Plants - OCR

Everything to do with plant, translocation, transpiration etc!


Transport in Plants

Why do all plants need a transport system?

All living things take substances from environment and return wastes. Every cell of a plant needs a regular supply of water and nutrients.  Many cells inside the plant are far away from the supply, they wouldnt not receive enough nutrients without a transport system.

Xylem and phloem in the young root..

Vascular bundles are found in the centre of a young root. There is a central core of Xylem, usually the shape on an 'X'. Phloem is found in between the arms of the X-shaped Xylem. This arrangement provides strength to withstand the pulling forces to which roots are exposed. Around Vascular bundle is a sheath of cells called the endodermis, which gets water into the xylem vessels. Inside the endodermis is meristem cells.

Xylem and Phloem in stem ..

Vascular bundles found at outer edge of the stem. Ring like arrangement provides strength and flexibility to withstand the bending forces to which stems and branches are exposed. Xylem is found towards inside of each vascular bundle. Phloem is found towards outside of vascular bundle. In between these two is the cambium, which is a layer of meristem cells that divide to produce either new xylem or phloem.

Xylem and Phloem in the leaf..

Vascular bundles form the midrib and veins of a leaf. A dicotyledon leaf has a branching network of veins that get smaller as they spread away from the midrib. Within each vein, xylem can be seen on top of the phloem. 

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Practise Questions.

What is transported in the xylem, and in which direction does it go?

Xylem transports water up the plant.

Name the tissue that transports sugars, and describe its distribution inthe stem and roots?

Phloem, in between the arms of the xylem in the centre of the roots and on outer edge of vascular bundle in stems.

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Structure and function of xylem vessels and phloem

Xylem tissue consists of tubes to carry the water and dissolved minerals, fibres, to help support the plant.

In dicotyledonous plants, the obvious feature of xylem are the vessel elements. Long cells with thick walls, they have been impregnanted by lignin. As the Xylem develops, lignin waterproofs walls of the cells. In result, cells die and end walls and contents decay, leaving a long column of dead cells with no end walls and a tube. Lignin strengthens the vessel walls and prevents the vessel from collapsing, which keeps vessels open.

Lignin thickening forms patterns in cell wall. These may be spiral, annular, or reticulate. Prevents vessel from being too rigid, allows flexibility. Some places lignification is not complete, leaves pores in wall of the vessel which or called pits. Allow water to leave one vessel and pass into an adjacent vessel.

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