F4 Biology teaching notes Ch 10: 2nd Term NE 19

10.4  Support in plants (Book 1B, p. 10-29)

Ø   The importance of support in terrestrial plants:

n           To hold the leaves in the best position to receive the

maximum amount of (1) light for photosynthesis

n           To raise their flowers to a higher position that favours (2) pollination and (3) dispersal of fruits and seeds

Ø   Support (支持) in plants is mainly provided by:

n   the (4) turgidity of thin-walled cells and

n   the (5) rigidity of thick-walled cells.

A

Turgidity of thin-walled cells (Book 1B, p. 10-29)

     

Ø   provide support to herbaceous stems and other (6) non-woody parts of plants.

Ø   Support provided by turgidity of thin-walled cells is affected by the (7) water supply

When water supply is adequate	When water supply is inadequate
By osmosis, the thin-walled cells become
(8) turgid and press against each other to support the plant.	(9) flaccid and do not press against each other. No support is provided to the plant.
The plant stands straight.	The plant (10) wilts (凋謝).

B

Rigidity of thick-walled cells (Book 1B, p. 10-30)

Ø  Thick-walled cells are mostly (11) xylem vessels. Their cell walls contain (12) lignin (木質素), which makes them hard and rigid.

Ø  Support provided by thick-walled cells is independent of the water content of the plant.

Ø  As woody plants grow, more lignin is deposited積聚 in the cell walls of the older xylem.

The older xylem finally becomes (13) wood, which provides great support to the plants.