Tag: human influences on the environment

Questions Related to human influences on the environment

A large quantity of urban sewage is drained to a nearby river. Which among the given conditions would happen after mixing of sewage into the river?
(i) BOD of receiving water body increases.
(ii) DO of receiving water body decreases.
(iii) It will not cause mortality among fishes and other aquatic creatures.
(iv) It will lead to nutrient enrichment of receiving water body.

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. i, ii and iii

  2. i, ii and iv

  3. ii and iii

  4. iii and iv

Show answer
Correct Option: B
Explanation:

A large quantity of urban sewage will have a large amount of organic and inorganic material. Due to this, the decomposition of the organic mass will initiate the use of dissolved oxygen and so, the DO of receiving water body decreases. This will cause increase in the biological oxygen demand (BOD) by the decomposing bacteria. As the DO decreases, the aquatic animals will suffocate and die. Also, the inorganic nutrients, as well as the decomposed nutrients, will cause lush growth of algae, causing algal bloom over the surface of the water, which will further decrease the DO by not allowing the mixing of atmospheric oxygen.

Hence, the correct answer is 'i, ii, iv'

Polluting strength of sewage is characterised by its

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. BOD

  2. Ozone content

  3. Nitrogen content

  4. Eutrophication

Show answer
Correct Option: A
Explanation:

The BOD test measures the amount of dissolved oxygen in the water that is used up due to the breakdown of organic pollutants, such as sewage, in a certain number of days. Raw sewage has a BOD of forty to 150 milligrams per litre, whereas drinking water has a BOD of less than 0.5 milligrams per litre. The BOD indicates the content of oxygen needed to decompose organic compounds in wastewater by bacteria.

So the correct answer is 'BOD'.

Relation between DO and BOD is that they

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. Are directly proportional

  2. Are inversely proportional

  3. Are not related

  4. Always remain equal to each other

Show answer
Correct Option: B
Explanation:

Biological Oxygen Demand (BOD) is a measure of the oxygen used by microorganisms to decompose this waste. This results in a high BOD level. When BOD levels are high, dissolved oxygen levels decrease because the oxygen that is available in the water is being consumed by the bacteria.

So the correct answer is 'Are inversely proportional'.

A river/ lake with an inflow of domestic sewage rich in organic waste may result in

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. Death of fish due to lack of oxygen

  2. Drying of the river/lake very soon due to algal bloom

  3. Increase population of aquatic food web organisms

  4. An increased production of fish due to biodegradable nutrients

Show answer
Correct Option: A
Explanation:

A river with an inflow of domestic sewage rich in organic waste will reduce the dissolved oxygen (DO). The organic waste will increase biological oxygen demand of the river thus depleting the O2 content and may result in the death of fish due to lack of oxygen.

So the correct answer is 'Death of fish due to lack of oxygen'.