Q1.
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.
Answer
Different tissues: the coconut husk is sclerenchyma, the coriander leaf stalk is collenchyma (with parenchyma).
| Coconut husk fibre | Coriander leaf stalk | |
|---|---|---|
| Tissue | Sclerenchyma | Collenchyma + parenchyma |
| Wall | Uniformly thick, heavily deposited with lignin | Thin, thickened only at the corners with pectin |
| Living? | Mostly dead at maturity | Living, with cytoplasm and a vacuole |
| Behaviour | Hard, strong, brittle — resists a pull but snaps if bent far | Soft, flexible — bends and springs back |
Why the chemistry decides the feel: lignin is a rigid, waterproof polymer that locks the cellulose fibres of the wall in place. Once it is deposited, the wall cannot stretch, so the cell dies and the fibre becomes stiff and brittle. Pectin, in contrast, is soft and gel-like — the book compares it to rubber — so a collenchyma wall can deform and recover. Deposit lignin and you get a coir mat; deposit pectin and you get a stalk that bends in the wind.
Did you know? This is exactly why coir is used for ropes, mats and mattress filling — it is dead, lignified, rot-resistant and holds its shape, while a coriander stalk wilts within hours of being plucked because its support depended on living, turgid cells.