Question

The number of stomatal and epidermal in 1mn2 area of leaves of A, B, C, D plants are given below.

Plant	Number of stomata	Number of epidermal cells
A	40	730
B	60	510
C	70	450
D	30	620

Identify the two plants having least stomatal index.
(А) A,D
(B) A,C
(C) A,B
(D) B, C

Answer 1

Stomata are the tiny apertures found on the epidermis of leaves and young green stems. Each stomata is surrounded by two specialized epidermal cells, called guard cells. They differ from epidermal cells in their shape (kidney or bean shaped) and in the presence of chloroplasts

Complete answer:
Stomatal index is defined as the average number of the stomatal cells present per square millimetre of the epidermis of the leaf. It is represented by I.
$I = \dfrac{S}{{S + E}}$
Where I is the stomatal index S is the number of stomatal cells
E is the number of epidermal cells.
Now let us find stomatal index of every plant:-
Plant A : $I = \dfrac{S}{{S + E}}$ = no. Of stomata cells = 40 and epidermal cells = 730 . Putting the values $\dfrac{{40}}{{40 + 730}} = \dfrac{{40}}{{770}} = 0.052$
Plant B : $I = \dfrac{S}{{S + E}}$ = no. Of stomata cells = 60 and epidermal cells = 510 Putting the values $\dfrac{{60}}{{60 + 510}} = \dfrac{{60}}{{570}} = 0.105$
Plant C:$I = \dfrac{S}{{S + E}}$= no. Of stomata cells = 70 and epidermal cells = 450. Putting the values $\dfrac{{70}}{{70 + 450}} = 0.135$
Plant D : $I = \dfrac{S}{{S + E}}$ = no. Of stomata cells = 30 and epidermal cells = 620. Putting the values $\dfrac{{30}}{{30 + 620}} = 0.046$.
The two plants having least stomatal index are plant A with 0.052 and Plant D with 0.046

Thus our required answer is A that is A, D.

Note: Each stomata is surrounded by two specialized epidermal cells, called guard cells. They differ from epidermal cells in their shape (kidney or bean shaped) and in the presence of chloroplasts. The inner wall of the guard cell is thick and elastic, whereas the outer wall is thin. The immediate cause of the opening or closing of the stomata is a change in the turgidity of the guard cells. When turgidity increases within the two guard cells flanking each stomatal aperture or pore, the thin outer walls bulge out and force the inner walls into a crescent shape. Opening of the stoma is also aided due to the orientation of the microfibrils in the cell walls of the guard cells.