Unit 1 Section 6.1 Xylem and Phloem
- Created by: stephloupoole
- Created on: 17-04-14 18:34
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- Xylem and Phloem
- why do plants need transport systems?
- like animals, plants are a multicellular organisms
- meaning it has a small surface area to volume ratio
- plants could exchange substances by direct diffusion but that would be too slow
- plants need a transport system to move substances to and from individual cells quickly
- like animals, plants are a multicellular organisms
- location of xylem and phloem tissues
- Phloem Tissues
- Phloem transports dissolved substances like sugars up and down a plant
- Xylem Vessels
- Xylem transports water and mineral ions up a plants stem to the leaves
- Xylem acts as a support for the plant
- xylem and phloem are found throughout a plant
- Phloem Tissues
- adaptations of xylem vessels
- xylem vessels are very long
- they are tube like structures formed from cells joined end to end
- there are no end walls, they form a continuous tube for water to flow through the middle easily
- the cells are dead, so they contain no cytoplasm
- there are no end walls, they form a continuous tube for water to flow through the middle easily
- they are tube like structures formed from cells joined end to end
- the cell walls are thickened with a woody substance called lignin
- which helps support the walls and stops them from collapsing inwards
- the lignin is present in spiral patterns, which allows flexibility and prevents the stem from breaking
- the amount of lignin increases as the cell gets older
- the lignin is present in spiral patterns, which allows flexibility and prevents the stem from breaking
- which helps support the walls and stops them from collapsing inwards
- water and mineral ions move into and out of the vessels through small pits in the walls where there's no lignin
- this is how other types of cells are supplied with water
- xylem vessels are very long
- adaptations of phloem tissue
- phloem tissue transports sugars like sucrose
- like xylem phloem is formed from cells arranged in tuibes
- but unlike xylem, its purely a transport tissue
- phloem tissue contains phloem fibres, phloem parenchyma, sieve tube elements and companion cells
- sieve tube elements and companion cells are the most important cell types in phloem for transport
- sieve tube elements
- these are living cells that form the tube for transporting sugars through the plant
- the sieve parts are the end walls, which have lots of holes in them to allow sugars to pass through
- unusually for living cells sieve tube elements have no nucleus, a very thin layer of cytoplasm and few organelles
- the sieve parts are the end walls, which have lots of holes in them to allow sugars to pass through
- these are living cells that form the tube for transporting sugars through the plant
- Companion cells
- the lack of a nucleus and other organelles in sieve tubes means that they cant survive on their own
- so there's a companion cell for every sieve tube element
- companion cells carry out the living functions for both themselves and their sieve cells
- so there's a companion cell for every sieve tube element
- the lack of a nucleus and other organelles in sieve tubes means that they cant survive on their own
- sieve tube elements
- sieve tube elements and companion cells are the most important cell types in phloem for transport
- phloem tissue contains phloem fibres, phloem parenchyma, sieve tube elements and companion cells
- but unlike xylem, its purely a transport tissue
- like xylem phloem is formed from cells arranged in tuibes
- phloem tissue transports sugars like sucrose
- why do plants need transport systems?
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