Tag: permanent tissues and their types

Parenchyma is thin walled, polyhedral, isodiametric, mostly non-lignified, soft living cells with sufficient cytoplasm and one or more nuclei. 

Sclerenchyma cell is a simple permanent tissue which is mainly composed of dead cells. It is the hard, thick walls that make sclerenchyma cells important strengthening and supporting elements in plant parts that have ceased elongation. Their cell walls contain, besides cellulose, a high proportion of lignin. It forms a protective coating on seeds and nuts. Since sclerenchyma cells are dead at maturity, it does not contain plastids. Parenchyma and collenchyma cells are living cells which have plastids.

Sclereids or stone cells are a reduced form of sclerenchyma cells. It has highly thickened, lignified cellular walls that form small bundles of durable layers of tissue in most plants. They are type of sclerenchyma cell that differs from the fibre cell by not being greatly elongated. Often occurs singly (an idioblast) or in small groups, giving rise to a gritty texture in, for instance, the pear fruit, where it is known as a stone cell. May also occur in layers, for example in hard seed coats. A type of cell with thick cell walls, consisting of lignin, that is commonly found on the outer 'skin' of fruits. So, sclereids or stone cells are modified sclerenchyma.

Sclerenchyma is composed of dead tissue which mainly acts as protective coating on fruits and nuts. The reduced form of sclerenchyma cells with highly thickened, lignified cellular walls are known as sclereids. It forms small bundles of durable layers of tissue in most of the plants. 

Senescence is also known as aging. It leads to metabolic degradation. It is the characteristic feature of the period between reproductive maturity and death of a plant or plant part or cell.

Parenchyma cells are thin-walled, flexible and loosely packed cells. They are alive at maturity. Their shape changes as per function. 
Collenchyma cells are living, elongated and irregularly thickened at corners with less intercellular space. 
Sclerenchyma is a type of permanent tissue. They are dead, elongated, thin, narrow cells with thickened walls without any internal space. Therefore, option C is correct.  

• Sclerenchyma cell is a simple permanent tissue which is mainly composed of dead cells. It provides strength and rigidity to the stem. 
• It forms the protective covering of nuts and fruits. Their cell walls contain, besides cellulose, a high proportion of lignin. 
• It forms a protective coating on seeds and nuts.

Collenchyma contains living, elongated cells with protoplasm at maturity. 
Parenchyma cells are thin-walled, flexible and loosely packed cells. They are alive at maturity. Their cells show protoplasm at maturity.
Sclerenchyma cells are dead, long, thin, narrow with thickened walls without any internal space. They do not possess any protoplasm at maturity. Hence, option A is correct. 

• Sclereids are a reduced form of sclerenchyma cells with highly thickened, lignified walls. These have the shape of a star. They are small bundles of sclerenchyma tissue in plants that form durable layers, such as the cores of apples and the gritty texture of pears (Pyrus communis). 
• Sclereids are variable in shape. The cells can be isodiametric, prosenchyma, forked or elaborately branched. 
• They can be grouped into bundles, can form complete tubes located at the periphery or can occur as single cells or small groups of cells within parenchyma tissues.
•  But compared with most fibers, sclereids are relatively short. Sclerenchyma, tracheids, and collenchyma do not cause the Grittiness of the fruit wall. 

1. Parenchyma forms the major component within organs and are closely packed or have intercellular space and are living with the ability of division. They perform functions of photosynthesis, storage, and secretion.
2. Sclerenchyma is long, narrow cells with thick and lignified cell walls having a few or numerous pits. These are commonly found in fruit wall of nuts, the husk of the coconut, seed coat of legumes, etc.
3. Collenchyma is found in the hypodermis in dicot plants and provide mechanical support to the plant.
4. Chlorenchyma is the modified parenchymatous tissue that helps in photosynthesis.