Basic information about phloem structure.pptx

It contains Basic information about phloem

1. PHLOEM

2. Phloem Phloem are living conducting tissues. They conduct prepared food from leaves to different part of the plant. They are also involved in storage of food and mechanical support. They are always associated with xylem to form vascular tissues.

3. Components of phloem Phloem is composed of S ieve elements C ompanion cells P hloem parenchyma P hloem fibers

4. 1.Sieve elements: The elongated cells with characteristic sieve areas in their walls are called sieve elements. Sieve areas are formed by modified pits. The protoplasts of the adjoining cells are continuous through the pores of sieve areas. The elements have primary thin walls.

5. S ieve areas : an area in the wall of a sieve-tube element, sieve cell, or parenchyma cell in which are clustered pores through which cytoplasmic connections pass to adjoining cells have pores with cytoplasmic connecting strands.

6. Some sie v e elements are oblique. Such sieve elements have several prominent  areas. The sieve elements are divided into sieve tube members and sieve cells.

7. Sieve tube members Sieve areas are well developed in sieve tube members. Sieve areas are confined only to end walls of cells. They form sieve plates at end walls. The sieve tube members join end to end to form long tubes called sieve tubes. The phloem of angiosperms is composed of mainly sieve tube members.

8. Sieve  cells Sieve cells are long, conducting cells in the phloem that do not form sieve tubes . The major difference between sieve cells and sieve tube members is the lack of sieve plates in sieve cells . They have a very narrow diameter and tend to be longer in length than sieve tube elements as they are generally associated with albuminous cells .

9. 2 .Companion cells The thin walled parenchyma cells closely associated with the sieve elements are called companion cells. Companion cells are living. They are physiologically active. They have a prominent nucleus.

10. The sieve tube element and companion cell have close contact. Companion cells are absent in gymnosperms and lower vascular plants. But certain parenchyma cells called albuminous cells are closely’ associated with sieve elements in these plants. These albuminous cells are similar to the companion cells in their function.

11. 3 . phloem fibers The fibers occupy the outer portion in the primary phloem. They are used as commercial Fibers. e.g. Hibiscus . Phloem fibers are elongated. They have thick secondary wall. They may be living or dead at maturity.

12. T he phloem fibers may be septate in certain cases. The thick w all of fibers is not lignified. It is composed of only cellulose. The fibers are also arranged axially (vertically ) in secondary phloem.

13. 4.Parenchyma : Small parenchymas are present in both primary and secondary phloem. These parenchyma cells are arranged vertically in primary phloem. But these are arranged vertically and radially in secondary phloem.

14. These cells become thick wall in older portion of phloem and change into sclerenchyma cells. Phloem parenchyma cells are thin walled. They are living and physiologically active. They store different compounds like starch, tannins, and different crystals.

15. Types of phloem Phloem may be primary or secondary.   Primary phloem: The phloem formed as a result of primary growth is called primary phloem. Primary phloem is initiated in the embryo. It develops from procambium . Primary phloem has two types . Proto Phloem Meta Phloem

16. Primary phloem :  Proto Phloem :  Proto phloem is composed of elongated sieve elements only. They lack companion cells. Sieve tube elements lack nucleus. So they remain active only for a short time. Thus they soon disappear. Meta Phloem :  Meta phloem mature later than proto phloem . So they remain active for longer time. Secondary growth does not occur in monocot plants. So they remain active in monocot throughout life.

17. The phloem formed as a result of secondary growth is called secondary phloem. It has two types: Vertical system: Vertical system is composed of sieve elements, companion cells, phloem fibers and phloem parenchyma. Ray system: Ray system is composed of ray parenchyma only.  Secondary phloem: