Biology Class 12 NCERT Solutions: Chapter 10 Microbes in Human Welfare Part 4

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Q.11 Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?

Answer:

  • Biological oxygen demand (BOD) is the method of determining the amount of oxygen required by micro-organisms to decompose the waste present in the water supply.

  • If the quantity of organic wastes in the water supply is high, then the number of decomposing bacteria present in the water will also be high. As a result, the BOD value will increase.

  • Therefore, it can be concluded that if the water supply is more polluted, then it will have a higher BOD value.

  • Out of the above three samples, sample C is the most polluted since it has the maximum BOD value of 400 mg/L.

  • After untreated sewage water, secondary effluent discharge from a sewage treatment plant is most polluted.

  • Thus, sample A is secondary effluent discharge from a sewage treatment plant and has the BOD value of 20 mg/L, while sample B is river water and has the BOD value of 8 mg/L.

  • Hence, the correct label for each sample is:

Table of BOD Value and Sample
Table of BOD Value and Sample

Label

BOD value

Sample

A.

20 mg/L

Secondary effluent discharge from a sewage treatment plant

B.

8 mg/L

River water

C.

400 mg/L

Untreated sewage water

Q.12 Find out the name of the microbes from which Cyclosporine A (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.

Answer:

Table of Drug and this Function
Table of Drug and this Function

Drug

Function

Microbe

1.

Cyclosporine −A

Immuno suppressive drug

Trichoderma polysporum

2.

Statin

Blood cholesterol lowering agent

Monascus purpureus

Q.13:

Find out the role of microbes in the following and discuss it with your teacher.

(a) Single cell protein (SCP)

(b) Soil

Answer:

(a) Single cell protein (SCP)

  • A single cell protein is a protein obtained from certain microbes, which forms an alternate source of proteins in animal feeds.

  • The microbes involved in the preparation of single cell proteins are algae, yeast, or bacteria.

These microbes are grown on an industrial scale to obtain the desired protein.

  • For example, Spirulina can be grown on waste materials obtained from molasses, sewage, and animal manures.

  • It serves as a rich supplement of dietary nutrients such as proteins, carbohydrate, fats, minerals, and vitamins.

  • Similarly, micro-organisms such as Methylophilus and methylotrophus have a large rate of biomass production. Their growth can produce a large amount of proteins.

Image of Single Cell Protein

Image of Single Cell Protein

(b) Soil

  • Microbes play an important role in maintaining soil fertility. They help in the formation of nutrient-rich humus by the process of decomposition.

  • Many species of bacteria and cyanobacteria have the ability to fix atmospheric nitrogen into usable form.

  • Rhizobium is a symbiotic bacteria found in the root nodules of leguminous plants.

  • Azospirillium and Azotobocter are free living nitrogen-fixing bacteria, whereas Anabaena, Nostoc, and Oscillitoria are examples of nitrogen-fixing cyanobacteria

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