Question

The number of stomata and epidermal cells in 1mm² area of abaxial surface of leaves a, b, c, and d are:

Plant	Number of Stomata	Number of Epidermal cells
a	40	730
b	60	510
c	70	450
d	30	620

Identify two plants having the least stomatal index
(a) b and c
(b) a and d
(c) a and c
(d) a and b

Answer 1

Hint: Stomatal index is the percentage in which the number of stomata forms to the total number of epidermal cells, each stoma being counted as one cell. The stomatal number is defined as the average number of stomata per mm² of the epidermis of the leaf. Epidermal cells are the several types of cells that make an epidermis of the leaf.

Complete step by step solution:
Stomata are microscopic pores present in the epidermis of leaves and young shoots of plants. They are chiefly concerned with the exchange of gases during photosynthesis and respiration. They are also responsible for the loss of water through transpiration.
The distribution of stomata on the upper and lower surface of the leaf can be studied by taking out peels of the leaf from two surfaces and observing the same under a microscope.
The epidermal peels from the upper and lower surface of the leaf are taken out by tearing the leaf obliquely with a single jerk or scraping it with a blade. The peels are stained with safranin while adding a few drops of stain in the watch glass. A small rectangular or square piece is cut off from each peel and is mounted in glycerin on separate slides. These slides are observed under a microscope and the number of epidermal cells in the peels of both the upper and lower epidermis of the leaf is counted. This is done for all the four plants and the stomatal index is calculated using the following formula.
$Stomatal\quad Index\quad =\quad \frac { No.\quad of\quad stomata }{ No.\quad of\quad stomata\quad +\quad No.\quad of\quad epidermal\quad cells } \times { 100 }$
In the leaf of both plants a and d, the stomatal index is least.
So, the answer is, ‘(b) a and d.’

Note: - The leaves of most dicot plants possess stomata only on the lower surface. However, the leaves of some plants such as potato possess stomata on the upper surface also. - In grasses and cereals, stomata are distributed equally on the surfaces of leaves. - In Potamogeton, stomata are either absent or vestigial. - In submerged aquatic plants, stomata are absent as the exchange of gases takes place through the general surface by diffusion.