ICSE Solutions for Chapter 9 Economic Importance of Bacteria and Fungi Class 9 Biology Selina

Exercise 1

Progress Check

1. Name the three common shapes of bacteria.

Solution

The three common shapes of bacteria are as follows:
• Spherical shape (cocci)
• Rod-shaped (bacilli)
• Spirilla (spiral or twisted bacteria)

 

2. Give the technical terms for the following patterns of occurrence of bacteria
(i) In pairs
(ii)In long chains
(iii)In clusters

Solution

The technical terms are as follows:
(i)In pairs – Diplococci
(ii)In long chains – Streptococci
(iii)In clusters – Staphylococci

 

3. List the kinds of nutrition in bacteria

Solution

Bacteria are heterotrophs as they do not have chlorophyll. Furthermore, bacteria can obtain their nutrition from the following modes of nutrition:
• Saprotrophic — Obtaining nutrition from decaying dead organisms
• Parasitic — Obtaining nutrition from the body of their hosts

 

4. What is the common method of reproduction in bacteria?

Solution

Bacteria reproduces through asexual means such as cell division or fission.

 

5. Why do bacteria produce spores?

Solution

Bacteria produces spores to overcome unfavorable conditions such as drying up of vegetation. In such conditions, bacterial cell draws its content into a spherical mass that gets surrounded by a thick and hard protective wall forming a spore. Spores can tolerate extreme dryness and cannot be killed even at extreme temperatures.

 

Review Questions

A. Multiple Choice Type

1. Bacteria are no more classified as plants primarily because:
(a) These are unicellular
(b) These are microscopic
(c) Many of them are parasitic
(d) They have no chlorophyll

Solution

(d) They have no chlorophyll
As per the recent five kingdom classification, bacteria are not plants as they do not have chlorophyll.

 

2. A particular species of which one of the following, is the source bacterium of the antibiotic, discovered next to penicillin, for the treatment of tuberculosis?
(a) Escherichia
(b) Streptomyces
(c) Rhizobium
(d) Nitrobacter

Solution

(b) Streptomyces
Streptomycin was discovered by Selman Waksman in a similar way. The source is the bacterium Streptomyces griseus.

 

3. Which bacteria is rod shaped?
(a) Coccus
(b) Spirillum
(c) Bacillus
(d) Vibrio

Solution

(c) Bacillus
Bacteria are usually of four different shapes, one of which is rod-shape, they are referred to as Bacilli.

 

4. Which bacteria fixes nitrogen in the soil?
(a) Nitrobacter
(b) Nitrosomonas
(c) Rhizobium
(d) Clostridium

Solution

(c) Rhizobium
They are the soil bacteria found in small nodules on the roots of leguminous plants such as beans. Commonly referred to as nitrogen-fixing bacteria.

 

B. Very short answer type

1. Name the three common types of bacteria.

Solution

The three common types of bacteria are:

  1. Cocci (spherical bacteria)
  2. Bacilli (rod-shaped bacteria)
  3. Spirilla (spiral bacteria)

 

2. Match the items in Column A with those in Column B.

Column A

Column B

(i) Penicillium

(a) Bacteria occurring in chains

(ii) Diplococci

(b) Antibiotic

(iii) Streptococci

(c) Bacteria occurring in pairs

Solution

Column A

Column B

(i) Penicillium

(b) Antibiotic

(ii) Diplococci

(c) Bacteria occurring in pairs

(iii) Streptococci

(a) Bacteria occurring in chains

 

C. Short Answer Type

1. Would you consider the bacteria and yeast as plants? Give reason.

Solution

No, bacteria and yeast are not considered as plants because they do not have chlorophyll and their mode of nutrition is not autotrophic, which are characteristic features of plants.

 

2. In what form bacteria may be present in the air?

Solution

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


3. Why is spore formation in bacteria not considered a form of reproduction?

Solution

Spore formation in bacteria is not considered as a form of reproduction because bacteria reproduce only asexually by means of fission or cell division. Spore formation is just a method of escaping unfavourable conditions.

 

4. In what respect do you consider bacteria as simple organisms?

Solution

Bacteria are unicellular organisms that lack membrane bound cell organelles like chloroplast, mitochondria, etc. and even a well-defined nucleus is absent which states that they have a simpler cellular organization.

 

5. State the differences between
(a) Decay and putrefaction.
(b) Pasteurization and sterilization of food/objects/equipments.

Solution

(a) Difference between Decay and Putrefaction

Decay

Putrefaction

It is the complete breakdown of organic matter by bacteria.

It is the incomplete breakdown of organic matter by bacteria.

Does not emit a foul smell.

Emits a foul smell.

 

(b) Difference between Pasteurization and Sterilization

Pasteurization

Sterilization

Temperature -60°C

Temperature -110°C

Does not kill spores

Kills even spores

Partial sterilization

Complete sterilization

Example: Pasteurization of milk

Example: Sterilization of canned food

 

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

Solution

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

 

7. Would there be any bacteria in an aquarium?

Solution

Yes, bacteria can exist in aquarium. Bacteria can exist practically everywhere, as they can withstand any climatic condition.

 

D. Long Answer Type

1. Both bacteria and yeast reproduce by asexual method, but how does this method differ in them?

Solution

Bacteria reproduce asexually by means of fission (binary fission), while yeast reproduces asexually by budding producing chains.

 

2. Describe the role of micro-organisms in industrial production.

Solution

Role of micro-organisms in industrial production:

  1. Bacteria are used in the production of vinegar and in the processing of coffee, tobacco, etc.
  2. Different flavours of tea, coffee, etc. are produced by certain bacteria.
  3. Tanning of leather is basically brought about by sunlight, but there are a few micro-organisms which are involved in this process.
  4. Fibres used for making rope, linen, etc. are obtained by loosening the fibres of hemp and flax by ratting, which Involves the use of bacteria.
  5. Bacteria are used for the large-scale production of antibiotics, enzymes, hormones, serum, vaccines and toxoids.

 

3. How do bacteria obtain their nourishment?

Solution

Modes of nutrition in bacteria:

(i) Autotrophic bacteria: Able to synthesize their own food.

  1. Photoautotrophs: Contain chlorophyll and use light energy for the synthesis of food.
  2. Chemoautotrophs: Obtain energy by oxidizing inorganic compounds.

(ii) Heterotrophic bacteria: Require organic compounds as their main source.

  1. Saprophytes: Grow on dead and decaying organic matter.
  2. Parasites: Obtain their food from living host on which they grow.

 

4. Describe any two uses of bacteria in industry.

Solution

Uses of bacteria In Industry:

  1. Tea curing: Certain bacteria are used to produce different flavours of tea.
  2. Tanning of leather: Tanning of leather is basically brought about by sunlight, but there are a few bacteria which are involved in this process.

 

5. What are antibiotics? Name any two examples.

Solution

Antibiotics are 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


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

Solution

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.

 

E. Structured/Application/Skill Type

1. Study the diagram given below and then answer the questions that follow:

(a) Briefly describe how nitrogen of the atmosphere is converted to nitrates by leguminous plants.

(b) Name the bacteria that converts
(i) Ammonium compounds to nitrites
(ii) Nitrites to nitrates

(c) State how the nitrates in the soil get converted to nitrogen of the atmosphere.

(d) Role of plants and animals in the formation of ammonium compounds.

Solution

(a) Soil bacteria such as Rhizobium are present in the root nodules of leguminous plants. These bacteria convert free nitrogen of the soil atmosphere to soluble nitrates.

(b) (i) Nitrosomonas converts ammonium compounds to nitrites.
(ii) Nitrobacter converts nitrites to nitrates.

(c) Denitrifying bacteria in the soil break down nitrates present in the soil to release nitrogen gas which enters the atmosphere.

(d) Nitrifying bacteria present in the soli convert nitrogenous wastes of animals and dead remains of plants and animals to ammonia. Ammonia is then converted to ammonium compounds. In this way, plants and animals help in the formation of ammonium compounds.

 

Exercise 2

Progress Check

1. Which is the most common variety of cultivated mushroom?

Solution

The most common variety of cultivated mushroom is Agaricus bisporus or the white button mushroom.

 

2. What is meant by “mushroom seed”?

Solution

One of the cultivation steps of white button mushroom is spawning. “Mushroom seed” -mycelium of the selected type of mushroom is introduced into the compost and allowed to spread for a few days.

 

3. What is done in the step called “casing”?

Solution

In this step, a thin layer of soil is spread over the compost.

 

Review Questions

A. Multiple Choice Type

1. Production of ethanol (C2H5OH) occurs in one of the life processes of:
(a) Bread mould
(b) Yeast
(c) Mushroom
(d) Penicillin

Solution

(b) Yeast
Yeast respires anaerobically producing ethanol.

 

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.

Solution

(c) Spore formation
This characteristic is observed in all the fungi, but not in all bacteria.

 

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

Solution

(d) They do not have a true nucleus
Prokaryotes do not have a distinct nucleus with a membrane nor other specialized organelles.

 

4. Yeast is used in the production of:
(a) Ethyl alcohol
(b) Acetic acid
(c) Cheese
(d) curd

Solution

(a) ethyl alcohol
Yeast is of great economic importance through its property of alcoholic fermentation and is used in the production of ethyl alcohol.

 

Very Short Answer Type

1. Tick mark 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

Correct statements are ticked as shown below:

All mushrooms are poisonous

All toadstools are poisonous ✓

Some toadstools are poisonous

Some mushrooms are edible ✓

 

C. Short Answer Type

1. Where can the mould Rhizopus be most easily found?

Solution

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.

 

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

Solution

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

 

3. Describe the role of certain fungi in industrial production.

Solution

Role of certain fungi in industrial production:

  1. Preparation of fermented roods 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

 

4. Mention two useful and two harmful effects of wine.

Solution

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.

 

5. Differentiate between:
(a) Saprophyte and Parasite
(b) Aerobic and anaerobic respiration with regard to products
(c) Decay and putrefaction.

Solution

(a) Difference between Saprophyte and Parasite

Saprophyte

Parasite

Saprophyte Parasite Obtains nourishment from dead and decaying organic matter.

Obtains nourishment from the body of the living host.


(b) Difference between 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) Difference between Decay and putrefaction

Decay

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.

 

D. Long Answer Type

1. What are antibiotics? Name any two examples.

Solution

Antibiotics are 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

 

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

Solution

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.

 

3. Would there be any bacteria in an aquarium?

Solution

  • 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 0°C. 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.

 

E. Structured/Application/Skill Type

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 appears 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

(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.

 

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

Solution

Five 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 50°C. 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 20°C-25°C 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 15°C, freeze drying in a solution of citric acid, ascorbic acid and brine, etc. are used for the preservation of mushrooms.

 

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

(a) 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. 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.

(b) 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.

Tags
Previous Post Next Post