- Translocation water and mineral ions (e.g phosphates (fruit formation), nitrates and magnesium (involved in chlorophyll formation)) via transpiration.
- Lignified walls provide support for the plant and prevents walls from collapsing
- One directional flow (due to the evaporation in the leaves creating a transpiration pull)
- No end walls between cells
- Consists of 3 main tissue types: Vessels (only found in angiosperm phylum), tracheids (fund in more primitive plants) and fibres
- Only the vessels and tracheids are conductive (are able to carry mineral ions)
- Fibres completely lignified (sclerenchyma) and provide structural support
- Have large empty (no cell contents) lumen=less resistance and a larger
Phloem
- Transport sucrose, amino acids and plant growth regulators
- Cells have end walls with perforations (sieve tube elements)
- Two-way flow
- 2 cell types: Sieve tube and companion cells
- Companion cells contain numerous mitochondria to produce the ATP needed for active processes. They carry out metabolic processes needed by the sieve tube elements. They also provide cytoplasmic contact with the sieve tube for loading.
- Sieve tubes are lined end-to-end to form a tube, in which the plants transports assimilates. These are dissolved in water to form sap. They have limited cell content meaning the vessel is hollow allowing a larger capacity. They also have many plasmodesmata allowing movement. The sieve plates stop the cell from bursting by bracing.
- Water enters the sieve tubes from the xylem due to osmosis through the plasmodesmata from an area of high water potential to an area of low water potential (due to dissolved sucrose) down a concentration gradient.
Distribution in:
Root:
Stem:
Leaf:
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