Class 12 Biology Chapter 10 Microbes in Human Welfare The answer to each chapter is provided in the list so that you can easily browse through different chapters Assam Board HS 2nd Year Biology Chapter 10 Microbes in Human Welfare Question Answer.
Class 12 Biology Chapter 10 Microbes in Human Welfare
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IV. Long Questions 5 Marks :
Q.1. What is sustainable agriculture? Discuss the role of biopesticides and biofertilizers in sustainable agriculture.
Ans : Sustainable agriculture means an agricultural practice in which the quality of soil is maintained without application of any external source of energy, fertilizer, pesticide etc. The productivity of soil is maintained as it is years after years by following natural practices like use of biofertilizers, biopesticides, crop rotation, conventional crop improvement method, suitable crop ecology and so on.
Role of Biopesticides : With the aim-of eradicating pest from crops the farmers use pesticides randomly. In that process not only the target pest die but also many non-target organisms also die. We know that all insects and such other organisms are not harmful. Only a few of them sometime cause harry. Generally in nature each type is counter balanced .by the other. So in a population no particular type gets predominance over the other, because one checks the other and thus there exl. population balance in an ecosystem. However, due to over utilization of ecosystem potentiality monocropping, eradication of host plants etc some pests have been eradicated giving space for others. In the absence of one the other gets predominance and become harmful for the crop. It is normal circumstances one counter balances the other and thus their population sizes remain controlled.
The chemical pesticides are not only harmful for non-target organisms but also to health human being, animal and the environment as a whole. Such chemical pesticides persist for ion in the environment as they breakdown slowly.
Bio-control of pest is a good option if used judiciously. The principle of bio-control! is that one organism is used against other in a judicious manner so that the one that cheeks the other does not in turn become a menace. For this purpose the mode of life and action of most such organisms must be studied in detail including their host, predisposing condition, life-cycle etc.
Role of Biofertilizer: In one hand the use and cost of inorganic fertilizer are on the rise and on the other hand the organic fertilizer becoming scarce day by day because the dung and agricultural waste are being used for
various other purposes. The production of inorganic fertilizer is limited by the dwindling energy resource such as petroleum and coal. The cost of production is also increasing day-by-day. Moreover the constant use of inorganic fertilizer on soil brings some adverse effect on the soil metabolic processes and ultimately renders the soil into a dead unproductive mass. In view of the above facts attention has been given to the use of such substances which in one hand increase fertility of the soil and on the other hand do not cause any adverse effect on the soil. This has led to the development of the idea of using biological processes for increasing fertility of the soil. This idea was existed since ancient time among farmers all over the world. Only in recent time the scientific basis of such belief has been explained and effort is being made to popularise the idea.
Q.2. What are organic acids? Give an account on different kinds of organic acids manufactured in the industry with the help of respective microbes.
Ans : An acid made up of molecules containing organic radicals; acetic acid, citric acid, which contain the ionizable – COOH group. Organic acids are manufactured both chemically and biologically. Here we mean organic acids manufactured using microorganisms. Some microorganisms have the ability to convert organic substances into organic acids by fermentation. For this purposes we need to supply appropriate raw materials, appropriate fermentation conditions, refining process etc. to obtain the products. The acids so obtained are comparable equally with the products obtained through chemical method and in some cases superior also. The advantage is that it is less costly use waste materials do not pollute the environment and is easy to operàte.
Some organic acids :
| Acids | Organisms |
| Citric acid | Aspergillus niger |
| Acetic acid | Acetobacter aceti |
| Butyric acid | Clostridium butylicum |
| Lactic acid | Lactobacillus delbrueckii |
3. Draw a diagrammatic sketch of a biogas plant and label its components.
Ans :
Q.4. Describe the main idea behind biological control of pests and diseases. Give at least two examples each from biopesticides and bioinsecticides.
Ans : Biological control of pests and disease arose from the fact that chemical pesticides, fungicides,bactericides are harmful to the non-target organisms which are beneficial to our agriculture. Moreover the chemicals are harmful to the environment in many ways. These chemical enter into human animal and microbial cells, through food chain and undergoes biomagnifications. In addition to all these the chemical pesticides etc. are costly also.
Aspects of Biological Controls :
(i) It control the pest effectively.
(ii) It is not polluting the environment.
(iii) It is easy to use.
(iv) It is a permanent method.
Bioinsecticides: Biostorm VBT.
Biopesticide : Trichoderma viridal Bacillus thuringiensis.
Q.5. In which way sewage can be harmful to us? Mention the principle of sewage treatment. Write the key differences found in between primary and secondary sewage treatment.
Ans: Sewage contain a large quantity of harmful substances such as disease causing germ, toxins chemicals, dirty matters, drainage materials from industries, factories, latrines and so on. These mix up with drinking water, as these find outlet into river, lakes and sometime tanks. Use of this kind of water is harmful.
Sewage Treatment: Sewage or waste water contain excreta, industrial and agricultural waste. It contain water and 0.5- 1% organic or inorganic matters. The solid remains, suspended cellulose, lingo cellulose proteins, fast etc. are found in colloidal form. The inorganic materials remain in dissolved state. Detergent, paints, toxic chemicals, cellulose matter etc. are discharged by industrial. Chemical fertilizer, pesticides, herbicides, animal excreta etc. are discharged due to agriculture operation. Sewage is a store house of pathogens. It is therefore necessary to treat the sewage before releasing. Removing harmful and polluting substances is difficult. However, microbial treatment can be done to clean it partially. The heterotrophic microbes are used which digest organ residue under aerated condition. The treatments are done in two stages –
(i) Primary Treatment: Primary treatment is the physical removal (1) of 20-30% organ materials present in sewage. This is done by screening precipitation of small particulate matter filtration and sedimentation. The sludge that form due to such treatment is removed and the required portion is piped into aeration tank for secondary treatment.
(ii) Secondary Treatment: It is a biological treatment done in aeration tank. A large variety of microbes remain present in it. Constant agitation cause aeration which help quicker decomposition of organic substances. A large number of aerobic microbes grow in the process. Sometime, filamentous microbes and bacteria together form a mesh like structure over the surface. With gradual consumption of organic materials, the number of microorganisms present in affluent reduced clue to reduced availability of organic substances. This lower the biological oxygen demand (BOD) of the affluent. More the number of microbes more will be the demand oxygen in the affluent. Till the BOD is significantly reduced the aeration of the tank continue.
Q.6. What are enzymes? Name some major enzymes used in industry and explain their importance.
Ans : Enzymes are proteinaceous substances of biological origin and catalyse the specific biochemical reactions. A number of enzymes have been commercially produced by the metabolic activities of microbes, especially different species of fungi.
Microbial source and use of enzymes.
| Enzyme | Microbial source | Usess |
| 1. Lipases | Candida lipolytica (fungus) laundry. Also used in | Used in detergents to remove the oil stains from the flavouring of cheese. |
| 2. Proteases and pectinases | Aspergillus niger (fungus) | For clarification of fruit juices. |
| 3. Streptokinase | Streptococcus (bacterium) | Used as a ‘clot buster’ to dissolve the blood clot in the blood vessels of the patients suffering from myocardia infarction, so is fibrinolytic. |
| 4. Glucose oxidase. | Penicillium chrysogenum | (Fungus) |
| 5. Invertase | Saccharomyces cerevisiae (yeast) | Hydrolysis of sucrose, so also called sucrase. |
| 6. α -Amylase | Rhizopus japonicus and R. oryzae (fungus) | Digestion of starch and preparation of soft centred candles.Also in softening and sweetening of bread. |
| 7. Dextran | Leuconostoc mesenteroides | Polymerization of simple sugars to form dextrins. |
Q.7. Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished.
Ans : The key role of fertilizers and their judicious use in crop husbandry is well understood, when one is familiar with the general facts about plant nutrition. Most of the plant nutrients, besides carbon, hydrogen and oxygen, originate from soil. The soil system is viewed by soil scientists as triple phase system of solid, liquid and gas. The use of fertilizers has caused short term increases in agricultural productivity. Use of fertilizers to the soil is an essential component of modern agricultural system.
Indian soils are usually very poor in organic matter as well as in nitrogen.Constant leaching (dissolution in water) and harvesting or crops deprive the soil of mineral contents. It is estimated that different agricultural crops in India remove above 4.27 million tonnes of nitrogen, 2.13 million tonnes of phosphoric acid, 7.24 million tonnes of potash and 4.88 million tonnes of lime every year.
The total consumption of fertilizers in India is about 9.2 Million tonnes and was expected to touch 20 million tonnes by the end to twentieth century. Fertilizers are inorganic materials containing elements in the form of soluble or readily available chemical compounds. In common parlance, the fertilizers are sometimes called chemical, artificial or inorganic manures. Green manures, biofertilizers and biological control methods have been introduced to combat the ill effects of agricultural chemicals.
The ill-effects of chemical fertilizers are:
(a) They are expensive.
(b) Their manufacture depends upon the dwindling resources of energy as petroleum and coal etc.
(c) Their production releases pollutants.
(d) They are lost readily when applied in field by surface run-off and thus pollute soil and other water resources.
Biofertilizers are organisms which can bring about soil nutrient enrichment. The main sources of biofertilizers are bacteria, cyanobacteria and fungi.
(i) Bacteria as N₂ fixers :
(a) Legume – Rhizobium symbiosis. At present the primary nutrient, limiting agricultural yields is nitrogen. Some plants are capable of producing more nitrogen than they consume. These plants show symbiotic relationship with nitrogen fixing bacteria, Rhizobium bacteria produce root nodules in leguminous plants. It has the capacity to fix free nitrogen. Root nodules of legumes differ considerably in shape and size. They may be spherical, elongated, flat etc.
(ii) Cyanobacterial as N₂ fixers. Some of the cyanobacteria (blue green algae) are important nitrogen fixers of rice fields. Nearly 40 species of blue green algae are known to fix nitrogen. These plants usually bear thick walled, hyaline heterocysts, which is thought to be the site of nitrogen fixation. Some of the nitrogen fixers are Anabaena, Nostoc, Aulosira. They derive their energy by photosynthesis. They are being widely used a biofertilizers in institutes like IARI, New Delhi and 20, 30 kg/ha of nitrogen is fixed by them.
(a) Azolla – Anabaena symbiosis. Among the symbiotic cyanobacteria (blue – green algae Anabaena azollae occurs as an end phyte in the leaves of Azolla pinnata which is free floating aquatic pteridophyte. It has the capacity to fix atmospheric nitrogen and excretes the nitrogenous compounds into the cavity of the fern.
(b) Anabaena cycadae lives in the coralloid roots of gymnosperm Cycas.
(c) Azolla and Nostoc (Cyanobacteria) are added in the agricultural fields to increase the rice yield by more than fifty percent.
It has been estimated that blue green algae can provide 7-8 lakh tonnes of fixed nitrogen, equivalent to 15-17 lakh tonnes of urea. Thus entire needs of nitrogen supply to rice crop can be provided through nitrogen fixed by blue-green algae. Further these nitrogen fixers are based on simple technology and bear low cost.
(ii) Mycorrhizae: It refers to symbiotic association between the fungus and roots of higher plants. These are more commonly found in oligotrophic soils. Mycorrhizae are formed by many members of genus Glomus. These can be classified into two types:
(a) Ectomycorrhizae: Here, fungal mycelia form mantle on root surface. From the mantle, fungal hyphae penetrate into cortex of (n) root as well as into the soil. This leads to increase in surface area for absorption of water and minerals (N,P and K). Fungal hyphae in soil further solubilize some insoluble organic compounds which are easily absorbed by plants. Ectomycorrhizae have been found in oaks, pines, Fagus and Eucalyptus. Plants with mycorrhizal roots are resistant to root-borne pathogens, tolerance to salinity and drought and with increased growth and development.
(b) Endomycorrhizae: Here, fungus does not form a mantle on root surface, instead it produces loosely interwoven hyphae. Some of these mycelia penetrate into soil. Still some other hyphae enter into cortex of root.
Endo mycorrhizae have been reported in certain orchids and woody plants. They are produced by septate as well as non-septate fungi. In the cortex hyphae grow intracellularly and some penetrate the cells to form vesicles or finally branched hyphal coils called arbuscules. Such association is also called vesicular arbuscular. Such association is also called vesicular-arbuscular mycorrhizae or VAM. VAM have shown their importance in phosphate nutrition of plants. Mycorrhizal are known to accumulate more nutrients per unit area of the host. Mycorrhizae association reduces the dependency on synthetic fertilizers and converts the marginal soil into a productive field.
Q.8. Discuss briefly what would happen if a large volume of untreated sewage is discharged into a river.
Ans : If untreated sewage is discharged into the river the following problems would happen :
(a) Excess of nitrates from fertilizers will increase in river water which will help in eutrophication.
(b) Organic pollutants like phenol, naphtha, proteins, cellulose, aromatic compounds will increase in water.
(c) Radioactive elements will increase in the water which may affect the aquatic animals.
(d) Cadmium mixing with water may result itai disease which may lead to the cancer of liver and bone.
(e) The water may have sand, clay, silt, etc. along with fecal water, bacteria, paper, fibers, etc. which are harmful for us.
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