Xylem and phloem Flashcards
Why do plants need multicellular transport systems?
1)Plants need substances like water, minerals and sugar to live. They also need to get rid of Waste substances
2) Like animals plants are multicellular so they have a small surface area to volume ratio. They’re also relatively big with a relatively high metabolic rate.
3) Exchanging substances by direct diffusion would be too slow to meet their metabolic needs
4) So plants need transport systems to move substances to and from individual cells quickly
What does xylem tissue do?
Transports water and mineral ions in solution. These substances move up the plant from the roots to the leaves.
What does phloem tissue do?
Mainly transport sugars also in solution both up and down the plant
What do xylem and phloem make up?
Vascular system
Describe the structure of the xylem and phloem in the root
Xylem is in the centre, surrounded by the phloem to provide support for the root as it pushes for the soil
Describe the structure of the xylem and phloem in the stems
Xylem and phloem near the outside to provide a sort of scaffolding that reduces bending
Describe the structure of xylem and phloem in the leaf
make the network of veins which support the thin leaves
How was xylem vessels adapted for transporting water and mineral ions?
1)Very long tube like
2)No, end walls on the cells, making uninterrupted tube, allowing easy passage
3)The cells are dead, so they contain no cytoplasm
4)The walls are thickened, but a woody substance called lignin, which helps support the xylem vessels and stops, collapsing inwards
4)Water and ions move into and out of the vessels through small pits in the walls where there is no lignin
What is lignin?
A woody substance, which helps supports the xylem vessel and stops collapsing inwards
lignin can be deposited in xylem walls in different ways, for example, in a spiral or as distinct rings
How is flowing adapted for transporting salute?solutes
1)Formed from cells arranged in tubes purely transport tissue isn’t used for support as well
2)Contain phloem fibres, phloem parenchyma sieve tube elements in companion cells
What are sieve tube elements?
1)Living cells that form the tube for transporting solutes through the plant
2)Joined into and forms sieve tubes
3)the sieve parts form the end walls, which have lots of holes in them, allowing solutes to pass through
4)Unusually for living cells sieve tube elements have no nucleus very thin cytoplasm and few organelles
5)The cytoplasm of adjacent cells is connected through the holes in the sieve plates
What a companion cells
The lack of nucleus, And other organelles in sieve tube elements mean that they can’t survive on their own so there’s companion cell for every sieve tube elements.
They carry out the living functions for both Their selves and their sieve cells
