You may have noticed that fibres of coconut husk are hard and brittle. Class 9

You may have noticed that fibres of coconut husk are hard and brittle. Class 9

Pause and Ponder (Page 33)

Question 1.

You may have noticed that fibres of coconut husk are hard and brittle, whereas the leaf stalks of coriander are soft and flexible. Find out the reason. Class 9

Answer:

Coconut husk fibres are hard and brittle because they are composed mainly of sclerenchyma tissue. Sclerenchyma cells have thick walls due to deposition of lignin - a hard substance that makes cells dead, rigid and very strong, giving coconut husk its hard, brittle nature. On the other hand, leaf stalks of coriander are soft and flexible because they contain collenchyma tissue. Collenchyma cells are living cells with unevenly thickened corners due to pectin (a flexible chemical, similar to rubber), which provides flexibility and allows the stalks to bend without breaking.

Question 2.

Why do you think that a thick cuticle on the outer wall of epidermis is advantageous for a plant living in the desert but disadvantageous for a plant living underwater? (Page 34) Class 9

Answer:

For a desert plant, a thick cuticle is advantageous because it acts as a waterproof layer that greatly reduces water loss through transpiration. Since water is very scarce in desert conditions, minimising water loss is essential for the plant's survival. For a plant living underwater, a thick cuticle is disadvantageous because such plants need to absorb water, minerals and dissolved gases directly from the surrounding water through their entire surface. A thick cuticle would block this absorption and gaseous exchange, harming the plant's survival.