//M0//QN1//SUB//DL0

Three water samples namely river water, untreated sewage water and secondary effluent discharged from sewage treatment plant were subjected to BOD test. The samples were labelled in 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 20 mg/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?

//X

BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria.
The greater the BOD of waste water, more is its polluting potential
Water having least BOD is less polluted or river water.
Sample A (20 mg/L) is effluent which is obtained from after the secondary sewage treatment.
Sample B (8mg/L) is a river water.
Sample C (400mg / L) is not treated in sewage treatment plant.
Reason :
Sample C is the highly polluted water as the BOD is high.
Conclusion :
BOD of a river water is least among three very high. So, we can say that river water is clean as compared to other two samples.

//M2//QN2//SUB//DL0

Describe primary treatment of sewage treatment plant. OR Explain Primary Treatment of sewage.(JULY 2022, MAY 2021)

//X

Primary treatment steps basically involve physical removal of particles large and small from the sewage through filtration and sedimentation. These are removed in stages; initially, floating debris is removed by sequential filtration.
Then the grit soil and small pebbles are removed by sedimentation.
All solids that settle from the primary sludge and the supernatant from the effluent. The effluent from the primary settling tank is taken for secondary treatment.

//M2//QN3//SUB//DL0

Mention the importance of methanogens bacteria.

//X

Certain bacteria which grow anaerobically on cellulosic material produce large amount of Methane along with CO2 and H2. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium.
These bacteria are commonly found in the anaerobic sludge during sewage treatment.
These bacteria are also present in the rumen, (a part of stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen.
In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle.
The excreta (dung) of a cattle, commonly called gobar, is rich in these bacteria.
Dung can be used for generation of biogas, commonly called gobar gas.

//M2//QN4//SUB//DL0

Certain bacteria are useful to mankind in many ways. Give examples.

//X

The given microbes give useful products to us.

Bacteria

Use / Product

1.

Lactobacillus

Curd

2.

Saccharomyces cerevisiae

To prepare bread and alcoholic beverages.

3.

Propionibacterium sharmanii

Swiss cheese

4.

Penicillium roquefortii

Roquefort cheese

5.

Aspergillus niger fungi

Citric acid

6.

Acetobacter aceti

Acetic acid

7.

Clostridium butyricum

Butyric acid

8.

Penicillium notatum

Penicillin

9.

Streptococcus

Streptokinase enzyme which is used as a clot buster

//M0//QN5//SUB//DL0//EQ

What is sewage? How sewage is harmful for us?

//X

Large quantities of waste water is generated everyday in cities and towns. A major component of this waste water is human excreta. This municipal waste water is also called sewage.
It contains large amounts of organic matter and microbes, many of which are pathogenic.
This cannot be discharged into natural water bodies like rivers and streams directly.
Before disposal, hence, sewage is treated in Sewage Treatment Plant (STPs) to make it less polluting.
Sewage / untreated water harmful to us because the pollutants and pathogens in sewage cause water-borne animal disease like typhoid, cholera etc.
Sewage cannot be discharged into natural water bodies like rivers and streams directly.
Before disposal, hence, sewage is treated in sewage treatment plants (STPs) to make it less polluting.

//M4//QN6//SUB//DL0

What is sewage? Describe secondary treatment (biological treatment) in sewage treatment plant. OR Explain biological treatment in sewage treatment. (diagram is not required)OR Explain biological treatment of sewage treatment plant.

//X

Large quantities of waste water are generated everyday in cities and towns. A major component of this waste water is human excreta. This municipal waste water is also called sewage.
It contains large amounts of organic matter and microbes, many of which are pathogenic.
This cannot be discharged into natural water bodies like rivers and streams directly.
Before disposal, hence, sewage is treated in Sewage Treatment Plant (STPs) to make it less polluting.
Treatment of waste water is done by heterotrophic microbes naturally present in the sewage.
There are two stages of the process:

(1) Primary treatment

(2) Secondary treatment (biological treatment)

The following sequential treatment is done in secondary treatment.

(1) The primary effluent is passed into large aeration tanks, where it is constantly agitated mechanically and air is pumped into it.

This allows vigorous growth of useful aerobic microbes form flocs (masses of bacterial associated with fungal filaments to form mesh like structures).
While growing, these microbes consume the major part of the organic matter in the effluent.
This results in significant reduction of the BOD (Biochemical Oxygen Demand) of the effluent.
The greater the BOD of waste water, the more is its polluting potential.
Once the BOD of sewage or waste water is reduced significantly, the effluent is then passed into a settling tank.
Where bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge.

(2) A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum.

(3) The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.

Here, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge.
During this digestion, bacteria produce a mixture of gases from the biogas such as carbon dioxide, methane and hydrogen. (CO2, CH4 and H2) These gases from biogas and can be used as source of energy as it is inflammable.

//M0//QN7//SUB//DL0//EQ

What is the key difference between primary and secondary treatment?

//X

Sewage treatment plant contains mainly two steps :

Primary treatment

Secondary treatment (biological treatment)

1.

Primary treatment steps basically involve physical process during which removal of particles- large and small is done from the sewage.

1.

This is a biological process in which organic matter is decomposed by microbes.

2.

This process, filtration and sedimentation are done repeatedly.

2.

Here, by using aerobic and anaerobic microbes, organic matter is decomposed.

3.

This treatment is less expensive and comparatively simple process.

3.

This process is complex and expensive.

//M4//QN8//SUB//DL0//EQ

Explain the structure and working of biogas plant with diagram.OR Draw a typical biogas plant and explain in detail.

//X

10-15 feet deep concrete tank is prepared for biogas plant.
This tank is fed by collected bio-waste and a slurry.
A floating cover is placed over the slurry.
Due to microbial activity (Methanogens) this slurry keeps rising as the gas is produced.
The biogas plant has an outlet.
This is connected to a pipe to supply biogas to nearby houses.

The spent slurry is removed through another outlet and may be used as a fertiliser.
The biogas plants are more often built in rural areas.
The biogas thus produced is used for cooking and lighting.
In biogas plant, bacteria produce a mixture of gases from biogas such as carbon dioxide, methane and hydrogen. (CO2, CH4 and H2)
These bacteria are collectively called as Methanobacterium.

//M2//QN9//SUB//DL0//EQ

Do you think microbes can also be used as source of energy? If yes, how? OR Role of microbes in production of biogas.

//X

Yes, microbes are used as a source of energy.
For example microbes are used to produce biogas or gobar gas from dung and bio waste.
Biogas (gobar gas) is a product of anaerobic respiration of which main component is methane gas.
The spent slurry from the biogas plant is used as fertiliser.

//M0//QN10//SUB//DL0

The use of biocontrol measures will greatly reduce our dependence on toxic chemicals and pesticides. OR Give an importance of virus included in genus Nucleopolyhedrovirus. (March 2023)OR How microbes are useful as Biocontrol agents? Explain.OR Explain biocontrol agent which are pathogens that attack insects and other arthropods.

//X

In agriculture, there is a method of controlling pests that relies on natural predation rather than introduced chemicals.
A key belief of the organic farmers is that biodiversity promotes health.
The use of biocontrol measures will greatly reduce our dependence on toxic chemicals and pesticides.
An important part of the biological farming approach is to become familiar with the various life forms that inhabit the field, predators as well as pests, and also their life cycles, patterns of feeding and the habitats that they prefer. This will help develop appropriate means of biocontrol.
Different biocontrol agents are as follows:

(1) Ladybird and Dragonflies :

  • These beetles are useful to get rid of aphids and mosquitoes.

(2) Bacillus thuringiensis:

  • An example of microbial biocontrol agents that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt).
  • These are available in sachets as dried spores which are mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees, that are where eaten by the insect larvae.
  • In the gut of the larvae, the toxin is released and the larvae get killed.
  • The bacteria will kill the caterpillars, but leave other insects unharmed.
  • The scientists have introduced Bt toxin genes into plants. Such plants are resistant to attack by insect pests.

(3) Trichoderma :

  • Trichoderma species are free living fungi that are very common in root ecosystems.
  • These fungi are used as biocontrol agent for the treatment of plant disease.
  • They are effective biocontrol agents of several plant pathogens.

(4) Baculoviruses :

  • The majority of baculoviruses used as biocontrol agents are of genus Nucleopolyhedrovirus.
  • Baculoviruses are pathogens that attack insects and other arthropods.
Various biocontrol agents have shown no negative impacts on plants, mammals, birds, fish or even on non target insects.
Inspite of this, they are desirable when beneficial insects are being conserved to aid in an overall Integrated Pest Management (IPM) programme, or when an ecologically sensitive area is being treated.

//M0//QN11//SUB//DL0//EQ

Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished. OR How do biofertilisers increase the fertility of soil?

OR Describe the importance of microbes as

bio-fertilisers.

//X

Due to our present day life styles, environmental pollution is a major cause of concern.
The use of chemical fertilisers to meet the ever-increasing demand of agricultural produce has contributed significantly to this pollution.
There are problems associated with the overuse of chemical fertilisers and there is a large pressure to switch to organic farming – the use of biofertilisers.
Biofertilisers are organisms that enrich the nutrient quality of the soil.
The main sources of biofertilisers are bacteria, fungi and cyanobacteria.
The nodules on the roots of leguminous plants are formed by the symbiotic association of Rhizobium.
These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient.
Other bacteria can fix atmospheric nitrogen while free-living in the soil Azospirillum and Azotobacter, enriching the nitrogen content of the soil.
Fungi are also known to form symbiotic associations with plants (mycorrhiza).
Many members of the genus Glomus form mycorrhiza.
The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant.
In paddy fields, Cyanobacteria serve as an important biofertiliser.
Currently, in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers.
In agriculture, there is a method of controlling pests that relies on natural predation rather than introduced chemicals.

//M0//QN12//SUB//DL0//EQ

Find out the role of microbes in the following and discuss it with your teacher. (a) single cell protein (SCP) (b) soil

//X

(a) Single cell protein (SCP)
The source of single cell protein is a non harmful bacteria which is an alternative source of good protein.
For example; edible mushrooms (fungi) which is used by human is a source of protein.
Microbes can be cultured on industrial waste to produce protein.
Microbes like Spirulina and Methylophilus methylotropus can easily grow on materials like waste water from potato processing plants, straw, molasses, animal manure and waste water sewage to produce large quantities and can serve as food rich in protein, minerals, fats, carbohydrates and vitamins.
(b) Soil
For the fertility of soil, microbes play an important role.
By decomposition of organic matter, microbes enrich the soil with nutrients.
Many species of bacteria and cyanobacteria can fix atmospheric nitrogen into the soil.
Example : Symbiotic bacterium : Rhizobium
Free living bacterium : Azospirillum and Azotobacter
Cyanobacteria : Anabena, Nostoc and Oscillatoria

//M0//QN13//SUB//DL0//EQ

Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a microscope, which sample would you carry and why?

//X

Curd can be used as a sample for the study of microbes. Curd contains numerous lactic acid bacteria (LAB) or Lactobacillus.
These bacteria produce acids that coagulate and digest milk proteins.
A small drop of curd can be carried to the biology laboratory because it contains multitude of bacteria, which can be easily observed under a microscope which are of various shapes and sizes.

//M0//QN14//SUB//DL0//EQ

Give any two names of fungi used for antibiotic synthesis.

//X

(i) Penicillium notatum (ii) Streptomyces

//M0//QN15//SUB//DL0//EQ

Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. (Biogas, Citric acid, Penicillin and Curd)

//X

Penicillin > Biogas > Curd > Citric acid.