The diagram given below shows a river and the types of land uses

CBSE Class 12 CBSE Class 12 Biology
1

The diagram given below shows a river and the types of land uses on two sides of the river in a countryside.
the-diagram-given-below-shows-a-river-and-the-types-of-land-uses-5
The water quality of the river was studied by measuring the amount of dissolved oxygen and ammonia in the water, collected at sites X, Y and Z. The results are presented in the table below:
the-diagram-given-below-shows-a-river-and-the-types-of-land-uses-6
(i) Explain why site Fhas the lowest content of dissolved oxygen.
(ii) Why are very few fishes found at site ‘Z’?
(iii) Which organism will thrive just after site ZP

2

(i) Site Y has lowest content of dissolved oxygen due to increased bacterial population. It is caused by sewage run-off from pig farm.
(ii) There are very few fishes at site Z due to low oxygen concentration and choked lake (by algae and weeds).
(iii) Algae and weeds will thrive after site Z.