Mature sclerenchyma cells have _______.
lignified wall and are dead
Understanding Mature Sclerenchyma Cells
Let's break down the characteristics of mature sclerenchyma cells. Sclerenchyma is a type of simple permanent tissue found in plants. Its main function is to provide mechanical support and rigidity to the plant body. Unlike parenchyma and collenchyma, sclerenchyma cells are typically dead at maturity.
Key Features of Mature Sclerenchyma Cells
Mature sclerenchyma cells have distinct features that differentiate them from other plant cells:
- Cell Wall Composition: The cell walls of sclerenchyma are thick and heavily lignified. Lignin is a complex polymer that makes the cell wall strong, rigid, and impermeable to water. This lignification provides significant mechanical strength.
- Protoplast Condition: At maturity, the protoplast (the living content of the cell, including cytoplasm and nucleus) is absent. This is why sclerenchyma cells are considered dead. The cell lumen (the space inside the cell wall) is usually empty.
- Function: Due to their thick, lignified walls and dead state, sclerenchyma cells are excellent for providing mechanical support, strength, and protection to various parts of the plant, such as providing stiffness to stems or hardness to seed coats and nutshells.
Analyzing the Options
Now let's evaluate each option based on our understanding of mature sclerenchyma cells:
- Option 1: cellulose wall and are living
Cellulose walls are primary components of most plant cells, but sclerenchyma walls are also heavily thickened with secondary material, primarily lignin. Mature sclerenchyma cells are dead, not living. This option is incorrect. - Option 2: lignified wall and is living
Mature sclerenchyma cells do have lignified walls, but they are dead at maturity, not living. This option is incorrect. - Option 3: suberized wall and are dead
Suberin is a waxy substance found in the walls of cork cells (part of periderm), not typically in sclerenchyma cells. While mature sclerenchyma are dead, the wall composition described is incorrect for sclerenchyma. This option is incorrect. - Option 4: lignified wall and are dead
This option accurately describes the two main characteristics of mature sclerenchyma cells: their walls are heavily lignified, providing strength, and the cells themselves are dead, having lost their protoplast. This option is correct.
Therefore, mature sclerenchyma cells are characterized by having a lignified wall and being dead.
| Tissue Type | Cell Wall Composition | State at Maturity | Primary Function |
|---|---|---|---|
| Parenchyma | Thin, mainly cellulose | Living | Storage, photosynthesis, secretion |
| Collenchyma | Unevenly thickened (cellulose, pectin) | Living | Mechanical support in growing parts |
| Sclerenchyma | Thick, heavily lignified | Dead | Mechanical support, protection (in mature parts) |
Revision Table: Comparing Simple Plant Tissues
| Feature | Parenchyma | Collenchyma | Sclerenchyma |
|---|---|---|---|
| Cell Shape | Usually isodiametric | Elongated, irregular | Variable (fibers are long, sclereids are diverse) |
| Cell Wall Thickness | Thin primary wall | Unevenly thickened primary wall | Thick secondary wall |
| Cell Wall Composition | Cellulose | Cellulose, hemicellulose, pectin | Cellulose, heavily lignified |
| Living/Dead at Maturity | Living | Living | Dead |
| Function | Storage, photosynthesis, secretion, etc. | Mechanical support to growing organs | Mechanical support and rigidity to mature organs |
Additional Information on Sclerenchyma Tissue
Sclerenchyma tissue is crucial for the rigidity and structural integrity of many plant parts, especially mature ones. It provides strength that allows plants to withstand various mechanical stresses like bending and pulling.
There are two main types of sclerenchyma cells:
- Fibers: These are long, narrow, elongated cells, often with pointed ends. They are commonly found in strands, like in the phloem or xylem, or associated with vascular bundles. They provide significant mechanical support. Examples include jute, flax, and hemp fibers used commercially.
- Sclereids: These are shorter, irregularly shaped cells. Their walls are also thick and lignified, with narrow lumens and often prominent pits. Sclereids can be found individually or in groups in various tissues. They contribute to the hardness of tissues like nutshells, seed coats, and the gritty texture of fruits like pears (stone cells).
The presence of lignin is a defining feature, making the walls very hard and strong but also preventing the movement of substances through the wall, which is why the cells die after the wall fully develops.
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