Why are xylem and phloem
called complex tissues?
Why are xylem and phloem called complex tissues?
Xylem and
phloem are known as complex tissues as they are made up of more than
one type of cells. These cells work in a coordinated manner, as a
unit, to perform the various functions of the xylem and phloem.
Xylem
helps in conducting water and minerals. It also provides mechanical
support to plants. It is made up of the following components:
Tracheids
(xylem vessels and xylem tracheids)
Xylem
parenchyma
Xylem
fibres
Tracheids
are elongated, thick-walled dead cells with tapering ends. Vessels
are long, tubular, and cylindrical structures formed from the vessel
members, with each having lignified walls and large central cavities.
Both tracheids and vessels lack protoplasm. Xylem fibres consist of
thick walls with an almost insignificant lumen. They help in
providing mechanical support to the plant. Xylem parenchyma is made
up of thin-walled parenchymatous cells that help in the storage of
food materials and in the radial conduction of water.
Phloem
helps in conducting food materials. It is composed of:
Sieve
tube elements
Companion
cells
Phloem
parenchyma
Phloem
fibres
Sieve tube
elements are tube-like elongated structures associated with companion
cells. The end walls of sieve tube elements are perforated to form
the sieve plate. Sieve tube elements are living cells containing
cytoplasm and nucleus. Companion cells are parenchymatous in nature.
They help in maintaining the pressure gradient in the sieve tube
elements. Phloem parenchyma helps in the storage of food and is made
up of long tapering cells, with a dense cytoplasm. Phloem fibres are
made up of elongated sclerenchymatous cells with thick cell walls.
Xylem and phloem are known as complex tissues as they are made up of more than one type of cells. These cells work in a coordinated manner, as a unit, to perform the various functions of the xylem and phloem.
Xylem helps in conducting water and minerals. It also provides mechanical support to plants. It is made up of the following components:
Tracheids (xylem vessels and xylem tracheids)
Xylem parenchyma
Xylem fibres
Tracheids are elongated, thick-walled dead cells with tapering ends. Vessels are long, tubular, and cylindrical structures formed from the vessel members, with each having lignified walls and large central cavities. Both tracheids and vessels lack protoplasm. Xylem fibres consist of thick walls with an almost insignificant lumen. They help in providing mechanical support to the plant. Xylem parenchyma is made up of thin-walled parenchymatous cells that help in the storage of food materials and in the radial conduction of water.
Phloem helps in conducting food materials. It is composed of:
Sieve tube elements
Companion cells
Phloem parenchyma
Phloem fibres
Sieve tube elements are tube-like elongated structures associated with companion cells. The end walls of sieve tube elements are perforated to form the sieve plate. Sieve tube elements are living cells containing cytoplasm and nucleus. Companion cells are parenchymatous in nature. They help in maintaining the pressure gradient in the sieve tube elements. Phloem parenchyma helps in the storage of food and is made up of long tapering cells, with a dense cytoplasm. Phloem fibres are made up of elongated sclerenchymatous cells with thick cell walls.
