Question

Number of stomata and epidermal cells/ $m{m}^2$ of lower epidermis of X, Y and Z plants are as follows. Arrange them in decreasing order of their stomatal index

Plant	Stomata	Epidermal Cells
X	30	150
Y	60	240
Z	90	400

• A. Z, Y, X
• B. X, Y, Z
• C. Y, X, Z
• D. Y, Z, X

Answer 1

The correct option is D Y, Z, X

Stomatal index is the percentage which the number of stomata forms to the total number of epidermal cells, both per unit area of concern. Stomatal index can be calculated using the equation: SI % = (S / (E+S)) * 100 where,

S = No. of stomata per unit area,

E = No. of epidermal cells in the same unit area.

From the question, it is given that

Plant X : S = 30,

E = 150,

SI % = (30 / (30+150)) * 100 = (30 / 180) * 100 = 0.1666 * 100 = 16.66

Plant Y : S = 60,

E = 240,

SI % = (60 / (60+240)) * 100 = (60 / 300) * 100 = 0.2 * 100 = 20

Plant Z : S = 90,

E = 400,

SI % = (90 / (90+400)) * 100 = (90 / 490) * 100 = 0.1836 * 100 = 18.36

Therefore, decreasing order of their stomatal index is 20, 18.36, and 16.66 i.e, Y, Z, and X.

So, the correct answer is option D.