Sclerenchyma
Explanation
Plant tissues are classified based on their structure, function, and cell wall composition. Simple permanent tissues include Parenchyma, Collenchyma, and Sclerenchyma. The chemical nature of the cell wall deposition is a key differentiating factor among these tissues.
Detailed Analysis:
- Parenchyma is incorrect: Parenchyma cells are living cells with thin cell walls primarily composed of cellulose. They are responsible for photosynthesis, storage, and secretion but do not possess lignified walls.
- Collenchyma is incorrect: Collenchyma cells are living cells characterized by uneven thickening of the cell walls, particularly at the corners. These thickenings are composed of cellulose, hemicellulose, and pectin, not lignin. They provide mechanical support to growing parts of the plant.
- Sclerenchyma is correct: Sclerenchyma consists of long, narrow cells with thick and lignified cell walls. Lignin acts as a cementing material that hardens the cell wall and makes it impermeable to water. Due to heavy lignification, these cells are usually dead at maturity (protoplasm is absent) and provide mechanical strength and rigidity to the plant.
- Phloem Parenchyma is incorrect: Phloem Parenchyma consists of living parenchyma cells associated with the phloem. Like standard parenchyma, their cell walls are composed of cellulose.
Key Takeaway:
Lignin is the characteristic chemical substance found in the thick cell walls of Sclerenchyma, rendering them dead and providing structural hardness (e.g., shells of nuts, pulp of fruits like guava).