Q12 of 67 Page 48

Explain the mechanism of closing and opening of the stomata.

The opening and closing of stomata depending on the turgidity of guard cells. These guard cells have a thicker wall facing the stoma and a comparatively thinner wall opposite to it. They also have chloroplasts; thus they photosynthesize. As a result of the synthesis of glucose and other substances, the osmotic pressure of the content of the guard cells increases leading to the absorption of more water from neighboring cells. This leads to turgidity of the guard cells thus arching outwards and widening the stomatal aperture enclosed between them. At night or during a shortage of water in the leaf these guard cells become flaccid and the walls enclosing stomata becomes straight thus closing the stomata.


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5

Mention whether the following statements are true (T) or false (F) and give an explanation in support of your answer.

(a) Plasmolysis is the reverse of deplasmolysis. (T/F)


(b) Guttation is another name for bleeding in plants. (T/F)


(c) Soaked seeds burst their seed coats. (T/F)


(d) If the phloem of a twig is removed keeping the xylem intact, the leaves of a twig wilt. (T/F)


(e) Guttation in plants occurs maximum at mid-day. (T/F)


(f) Dry seeds when submerged in water swell up due to endosmosis. (T/F)

 1

Give two examples of turgor movements in plants.

 3

The concentration of mineral nutrient elements is higher inside the root-hairs than in the surrounding soil. How do roots take them in from the soil?

 4

Explain how soaked seeds swell up and burst their seed coats.