Question

Inorganic fertilizers are applied each year to fields bordering a lake. The fertilizers run off into the lake and cause the following six changes which together cause high mortality of fishes.
(i) Aerobic bacteria feed on dead plants.
(ii) Algae reproduce faster.
(iii) Light cannot penetrate the water.
(iv) Oxygen level falls.
(v) Water becomes green.
(vi) Plants under water die.
Which of the following shows the correct order of the changes taking place?

• A. (iv) $\to$ (vi) $\to$ (i) $\to$ (ii) $\to$ (v) $\to$ (iii)
• B. (ii) $\to$ (v) $\to$ (iii) $\to$ (vi) $\to$ (i) $\to$ (iv)
• C. (v) $\to$ (ii) $\to$ (iii) $\to$ (vi) $\to$ (i) $\to$ (iv)
• D. (ii) $\to$ (iii) $\to$ (v) $\to$ (iv) $\to$ (vi) $\to$ (i)

Answer 1

The correct option is B (ii) $\to$ (v) $\to$ (iii) $\to$ (vi) $\to$ (i) $\to$ (iv)

Run off water containing inorganic fertilizers from agricultural lands enter water bodies which increases nutrient concentration of water. As a result, algae grow and reproduce faster. Due to over growth of algae water appears green. Dense surface growth of algae prevents entry of light into deeper water. As a. result, underwater plants die. Aerobic bacteria feed on dead plants and cause decrease in oxygen content of water.

(ii) $\to$ (v) $\to$ (iii) $\to$ (vi) $\to$ (i) $\to$ (iv)