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The transport system in plants moves water soluble molecules by vascular tissue. There are two types of vascular tissue which are Xylem and Phloem.

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Introduction

Xylem and Phloem The transport system in plants moves water soluble molecules by vascular tissue. There are two types of vascular tissue which are Xylem and Phloem. Both of them are specialised to carry out their role in the plant and they are normally found together in vascular bundles throughout the plant. The xylem tissue transports water and soluble minerals up the plant towards the leaves for photosynthesis whereas the phloem tissue transports the sugars made by the reaction up and down the plant to places where it is needed. Both of the tissues are highly specialised and they have other tissues accompanying them in the vascular bundles to give strength. ...read more.

Middle

Xylem The xylems are many endless vessels starting from the roots and going to all the area of a plant. The walls of the vessel are made up of dead cells strengthened by lignin forming an endless tube. The lignin is water proof and strengthens the vessels and internal structure which prevents the vessels collapsing when there is a low pressure potential of water inside which maybe in summer time when less water is available. The lignin forms patterns in the wall which also allow the vessels to be flexible and stretch to accommodate water however in some places the lignin is slightly not complete to leave pits. ...read more.

Conclusion

The sieve tube cells are not true cells as they do not have a nucleus or cytoplasm as this enables them to carry out their role. The sugar is dissolved in water to form sap as the phloem has to transport water based substances. At the end of each cell in the phloem vessel there are sieve walls which allow the sap to flow through the vessel. In between the sieve tubes are true companion cells and their role is to produce ATP energy which is used to load sucrose into the sieve tubes therefore the companion cells contain many mitochondria. The companion cells and sieve tubes have small gaps between them which allow minerals and substances to flow via the apoplastic pathway. ?? ?? ?? ?? Bilaal Hussain ...read more.

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This is a summary of the roles of xylem and phloem. It is too short to explain ideas fully, some relevant biology is missing altogether, and in places scientific language has not been used carefully.

Marked by teacher Adam Roberts 20/08/2013

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