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

BOD is

  1. Biological oxygen deficit

  2. Biosphere oxygen demand

  3. Biological oxygen demand

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

BOD refers to the Biological Oxygen Demand. It refers to the amount of the oxygen required by the aerobic bacteria to decompose the organic compounds present in the water body. If the BOD of a water body is low, it is considered to be less polluted. The high BOD shows a large level of pollution because more organic pollutants are present now and the bacteria will need more oxygen to decompose them.

Hence, the correct answer is 'Biological Oxygen Demand'.

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

BOD (biological oxygen demand) is

  1. Amount of oxygen consumed by microorganisms for decaying organic matter per unit volume of water
  2. Amount of $CO _2$ consumed by microorganisms per unit of sewage water

  3. Amount of oxygen required by aquatic plants for survival

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Biological oxygen demand refers to the amount of oxygen required for the complete decomposition of the organic mass present in the water body by the decomposing bacteria. More the amount of the organic mass, higher will be the BOD and more will be the level of pollution in the water body. As more and more oxygen will be consumed, the aquatic animals, especially fishes will die due to hypoxia. Their dead bodies will further enhance the organic mass.  

Hence, the correct answer is 'Amount of oxygen consumed by microorganisms for decaying organic matter per unit volume of water'

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

Limit of BOD prescribed by Central Pollution Control Board for discharge of industrial and municipal waste waters into natural surface waters is

  1. $< 3.0$ ppm
  2. $< 10$ ppm
  3. $< 30$ ppm
  4. $< 100$ ppm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
BOD or Biochemical oxygen demand is the amount of oxygen required to decompose the organic matter in one litre of polluted water. More BOD means more organic matter is present in the water. Hence, a high BOD value means that the water is heavily polluted. 
According to Central Pollution Control Board, limit of BOD for discharge of industrial and municipal waste waters into natural surface waters is less than 10 ppm i.e. < 10 ppm.
So, the correct answer is '< 10 ppm'
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

High BOD indicates

  1. Highly polluted water

  2. Less pollution in water

  3. Less sewage

  4. Less microorganisms
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

BOD or the Biological Oxygen Demand that is created when there is a large concentration of the organic matter in the water. To decompose this organic mass, the decomposing bacteria will be activated and there would be consumption of the dissolved oxygen in this process. So, more the organic matter, higher will be the BOD and as a result more will be the pollution in the water body. This causes severe decrease in the dissolved oxygen and kills the aquatic animals.

Hence, the correct answer is 'Highly polluted water'.

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

Biochemical oxygen demand in a river water 

  1. Remains unchanged when algal bloom occurs

  2. Increases when sewage gets mixed up with river water

  3. Has no relationship with concentration of oxygen in water

  4. Gives a measure of Salmonella in water
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Biochemical oxygen demand or BOD is the amount of oxygen required to decompose organic matter in one litre of polluted water.
If the water is more polluted, more will be the BOD because more will be the organic matter present in it and hence, more oxygen will be required to decompose it.
Hence, BOD in a river water will increase if sewage gets mixed up with the river water because more organic matter will be added in the river.
So, the correct answer is 'Increases when sewage gets mixed up with river water'.
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

BOD of eutrophied lake will be

  1. Lower

  2. Moderate

  3. Higher

  4. Same as any other lake
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Eutrophication is the phenomenon of nutrient enrichment of nitrogen and phosphorus in a water body that supports a dense growth of plants and animal life. Due to nutrient enrichment, excess growth of algae occurs which is called algal bloom. When these algae die, their organic matter gets decomposed and this results in the depletion of oxygen leading to death of aquatic animals. This process is called eutrophication. 
Biochemical oxygen demand or BOD is the amount of oxygen required to decompose organic matter in one litre of polluted water.
Hence, BOD of a eutrophied lake will be higher as it will have more organic matter and more oxygen will be needed to decompose it.
So, the correct answer is 'Higher'.
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

BOD level in fresh water should not exceed beyond

  1. $5$ ppm
  2. $10$ ppm
  3. $25$ ppm
  4. $50$ ppm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
BOD or Biochemical Oxygen Demand is the amount of oxygen required to decompose organic matter present in one litre of polluted water.
More the value of BOD,more will be the amount of organic matter in the water. Hence, a high BOD value means heavily polluted water.
Water with BOD value of 1-2 ppm is considered clean. 
In freshwater, BOD value should not exceed 5 ppm as the dissolved oxygen will be used up in the decomposition of organic matter and will not be available for the survival of aquatic organisms which will lead to their death.
So, the correct answer is '5 ppm'. 
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

When domestic sewage mixes with river water, __________

  1. Small animals like rats will die after drinking river water

  2. The increased microbial activity released micronutrients such as iron

  3. The increased microbial activity uses up dissolved oxygen
  4. The river water is still suitable for drinking as impurities are only about $0.1\%$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Domestic sewage contains large amounts of organic matter. When domestic sewage mixes with river water, organic matter will content will increase in the river. This will lead to increase in BOD or Biochemical Oxygen Demand. 

BOD is the amount of oxygen required by bacteria to decompose organic matter in one litre of polluted water.
If the water is more polluted, more will be the BOD because more will be the organic matter present in it and hence, more oxygen will be required to decompose it.
Hence, the dissolved oxygen will be used up by the bacteria to decompose the organic matter.
So, the correct answer is 'The increased microbial activity uses up dissolved oxygen'.

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

Match and find the correct option.

I II III
(a) BOD (i) Supernatant as effluent (p) Useful aerobic microbes 
(b) Flocs (ii) Measure of organic matter (q) All settled solids
(c) Primary sludge (iii) Masses of bacteria associated with fungi (r) Methane hydrogen sulphide carbon dioxide
(d) Biogas (iv) Anaerobic sludge digester (s) Polluting water has more BOD

  1. a-ii-s, b-iii-p, c-i-q, d-iv-r

  2. a-ii-p, b-i-r, c-iv-q, d-iii-s

  3. a-i-s, b-iii-q, c-iv-p, d-ii-r

  4. a-iv-r, b-ii-s, c-iii-p, d-i-q
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

(a)BOD - (ii)Measure of organic matter-(s)Polluting water has more BOD-Biochemical Oxygen Demand is the amount of dissolved oxygen needed by aerobic microbes to break down organic material present in a given water sample at certain temperature over a specific time period. Polluting water has more organic matter thus required more oxygen for the breakdown. Hence polluting water has more BOD.

(b)Flocs- (iii)Masses of bacteria associated with fungi -(p)Useful aerobic microbes-Flocs are the masses of bacteria associated with fungi. Flocs are helpful in increasing the decomposition rate and are put in the aeration tank while the secondary sewage treatment process is in effect
(c)Primary sludge-(i)Supernatant as effluent-(q)All settled solids-Primary sludge includes settleable solids removed during primary treatment in primary clarifiers.
(d)Biogas-(iv)Anaerobic sludge digester-(r)Methane, hydrogen sulfide, carbon dioxide-Biogas is the mixture of gases(Methane, hydrogen sulfide, carbon dioxide)- produced by the breakdown of organic matter in the absence of oxygen(I.e from anaerobic sludge digesters).

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

Water above the dissolved $O _2$ content may be considered uncontaminated.

  1. $0.8$ mg/l
  2. $0.008$ mg/l
  3. $8.0$ mg/l
  4. 8 $\mu$g/l
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The microorganisms in water decompose organic matter using dissolved oxygen. More the amount of dissolved oxygen in the water, more is its purity and vice versa. Water below 5mg/l is considered contamined and water above 8mg/l is considered as uncontaminated.

So, the correct answer is "8.0mg/l".