Question

Describe the different types of permanent tissues.

Answer 1

1. Permanent tissues are those cells that are formed from meristematic tissue but have lost the ability to divide and became specific for certain functions. Two types of permanent tissues are there. Simple and complex tissue.
2. Simple tissue includes those which have same type of cells and includes parenchyma, sclerenchyma and collenchyma.

1. Parenchyma cells are simple permanent tissues made up of same type of cells, non specific, living cells with intercellular spaces in between. Xylem and phloem tissues are complex tissue composed of different types of cells, which function as a single unit.
2. Sclerenchymatous cells are hard, dead and thick walled cells with lignin deposition in their cell wall. This make these cells strong, rigid and impermeable to water. The functions of sclerenchyma includes mechanical support, protective covering around seeds and nuts. The two components of sclerenchyma includes:

1. Fibers - Fibers are elongated cells with tapering ends and are usually seen in hypodermis, secondary xylem and phloem.
2. Sclerids - Sclerids are short cells with lamellated lignified walls and are usually seen cortex, pith, hard seed coats, hard endocarp of almond, coconut, grit of apple, pear and guava.

iii. Collenchyma are living cells with secondary thickenings of cellulose and pectin in the corners of the cell This provide flexibility to soft aerial parts like stem, leaves etc.

3. Xylem and phloem are complex permanent tissue composed of different types of cells which function as a unit.

Xylem is responsible for the conduction of water and inorganic solutes. It is composed of:

1. Tracheids
2. Vessels
3. Xylem parenchyma
4. Xylem fibers

1. Xylem tracheids and xylem vessels are mainly involved in conduction of minerals and water.
2. Xylem parenchyma is involved in storage of food reserves and organic solutes.
3. Xylem fibers provide mechanical support to the plant body.

Phloem is the chief conducting tissue of organic solutes. It is composed of 4 elements:

1. Sieve tube
2. Companion cells
3. Phloem parenchyma
4. Phloem fibers

1. Sieve tubes are long tubular live structures made up of long sieve tube elements. The end walls have numerous perorations.
2. Sieve tubes are associated with other kind of living cells called companion cells. Both cells arise from same initials cells thus forming a single functional unit.
3. Living parenchymatous cells present in phloem is known as phloem parenchyma. Companion cells are cells that are associated sieve tubes. Both cells arise from same initials cells thus forming a single functional unit. Companion cells contain all the essential cellular contents like mitochondria, nucleus, endoplasmic reticulum etc. They lose their nucleus on maturity.
4. Phloem fibers are dead sclerenchymatous fibers seen in phloem.

These are the different types of permanent tissues found in plant.