which protects plant tissue from attack by herbivores.
Why isn’t the flow of water impeded in the xylem? (3 reasons)
- There are no cross walls
- There are no cell contents, nucleus, or cytoplasm - as the vessel is not living.
- Lignin thickening prevents the walls from collapsing
What is the function of the phloem?
Transports assimilates (sucrose and amino acids) which are dissolved in water to form sap up and down the plant.
What is the phloem tissue made up of?
Sieve tube elements and companion cells
What are sieve tube elements, and describe their structure.
They are elongated cells, lined end to end to form sieve tubes.
The ends have perforated walls called sieve plates, which allow for the sap to move from one sieve tube to another.
They also have no nucleus and very little cytoplasm which leaves space for the sap to flow.
What is the function of the sieve plates?
They support the vessels lumen, keeping it open.
They also become blocked if the sieve tube element becomes injured which prevents the sap from escaping.
How are companion cells linked to sieve tube elements?
By cytoplasmic strands through gaps in the cell wall.
Describe the structure of companion cells
They have a large nucleus and lots of mitochondria, needed to help load assimilates into the sieve tubes by active transport.
Compare the structure of xylem tissue with phloem tissue.
- Xylem tissue is lignified, meaning it is not living, whereas phloem tissue is living.
- The phloem transports assimilates, such as sucrose and amino acids, whereas the xylem transports water and mineral ions
- The xylem transports its containments up the plant only whereas the phloem transports substances both up and down the plant.
Why aren’t sieve tube elements true cells?
As they lack key cellular components such as a nucleus and most other organelles.
Why do xylem vessels have bordered pits?
To allow water to leave one vessel and pass into the next
Suggest why the phloem does not have walls impregnated with lignin.
As this would kill the sieve tube elements, as phloem is a living tissue.
