Transport system in plants


For plants to maintain themselves, they need regular supply of various things.  Therefore, plants need a TRANSPORT SYSTEM.  Xylem and Phloem are two separate sets of tubes for transporting materials around the plant.  They are independent of each other and are found in every part of the plant.  However, they are usually found close together.  A group of xylem vessels and phloem tubes is called a VASCULAR BUNDLE. 


Xylem and Phloem vessels are used to carry different things around the plant.


Xylem Vessels - Xylem helps to support plants and take up water:

Xylem vessels are like a long drainpipe.  

Xylem Vessel

They are made from dead hollow cells, joined end to end without any end walls between them, forming a long open tubes.

Xylem vessels run from the roots of a plant, right up through the stem and spread out into every leaf.
They carry water and minerals from the root up to the leaves. This is known as TRANSPIRATION STREAM.
 Xylem vessels contain no cytoplasm or nuclei.
Side walls of Xylem vessels are strong and firm containing lignin, which gives the plant support and keeps it upright.
Wood is made almost entirely of lignified xylem vessels.

Phloem Tubes - carry food materials which the plant has made and needs:

Phloem contain sieve-tube elements.

Phloem Tube

Sieve tube elements have no nucleus, but contain cytoplasm.

They do not have any lignin in their cell walls.

Made from living cells, joined end to end, with punctured end-plates so that materials can flow through.

Each sieve tube element has a companion cell next to it.  Companion cell has many organelles, except the nucleus.

It is thought that companion cells help the sieve tube elements with some of their requirements.

Phloem tubes carry food made in the leaves to all other parts of the plant, in either direction.

The growing part of the plant, in the root tips and shoot tips, receives regular supply of sugars, fats, proteins etc. by the phloem tubes to/from storage organs in the roots.

In summary, Phloem carries food to/from the roots for growth and storage from other parts of the plants.

Xylem transports water and minerals from the roots up to the leaves.



Tags:Photosynthesis, Roots, Leaf structure, Stem, Xylem, Phloem, Cytoplasm, Nuclei, Transpiration




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