the cells that help to load sucrose into the sieve tubes.
1 of 24
sieve tube elements =
make up the tubes in phloem tissues that carry sap up and down the plant. They are separated by sieve plates.
2 of 24
xylem vessels =
the tubes which carry water up the plant.
3 of 24
xylem tissue consists of:
vessels to carry the water and dissolved mineral ions.
4 of 24
xylem tissue consists of:
fibres to help support the plant.
5 of 24
xylem tissue consists of:
living parenchyma cells which act as packaging tissue to separate and support the vessel.
6 of 24
Lignin
As the xylem vessels develop, lignin impregnates the cell walls, making the walls waterproof. It kills the cells.`
7 of 24
structure
the end walls and contents of the cell decay, leaving a long column of dead cells with no content - this tube is called a xylem vessel. The lignin strengths the xylem walls and stops the vessel from collapsing. This keeps the vessel open.
8 of 24
The lignin thickening forms patterns in the vessel walls, which may be:
spiral, annular (rings) or reticulate (a network of broken rings). This prevents the cell wall being too rigid and allows the stem/branch some flexibility.
9 of 24
Sometimes lignification is incomplete which leaves holes in the cell wall. These gaps form:
pits or bordered pits. The bordered pits in 2 adjacent vessels are aligned to allow water to leave and pass to the next vessel. They also allow water to leave the xylem and enter the living parts of the cell.
10 of 24
Adaptions of xylem to its function:
they are made from dead cells aligned end-to-end to form a continuous column.
11 of 24
Adaptions of xylem to its function:
the tubes are narrow, so that the water column doesn't break easily and capillary action can be effective.
12 of 24
Adaptions of xylem to its function:
bordered pits in the lignified walls allow water to move sideways from one vessel to another.
13 of 24
Adaptions of xylem to its function:
lignin deposited into the cell walls in spiral, annual or reticulate patterns allows the xylem to stretch as the plant grows and enables the stem or branch to bend.
14 of 24
The flow of water is not hindered because:
there are no cross-walls.
15 of 24
The flow of water is not hindered because:
there are no cells contents, nucleus or cytoplasm.
16 of 24
The flow of water is not hindered because:
lignin thickening prevents the walls from collapsing.
17 of 24
structure and function of phloem:
phloem tissues transports sugras and assimilates (mainly sucrose and amino acids). The sucrose is dissolved in watre to form sap. Phloem tissue consists of seive tubes - made up of sieve tube elements and companion cells.
18 of 24
sieve tube elements
Elongated sieve tube elements are lined up end-to-end to form sieve tubes.
19 of 24
sieve tube elements
they contain no nucleus and very little cytoplasm, leaving space for mass flow of sap to occur.
20 of 24
sieve tube elements
at the ends of sieve tube elements are perforated cross-walls called sieve plates. The perforations allow movement of the sap from one element to the next.
21 of 24
sieve tube elements
The sieve tubes have very thin walls and when seen in transverse section are usually 5-6 sided
22 of 24
companion cells
in between the sieve tubes are small cells, each with a large nucleus and dense cytoplasm. These are called companion cells.
23 of 24
companion cells
have mitochondria to produce the necessary ATP for active processes. They carry out metabolic processes of loading assimilates into the sieve tube.
24 of 24
Other cards in this set
Card 2
Front
make up the tubes in phloem tissues that carry sap up and down the plant. They are separated by sieve plates.
Back
sieve tube elements =
Card 3
Front
the tubes which carry water up the plant.
Back
Card 4
Front
vessels to carry the water and dissolved mineral ions.
Comments
No comments have yet been made