Question

When fertilizers run off farmland into streams and ponds, the nitrogen content of the water increases. This can lead to rapid growth of algae in a process called eutrophication. How can this process affect other organisms in the water?

Question 1 options:

The algae provide food for fishes and other organisms, leading to decreased algae populations.


The water becomes better able to support aerobic organisms.


The extra nitrogen provides additional food for the other organisms, increasing their population.


Oxygen is used up as algae is decomposed, reducing the amount available to other organisms.

Answer 1

The answer is (D) Oxygen is used up as algae is decomposed, reducing the amount available to other organisms.

Fertilisers used in farm contain urea, a compound of nitrogen. When fertilisers from the farms run off into the streams and ponds, they lead to an increase in the nitrogen content of the water. The algae that live on the water bodies, bloom in large numbers by absorbing this dissolved nitrogen. The water bodies also contain a lot of aerobic bacteria that use dissolved oxygen for their functioning and survival. These aerobic bacteria start feeding on the dead and decomposed algae. This leads to a drastic reduction in the amount of oxygen present in the water leading to death of other aerobic organisms present in the water body.

Answer 2

The answer is D) Algae is decomposed by bacteria which use a lot of oxygen