Transport system in Dicotyledonous Flashcards
Why do they need a plant transport system?
- Metabolic demands - Many internal and underground parts of the plant do not photosynthesise. They need O2 and glucose transported to them And the waste products of cell metabolism removed.
Hormones made in 1 part of the plant need transporting to the area where effected. Mineral ions absorbed by the roots need to be transported to all cells to make the proteins required for enzymes. - Size - Plants need v effective transport systems to move substances both up and down from the tip of the roots to the topmost leaves and stems
- SA:V - Small SA:V means they cannot rely on diffusion alone to supply their cells with everything they need
What do xylem tissue do?
- transports water and mineral ions in solution. These substances move up the plant from the roots to the leaves
What do phloem tissue do?
- mainly transports sugars both up and down the plant.
Xylem and phloem make up the vascular system.
Where are they found and why does is that connected to the xylems function?
In a root, the xylem is in the centre surrounded by the phloem to provide support for the root as it pushes through the soil.
In the stems, the xylem and phloem are near the outside to provide ‘scaffolding’ that reduces bending
In a leaf, xylem and phloem make up a network of veins which support the thin leaves.
How are xylem vessels adapted for their function?
They are long, tube-like structures formed from cells joined end to end
There are no end walls on these cells, making an uninterrupted tube that allows water to pass up through the middle easily.
The cells are dead, so no cytoplasm
Their walls are thickened with lignin, which helps to support the xylem vessels and stops them collapsing inwards. Lignin can be deposited in xylem walls in different ways (spiral/distinct rings).
The amount of lignin increases as the cell older
Water and ions move in and out of the vessels through small puts in the walls where there’s no lignin
How are phloem tubes adapted for transporting solutes?
Phloem tissue transports solutes (dissolved substances), mainly sugars, round plants
Arranged in tubes - transport tissue not support as well
Phloem tissue contains phloem fibres, parenchyma, sieve tube elements and companion cells.
Sieve tube elements and companion cells are the most important cell types in phloem for transport
What are sieve tube elements?
These are living cells that form the tube for transporting solutes through the plant
They are joined end to end to form sieve tubes
The sieve parts are the end walls, which have lots of holes in them to allow solutes to pass through
Unusually for living cells, sieve tube elements have no nucleus, a very thin layer of cytoplasm and few organelles
The cytoplasm of adjacent cells is connected through the holes in the sieve plates.
What are companion cells?
The lack of a nucleus and other organelles in sieve tube elements means that they can’t survive on their own. So there’s a companion cell for every sieve tube element.
They carry out living functions for both themselves and their sieve cells
