name and give the function of each cell of xylem
Answers
(1) Xylem parenchyma: store metabolites produced from metabolism of plant. Also help in short distance transport.
(2) Xylem fibres: provide mechanical support. The walls of xylem fibres are lignified and protoplasm is absent.
(3) Xylem tracheids: transport of water and mineral salts.
(4) Xylem vessels: conduction of water and mineral. These cells are dead.
Phloem also contains four types of cells such as phloem parenchyma, phloem fibres, companion cells and sieve tubes.
(1) Phloem parenchyma: transport of nutrients and storage of organic food.
(2) Phloem fibres: they are non-living component of phloem. They provide mechanical support.
(3) Companion cells: provide ATP and nutrients to carry out cellular functions.
(4) Sieve tubes: Transport of carbohydrates especially sucrose.
Answer:Xylem
Xylem originates from the Greek word “xylon” that means wood. Nigeli coined the word xylem. Xylem is a type of vascular tissue present in plants, which primarily transports water and nutrients from roots to stem and leaves. They also provide mechanical strength to the plants.
On the basis of origin there are two types of xylem cells:
Primary xylem: originating from procambium, further divided into protoxylem and metaxylemSecondary xylem: originating from the vascular cambium
Xylem is composed of four different kinds of elements:
Tracheids: Dead, tube-like cells with a tapering end. They are present mostly in gymnosperm and lower angiosperm. They have a thick lignified wall and lack protoplasm. Their main function is water and mineral transportationVessels: They are present in angiosperms. These are a long cylindrical structure having tube-like appearance. The walls are lignified and have a large central cavity. They are also dead and lack protoplasm. They have many cells called vessel members which are interconnected through a perforation in common walls. Mostly involved in the conduction of water, minerals and give mechanical strength to the plantXylem Fibre: Dead cell with lignified walls and a central lumen. Involved in water transportation and providing mechanical supportXylem Parenchyma: Only living cells of xylem and store starch and fat. They assist in the short distance transportation of waterStructure of Xylem Parenchyma
Parenchyma cells associated with xylem are called “xylem parenchyma”.
There are two major types of parenchyma cells in secondary xylem
Axial parenchyma cells arranged around the axisRadial parenchyma cells arranged like a ray, radiating out of the common centre
The main characteristics of xylem parenchyma are:Only living cells of xylemThe cell wall is cellulosic and thinThey have prominent nucleus and protoplastCells are colourless and have large vacuolesLiving parenchyma cells are found in both primary and secondary xylemFat and storage protein contents of parenchyma cells vary seasonallyCrystal containing parenchyma cells have lignified walls with secondary thickening may be subdivided by septaIn herbaceous plants and young twigs of woody plants, chloroplasts occur in xylem parenchyma cells, particularly in ray parenchyma cellsBoth axial and ray parenchyma cells which are present beside vessels form outgrowths called “tyloses”The parenchyma cells that give rise to tyloses are termed as “contact cells”Nucleus and cytoplasm of xylem parenchyma cells migrate into tylosesTyloses store a variety of substances and may develop secondary wallsSome tylose might differentiate into sclereidsFunctions of Xylem Parenchyma
The main functions of xylem parenchyma include:
Storage of food material in the form of starch, fats, tannins and crystalsRadial conduction of water takes place by the ray parenchymatous cellXylem parenchyma cells are closely connected to vessels or tracheids through outgrowths called tylosesDuring drought or infection, these tyloses help to prevent damage of vascular tissuesXylem parenchyma cells are involved in the maintenance of xylem transport capacityThey are responsible for the restoration of vessels and tracheids functionality when there is blockage of the cavity due to the air bubble (embolism). Cavitation occurs due to the high tension of water in the xylem tissues.
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