Simple Tissues

Cells in a simple tissue are of the same type. In simple tissue, all the cells are identical in structure and have the same parts. There are three main types of simple permanent tissues. Those are the parenchyma, collenchyma, and sclerenchyma. Their shape, size, and function are so fixed that they cannot be divided and are no longer able to change. 

Types of Simple tissues

1. Parenchyma

• In simple terms, parenchyma is a tissue that is composed of living cells. Parenchymal cells possess thin walls, are oval, rounded, or polygonal in shape, and have well-defined spaces between them. 
• Aerenchyma is the intercellular air space of parenchyma in aquatic plants. Chlorenchyma cells develop chloroplasts when exposed to light and are called parenchyma cells. 
• A huge variety of succulents and xerophytes contain parenchyma to store water. Besides storing food reserves, absorbing, showing buoyancy, secreting, etc., it also serves as a storage facility. 
• Living cells in a cell wall typically have thin walls and are not highly specialised. This makes them more loosely packed and enables intercellular space to exist between them. Cells of this type tend to be isodiametric. 
• Vacuoles are either very few or absent in some cases. The vacuoles present are much smaller than those found in normal animal cells. Plants make use of this tissue for taking care of themselves and storing their food. 
• Photosynthesis is accomplished by chlorenchyma, a type of parenchyma containing chlorophyll. The idioblast cells within the aerenchyma contain metabolic waste.
• In addition to succulent parenchymal tissue, these cells are also supported by a spindle-shaped fibre. 
• Xerophytes store water in their parenchyma tissues.

2. Collenchyma

• Under the epidermis lies the collenchyma, a living tissue. The walls of the elongated cells are not lignified and are unevenly thickened. 
• Cells have oblique or tapering ends that are rectangular and contain persistent protoplasts.  
• In primary bodies, the collenchyma is the same as the parenchyma. 
• Pectocellulose is a natural substance that thickens cellulose, water, and other substances at corner junctions where multiple cells are connected. Cells in this tissue are compactly arranged and have very few spaces between them, providing the plant with tensile strength. 
• They are mostly located in stem and leaf hypodermis. Monocots and roots do not have these cells. Plant stems are supported by collenchymatous tissue. 
• Plant bodies are supported by it, making them flexible and tensile. Plants use it to make sugar and store it as starch.

3. Sclerenchyma

• They are thick, dead cells present in the sclerenchyma, and embryonic protoplasm is insignificant in this tissue.
• Cells with hard and extremely thick secondary walls are abundant in lignin and provide mechanical support since lignin is distributed uniformly and secreted in high amounts. 
• There are no intermolecular spaces in these cells.
• In addition to becoming impermeable to water, stone cells or sclereids also become strong and rigid from the thickening of the lignin layer. 
• Sclerenchyma fibres and sclereids are the two main types of these issues. 
• Fibres of sclerenchyma differ from axons in that they are long, narrow, and unicellular, with a narrow lumen.
• It is composed of elongated cells that are strong and flexible, and it is often used for manufacturing ropes and textiles.
• A sclereid, found in nutshells and legumes, has extremely thick walls and is brittle. Living protoplasts are not present in sclerenchyma cells at maturity. 

Fibres and Sclereids

Fibres and sclereids make up the sclerenchyma.

Fibre:

• The cells are elongated and taper or point at the end.
• The protoplasm will disappear when the cell reaches maturity.
• The middle part of the cell has a wide lumen.
• Lignin is the material that makes up the wall.
• Fibres are found in the pericycles of many dicots, as well as in the xylem and phloem tissue of many plants.
• The longest cellular structure in plants can be found in fibre.
• According to their position, fibres are divided into two types.
• A xylary fibre is a fibre that is associated with the xylem.
• Xylem fibres are fibres present elsewhere in a plant beside the xylem. There are a variety of fibre types, including phloem fibres, perivascular fibres, and cortical fibres.

Their functions include:

• Plasticity acts as a principal mechanism for mechanically supporting the plant body.
• In terms of commercial importance, hemp, jute flex, and ramie are the three major fibres.

Sclereids

• Plants contain a wide range of sclereids. These are generally large and can occur singly or in groups.
• The walls of sclereids are lignified, and they are isodiametric.
• They are characterised by pits.
• There are wall materials in the lumen. Similarly, sclereids occur in fruits and seeds.

Comparing parenchyma, collenchyma, and sclerenchyma

• Parenchyma

Cells have thin walls. Cells in the parenchyma are loosely packed. It is composed primarily of cellulose. The cells in this tissue are alive.

• Collenchyma

Cells have thick walls. These cells are closely packed. Cellulose and pectin are the components of these cells. They are living cells.

• Sclerenchyma

Cells have a thick cell wall. Intercellular space does not exist. Lignin fills the space. These are dead cells.

Differences between Collenchyma and Sclerenchyma

Collenchyma

• It is composed of living cells.
• The protoplasm of cells is present in the cells.
• Cellulose makes up the cell walls.
• The thickness of the walls differs from cell to cell.
• Large lumens are characteristic of cells.
• The pits are straight and simple.
• They support the body and allow for elasticity.

Sclerenchyma

• It is composed of dead cells.
• The cells are empty.
• It is composed of lignified cells.
• The cell walls are uniformly thick.
• Each cell has a narrow lumen.
• There are simple oblique pits that occasionally branch.
• They only serve as mechanical supports

Differences between Sclereids and Fibres

Sclereids

• They are typically broad.
• Their end walls are blunt.
• They appear singly.
• They have deep pits.

Fibres

• They are narrow, thread-like in appearance.
• Tapers at end walls.
• Occurs as bundles.
• They have narrow pits.

Conclusion

All the cells are identical in structure and have the same parts. There are three main types of simple permanent tissues. Those are the parenchyma, collenchyma, and sclerenchyma. Their shape, size, and function are so fixed that they cannot be divided and are no longer able to change.