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

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Chapter 9 - Economic Importance Of Bacteria And Fungi Exercise Ex. 1

Question A

1. Production of ethanol (C2H5OH) occurs in one of the life processes of:

(a) Bread mould

(b) Yeast

(c) Mushroom

(d) Penicillium

2. Which one of the following characteristics is found in all fungi but not in all bacteria?

(a) Aerobic respiration

(b) Cell wall

(c) Spore formation

(d) A long circular DNA lying loose in the cytoplasm

3. Bacteria are referred to as prokaryotes because

(a) They have no chlorophyll.

(b) They are unicellular.

(c) They are free living.

(d) They do not have a true nucleus.

4. Yeast is used in the production of

(a) Ethyl alcohol

(b) Acetic acid

(c) Cheese

(d) Curd

Solution A

1. (b) Yeast

2. (c) Spore formation

3. (d) They do not have a true nucleus.

4. (a) Ethyl alcohol 

Question B.1

Tick Selina Solutions Icse Class 9 Biology Chapter - Economic Importance Of Bacteria And Fungimark the correct statement/statements.

(a) All mushrooms are poisonous.

(b) All toadstools are poisonous.

(c) Some toadstools are poisonous.

(d) Some mushrooms are edible.

Solution B.1

(a) All mushrooms are poisonous.

(b) All toadstools are poisonous.Selina Solutions Icse Class 9 Biology Chapter - Economic Importance Of Bacteria And Fungi

(c) Some toadstools are poisonous.

(d) Some mushrooms are edible.Selina Solutions Icse Class 9 Biology Chapter - Economic Importance Of Bacteria And Fungi

Question C.1

Where can you find the mould Rhizopus most easily found?

Solution C.1

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.

Question C.2

Why is it generally advised that every living room in the house should get direct sunlight at least for a short time?

Solution C.2

Direct sunlight contains ultraviolet radiations of the sun which help in killing of mould spores present in air.

Question C.3

Describe the role of certain fungi in industrial production.

Solution C.3

Role of certain fungi in industrial production:

(1) Preparation of fermented foods and bakery products

(2) Preparation of alcoholic beverages

(3) Preparation of organic acids

(4) Production of enzymes

(5) Production of antibiotics

(6) Production of alcohol

(7) Production of wine

(8) Bread-making

(9) Cheese making

(10) Mushroom cultivation

Question C.4

Mention two useful and harmful effects of wine.

Solution C.4

Useful effects of wine:

  • In mild quantities, wine acts as a stimulant.
  • It can be used to stimulate hunger, reduce anxiety and improve digestion.

Harmful effects of wine:

  • In large quantities, wine can trigger asthma attack and increase blood pressure.
  • It can cause body ailments, particularly liver cirrhosis.
Question C.5

Differentiate between:

(a) Saprophyte and parasite

(b) Aerobic and anaerobic respiration with regard to products

(c) Decay and putrefaction

Solution C.5

(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)


(c) Decay and putrefaction




Complete breakdown of organic matter by bacteria without the emission of foul smell

Incomplete breakdown of organic matter by bacteria along with the emission of foul smell

Question D.1

What are antibiotics? Name any two examples.

Solution D.1

Antibioticsare chemical substances produced by a living organism that kill or stop the growth of disease-causing micro-organisms such as fungi and bacteria.

Examples of antibiotics:

1. Penicillin

2. Streptomycin

Question D.2

Is tinned and sealed food always safe to eat? Give reasons in support of your answer.

Solution D.2

No, tinned and sealed food are not always 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.

Question D.3

Would there be any bacteria in an aquarium?

Solution D.3

Bacteria can be present in an aquarium.

Bacteria are present everywhere; in air, soil, water and foodstuffs. They are found in boiling water and also below 0C. They are present on the bodies of all living and non-living organisms. They live on readymade food. In short, they are omnipresent.

Bacteria are heterotrophic and may be decomposers or micro-aerobic in nature. Their mode of reproduction is very fast.

Question E.1

If you leave a piece of moist bread covered under a small bell jar at a warm place, mould grows on it in a few days. Answer the following with reference to this observation:

(a) How did the mould get inside the bell-jar?

(b) What would happen if the bread was not covered by the bell-jar?

(c) What would happen if moist bread was placed in a refrigerator?

(d) What happens first on the bread-the mycelia or the spores?

(e) How does bread mould obtain nourishment? What type of nourishment is it- epiphytic, autotrophic, parasitic symbiotic, or saprophytic?

Solution E.1

(a) Moulds are commonly present in air, water, etc. Hence, they were already present when moist bread was kept covered with the bell-jar.

(b) 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.

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

(d) Mycelia appear first on the bread.

(e) Bread mould obtains its nourishment through extracellular digestion from the substratum on which it grows. This mode of nourishment is called saprophytic nutrition.

Question E.2

Write in proper sequence the five major steps in cultivation of the common edible mushrooms.

Solution E.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.

Question E.3

Comment on the following:

(a) Denitrifying bacteria are a blessing as well as a curse to farmers.

(b) Yeast is used in bakeries and breweries.

Solution E.3
  1. Denitrifying bacteria are a boon to farmers because they curb the excess supply of nitrates to plants. Excessive nitrates can even harm the ecosystem as a whole because some wild plants like cultivated crops can thrive on nitrogen. Growth of these plants is favoured in nitrogen-saturated environments which can upset the ecosystem. Denitrifying bacteria are a curse to farmers because they breakdown soil nitrates to release free nitrogen gas into the atmosphere, thereby reducing the levels of nitrogenous compounds in the soil.
  2. Yeast respires anaerobically in the absence of oxygen. It breaks down carbohydrates into simpler products such as ethanol by fermentation. The quality of alcohol produced varies with the kind of yeast employed.
  3. During the baking process, yeast added to the dough ferments sugar and produces carbon dioxide. This causes the dough to rise, and when baked, the gas bubbles expand, giving the bread a light and spongy texture. Therefore, yeast is used in bakeries and breweries.