Plants have two transport systems, the xylem and the phloem. All multi cellular organisms with specialised cells for different functions need these transport systems. The Xylem is the vascular tissue made up of dead cells that conducts the flow of water and dissolved nutrients upwards from the roots to the leaves. The phloem is the vascular tissue made up of living cells that conducts the flow of sugars and metabolic products downwards from the leaves. The environment plays an important role on the way plants react and is vital factor for growth and sustainability. The temperature in particular gives an important indication of the speed of transportation of nutrients and minerals from its food source as well as its survivability in different environments with many different factors affecting it such as terrain and water supply. These factors may also may speed up or slow down processes such as photosynthesis. Structures
Xylem were once living cells, but the cells die and the top and bottom ends of the cell breaks down leaving a long continuous tube. The cell walls are made of lignin and are thick and make them strong and impermeable. Xylem allow a lot of water to be transported and quickly. •
Smaller vessels called tracheids transport a lower amount of water and slower too. These vessels form thinner but also long overlapping cells. •
Pits develop in the walls of the xylem and tracheids to allow water and mineral ions to pass out of the xylem and tracheids and into the surrounding cells. Pits are not holes but are areas where the cell wall is very thin.
In the xylem, the main forces acting on the water is transpiration. It acts in this way: 1.
Evaporation of water from leaf cells via the stomates initiates the pulling force of transpiration that causes the main sucking force of water in xylem that keeps water moving. 2.
cohesion which means that water molecules stick together in a chain, keeps the water column intact 3.
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