MEthanogens are found in
(i) the anaerobic sludge
(ii) rumen of cattle
(iii) marshy places
(iv) flooded rice fields.

1. Methanogens grow anaerobically on celluloric material and produce large amount of methane along with carbon dioxide an hydrogen.
2. Biogas is a mixture of methane and carbon dioxide.

Streptococcus
Streptokinase functions as a clots from the blood vessels of patients who have suffered myocardial infarction.

1. The fungus absorbs phosphorus from the soil and passes it to the plant.
2. Plants with mycorrhiza show resistance to root-borne pathogens.
3. They show increased tolerance to salinity and drought.
4. These show an overall increase in plant growth and development.

Four advantages are as follows

1. The fungus absorbs phosphorus from the soil and passes it to the plant.
2. Plants with mycorrhiza show resistance to root-borne pathogens.
3. They show increased tolerance to salinity and drought.
4. These show an overall increase in plant growth and development.

Control of pests and plant diseases by using the biological methods is called biocontrol. It is a natural method of pest and pathogen control which is based natural predation. This involves the use of microorganisms like bacteria viruses, fungi, cyanobacteria and other natural predators and which bring about the control of pest and diseases e.g. Dragonfly prey upon mosquitoes, Baculorirusis attack insects and other arthropodes. They are species specific and do not cause harm to the non target beneficial organisms.

(a) Single Cell Protein (SCP) are basically produced from the microbes, for example Candida utilis, Chlorella, Spirulina, Saccharomyces. SCP may be used directly as human food supplement or else it can be used in animal feed as protein-rich supplement.
(b) Soil It is a unique habitat which harbours a variety of microflora and fauna, and gives mechanical and nutritional support to higher plants on which human civilization is based.
Examples The rhizosphere micro-organisms have beneficial effects on the development of plant. The microorganisms catalyze the reactions in the rhizosphere and produce \({ CO }_{ 2 }\) and form organic acids that in turn solubilize the inorganic nutrients of plants. Some of the rhizosphere micro-organisms also produce growth stimulating substances.

(i) Acetic acid - Acetobacter aceti
(ii) Butyric acid - Clostridium butylicum
(iii) Lacteric acid - Lactobacillus delbruekii

The treatment of sewage Involves two steps:
(i) Primary treatment and
(ii) Secondary treatment.
(i) Primary treatment
1. Primary treatment is a physical process of removal of small and large particles through filtration and sedimentation.
2. The first step is to remove the floating objects (like polythene bags) by letting the sewage to pass through wire mesh screens of sequentially smaller pore sizes.
3. Then the sewage is passed into the grit chamber, where grit is sedimented.
4. The sewage is allowed to go into the primary settling tank, where the suspended materials settle down to form primary sludge.
The effluent is taken for secondary treatment.
(ii) Secondary Treatment
1. It is a biological process, that employs the heterotrophic bacteria naturally present in the sewage.
2. The effluent from the primary treatment is passed into large aeration tanks, where it is constantly agitated and air is pumped into it.
3. This allows the rapid growth of aerobic bacteria into flocs, which consume the organic matter of the sewage and reduce the BOD.
4. The effluent is passed into a settling tank, where the flocs are allowed to sediment forming the activated sludge.
5. A small part of the activated sludge is pumped back into aeration tank as inoculum.
6. The remaining major part of the sludge is pumped into anaerobic sludge digesters, where the anaerobic bacteria digest the organic matter and produce methane, hydrogen sulphide and carbon dioxide.
7. The effluent from this is passed into the waterbody.

Baculoviruses belong to the genus Nucleopolyhedrovirus.
They are the pathogens which attack insects and other arthropods.
They are species-specific, narrow spectrum insecticides, which have no negative impacts on plants, birds, mammals, fish, and even non-target insects.
This is desirable because beneficial insects are conserved to aid in integrated pest management (IPM) programmes.

(a) Secondary treatment of sewage be explained in detail.
(b) Purification of water before dumping it into the source in order to avoid water from being more polluted.
(c) Values-Not to disturb nature's balance, self sufficiency, develop confidence, concern about the environment.

1. Aeration to prevent alcohol formation.
2. Optimum pH = 5.
3. Ammonium phosphate that stimulates then growth of yeast.

(a) Untreated sewage contains large amounts of organic matter and microbes. Many microbes are pathogenic. So the consumption of such water by humans and useful animals increases the chances of spread of a number of water-borne diseases like cholera, typhoid and diarrhea diseases.
The presence of high amounts of organic wastes in water increases the biochemical oxygen demand (BOD) while decreases the Dissolved Oxygen(DO) which causes the death of aquatic animals like fishes.
(b) Major part of activated sludge is pumped into anaerobic sludge digesters where anaerobic bacteria digest the bacteria and fungi during which a mixture of gases like methane, \({ Co }_{ 2 }\) and \({ H }_{ 2 }S\) is produced which can be used as biogas as source of energy. It also produces manure. 

Biofertilisers are those organisms which enrich the soil fertility.
Categories of organisms:
(i) Bacteria, e.g. Rhizobium, Azotobacter
(ii) Cyanobacteria, e.g. Nostoc, Aulosira
(iii) Mycorrhizae/fungi, e.g. Glomus
Functions:
1. Bacteria and Cyanobacteria fix atmospheric nitrogen and increase the nitrogen content of the soil.
2. Cyanobacteria also add organic matter to the soil through their photosynthesis.
3. The fungi decompose the organic matter of the soil and make the nutrients available to the roots.
4. Mycorrhizae help in absorption and storage of some mineral nutrients like phosphorus for the plants.