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NAME VARIOUS COMPONENTS OF PHLOEM :--
Ø Phloem is a complex tissue, composed of FOUR types of cells (phloem elements)
The components of phloem are:
(1). Sieve elements
(2). Companion cells
(3). Phloem parenchyma
(4). Phloem fibres and Sclereids
Ø In some plants, in addition to the above mentioned cell types, the phloem also have internal secretary tissues such as Laticifers (Hevea) and resin canals.
(1). Sieve elements:-
Ø Sieve elements are the fundamental cell type in the phloem.
Ø They are the food conducting cells in the phloem.
Ø They are living cells in the phloem with protoplasm.
Ø Nucleus is absent in the sieve elements
Ø Lignified secondary cell wall is absent in sieve elements.
Ø Two types of sieve elements are found in the phloem, they are:
(A). Sieve cells
(B). Sieve tubes
(A). Sieve cells
Ø Sieve cells are less specialized and primitive type of sieve elements.
Ø They occur in the phloem of Pteridophytes and Gymnosperms.
Ø They are absent in Angiosperms.
Ø They are elongated cells with steep inclined end walls.
(2). Sieve tubes:-
Ø They are advanced type of sieve elements.
Ø They occur in the phloem of Angiosperms.
Ø They are longitudinal series of cells connected one above the other.
Ø Each cell is called sieve tube member or sieve tube element.
Ø In sieve tubes, the sieve area is located on the end wall called sieve plate.
Ø The sieve area in sieve tubes is more specialized and advanced than sieve cells.
Ø The end wall of sieve tubes may be inclined to transverse in their arrangement.
(2). Companion cells :-
Ø Companion cells are specialized parenchymatous cells associated with the sieve tubes of Angiosperms.
Ø Sieve tube member and companion cell arise from common mother cell.
Ø Number of companion cell per sieve tube member varies (one to many).
Ø Companion cells are narrower than sieve tube elements.
Ø Companion cells are thin walled cells with only primary cellulosic cell wall.
Ø They contain a large and prominent nucleus.
Ø They connect to sieve tube elements through plasmodesmata.
Ø They contain many plastids and ribosomes.
Ø Companion cells are metabolically very active.
Ø Physiologically it is associated with sieve tube members
Ø Companion cells provide energy to sieve tube elements for phloem transport.
Ø Companion cells are absent in lower plants (Pteridophytes and Gymnosperms).
(3). Phloem parenchyma :-
Ø Parenchyma occurs in both primary and secondary phloem.
Ø They are thin walled cells with protoplasm and nucleus.
Ø They have primary pit fields on their cell wall.
Ø Some parenchyma cells in the phloem can store starch as grains.
Ø Two types of parenchyma occurs in secondary phloem:
Ø Axial parenchyma
Ø Ray parenchyma
this is your answer...☺☺☺
Ø Phloem is a complex tissue, composed of FOUR types of cells (phloem elements)
The components of phloem are:
(1). Sieve elements
(2). Companion cells
(3). Phloem parenchyma
(4). Phloem fibres and Sclereids
Ø In some plants, in addition to the above mentioned cell types, the phloem also have internal secretary tissues such as Laticifers (Hevea) and resin canals.
(1). Sieve elements:-
Ø Sieve elements are the fundamental cell type in the phloem.
Ø They are the food conducting cells in the phloem.
Ø They are living cells in the phloem with protoplasm.
Ø Nucleus is absent in the sieve elements
Ø Lignified secondary cell wall is absent in sieve elements.
Ø Two types of sieve elements are found in the phloem, they are:
(A). Sieve cells
(B). Sieve tubes
(A). Sieve cells
Ø Sieve cells are less specialized and primitive type of sieve elements.
Ø They occur in the phloem of Pteridophytes and Gymnosperms.
Ø They are absent in Angiosperms.
Ø They are elongated cells with steep inclined end walls.
(2). Sieve tubes:-
Ø They are advanced type of sieve elements.
Ø They occur in the phloem of Angiosperms.
Ø They are longitudinal series of cells connected one above the other.
Ø Each cell is called sieve tube member or sieve tube element.
Ø In sieve tubes, the sieve area is located on the end wall called sieve plate.
Ø The sieve area in sieve tubes is more specialized and advanced than sieve cells.
Ø The end wall of sieve tubes may be inclined to transverse in their arrangement.
(2). Companion cells :-
Ø Companion cells are specialized parenchymatous cells associated with the sieve tubes of Angiosperms.
Ø Sieve tube member and companion cell arise from common mother cell.
Ø Number of companion cell per sieve tube member varies (one to many).
Ø Companion cells are narrower than sieve tube elements.
Ø Companion cells are thin walled cells with only primary cellulosic cell wall.
Ø They contain a large and prominent nucleus.
Ø They connect to sieve tube elements through plasmodesmata.
Ø They contain many plastids and ribosomes.
Ø Companion cells are metabolically very active.
Ø Physiologically it is associated with sieve tube members
Ø Companion cells provide energy to sieve tube elements for phloem transport.
Ø Companion cells are absent in lower plants (Pteridophytes and Gymnosperms).
(3). Phloem parenchyma :-
Ø Parenchyma occurs in both primary and secondary phloem.
Ø They are thin walled cells with protoplasm and nucleus.
Ø They have primary pit fields on their cell wall.
Ø Some parenchyma cells in the phloem can store starch as grains.
Ø Two types of parenchyma occurs in secondary phloem:
Ø Axial parenchyma
Ø Ray parenchyma
this is your answer...☺☺☺
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luckythelakshya:
nice answer thanks
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