This set of Class 12 Biology Chapter 16 Multiple Choice Questions & Answers (MCQs) focuses on “Environmental Issues – Biomagnification and Eutrophication”.
1. Which of the following is the test to the determine amount of oxygen needed to oxidize all pollution materials?
a) Biological Oxygen Demand
b) Chemical Oxygen Demand
c) Botanical Oxygen Demand
d) Physical Oxygen Demand
View Answer
Explanation: Chemical Oxygen Demand (COD) is the measure of the amount of oxygen necessary to oxidize all the pollutants present in water. The value of the chemical oxygen demand is much higher as compared to the biological oxygen demand.
2. How is the value of COD compared to BOD?
a) Much higher
b) Zero
c) Much lower
d) Low
View Answer
Explanation: Chemical Oxygen Demand is designated by COD. It is the measure of the amount of oxygen necessary to oxidize all the pollutants present in water. The value of the biological oxygen demand is less than the chemical oxygen demand.
3. What happens when phosphorus, nitrates, and detergents in water lead to an acceleration in the growth of algae?
a) Extinction
b) Eutrophication
c) Increase in the number of fishes
d) Increase in the number of aquatic plants
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Explanation: The excessive richness of nutrients (phosphorus, nitrates, and detergents) in a lake or other body of water that leads to acceleration in the growth of algae and the natural aging of the lake is known as eutrophication. Excess algal growth deoxygenates water leading to the death of aquatic life.
4. What happens when water is deoxygenated due to algal growth?
a) Increase in the number of fishes
b) Increase in the number of aquatic plants
c) Eutrophication
d) Death of aquatic animals
View Answer
Explanation: The excessive richness of nutrients in a water body leads to an acceleration in the growth of algae and the natural aging of the lake. This excess growth deoxygenates water leading to the death of aquatic life.
5. What is the increased productivity of ponds and lakes due to excess nutrients called?
a) Bio-magnification
b) Extinction
c) Eutrophication
d) Deforestation
View Answer
Explanation: The excessive accumulation of nutrients such as phosphorus, nitrates, and detergents in a lake or any other water body that leads to the increased productivity of ponds and lakes. This process is known as eutrophication.
6. What is the reason for the reduction in dissolved oxygen?
a) Bio-magnification
b) Eutrophication
c) Extinction
d) Pollution
View Answer
Explanation: The excessive richness of nutrients (phosphorus, nitrates, and detergents) in a lake or other body of water that leads to acceleration in the growth of algae and the natural aging of the lake is known as eutrophication. Excess algal growth deoxygenates water and reduces the dissolved oxygen content.
7. When do the planktonic algae utilize oxygen?
a) Day
b) Afternoon
c) Evening
d) Night
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Explanation: Planktonic algae are microscopic organisms and are the foundation of the aquatic food chain in all lakes, ponds, and rivers. However excess growth can lead to an algal bloom. They utilize the oxygen at night and reduce the dissolved oxygen content.
8. What is the reason for choking of the surface off any pond or lake?
a) Nutrients
b) Fecal matter
c) Algal bloom
d) Bacteria
View Answer
Explanation: The microscopic organisms called planktonic algae are the foundation of the aquatic food chain in all lakes, ponds, and rivers. However, their excess growth can lead to an algal bloom, choking the surface of any pond or lake.
9. What phenomenon occurs due to the accumulation of certain pollutants that increase in concentration along the food chain?
a) Eutrophication
b) Pollution
c) Deforestation
d) Bio-magnification
View Answer
Explanation: Biomagnification, also known as bioamplification is the accumulation of certain pollutants (toxins) in the tissues of organisms whose concentration increases along the food chain. These toxins accumulate in the body because they can’t be digested by organisms.
10. Which of the following is an example of pollutants whose concentration increases in each trophic level?
a) Potassium
b) Glucose
c) DDT
d) Nitrogen
View Answer
Explanation: The process of accumulation of certain pollutants (toxins) in the tissues of organisms whose concentration increases along the food chain is known as biomagnification or bioamplification. DDT, methylmercury, toxaphene are examples of such pollutants.
11. What happens to the concentration of DDT in each trophic level?
a) Decrease
b) Increases
c) Remains unchanged
d) Becomes zero
View Answer
Explanation: Sometimes there is the accumulation of certain pollutants (toxins) in the tissues of organisms whose concentration increases along the food chain; this process of increasing accumulation of toxins is known as bioamplification or biomagnification. An example is DDT whose concentration increases at each trophic level.
12. Which of the following is a primary treatment for water pollution?
a) Sludge method
b) Trickling filter method
c) Sedimentation
d) Removal of nitrates
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Explanation: The primary treatment involves the separation of solid matter from the wastewater. In this, the wastewater is poured into big tanks and the solid matter is allowed to settle at the surface of the tanks. This is done by sedimentation, filtration, flotation, etc.
13. Which of the following is a secondary treatment for water pollution?
a) Sedimentation
b) By the action of microbes
c) Removal of nitrates
d) Filtration
View Answer
Explanation: Also known as the active sludge process, in this method, the seed sludge is added to the wastewater for its further breakdown. This happens with the help of microbes that consume the remaining organic matter.
14. What happens in the tertiary treatment for water pollution?
a) Sedimentation
b) Filtration
c) Sludge method
d) Removal of nitrates, phosphates
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Explanation: The tertiary treatment is the stage of wastewater treatment in which the water is disinfected chemically or physically prior to discharge into any water body. It involves the removal of nitrates, phosphates, disinfection to reduce the number of microorganisms in the water.
15. What is the acceleration in the natural aging process of the lake due to the release of effluents from the industries called?
a) Accelerated Eutrophication
b) Eutrophication
c) Sedimentation
d) Bioamplification
View Answer
Explanation: The acceleration in the natural aging process of the lake due to the release of effluents from the industries is known as accelerated or cultural eutrophication. It occurs due to the runoff of fertilizers from the nearby field or increase in the temperature and BOD of the water body leading to algal blooms.
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