Economic Importance Of Bacteria And Fungi 5rcf

Question Bank Economic Importance of Bacteria And Fungi 1. Name the sciences which deal with the study of bacteria and fungi. Ans. Study of bacteria — Bacteriology Study of fungi — Mycology. 2. Where can we find bacteria? Ans. Bacteria are distributed widely in air, water and land. They are found in (i) intestine of animals, (ii) decaying plant and animal bodies, (iii) hot springs and snow (only a few species). 3. Draw a diagram showing the detailed structure of a bacterium. Ans.

Bacterium

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Differentiate between : (i) Parasite and Saprophyte. (ii) Aerobic and Anaerobic respiration. (iii) Bacteria and Fungi. Ans. (i) Differences between Parasite and Saprophyte (Both are heterotrophs) Parasite 1. Parasites obtain their food from other living organisms. 2. They live on or inside the bodies of living organisms and do not secrete enzymes.

Saprophyte They derive their food from dead and decaying plants and animals. They secrete enzymes to dissolve the food material.

(ii) Differences between Aerobic and Anaerobic respiration 1. 2. 3. 4.

Aerobic respiration Takes place in the presence of oxygen. Complete breakdown of food molecules takes place. More energy is released (683 kcals per mole of glucose). By-products are CO2 and H2O.

Anaerobic respiration Anaerobic respiration takes place in the absence of oxygen. Partial breakdown of food takes place. Less energy is released (50 kcals per mole of glucose). By-products are ethyl alcohol and CO2.

(iii) Differences between Bacteria and Fungi 1. 2. 3.

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Bacteria They are unicellular. They are prokaryotes. They are mostly heterotrophic; some are autotrophic (photosynthetic and chemosynthetic bacteria). No hyphae present.

5. Commonly reproduce asexually by binary fission.

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Fungi They are uni- or multi-cellular. They are eukaryotes. They are heterotrophic.

Plant body consists of thin microscopic filaments called hyphae. Asexual reproduction is found commonly by spore formation.

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5. Name different kinds of bacteria. Ans. Different kinds of Bacteria — (i) Rod-shaped — Bacilli (ii) Spherical — Cocci (iii) Spiral-shaped — Spirilli (iv) Short incomplete spirals — Vibrio. 6. How do bacteria (i) respire and (ii) obtain food. Ans. (i) Respiration: Many bacteria use oxygen in their respiration process and are called aerobic bacteria, while others obtain their energy by breaking down complex food substances in the absence of oxygen. Such bacteria are called anaerobic bacteria. During aerobic respiration, complete breakdown of food molecules takes place resulting in the production of more energy in comparison to anaerobic respiration. During anaerobic respiration, partial breakdown of food takes place releasing less energy. The by-products are ethyl alcohol and CO2. C6H12O6 + 6O2 → 6CO2 + 6H2O + 683 Kcal (Aerobic pathway) C6H12O6 → 2C2H5OH + 2CO2 + 50 Kcal (Anaerobic pathway) sugar (ii) Food : (a) Autotrophic nutrition : Certain bacteria contain chlorophyll (bacteriochlorophyll) which enables the bacteria to manufacture their own food. Such bacteria are called photosynthetic bacteria. There is another category of autotrophic bacteria. These bacteria obtain energy by oxidising inorganic compounds and are called chemosynthetic bacteria. (b) Heterotrophic nutrition: Bacteria lacking chlorophyll are dependent on other organisms for their food, and are called heterotrophic bacteria. These bacteria may be saprophytic or parasitic. Saprophytic bacteria derive their food from dead and decaying organic matter of plants and animals. They secrete enzymes to dissolve the food Biology Class-IX

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material. Parasitic bacteria obtain their food from other living organisms. They live on or inside the bodies of living organisms. 7. Explain the following : (i) Nucleoid (ii) Chemosynthesis (iii) Extracellular digestion (iv) Prokaryotic cell (v) Antibiotics (vi) Pasteurization (vii) Mycelium (viii) Botulism Ans. (i) Nucleoid — In prokaryotic organisms like bacteria, nuclear material is not enclosed in a nuclear membrane. Such a structure lacking the nuclear membrane is called the nucleoid or incipient nucleus. (ii) Chemosynthesis — Synthesis of food by autotrophic bacteria by using energy from the oxidation of inorganic compounds is called chemosynthesis. (iii) Extracellular digestion — In Mucor and Rhizopus, nutrition is obtained saprophytically from the organic matter. The hyphae of these fungi secrete enzymes which convert complex food into simpler and soluble form. The food in this form is absorbed by the hyphae. Since the digestion takes place outside the cell, it is called extracellular digestion. (iv) Prokaryotic cell — It is a primitive cell in which true nucleus and cell organelles are lacking, as in bacteria. (v) Antibiotics — These are chemicals produced by microorganisms like bacteria which inhibit growth of other microorganisms. (vi) Pasteurization — It is a method of sterilization of milk and other drinks by heating at temperature below boiling point to destroy bacteria, for example, milk is pasteurized by heating at 62°C for 30 minutes. (vii) Mycelium — Mycelium is the filamentous mass which comprises the fungal thallus. Individual filament of mycelium is called a hypha. Biology Class-IX

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(viii) Botulism — Botulism is the food poising caused by the infection of Clostridium botulinum. 8. Explain briefly the role of bacteria in nitrogen cycle. Ans. Role in Nitrogen cycling Nitrogen is an important element for all living organisms. The free atmospheric nitrogen, however, cannot be used by animals and most of the plants. Only the nitrogen-fixing bacteria and blue-green algae have the ability to fix it into suitable compounds which can be utilized by other plants. Animals obtain their nitrogen requirements from the green plants in the form of proteins and amino acids.

Nitrogen cycle

Plants and animals after their death undergo decomposition. The ammonifying bacteria convert the dead organic matter into ammonia. In the soil, ammonia is converted into ammonium compounds. The nitrifying bacteria convert the ammonium compounds first into nitrites and finally the nitrites are converted into nitrates. The process of converting animal and plant proteins into ammonia and other simpler nitrogenous compounds like nitrites and nitrates is known as nitrification. At the same time, another group of bacteria called the denitrifying

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bacteria transform the nitrates to free atmospheric nitrogen. This process is called denitrification. The process of conversion of atmospheric nitrogen into various nitrogeneous compounds, and final release of free nitrogen to the atmosphere constitutes the nitrogen cycle. 9. Explain the role of bacteria in (a) Nitrification and (b) Nitrogen fixation. Ans. (a) Role of bacteria in nitrification Bacteria play an important role in nitrogen cycle through the processes of ammonification, nitrification and denitrification. Nitrification follows ammonification, and involves the action of nitrifying bacteria in two steps— Ammonium compounds → Nitrites → Nitrates Nitrogen in the form of nitrates is taken up by the plants from the soil. (b) Role of bacteria in Nitrogen fixation Nitrogen fixation : The process of converting free atmospheric nitrogen into suitable forms like nitrates which can then be used by plants is called nitrogen fixation. Certain bacteria are helpful in the fixation of atmospheric nitrogen. Bacteria like Azotobacter and Clostridium are present in the soil and fix elemental nitrogen from the atmosphere. Species of Rhizobium bacteria are present in the root nodules of leguminous plants, and they also increase the nitrogen content of the soil by fixing the atmospheric nitrogen. This is known as symbiotic nitrogen fixation.

Root nodules in a leguminous plant. Biology Class-IX

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10. Name the substances that make the cell wall of a fungus. Ans. Cell wall of a fungus is mainly composed of chitin. In addition, cellulose may be present. 11. Give three distinguishing features of fungi. Ans. Characters of Fungi (a) They lack chlorophyll. (b) The plant body consists of thin microscopic filaments called hyphae. (c) Chitinous cell wall is present. (d) Nutrition is heterotrophic — parasitic or saprophytic. 12. Give two differences between a fungal cell and the cell of a green plant. Ans. Differences between Fungal cell and Cell of a green plant Fungal cell 1. It lacks chlorophyll. 2. Cell wall is chitinous.

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Cell of a green plant It contains chlorophyll. Cell wall is cellulosic.

Label the parts marked 1, 2, 3 and 4 in the figure shown below.

Ans. 1. Sporangium 2. Sporangiophore 3. Stolon 4. Rhizoidal hyphae (or rhizoids).

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14. List three harmful effects each of bacteria and fungi. Ans. Harmful Effects of Bacteria A. Spoilage of Foodstuffs Cooked food, fruits, vegetables, butter, fish and meat are spoiled by bacteria, particularly during summer months by causing putrefaction of food materials. Certain bacteria like Salmonella typhimurium and Clostridium botulinum cause severe type of food poisoning when bacteriacontaminated food is consumed. Clostridium botulinum causes food poisoning commonly known as botulism. B. Reduction of Soil fertility Certain species of anaerobic bacteria inhabit soils which are either water-logged or have high organic matter content. These bacteria reduce soil fertility by depleting the nitrogen content of the soil. They break down nitrates present in the soil and release free nitrogen which escapes into the air thereby reducing soil fertility. C. Diseases in animals, man and plants (a) Animal diseases Bacteria cause tuberculosis of cattle, anthrax of sheep, chicken cholera and pneumonia in horses, sheep and goats. (b) Human diseases Many serious diseases are caused by bacteria in human beings. Some of these are as follows: Disease Bacterium Cholera Vibrio cholerae Diphtheria Corynebacterium diphtheriae Diarrhoea Bacillus coli Leprosy Mycobacterium leprae Plague Pasteurella pestis Tetanus Clostridium tetani Tuberculosis Mycobacterium tuberculosis Biology Class-IX

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Pneumonia Streptococcus pneumoniae Typhoid Salmonella typhii (c) Plant diseases A number of plant diseases are induced by bacteria. They cause leaf spots, soft rots, vascular diseases, bacterial galls. Harmful Effects of Fungi A. Human diseases A number of skin diseases are caused by several species of fungi. High fever and allergies also result from fungal infection. Athelete’s foot is a fungal infection between the toes. B. Plant diseases Diseases like white rust of crucifers, blight of potato, powdery mildews, rusts in wheat and smuts in maize, wheat and other cereal crops are caused by fungi. C. Spoilage of Food Penicillium, Aspergillus and moulds like Mucor and Rhizopus cause food spoilage. 15. (i) How can we protect food from bacterial contamination? (ii) Name four chemicals used as food preservatives. Ans. (i) Food can be protected from bacterial contamination by the following methods: (I) High Temperature (Sterilization) The food articles are steamed at 120° to 126°C under 15 Ibs pressure for 12 to 90 minutes. During this period bacteria, their endospores and all other living organisms are killed. This method is used in canning foods. (II) Pasteurization This method was first used by Louis Pasteur in 1866. There are two practices — (i) the low-temperature method where milk is heated to 145°F (62.8°C) for 30 minutes, and (ii) high-temperature method where milk is heated to 161°F (71.7°C) for 15 seconds. The above Biology Class-IX

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treatment kills bacteria. The finished product is stored at low temperature to retard the growth of microorganisms which survive pasteurization. (III) Low temperature storage The food substances kept in the refrigerator (5°C) and freezer (–5°C) remain unspoiled for a long period. Low temperature does not kill the bacteria but reduces their metabolic activities and growth to the negligible. In cold storage the temperature is about –10°C to –18°C at which bacterial activities are completely inhibited. Some of the bacterial cells are even destroyed while endospores remain alive but inactive. Biochemical processes like respiration, are at their lowest. Vegetables, juices of fruits, eggs, meat, fish etc., can be preserved by this method. (IV) Dehydration Dehydration of meat, fish, vegetables, fruits, etc. reduces the water content of these articles and thereby the bacterial growth is completely checked. Reduction of water content to 10% checks bacterial growth. (V) Preservatives Pickles, jams, jellies, etc., can be preserved by adding salt or sugar. By doing so bacteria get plasmolysed and subsequently killed. In this way these food articles can be preserved from bacterial contamination. Chemical preservatives such as ascorbic acid, sodium benzoate, benzoic acid and propionic acid are commonly used as preservatives. (ii) Ascorbic acid, sodium benzoate, benzoic acid and propionic acid. 16. Name two diseases each caused in animals and plants by (i) bacteria and (ii) fungi. Ans. See answer to Q. 14 above.

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17. Why is it dangerous to use contaminated food? Ans. Bacteria and fungal moulds (like Penicillium, Aspergillus, Mucor and Rhizopus) often contaminate and spoil food. Consuming such contaminated food can cause food poisoning. 18. List four uses each of the following : (a) bacteria and (b) fungi. Ans. (a) Uses of Bacteria A. In Industry A large number of products are obtained due to bacterial activity. (i) Formation of curd : Milk is converted into curd by bacterial action in which lactose of the milk is converted into lactic acid. Sour taste of the curd is due to the formation of lactic acid. (ii) Curing of cheese : Bacteria help in producing cheese of a particular flavour. (iii) Curing and ripening of tea and tobacco leaves is carried out by bacteria to produce special flavours. (iv) Leather Industry : Certain species of bacteria are used in the preparation of leather from hides and skins of animals. B. In Medicine Some bacteria have been exploited to produce antibiotics. Antibiotics like terramycin, streptomycin, tetracycline, aureomycin, neomycin are obtained from different bacterial species. C. In Maintenance of Environmental Balance Bacteria decompose the complex organic substances to simpler substances like carbon dioxide, nitrate, sulphate etc. Bacterial activity results in the return of the nutrients to the soil and gases to the atmosphere, thereby playing an important role in the recycling of materials, and increasing soil fertility.

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D. Nitrogen fixation and soil fertility Certain bacteria are helpful in fixation of atmospheric nitrogen. Bacteria like Azotobacter and Clostridium are present in the soil and fix elemental nitrogen from the atmosphere. Species of Rhizobium bacteria, present in the root nodules of leguminous plants, increase the nitrogen content of the soil by fixing atmospheric nitrogen. This is known as symbiotic nitrogen fixation. Nitrogen fixation : The process of converting free atmospheric nitrogen into suitable forms like nitrates which can then be used by plants is called nitrogen fixation. (b) Uses of Fungi A. As Food (i) A number of mushrooms are edible. Being rich in proteins and vitamins, they have high nutritive value. (ii) Dried yeasts contain about 50% protein and are rich in vitamins of the B group. B. In Medicine (i) A number of antibiotics are obtained from fungal species. Antibiotics are substances produced by microorganisms like bacteria and fungi which inhibit or kill other microorganisms. The first antibiotic penicillin was obtained from a fungus Penicillium notatum by Alexander Fleming in 1928. (ii) A powerful abortifacient is obtained from a fungus, Claviceps purpurea. C. In Agriculture Soil fertility : Saprophytic fungi decompose the dead remains of plants and animals returning the locked up mineral elements to the soil, making soil fertile.

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D. In Industry Different fungi find use in following industries : (i) In bakeries, yeast is used for baking of bread. (ii) In breweries, yeast and Aspergillus niger are used for alcohol production. (iii) Species of Penicillium and Aspergillus are used for flavouring cheese. (iv) In chemical industries, species of Mucor, Rhizopus, Penicillium and Aspergillus are used for the manufacture of organic acids such as lactic acid, citric acid and oxalic acid. 19. Mention whether the following statements are True (T) or False (F) : (i) Bacteria are very small unicellular organisms which multiply by fission. (ii) Rod-shaped bacteria are called cocci. (iii) Bacteria are prokaryotic in organization. (iv) The bacterium Rhizobium is found in the root nodules of leguminous plants. (v) Fungi are non-green prokaryotic organisms. (vi) The mycelium in Rhizopus is coenocytic. Ans. (i) T (ii) F (iii) T (iv) T (v) F (vi) T

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20. Complete the following by selecting the correct word : (i) Bacteria were first discovered by _________. (Pasteur / Leeuwenhoek / Koch) (ii) A cell wall is _________ in bacteria. (present / absent) (iii) Botulism is caused by a species of _________. (Clostridium / Rhizobium / Acetobacter) (iv) Rhizopus is _________ in nutrition. (Saprophytic / parasitic) (v) Short, incomplete, spiral bacteria are called _________. (Vibrio / spirilla / cocci) Ans. (i) Leeuwenhoek (ii) Present (iii) Clostridium (iv) Saprophytic (v) Vibrio

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