Xylem and Phloem

 

Multicellular Plants Need Transport Systems

 

Two Types of Tissue are Involved in Transport in Plants

Xylem Vessels are Adapted for Transporting Water and Mineral Ions

 

Phloem Tissues is Adapted for Transporting Solutes

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  • Created by: Benedicta
  • Created on: 07-01-11 14:03
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XYLEM AND PHLOEM
Phloem Tissues is Adapted for Transporting Solutes
1.
Formed from cells arranged in tubes
2.
Purely a transport tissue - isn't used for support like xylem
3.
Contain phloem fibre, phloem parenchyma, sieve tube elements and companion cells
4.
Sieve tube elements and companion cells are the most important cell types in phloem for
transport
1. Sieve Tube Elements
1. Living cells, form tube for transporting solutes through plant
2. Joined end to end to for sieve tubes
1. Sieve parts are end walls, have lots of holes in them to allow solutes to pass
2. Sieve tube elements have no nucleus, very thin layer of cytoplasm and few organelles
3. Cytoplasm of adjacent cells connected through holes in sieve plates
2. Companion Cells
1. Lack of nucleus and other organelles in sieve tube elements mean they can't survive on
their own
1. Companion cell for every sieve tube element
1. Carry out living functions for both themselves and sieve cells. For example, they provide
energy for active transport.
01 January 2011
19:49
Multicellular Plants Need Transport Systems
Plant cells need substances like water, minerals and sugars to live
Need to get rid of waste substances
Plants are multicellular so have small surface area: volume ratio
Can exchange substances by direct diffusion but would be too slow
Need transport systems to move substances to and from individual cells quickly
Two Types of Tissue are Involved in Transport in Plants
Xylem tissue transports water and mineral ions
Phloem tissue transports dissolved substances, like sugars
Both transport materials to all parts of plant
Where they're found in each part is connected to the xylem's other function - support
In a root, the xylem and phloem are in the centre to provide support for root as it pushes
through soil
In stems, 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

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Xylem Vessels are Adapted for Transporting Water and Mineral Ions
Xylem is a tissue made from several different cell types
Are very long, tube-like structures formed from cells (vessel elements) joined end to end
No end walls, making an uninterrupted tub that allows water to pass up through the middle
easily
Cells are dead, contain no cytoplasm
Walls thickened with woody substance called lignin - helps support xylem vessels and stops
them collapsing inwards
Amount of lignin increases as cells gets older
Water and ions…read more

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