Which of the four most abundant element in most plants (C, H, O and N), does a terrestrial green plant procure mainly through its roots from the soil?

Options

A. H and O
B. H and N
C. C and O
D. O and N

Answer

B

Explanation

Hydrogen (H) is mainly obtained from soil water by roots. Oxygen (O) is either derived from the air or from the water. Carbon (C) is derived from atmosphere as `CO_(2)`. The plants are unable to use atmospheric nitrogen. It is inert and plants cannot make use of it directly. By the process of fixation of atmospheric `N_(2)` nitrates `(NO_(3)^(-))`, ammonium ion `(NH_(4)^(+))`, etc. These nitrogenous compounds enter plants as nutrients through the roots and are assimilated as organic nitrogen.