Cbse Class 12 Biology Revision Notes Chapter 10

Q.1 Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answers. Biogas, Citric acid, Penicillin and Curd.

Ans

1. Penicillin- It is used to obtain antibiotic which is used to cure many serious bacterial disease.
2. Biogas- It is an ecofriendly source of energy/fuel in rural areas.

3. Citric acid- It is used mainly as preservative of many food items and turning milk into paneer.

4. Curd- It is easily digestible and helps in killing many disease causing microbes in the stomach.

Q.2 Expand LAB.

Ans

Lactic Acid Bacteria.

Q.3 What is an antibiotics?

Ans

An antibiotic is an organic compound produced by a microorganism that inhibits the growth or kills another microorganism.

Q.4 Find out the name of the microbes from which Cyclosporine A (an immuno suppressive drug) and Statins (blood cholesterol lowering agents) are obtained.

Ans

Cyclosporin A is produced by the fungus Trichoderma polysporum, and Statins is produced by Monascus purpureus.

Q.5 In which food would you find lactic acid bacteria? Mention some of their useful applications.

Ans

Lactic acid bacteria are found in curd. These bacteria convert lactose sugar of milk into lactic acid. Useful applications of lactic acid bacteria:

i) They increase the Vit.B₁₂ content of the food.

ii) Check growth of disease causing microbes in the stomach.

Q.6 Do you think microbes can also be used as source of energy? If yes, how?

Ans

Yes, microbes present in the activated sludge are digested anaerobically to generate an inflammable biogas which is used as the source of energy.

Q.7 What is the botanical name of baker’s yeast?

Ans

Saccharomyces cerevisiae.

Q.8 Expand the term BOD.

Ans

Biological Oxygen Demand.

Q.9 How do biofertilizers enrich the fertility of the soil?

Ans

Biofertilizers enrich the nutrient quality of the soil in the following ways;
Bacteria-They fix atmospheric nitrogen into the usable form by

(a) forming root nodules in the leguminous plants in symbiotic relationship, e.g., Rhizobium.

(b) free living in the soil, e.g., Azotobacter and Azospirillum.
Fungi- They form symbiotic relationship with roots called mycorrhiza.

Mycorrhizal fungal component absorbs phosphorus from the soil and passes this to the plant. These plants develops other qualities also like resistance to root born pathogens, tolerance to salinity, drought and overall increase in the growth and development of the plant.
Cyanobacteria- They are autotrophic microbes widely distributed in the soil, they fix atmospheric nitrogen, e.g., Anabena, Nostoc, Oscillatoria etc.

Q.10 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 labeled 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 400 mg/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?

Ans

1. Sample A, having BOD 20 mg/l, is secondary effluent discharged from sewage treatment plant.
2. Sample B, having BOD 8mg/l, is river water.
3. Sample C, having BOD 400 mg/l, is untreated sewage water.
So, untreated sewage water is most polluted.

Q.11 Name three enzymes of industrial importance.

Ans

Proteases, Amylases and Rennin.

Q.12 Give examples to prove that microbes release gases during metabolism.

Ans

The puffed-up appearance of dough used for making dosa and idli is due to the production of CO₂ gas. It shows that microbes release gases during metabolism.

Q.13 Bacteria can not be seen with the naked eye, 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 under a microscope, which sample would you carry and why?

Ans

A sample of curd may be taken to a lab to demonstrate the presence of microbes. Microbes present in the curd are lactic acid bacteria.

Q.14 Name some traditional Indian foods made of wheat, rice and Bengal gram.

Ans

Wheat = Bhatura
Rice = Idli and Dosa
Bengal Gram (Besan) = Dhokla

Q.15 In which way microbes have played major role in controlling diseases caused by harmful bacteria?

Ans

Antibiotics used to cure some of the harmful bacterial diseases are obtained from some other bacteria.

Q.16 Name any two species of fungus, which are used in the production of antibiotics?

Ans

i) Penicillium notatum ii) Aspergillus fumigatus

Q.17 What is sewage? In which way this can be harmful for us?

Ans

Sewage is the municipal waste-water, containing human excreta. It contains large amount of organic matter and microbes. The microbes are mostly pathogenic. Sewage water is treated in sewage treatment plant to make it less polluting. Due to less availability of such treatment plants, this sewage water is often discharged directly into rivers resulting into pollution and water- born diseases.

Q.18 What is the key difference between primary and secondary Sewage treatment?

Ans

Primary treatment is purely mechanical removing small and large particles through filtration and sedimentation. Secondary treatment is biological in which microbes play a major role.

Q.19 Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished?

Ans

The use of the chemical fertilizers in order to meet the ever-increasing demand of agricultural produce adds to the significant pollution. To avoid or to minimize pollution, it is necessary to switch to biofertilizers-practising organic farming.

Q.20 Find out the role of microbes in Single Cell Protein (SCP).

Ans

Single Cell Protein (SCP):- Due to population rise of animals and human at the fast rate, the agricultural production is not sufficient to fulfill the demand of food required. More than 25% of human population is suffering from hunger and malnutrition. Single Cell Protein is one of the solutions for this.
To get single cell protein, microbes are being grown on an industrial scale as source of good proteins. Microbes like Spirulina can be grown easily on materials like waste water from potato processing plants (containing starch), straw, molasses, animal manure and even sewage, to produce large quantities of single cell protein. It also helps in reducing environmental pollution.

Q.21 Find out the role of microbes in soil.

Ans

The most favorable habitat of microorganisms is soil where they occur in abundance. Their geatest amount (1000000 per cu cm) is found generally in the top layer of the soil up to a depth of 5 to 15 cm.The microorganisms present in the soil increases the fertility of the soil by decomposing organic matter and by fixing the free nitrogen in the usable form.

Q.22 The doctor injects humulin injection to patient ‘B’ at regular intervals, but not to patient ‘A’ though both of them have inappropriate level of glucose in their bloodstreams.

Based on the given information, try to answer the following questions:

1. Why does only patient ‘B’ require humulin injection?
2. Prior to injection, which patient will have higher level of C-peptide?
3. Post injection, what will be the change in the level of C-peptide?

Ans

1. Patient ‘B’ is suffering from hyperglycemia in which there is not enough insulin in the blood. Therefore, he requires humulin injection.
2. Prior to injection, patient ‘A’ will have higher level of C-peptide in blood as he is suffering from hypoglycemia. In hypoglycemia, the level of insulin is more as compared to that of hyperglycemia. Hence, the level of C-peptide is also more.
3. Post injection, the level of insulin will increase in patient ‘B’ also and so the level of C-peptide.

Q.23 A specific diagnostic technique ‘X’ is used to determine the exposure to HIV virus. It uses an enzyme linked to an antibody or antigen as a marker for detection of a specific protein, especially an antigen or antibody.

Based on the given information, answer the following questions:

1. Identify the diagnostic technique ‘X’.
2. How is infection detected by the technique ‘X’?
3. Name any other technique which can be used to detect the presence of HIV virus.

Ans

1. The diagnostic technique ‘X’ is ELISA.
2. In ELISA, infection by a pathogen is detected either by the presence of antigens or by the antibodies synthesised against the pathogen.
3. PCR is another technique which can be used to detect the presence of HIV virus.

Q.24 Elsa used a chopping board to chop raw chicken; simultaneously she chopped other vegetables also on it. Her husband came and advised her to wash it before chopping other vegetables on the same board. What could be the possible implication behind such advice?

Ans

Raw chicken is the source of bacterium Campylobacter, which is often found in chicken and unpasteurised dairy products. Chopping board used to cut the raw chicken should be thoroughly washed before chopping other food items on it to prevent the transmission of bacteria to other food items. So, good food hygiene when handling raw poultry prevents the spread of bacteria to other food items.

Campylobacter is one of the most common causes of food poisoning. It is killed through cooking and its reproduction can be prevented by storing chicken at less than 4⁰C.

Q.25 When Jack opted for organ transplantation; the doctor prescribed him Cyclosporin A. How does a medicine of microbial origin help in survival of transplanted organ?

Ans

In organ transplantation, the body’s white blood cells try to reject the transplanted organ. So, Cyclosporin A, an immunosuppressive agent, is prescribed under this situation that suppresses the immune system so that the patient’s body can accept the foreign organ easily.

It is given along with a steroid to prevent the body from rejecting a transplanted organ like kidney, liver or heart.

Q.26 In a birthday party, a group of teenagers drank liquor in large amount. After some time, they started vomiting, felt muscle cramps and even one of them got unconscious.

(i)What went wrong there?

(ii)Can it be fatal?

Ans

(i) Fermented beverages include wine, beer, whisky, rum, etc. Saccharomyces crevisiae, also known as “brewer’s yeast”, is used for fermenting fruit juices and malted cereals to produce ethanol. Fermented beverages can be harmful to nervous system and brain when taken in large amount.

Since the teenagers drank liquor in large amount, their nervous system got affected due to which, they started vomiting, felt muscle cramps and became unconscious.

(ii) Yes, it can be fatal. Methanol is often used to adulterate these ethanol drinks that can be fatal.

Q.27 Tina decided to prepare curd at home. So, she took a little inoculum and put it into milk and kept the bowl in the refrigerator. Her mother suggested her to keep the bowl outside the refrigerator, but she denied.

i) What is the significance behind adding small amount of inoculum into milk?

ii) In the given situation, who is right? Justify your answer by giving a valid reason.

Ans

i) Small amount of curd (inoculum) contains millions of Lactic Acid Bacteria (LAB). At optimum temperature, these bacteria multiply and convert the milk into curd by producing lactic acid.

ii) In the given situation, the mother is right. Curd is formed by the action of Lactobaccilus spp. These bacteria grow at an optimum temperature of 30⁰ to 40⁰ C.

Inside the refrigerator, the temperature is very low. This does not allow the multiplication of bacteria and hence; prevents curdling of milk.

Q.28 Lisa was suffering from TB. The doctor prescribed her some antibiotics such as Streptomycin, Isoniazid, Rifampicin strictly for nine months.

After few months, the clinical symptoms of TB disappeared, so she stopped taking medicines. After sometime, similar symptoms reoccurred. So, Lisa started taking the same medicines as prescribed earlier. But these were no longer effective.

i) Why were these antibiotics not effective against reoccurrence of similar symptoms?

ii) Why does TB require antibiotics for a long time?

Ans

i) When the similar symptoms of TB re-appeared, the same antibiotics became ineffective because improper use of antibiotics made the bacteria resistant to them. Consequently, such bacteria resulted into multidrug-resistant TB.

ii) Antibiotics work when the bacteria are actively dividing. Bacteria of tuberculosis grow and divide very slowly. Hence for the treatment to be effective, patient needs to take antibiotics for a longer time.

Q.29 When we take an uprooted bean plant and wash its roots, we observe some node-like structures present on them.

(i) What are these structures?

(ii) Are they present in all plants?

(iii) Are they beneficial or harmful to plants? Justify your answer.

Ans

(i) These nodes-like structures present on roots are called root nodules in which Rhizobium bacteria are present.

(ii) These nodules are present in leguminous plants only. For example: pea, beans, etc.

(iii) They are beneficial for plants because in these nodules, a bacteria called Rhizobium is present that help in converting the atmospheric nitrogen into nitrates. Nitrate is the major source of nitrogen for plants. Nitrogen is an essential component of protein. Nitrate is the compound of nitrogen which increases the fertility of the soil.

Q.30 Jack wanted to save his crop from plant diseases and pests, but he was not ready for chemical pest control method as these chemicals are toxic and extremely harmful for us as well as for environment.

(i) Do you agree with him?

(ii) How can he save his crop without using chemicals?

(iii) Is this method beneficial over chemical method?

Ans

(i) Yes, chemicals used in chemical pest control method are toxic and extremely harmful for us as well as for environment.

(ii) He can save his crop from pests and diseases by using biological method as this method relies on natural predation rather than introducing chemicals.

(iii) Biological method is better than chemical method because it is an eco-friendly method which does not cause any type of pollution in environment.

Q.31 Many microbes are useful for human as well as for environment. Justify the given statements by giving reason to support your answer.

(i) Nitrate and phosphate fertilisers are added to encourage the breakdown of the crude oil spills by the bacteria.

(ii) In bread making, dough is left at warm place.

Ans

(i) Crude oil spills at sea level contain many harmful chemicals that harm the marine environment. Most petroleum hydrocarbons are biodegradable under aerobic conditions. Many microbes are able to oxidise harmful hydrocarbons and break down the oil. To increase the number of bacteria and speed up this process, nitrate and phosphate fertilisers are added to encourage the breakdown of the crude oil spills by the bacteria.

(ii) In bread making, Yeast converts the sugar into carbon dioxide and ethanol.

Wheat dough is left at warm place for a time being to allow the Yeast to feed on sugar and reproduce at its optimum temperature. On baking, the dough rises as the carbon dioxide becomes trapped between the gluten fibres of the wheat and ethanol is released.

Q.32 Biogas is a type of biofuel that is naturally produced from the decomposition of organic waste. In villages, its production is increasing gradually.

(i) Which microbe is involved in the production of biogas?

(ii) Is it aerobic or anaerobic?

(iii) How is it helpful to combat global warming?

(iv) How does biogas prevent respiratory diseases?

(v) Industrial biogas plants are more suitable for rural areas. Why?

Ans

(i) Methanobacterium present inside the rumen of cattle digests the cellulose present in grass, so its dung is rich in this bacterium. This dung is used to generate biogas in a biogas plant.

(ii) The decomposition of organic waste happens in an anaerobic environment thus; the process of producing biogas is also known as anaerobic digestion.

(iii) Biogas is a renewable, non-polluting as well as clean source of energy. No combustion takes place in this process that means there is zero emission of greenhouse gasses into the atmosphere; therefore opting this method is actually a great way to combat global warming.

(iv) Cooking on a gas stove, instead of over an open fire prevents the family from being exposed to smoke in the kitchen. This helps to prevent deadly respiratory diseases.

(v) Industrial biogas plants should be set up where raw materials like dung, food waste, and manure are in plentiful supply. For this reason, biogas generation is much more suitable for rural and suburban areas in comparison to urban areas.

Q.33 An industry ‘X’ has hired you to work on Myozyme, an Ɑ-glucosidase used to treat Pompe disease.

Myozyme is produced in mammalian cells. Suppose, presently, the cell density and product titer are very low and your colleagues are unable to find out how to develop a serum-free medium that will improve the production of Myozyme.

a) Share your strategy for developing a medium that fulfils the nutritional requirements of the cell.

b) Suppose you observe that the addition of ammonium chloride induces the production of Myozyme at a certain cell density. Unfortunately, this production facility got contaminated because your colleagues took samples directly from the reactor. How would you measure the cell density in the medium without taking a sample from the reactor?

Ans

1. The suggested strategy for developing a medium that fulfils the nutritional requirements of the cell is as follows:

1. Identify the amount of nutrients depleted by analysing the spent medium.
2. Identify further nutrients required by considering the metabolic pathways.
3. Add each component and determine its maximum non-inhibitory concentration.
4. Continue adding additional nutrients until the combination leads to the increase in growth and product expression.

2. To measure the cell density in the medium without taking a sample from the reactor:

Before culture:

• Measure volumetric oxygen transfer coefficient (kLa) of bioreactor.
• Measure qO₂ with the help of a respirometer.

During culture:

• Measure PO₂^G with the help of a flow meter on inlet gas stream.
• Measure PO₂^L with the help of a dissolved oxygen probe.

Q.34 Ashley is an entrepreneur for commercial production of protein ‘X’ in a liquid medium. He wants to know the answer of following questions:

1. Size of the air bubbles in a lab scale reactor is mainly determined by

1. agitator speed.
2. viscosity of the broth.
3. volume of the broth.
4. pH of the broth.

2. If the volume of the reactor is more, mixing time increases because of increase in the

1. turbulence.
2. flow rate.
3. viscosity.
4. circulation time.

3. In case of fungal fermentations, cells in the large reactors are

1. evenly aerated.
2. better aerated near edges of the reactor.
3. better aerated at the centre of the reactor.
4. better aerated at the bottom rather than top.

Ans

1. (i) agitator speed
2. (iv) circulation time
3. (iii) better aerated at the centre of the reactor

Q.35 With the advent of science and technology, the manufacturing of variety of fermented food items has increased. Many fermentable food items are good for our health; however some people may suffer from severe health problems like gas, bloating, constipation, burping and abdominal cramping, etc., after consuming them.

Based on the crisp information given, answer the following questions:

1. What is special about fermented food items that they create such health problems for some people?
2. How a new advancement in science and technology has found a solution to this problem?

Ans

1. Fermented food items contain the carbohydrates of short chain length, which are usually not absorbed completely by the body, highly osmotic and quickly fermented by the bacteria present in the large intestine. These factors increase the concentration of water and gas in the bowel and create such health problems in some people.
2. The low fermented diet, also called the low FODMAP diet (Fermentable Oligosaccharides, Disaccharides, Monosaccharides and Polyols), is a solution to this problem.

Q.36 Below given are the process of manufacturing of two commercial products ‘X’ and ‘Y’ as directed by FAO from soy.

Examine the two flow charts (I and II) and answer the following questions:

1. Fill the blanks (a), (X), (b) and (Y) in the flow chart
2. Which one of them is a fermented product? Support your answer with a reason.
3. Which among the two products ‘X’ and ‘Y’ is more nutritious?

Ans

• (a): Rhizopus oligosporus
• (X): Tempeh
• (b): Coagulant (CaSO₄.2H₂O)
• (Y): Tofu

2. Product ‘X’ (Tempeh) is a fermented product as it has required an inoculum of a fungal strain (Rhizopus oligosporus) in order to carry out fermentation.
3. Product ‘X’ (Tempeh) is more nutritious as compared to that of product ‘Y’ (Tofu) because. it contains more proteins, dietary fibres and vitamins. Moreover, it has less fat and is less processed.

Q.37 The doctor injects humulin injection to patient ‘B’ at regular intervals, but not to patient ‘A’ though both of them have inappropriate level of glucose in their bloodstreams.

Based on the given information, try to answer the following questions:

1. Why does only patient ‘B’ require humulin injection?
2. Prior to injection, which patient will have higher level of C-peptide?
3. Post injection, what will be the change in the level of C-peptide?

Ans

1. Patient ‘B’ is suffering from hyperglycemia in which there is not enough insulin in the blood. Therefore, he requires humulin injection.
2. Prior to injection, patient ‘A’ will have higher level of C-peptide in blood as he is suffering from hypoglycemia. In hypoglycemia, the level of insulin is more as compared to that of hyperglycemia. Hence, the level of C-peptide is also more.
3. Post injection, the level of insulin will increase in patient ‘B’ also and so the level of C-peptide.

Q.38 Emma’s mother got eye bags around her eyes. She thought that harmful UV rays have affected her mother’s skin and this might symptomise skin cancer.

When she took her to the doctor, the doctor prescribed her a drug which was extracted from yeast strain.

Based on the given information, answer the following questions:

1. Was Emma’s assumption correct?
2. The drug prescribed to her mother is possibly extracted from which microorganism?
3. Write the possible mechanism involved in the mode of action of the drugs.

Ans

1. No, Emma’s assumption was wrong. Her mother had high level of cholesterol in her blood, due to which doctor had prescribed a drug with statins.
2. Statins are extracted from yeast Monascus purpureus.
3. Statins act by competitively inhibiting the enzyme responsible for cholesterol synthesis. Statins resemble mevalonate and is a competitive inhibitor of ß-hydroxy-ß-methylglutaryl CoA reductase.

Q.39 Many proteins are modified post-transnationally by adding carbohydrates or lipids in order to increase their value to humans.

Many proteins, valuable for humans, contain carbohydrates or lipids which are added to the primary translation products.

1. Can bacteria be used for this purpose? Support your answer with a reason.
2. Is any approach of biotechnology applicable such protein production? If yes, mention the approach and elaborate it.

Ans

1. No, bacteria cannot be used for this purpose as they do not contain those specific enzymes required to add carbohydrates or lipids to the primary translation products.
2. Post-transnationally modified proteins can be produced either in transgenic eukaryotic cells growing in a culture medium or in transgenic organisms (plants or animals). Principally, this approach can be applied to produce any protein of interest.

Q.40 10 mL of wastewater was diluted to 350 mL distilled water. Initially, dissolved oxygen (Do) was found to be 10 mg/L, and after 5 days, it became 6 mg/L at DO after 5 days at 20°C.

Calculate the BOD of wastewater after 5 days (BOD₅) and the final BOD.

6 ml of wastewater is diluted to 300 ml distilled water in standard BOD bottle. Initial

DO in the bottle is determined to be 8.5 mg/l. DO after 5 days at 20 C is found to be 5 mg/l.

Determine BOD5 of wastewater and compute the ultimate BOD.

Ans

BOD₅ = [(DO₀– DO₅)/ V_w] X [V_w + V_d]

= [(10-6)/10] X [350]

= [4/10] X 350

= 140 mg/ L

Since BOD_t = BOD_u (1- e^-kt) at any particular temperature

BOD_u = [BOD₅]/ (1- e^-5k) = 140/ (1- e^-5X0.23)

= 140/ 0.683

≈ 205 mg/ L