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Class 9 SELINA Solutions Biology Chapter 9 - Economic Importance Of Bacteria And Fungi

Economic Importance Of Bacteria And Fungi Exercise Ex. 1

Solution A.1(a)

(i) they are unicellular and prokaryotic 

Solution A.1(b)

(ii) Streptomyces

Solution A.1(c)

(iii) Bacillus

Solution A.1(d)

(iii) Rhizobium 

Solution A.1(e)

(ii) Peptidoglycan 

Solution A.1(f)

(iii) Plasmid 

Solution A.1(g)

(iii) Binary fission

Solution A.1(h)

(iv) They do not have a well-defined nucleus enclosed in a nuclear membrane

Solution A.1(i)

(ii) Typhoid

Solution A.1(j)

(iv) Vaccines

Solution B.1

(a) Flagellum

(b) Tea curing

(c) Leather tanning

(d) Black rot

(e) Selman Waksman

Solution B.2


Solution B.3

(a) The first antibiotic penicillin was discovered by Alexander Fleming.

(b) Rhizobium bacteria is found living in the nodules on the roots of leguminous plants.

(c) The hormone insulin was the first substance produced by Escherichia coli.

(d) Pseudomonas is an example of denitrifying bacteria.

(e) Parasitic and saprotrophic are the two heterotrophic modes of nutrition in bacteria.

Solution B.4

(a) Nitrosomonas

(b) Nitrobacter

Solution C.1

Bacteria may be present in the air in the form of spores.

Solution C.2

Spore formation is not considered to be a form of reproduction in bacteria because bacteria reproduce only asexually through fission or cell division. Spore formation is simply a method of escaping unfavourable conditions.

Solution C.3

Bacteria are the most primitive, unicellular organisms that lack a well-defined nucleus. Their genetic material is in the form of a single chromosome dispersed in the cytoplasm without a nuclear membrane. They do not possess complex membrane-bound cell organelles such as chloroplasts, endoplasmic reticulum, and mitochondria, indicating a simpler cellular organisation.

Solution C.4

(a) Antibiotics are chemical substances produced by living microorganisms which can stop the growth of or kill some disease-producing bacteria and fungi.

(b) Antitoxin is a substance produced in animal bodies which reacts with the poison (toxin) produced by the invading germs.

(c) Serum is the clear liquid part of the blood that remains after blood cells and clotting proteins have been removed.

(d) Botulism is a serious food poisoning caused by a toxin produced by Clostridium botulinum often found in tinned and sealed foods.

(e) Pasteurization is a procedure in which packaged and unpackaged commodities (such as milk and fruit juices) are heated to 60°C for 30 minutes and then chilled quickly to kill the microorganisms and improve shelf life.

Solution C.5

(a) Bacterial diseases of cattle: Anthrax and Bovine tuberculosis

(b) Bacterial diseases in plants: Black rot of mustard and bacterial blight of cowpea

(c) Bacterial diseases in humans: Cholera and typhoid

(d) Nitrifying bacteria: Nitrosomonas and Nitrobacter

(e) Free living nitrogen-fixing bacteria found in soil: Azotobacter and Clostridium

Solution C.6

(a) TAB: Typhoid-Paratyphoid A and B

(b) BCG: Bacillus Calmette-Guerin

(c) DNA: Deoxyribonucleic acid

(d) GMO: Genetically Modified Organisms

Solution C.7

(a) It is critical to maintain every room dry and warm rather than fungus-infested and moist. Sunlight acts as a natural disinfectant. It keeps fungi away, and offers dryness to the walls, floor, and the room, and is thus helpful for the health of the human beings. Also, sunlight supplies vitamin D, which is necessary for bone growth and thus contributes to healthy living.

(b) Food that has been sealed or canned may not always be safe to eat as they may contain harmful bacteria like Clostridium botulinum, which may cause serious food poisoning resulting in botulism. In extreme cases, this condition may even prove to be fatal for life.

Solution C.8

(a) Differences between decay and putrefaction:


 (b) Differences between pasteurization and sterilization:


Solution C.9

Yes, bacteria would be present in an aquarium. The species found in the aquarium are Nitrosomonas and Nitrobacter. They aid in the elimination of ammonia and nitrates from the aquarium.

Solution D.1

Most bacteria depend on readymade food from different sources and thus, follow heterotrophic mode of nutrition.

Bacteria obtain their nourishment in the following ways:

(a) Saprotrophic nutrition- Bacteria draw nourishment from decaying dead organisms

(b) Parasitic nutrition - Bacteria obtain nourishment from the body of their hosts

Solution D.2

Uses of bacteria in industry:

(a) Bacteria are used in the production of vinegar and cheese, and in the processing of coffee and tobacco.

(b) Certain bacteria break down the soft perishable parts of skin (hide) and help in leather tanning.

Solution D.3

Antibiotics are chemical substances produced by living microorganisms which can stop the growth of or kill some disease-producing bacteria and fungi.

Examples - Penicillin and Streptomycin.

Solution D.4

A special category of soil bacteria (Rhizobium) are found living in small nodules on the roots of leguminous plant such as beans. These bacteria pick up free nitrogen from the soil atmosphere and convert it into soluble nitrates. These nitrates are used by the host plant and also by other plants sown later in the same soil. In this way, nitrogen of the atmosphere is converted to nitrates by leguminous plants.

Solution D.5

Denitrifying bacteria such as Pseudomonas present in the soil breakdown the soil nitrates to release nitrogen gas that enters the atmosphere.

Solution E.1



(i) Nitrification is process of conversion of ammonia or reduced nitrogen compounds into nitrates and nitrites with the help of nitrifying bacteria such as Nitrosomonas and Nitrobacter.

(ii) Denitrification is a process by which nitrates are converted back into atmospheric nitrogen by denitrifying bacteria such as Pseudomonas.

(b) Biological nitrogen fixation occurs when certain bacteria, such as Rhizobium, form a symbiotic relationship with leguminous plants and convert atmospheric nitrogen into a form that can be readily used by the plants. This process occurs naturally in the soil and forms an important part of the nitrogen cycle.

Industrial nitrogen fixation involves the use of high temperature and pressure to convert atmospheric nitrogen into ammonia, which can then be used to make fertilizers and other nitrogen-based products.

(c) Rhizobium bacteria form a symbiotic relationship with the leguminous plants. They live in the root nodules of these plants and convert atmospheric nitrogen into soluble nitrates which can be readily used by the host plant. In return, the plant provides the bacteria with carbohydrates and other nutrients.

Economic Importance Of Bacteria And Fungi Exercise Ex. 2

Solution A.1(a)

(ii) Yeast

Solution A.1(b)

(iiii) They prefer cold and dry conditions to grow 

Solution A.1(c)

(i) Ethyl alcohol

Solution A.1(d)

(iii) Yeast 

Solution A.1(e)

(iv) Agaricus bisporous 

Solution A.1(f)

(iv) Mycelium 

Solution A.1(g)

(ii) Saprophytic

Solution A.1(h)

(i) Glycogen and fat

Solution A.1(i)

(i) Absence of chlorophyll

Solution A.1(j)

(i) Ethanol or lactic acid

Solution B.1

(a) The specific genus to which several species of yeast belong is Saccharomyces.

(b) Yeast is a unicellular fungi.

(c) Alcoholics may develop body ailments like liver cirrhosis due to over consumption of alcohol.

(d) The curd from which moisture has been removed is termed as cottage cheese.

(e) Cheese is a good source of vitamin A and B.

Solution C.1

(a) Fermentation is a process in which microorganisms such as bacteria and yeast break down carbohydrates into simpler products such as ethanol or lactic acid in the absence of oxygen.

(b) Spawning is a step in the cultivation of mushrooms in which a mushroom seed consisting of mycelium of the selected type of mushroom is introduced into the compost and allowed to spread for a couple of days.

Solution C.2

Rhizopus is the common bread mould. It grows not only on bread, but also on a variety of organic matter such as paper, wood, cloth, animal dung, leather goods and food materials such as fruit, bread, pickles, chapati, etc. particularly in warm and humid climate.

Solution C.3

Chemical equation of fermentation:


Solution C.4

Vitamin B3 (niacin), Vitamin B5 (pantothenic acid) and Vitamin B7 (biotin) are the vitamins that are richly found in mushrooms.

Solution C.5

Role of certain fungi in industrial production:

  • Preparation of fermented foods and bakery products
  • Preparation of alcoholic beverages
  • Preparation of organic acids
  • Production of enzymes
  • Production of antibiotics
  • Producion of alcohol
  • Production of wine
  • Bread-making
  • Cheese making
  • Mushroom cultivation

Solution C.6

(a) Saprophyte and parasite



Obtains nourishment from dead and decaying organic matter

Obtains nourishment from the body of the living host

(b) Aerobic and anaerobic respiration with regard to products

Aerobic respiration

Anaerobic respiration

Products - Carbon dioxide (CO2), water (H2O) and energy (ATP)

Products - Ethanol (2C2H5OH), carbon dioxide (CO2) and energy (ATP)


Solution D.1

Role of yeasts in bakeries:

Yeast is a key ingredient in bakeries (bread making). Yeast added to the dough ferments sugar and produces carbon dioxide gas. This causes the dough to rise (leavening). When the dough is baked, the gas bubbles expand, giving a light, spongy texture to the bread.

Role of yeasts in breweries:

Yeast is also an important ingredient in brewery industry, especially in the production of wine and beer due to its property of alcoholic fermentation. Fermentation is the process in which microorganisms like yeast break down the carbohydrates into simpler products like ethanol or lactic acid. Grapes are crushed and fermented in large vessels with the help of yeast cells. Ethanol is produced at a concentration of about 12%. At this concentration, the yeast cells start getting killed, leaving wine behind.

Solution D.2

Major steps in the cultivation of common edible mushrooms:

(1) Composting: Composting involves mixing of various components such as wheat or paddy straw, chicken manure and organic and inorganic fertilizers in a fixed proportion. The temperature of compost is maintained at around 50C. The compost is kept undisturbed for about one week.

(2) Spawning: 'Mushroom seed' in the form of mycelium of mushroom to be grown is introduced into the heap of compost and left for spreading for around two days.

(3) Casing: Casing is the most important step of mushroom cultivation. It involves spreading of a thin layer of soil over the compost. This provides humidity and support to the mushroom. It also serves to prevent the desiccation of the compost heap and helps in temperature regulation at around 20C-25C to forbid the growth of pests and diseases. The provision for circulating air around the compost bed should also be made.

(4) Cropping and harvesting:Three major growth stages are observed, before mushrooms attain a fully grown form. Firstly, the mycelium, i.e. a network of fibrous mass, spreads out in 2 to 6 weeks, followed by the tiny pin head stage and finally the button stage, which is marked by an increase in the mushroom size, until it acquires marketable size.

(5) Preservation: Mushrooms have a very short shelf-life. Processes such as vacuum cooling, bombardment by gamma radiation, followed by storage at 15C, freeze drying in a solution of citric acid, ascorbic acid and brine, etc. are used for the preservation of mushrooms.

Solution D.3

Plants belong to the kingdom Plantae. They are multicellular and eukaryotic organisms. They contain chlorophyll with the help of which they prepare their own food and thus, follow autotrophic mode of nutrition.

Yeast and bacteria cannot be considered as plants because:

 They do not possess chlorophyll.

 They do not follow an autotrophic mode of nutrition.

 They are unicellular microorganisms.

 Yeasts are included under the kingdom Fungi while bacteria are categorized under the kingdom Monera.

Solution D.4

Although, both bacteria and yeast use asexual reproduction to produce offspring, the processes they use to do so differ due to variations in their cellular structure and growth pattern.

Asexual reproduction in bacteria:

Asexual reproduction in bacteria takes place through fission or cell division. The circular DNA duplicates. The cell expands and the two DNA are pulled apart. The cell constricts at the middle separating the two cells. Based on the type of bacteria, the two daughter cells may either remain attached or may separate from each other as independent cells.

Asexual reproduction in yeast:

Asexual reproduction in yeast takes place through budding. A tiny outgrowth called bud develops on the parent cell. The nucleus of the parent cell divides into a daughter nucleus, which migrates into the bud. The bud grows until it separates from the parent cell and becomes a new cell.

Solution E.1

(a) If bread was not covered with the bell-jar, moulds would have still appeared, but after some time. The warm and humid conditions inside the bell-jar promote rapid production of mould.

(b) Moulds do not grow below freezing point inside a refrigerator.

(c) Mycelia appear first on the bread.

Solution E.2

Structure of yeast cell


Solution E.3

(a) The organism is mould (fungi).

Common name: Bread mould

Scientific name: Rhizopus stolonifer

(b) 1 - Sporangium, 2 - Spores, 3 - Hyphae

(c) Two suitable habitats of bread mould are animal dung and leather goods.

(d) The main mode of reproduction in bread mould is asexual reproduction which occurs through spore formation.

(e) Extracellular digestion occurs in bread mould. The hyphae secrete certain enzymes which digest the food in the bread substratum and absorb it.

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