BIOLOGY 3 Marks Question

Labelled diagram of biogas plant :

Primary Sewage Treatment: Large and small particles are physically separated from the sewage by filtration and sedimentation. These are separated in different stages. Initially the floating waste is removed by sequential filtration. The grit (soil and small vesicle pebbles) is then removed by sedimentation. All the solids that are particles settled at the bottom form the primary sludge and the supernatant form the effluent. The effluent is taken from the primary filtration (settling) tank for secondary treatmentd.
Secondary Sewage Treatment: Primary effluent is passed through large pneumatic tanks. Where it is continuously stirred mechanically and the air is pumped into it. Due to this, beneficial aerobic microbes start growing vigorously into flocs.
During growth, this microbe consumes major part of organic substance present in the effluent. It starts reducing BOD (biochemical oxygen demand) of the effluent significantly. BOD refers to the amount of O₂ that the bacteria can consume and oxidize the organic substance present in 1 L of water. Sewage is treated until BOD is reduced.

Single Cell Protein (SSP) : It is one of the alternative sources of protein for animal and human nutrition. Microbes are being produced on a large scale as a good source of protein. In fact, mushrooms have started being eaten as food by most of the people. Therefore, mushroom cultivation on a large scale is a growing industry. As a result, it is now believe that microbes will become acceptable as food. Proteins, minerals fats, carbohydrates and vitamins are present in abundance in Spirulina microbe. It's use also reduces environmental pollution. Microbes like Methylophilus, Methylotrophus can potentially produce upto 25 tons of protein with high rates of growth and biomass production.

We use microbes or products derived from them every day. A common example of it is production of curd from milk. Microbes like lactobacillus and other commonly called lactic acid bacteria (LAB) grow in milk and convert it into curd.
Similarly a baker's yeast (Saccharomyces cerevisiae) is used in making bread.
If we have to take a sample from our home to biology lab and have to see the presence of microbes from this sample with the help of the microscope then we will take a piece of rotten bread or a small amount of curd with us. Because both of these are easily available and microbes are easily visible in them. The greenish colour visible on the bread is actually fungus. It's spores are present in the air, which keep growing in food items.

Habitat of Microbes : Microbes are omnipresent. These are found in the soil, water, air, inside our body and in other types of animals and plants. Where life is not possible by any means, such as deep inside geysers (thermal chimneys) where temperature reaches upto 100°C, deep in the soil, several meters below the ice layers and in highly acidic environments, they are found in such places. Microbes include various forms of protozoa, bacteria, fungi and microscopic plants (see figure).

Similar to bacteria and mostly fungi, microbes are grown on nutrient media so that they can grow and take the form of colonies and can bee seen with naked eye (see the figure given above). Such cultures are beneficial during microbial studies.

Bio-fertilizers : Microbes, that increase soil fertility, are called bio-fertilizers. Several nitrogen fixing bacteria like blue-green algae, root fungi etc. increase the fertility of the soil. Some of the important example are as follows :
1. Legume-Rhizobium Symbiosis : Rhizobium species residing in root glands of legume plants provide N2 in a usable form of to the plant.
2. Azolla-Anabaena Symbiosis : Azolla is an aquatic pteritophyte which grows on the surface of the water. Along with this, blue-green algae called Anabaena lives symbiotically and provides nitrate to the plants.
3. Free-living Cyanobacteria and Bacteria : Rivilaria and Nostoc (blug-green algae) and Chlostridium and Azobacter (free living bacteria) fix atmospheric nitrogen while living freely in the soil. Now-a-days efforts are being made to transfer the nitrogen fixing gene (Nif gene) of microbes to higher plants by application of biotechnology techniques.

Antibiotic and their sources :

S.No.	Antibiotic	Source
1	Clorotatracycline	Streptomyces orifices
2	Streptomycin	Streptomyces griseoves
3	Penicillin	Penicillium notatum
4	Cephalosporin	Cephalosporium acremonium
5	Cycloheximide	Streptomyces griseoves

Important microbes used in industries are as follows :
(1) Yeast (fungus)
(2) Fungi
(3) Bacteria
(4) Filamentous bacteria (Actinomycetes)
Microbes are used in the manufacture of following products :
(1) Alcoholic beverages
(2) Curd
(3) Antibiotic
(4) Organic chemical which include vitamins, steroid and enzymes (5) Biogas

Bt is a type of toxin. It is made from a bacteria called Bacillus thurigiensis (in brief Bt).
Bt toxin gets cloned from gene bacteria and get expressed in plants and creates resistance against insects (pests). As a result, there is no need to use pesticides. This is how biopesticides are manufactured, e.g. : Bt cotton, Bt corn, rice, tomato and potato etc.
Bt Cotton : Some breeds of Bacillus thuringiensis produce such proteins that are helpful in killing specific insects like lapidopterans (tobacco bud worm, soldier worm), coleopterans (beetles) and dipterans (flies and mosquitoes). Bt produces some toxic insecticidal proteins. Why does this toxin not kill the Bacillus? In fact, the Bt toxin protein, protoxin is in an active form, as soon as the insect eats this inactive toxin, alkaline pH changes it in its intestine. Due to this, they become soluble and get converted into active form. Active toxin bind to the surface of epithelial cells of the middle intestine and form holes in them due to which the cell swell and burst and as a result the insect dies.
The specific Bt toxin has been isolated from Bt and has been incorporated into many crops like cotton. The choice of genes depends on the crop and the specific pest. Whereas most Bt toxins depend on insect group specificity.

Spirulina is a member of blue-green algae. It can be used as a complete diet. Spirulina contains protein, carbohydrate, amino acid, vitamins, minerals, enzymes, fat and pigments. The speciality of protein present in spirulina is that it is excactly same as the body prepares for itself. It contains as much calcium as milk and 15 times more vitamin-A than carrots.

Differences between Viroids and Viruses :

S.No.	Viruses	Viroids
1	They are smaller than bacteria.	They are smaller than viruses.
2	They may have genetic substance RNA or DNA.	While they have only RNA.
3	They have a protein coating.	They don't have protein coating.
4	These cause the following diseas : AIDS, small pox etc.	While they cause a disease called potato spindle tuber.