Coconut husk fibres are used for mats which are tough and fibrous. Class 9

Coconut husk fibres are used for mats which are tough and fibrous. Class 9

Question 1.

Coconut husk fibres are used for mats which are tough and fibrous. Which tissue has structural features suitable for providing this strength? Explain why living parenchyma couldn’t serve the same purpose. Class 9

Answer:

The tissue responsible for the toughness and strength of coconut husk fibres is sclerenchyma. Sclerenchyma cells have very thick cell walls due to heavy deposition of lignin - a hard, rigid chemical. These cells are dead at maturity, with the cell wall being extremely hard and strong. This gives the fibres their characteristic toughness, hardness and fibrous nature, making them suitable for making mats and ropes.

Living parenchyma cells cannot serve this purpose because:

1. They have thin cell walls with no lignin deposition, making them soft and fragile
2. They are living cells filled with watery cytoplasm, which would make them soft and easily damaged
3. They cannot provide the rigidity, hardness or tensile strength needed for tough fibrous products

In contrast, the dead, lignin-rich sclerenchyma cells form a tough structural material that can withstand pulling forces and wear.

Question 2.

Vibha claims to her friend Neha that, “Meristematic cells are located only at the root and shoot apices”. What do you think about this statement? What question can Neha ask Vibha to help her understand further if the statement is incorrect? Class 9

Answer:

Vibha's statement is incorrect. Meristematic cells are NOT located only at the root and shoot apices. While apical meristem is present at root and shoot tips, there are two more types of meristematic tissue:

1. Lateral meristem - located along the circumference of stems; responsible for increase in girth/diameter
2. Intercalary meristem - located at the base of internodes or just above nodes; responsible for regrowth after cutting or grazing

Neha can ask Vibha the following questions to help her understand:

1. "If meristematic cells are only at root and shoot tips, how does a grass plant grow back after being mowed or grazed by animals?" (This would direct Vibha to think about intercalary meristem.)
2. "If meristematic cells are only at tips, how does the trunk of a tree become thicker and wider as it grows older?" (This would direct Vibha to think about lateral meristem.)