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

Progress Check

Question 1.
Name the three common shapes of bacteria.
………………, ………………, ……………….
Answer:
(a) cocci
(b) bacilli
(c) spirilla

Question 2.
Give the technical terms for the following patterns of occurrence of bacteria :
In pairs ………………..
In long chains ……………..
In clusters ……………..
Answer:
In pairs – Diplococci
In long chains – Streptococci
In clusters – Staphylococci

Question 3.
List the kinds of nutrition in bacteria :
Answer:
Heterotrophic – Depend on food from other sources.
Autotrophic – Manufacture their own food.
Saprophytic – Nourishment from decaying dead organisms.
Parasitic – Nourishment from bodies of their hosts.

Question 4.
What is the common method of reproduction in bacteria?
Answer:
Asexual reproduction
Binary Fission cell division

Question 5.
Why do bacteria produce spores?
Answer:
Spores are produced to overcome unfavourable conditions.

Review Questions

A. Multiple Choice Type :

Question 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
Answer:
(d) they have no chlorophyll

Question 2.
A particular species of which one 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) Nitrocbacter
Answer:
(b) Streptomyces

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

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

B. Very Short Answer Type

Question 1.
Name the three common types of bacteria.
Answer:

  1. Saprophytic Bacteria e.g., : Clostridium botulinum
  2. Parasitic Bacteria e.g., : Clostridium retain
  3. Symbiotic Bacteria e.g., : E Coli.

Question 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.
(ii) Streptococci (c) Bacteria occurring in pairs.
Answer:
(i) – b
(ii) – c
(iii) – a

C. Short Answer Type

Question 1.
Would you consider the bacteria and yeast as plants? Give reason.
Answer:
Bacteria as plants –
In exceptional cases, there may be chlorophyll within the bacterial cell and such bacteria manufacture their own food (autotrophic).

Yeast as plants –
After sexual reproduction, yeast form spores as plants. These spores are carried by wind which under proper conditions of nutrition and temperature germinate to form yeast cells. Inspite of the absence of chlorophyll in fungi and bacteria, they show other characteristics of plants such as presence of cell wall, absence of centriole.

Question 2.
In what form, bacteria may be present in the air?
Answer:
Bacteria may be present as spores in air.

Question 3.
Why is spore formation in bacteria not considered a form of reproduction ?
Answer:
Spore formation in bacteria is not considered a form of reproduction, as they are simply a method of escaping unfavourable conditions.

Question 4.
In what respect do you consider bacteria as simple organisms?
Answer:
Bacteria as plants –
In exceptional cases, there may be chlorophyll within the bacterial cell and such bacteria manufacture their own food (autotrophic).

Yeast as plants –
After sexual reproduction, yeast form spores as plants. These spores are carried by wind which under proper conditions of nutrition and temperature germinate to form yeast cells. Also inspite of the absence of chlorophyll in fungi and bacteria, they show other characteristics of plants such as presence of cell wall, absence of centriole.

Question 5.
State the differences between
(a) Decay and putrefaction.
(b) Pasteurization and sterilization.
Answer:
(a) Decay –
It is the complete breakdown of organic matter by bacteria.
Does not give a foul smell.

Putrefaction –
Incomplete breakdown of organic matter. Emits foul smell.

(b) Pasteurization –

  1. Temperature – 60°C.
  2. Doesn’t kill spores.
  3. Incomplete sterilization.
  4. e.g. milk

Sterilization

  1. Temperature – 110°C.
  2. Kill even spores.
  3. Sterilization is complete.
  4. e.g. Canned food.

Question 6.
Why is it generally advised that every living room in the house should get direct sunlight at least for a short time?
Answer:
Direct sunlight contains ultra-violet radiations which help in killing mould spores.

Question7.
Would there be any bacteria in an aquarium?
Answer:
Bacteria can be present in the aquarium.
Bacteria can be present in the air, water, soil, food stuffs. They are found in the boiling water, and below 0°C. These are found even under the soil. They are present in the all the living organisms and non living organisms. These are omni present. They live on ready made food and are heterotrophic and may be decomposers and micro-aerobic bacteria.

Their mode of reproduction is very fast. They divide after every half an hour and after 24 hrs these will reach to the number of 281, 514, 871, 750, 656.

D. Long Answer Type

Question 1.
Both bacteria and yeast, reproduce by asexual method, but how does this method differ in them?
Answer:
Asexual reproduction involves the participation of a single parent. This mode of reproduction does not involve formation of gametes. It includes types of vegetative propagation and asexual spore formation.

Bacteria reproduce mainly by fission. Sometimes, under unfavourable conditions, they produce spores. Cell on reaching a certain size, dictated by the nucleus to cytoplasmic ratio, reproduction takes place asexually by binary fission, that is by division into two identical daughter cells.

Yeast reproduce asexually through budding.
Budding involves the formation of a new individual from a protrusion called the bud. It is very common in plants, yeasts, and lower level animals such as Hydra.

In Hydra, the cells divide rapidly at a specific site and develop as an outgrowth called a bud. These buds, while attached to the parent plant, develop into small individuals. When this individual becomes large enough, it detaches itself from the parent body to exist as an independent individual.

Question 2.
Describe the role of micro-organisms in industrial production.
Answer:
Micro-organisms play an important role in our industry in the following way :

  • They help in the preparation of curd, cheese and butter.
  • Vinegar, alcohol and wines are produced by fermentation action of bacteria.
  • Curing of tea leaves is carried out with the help of bacteria.
  • A number of antibiotics out with the help of bacteria.
  • Vitamin B2is produced by yeast like microorganisms such as Eremothecium ashbyii, Clostridium acetobutylicum and certain species of Acetobacter.
  • Enzymes such as amylases, invertase, lactase, pectinases are produced for use in a variety of food and other industries like, chocolate, pasteurized milk, clarification of fruit juice and removal of stains and manufacture of liquid glue etc.

Question 3.
How do bacteria obtain their nourishment?
Answer:
Bacteria obtain their nourishment in following ways :
– Most bacteria depend on ready made food from other sources : Heterotrophic nutrition.
– Some bacterial cell contain chlorophyll which manufacture their own food : Autotrophic nutrition.
– Some bacteria draw nourishment from decaying dead organisms : Saprophytic.
– Some bacteria obtain nourishment from the body of their hosts : Parasitic.

Question 4.
Describe any two uses of bacteria in industry.
Answer:

  1. Bacteria are used in the production of vinegar, cheese, processing of coffee, tobacco etc.
  2. Curing of hides and skins.

Question 5.
What are antibiotics? Name any two examples.
Answer:
Antibiotic is a substance which is produced by certain bacteria and fungi and has the capability to inhibit or stop the growthof other bacteria or micro-organisms, e.g. 1. Penicillin (1st antibiotic discovered) 2. Streptomycin.

Question 6.
Is tinned and sealed food always safe to eat? Give reasons in support of your answer.
Answer:
No, tinned and sealed food are not always safe to eat as botulism is a very serious food poisoning due to special bacterium sometimes found in tinned and sealed foods.

E. Structured/Application/Skill Type

Question 1.
Study the diagram given below and then answer the following 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 nitrates
(ii) nitrites to nitrates.
(c) State how the nitrates in the soil get converted to nitrogen of the atmoshpere.
(d) Role of plants and animal in the formation of ammonium compounds.
Answer:
(a) 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 atmoshpere 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.

(b) (i) Nitrosomonas
(ii) Nitrobacter

(c) Nitrosomonas and nitrobacter are the dentrifying bacteria present in the soil, which break down the soil nitrates to release nitrogen gas (N2) that enters the atmosphere.

(d) Plants need nitrogen for synthesising proteins, but they cannot make use of the free atmospheric nitrogen. They can obtain it only in the form of nitrates, which they absorb from the soil through roots.These nitrates are replenished in the soil by bacteria through the process of nitrification.

For this, some bacteria first convert the nitrogenous wastes of animals and the dead remains of plants and animals into ammonia. Ammonia is then converted into ammonium compounds which in turn are first converted into nitrites by bacteria such as Nirtosomonas and then into nitrates by bacteria such as Nitrobacter.

Additional Questions

A. Tick the most appropriate answer.

Question 1.
Cocci bacteria are
a. rod-shaped.
b. spherical,
c. spiral.
d. triangular.
Answer:
b. spherical.

Question 2.
Bacteria that can grow only in the absence of oxygen are called
a. saprophytic bacteria.
b. parasitic bacteria,
c. anerobic bacteria.
d. aerobic bacteria.
Answer:
c. anaerobic bacteria.

Question3.
Pneumonia is caused by
a. virus.
b. Amoeba
c. bacteria
d. Paramecium.
Answer:
c. bacteria

B. Fill in the blanks
1. ………………… are the micro-organisms without chlorophyll.
2. The bacteria that need oxygen to grow are called ……………. bacteria.
3. ……………… bacteria decompose dead remains of plants
and animals.
Answer:
1. Bacteria are the microorganisms without chlorophyll.
2. The bacteria that need oxygen to grow are called aerobic bacteria.
3. Saprophytic bacteria decompose dead remains of plants and animals.

C.
Question 1.
How is a bacterial cell different from an ordinary plant cell?
Answer:
Bacterial cells differ from ordinary plant cells as following:

  • The nuclear membrane and nucleoli are absent in the nuclear body.
  • The mitochondria and endoplasmic reticulum are absent in the cytoplasm.
  • The nuclear body does not divide by mitosis.
  • The cytoplasm does not show streaming movements and has few, if any vacuoles.
  • Bacteria are prokaryotic and plants cells are eukaryotic.
  • Photosynthetic lamellae are not organised into chloroplasts.
  • The cell wall has murein which is characteristic of bacteria.
  • They are found everywhere, where life exists.
  • Bacteria reproduce mostly by fission.
  • Flagella when present are single fibrilled but in other plants are eleven fibrilled.

Question 2.
What are the conditions which facilitate growth of bacteria?
Answer:
Conditions which facilitate growth of bacteria :

  • They must have moisture.
  • They flourish in dim light or darkness. ,
  • They require damp soil, air, water, dead organic, matter.
  • Bacteria grow best in the range of temperature between 25° to 40° C.
  • Presence or absence of O2 may affect the growth of bacteria.

Bacteria can grow on any type of matter may be dead – or living organisms. The growth in bacteria is very fast. Some of these divide once every 20 minutes. A single bacterium may grow to 20,000 bacteria in 6 hours.

Question 3.
How are anaerobic bacteria different from aerobic bacteria?
Answer:

Aerobic bacteria

Anaerobic bacteria
1. Respiration takes place in presence of free gaseous oxygen. Respiration takes place in the absence of free oxygen.
2. Oxygen required for the process is taken from the surrounding medium and it enters the bacterial cell by diffusion through the cell wall. Oxygen required for oxidation is taken up from the breakdown of food materials present in the cytoplasm.
3. There is complete oxidation of the organic compounds. There is partial oxidation of organic compounds.
4. Oxidation products are CO2, H2O and release of energy. The products of oxidation are ethyl alcohol or organic acids, C02, Hydrogen and release of energy.
5. Great amount of energy is released. The energy released is much less than in aerobic respiration.

Question 4.
How do bacteria obtain their nutrition?
Answer:
Bacteria lack chlorophyll so they cannot make carbohydrates foods, so they are heterotrophic. A few bacteria are autotrophic which can make carbohydrates from CO2 and water.

I. Autotrophic bacteria may be photosynthetic and chemosynthetic
A. Photosynthetic bacteria have pigments and use sun’s energy to form food. These are of two types :

  1. Purple bacteria have bacteria chlorophyll which helps to make food. It is not similar to chlorophyll.
  2. Green bacteria have chlorobium chlorophyll which help to make food.

B. Chemosynthetic bacteria do not have pigments. They get energy for food making by the oxidation of the inorganic substances available to these bacteria as sulphur bacteria iron bacteria.

II. Heterotrophic bacteria :
Heterotrophic bacteria which obtain food from dead remains or wastes products are called saphrophytic bacteria or saprobes as Hay bacillus.
Some heterotrophic bacteria get their food from the living organisms both plants and animals are parasites.

Bacteria give out enzymes. Those enzymes break down the complex compounds and turn them into simple soluble compounds. Bacteria absorb through the general surface. These are used as a source of energy.

Question 5.
How do bacteria survive harsh conditions?
Answer:
It is very difficult for the bacteria to survive when the following conditions arise :
I Food and water supply gets exhausted.
II Space becomes limited.
III Accumulation of poisonous waste products as alcohol or acids.
IV Aerobic bacteria compete for oxygen as it becomes less. Under these bacteria can survive only by the following processes.

1. Endospore formation :
The cytoplasm along with nuclear body gets rounded off and is covered with hard coat.Thus the bacteria can survive the adverse conditions by turning them into endospores. The bacteria cell with endospore is called sporangium . It is covered by thick spore coat. These endospores can bear adverse conditions like high” temperature, drought, starvation. On the approach of favourable weather the endospores are set free from . the coat and the endospore forms the bacterium.

2. Cyst formation :
The bacterium in adverse conditions covered by a hard covering which is called cyst. The bacteria remain inactive in the cyst in the adverse conditions. In the favourable condition the hard covering is removed and the bacterium grows out of it.

Question 6.
List five ways by which bacteria are useful commercially.
Answer:
The bacterial action is involved in the following industrial processes.

  1. In the manufacture of vinegar, butter and cheese.
  2. The process of tanning hides in leather making and preparing sponges.
  3. The separation of flax and hemp fibres which are used for making linen cloth and ropes.
  4. Fermentation of green plants for the production of ensilage for animal food.
  5. Bacteria are used for forming lactic acid, vinegar, citric acid, and vitamins.
  6. For formation of antibiotics, serums and vaccines, vitamin B complex.

Question 7.
How are bacteria harmful to mankind?
Answer:
1. Some saprophytic bacteria excrete toxic substances such as ptomaines and cause spoilage by decay. They do rotting of meat, souring of milk, spoilage of butter, vegetables.

2. They cause many diseases as tetanus, typhoid, lock -jaw, cholera, gangrene, pneumonia, tuberculosis and many plant diseases as potato black leg, wilt of cucumber, soft of carrot, cabbage rot and citrus canker, blight of pear, pineapple rot, walnut blight, wilt of egg plant.

3. Many serious diseases of domesticated animals are caused by bacteria as chicken cholera, tuberculosis of cattle, anthrax, black leg, glanders, pneumonia etc.

4. Under anerobic condition the denitrifying bacteria convert nitrates into nitrogen gas, thus reduce the fertility of the soil.

5. Saprophytic bacteria spoil canned foods, jams by giving out toxic substances and cause dangerous disease botulism.

Question 8.
It is difficult to set curd in winters.
Answer:
For setting curd we require the activity of the lactic acid bacteria. In winters the bacteria cannot grow properly at low temperature so their activity is very low in the winters. The bacteria require moderate temperature to grow. At low temperature bacteria cannot grow in winters so it is difficult to set curd in winters.

D.
Question 1.
State whether the following statements are true or false:
(i) Stored food in fungi is glucose.
(ii) In bacteria the cell wall is composed of mainly chitin.
(iii) A bacterial cell is eukaryotic.
(iv) Measles is a bacterial disease in humans.
(v) Nucleolus is absent in a bacterial cell.
Answer:
(i) False
(ii) True
(iii) False
(iv) False
(v) True.

Question 2.
State briefly how the following types of bacteria obtain their nourishment.
(i) Saprophytic bacteria
(ii) Parasitic bacteria
(iii) Chemosynthetic bacteria
(iv) Photosynthetic bacteria
Answer:
(i) The bacteria that feed on dead and decaying plant or animal matter are called saprophytic bacteria.
(ii) The bacteria that obtain nourishment from the body of living hosts.
(iii) The bacteria that obtain energy by oxidising inorganic substances such as nitrogen, sulphur and iron compounds.
(iv) The bacteria that contain chlorophyll and other pigments which enable the bacteria to assimilate atmospheric carbon dioxide in the presence of light.

Extra Questions

Question 1.
Name the following :
(i) Two common bread moulds
…………………………………………..
Answer:
Mucor, Rhizopus

(ii) Finer hyphae of bread mould which penetrate the substratum.
…………………………………
Answer:
Rhizoids

(iii) The swollen tips of erect hyphae.
……………………………………
Answer:
Sporangium

(iv) The colour of mature spores of bread mould.
……………………..
Answer:
Black

(v) The new hypha produced from the germinating zygospore.
…………………………………………
Answer:
Promycelium

(vi) The mould which was the source of the first discovered antibiotic.
………………………….
Answer:
Penicillium notatum

Progress Check

Question 1.
Which is the most common variety of cultivated mushroom.
Answer:
Agaricus bisporous.

Question 2.
What is meant by “mushroom seed”?
Answer:
“Mushroom seed” consisting of mycelium of the selected type of mushroom is introduced into the compost, the allowed to spread for a couple of days.

Question 3.
What is done in the step called “casing”?
Answer:
A thin layer of soil is spread over the compost. This is a very important step.
It gives support to the mushroom, Provides humidity, Prevents quick drying of the compost and helps to regulate temperature.

Review Questions

A. Multiple Choice Type

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

Question 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
Answer:
(c) Spore formation

Question 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.
Answer:
(d) They do not have a true nucleus.

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

B. Very Short Answer Type

Question 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.
Answer:
(b) All toadstools are poisonous
(d) Some mushrooms are edible.

C. Short Answer Type

Question 1.
Where can the mould Rhizopus most easily found?
Answer:
Rhizopus is the common bread mould. It grows not only on bread but also on a variety of other organic matter such as fruits, animal dung and leather goods, in warm and humid climate.

Question 2.
Why is it generally advised that every living room in the house should get direct sunlight at least for a short time?
Answer:
Direct sunlight contains ultraviolet radiations which help in killing mould spores.

Question 3.
Describe the role of certain fungi in industrial production.
Answer:
Micro-organisms play an important role in our industry in the following way :

  • They help in the preparation of curd, cheese and butter.
  • Vinegar, alcohol and wines are produced by fermentation action of bacteria.
  • Curing of tea leaves is carried out with the help of bacteria.
  • A number of antibiotics out with the help of bacteria.
  • Vitamin B2 is produced by yeast like microorganisms such as Eremothecium ashbyii, Clostridium acetobutylicum and certain species of Acetobacter.
  • Enzymes such as amylases, invertase, lactase, pectinase are produced for use in a variety of food and other industries like, chocolate, pasteurized milk, clarification of fruit juice and removal of stains and manufacture of liquid glue etc.

Question 4.
Mention two useful and two harmful effects of Wine.
Answer:

  1. Wine is quickly absorbed into body.
  2. In very mild quantities it may be a stimulant.
  3. When consumed in large quantities it is harmful for health.
  4. Alcoholics may develop body ailments liver cirrhosis.

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

Parasite

Saprophyte
1. Parasites obtain their food from other living organisms. They derive their food from dead and decaying plants and animals.
2. They live on or inside the bodies of living organisms and do not secrete enzymes. They secrete enzymes to dissolve the food material.

(b)

Aerobic Respiration

Anaerobic respiration
1. Takes place in the presence of oxygen. Anaerobic repiration takes place in the absence of oxygen.
2. Complete breakdown of food molecules takes place. Partial breakdown of food takes place.
3. More energy is released (683) Kcals per mole of glucose. Less energy is released (50) kcals per mole of glucose.

(c)

Decay

Putrefaction
a. Decay is the complete breakdown of organic matter by bacteria and fungi, (decomposers) Putrefaction is the incomplete breakdown of organic matter by decomposers like bacteria and fungi.
b. No foul smell is given out during decay. A foul smell is given out during this process.

D. Long Answer Type

Question 1.
What are antibiotics? Name any two examples.
Answer:
Antibiotic is a substance which is produced by certain bacteria and fungi and has the capability to inhibit or stop the growth of other bacteria or micro-organisms, e.g. 1. Penicillin (1st antibiotic discovered) 2. Streptomycin.

Question 2.
Is tinned and sealed food always safe to eat? Give reason in support of your answer.
Answer:
No, tinned and sealed food are not always safe to eat as botulism is a very serious food poisoning due to special bacterium sometimes found in tinned and sealed foods.

Question 3.
Would there be any bacteria in an aquarium?
Answer:
Yes, Bacteria can be present in the aquarium.
Bacteria can be present in the air, water, soil, food stuffs. They are found in the boiling water, and below 0°C. These are found even under the soil. They are present in the all the living organisms and non living organisms. These are
omnipresent. They live on ready made food and are heterotrophic and may be decomposers and micro-aerobic bacteria.

Their mode of reproduction is very fast. They divide after every half an hour and after 24 hrs these will reach to the number of 281, 514, 871, 750, 656.

E. Structured / Application / Skill Type

Question 1.
If you leave a piece of moist bread covered under a small bell-jar at a warm place mould grows mould 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?
Answer:
(a) They are very common and are present in air, water etc. Hence, they are already present when bread is covered with a bell-jar.

(b) If the bread is not covered with a bell-jar mould will appear later, as the warm climate inside bell-jar promotes. Mould production.

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

(d) Mycelia appear first.

(e) Bread mould’s obtain their nourishment through extracellular digestion from the substratum on which they grow. This nourishment is saprophytic.

Question 2.
Write in proper sequence the five major steps in cultivation of the common edible mushroom.
Answer:
Five major steps in cultivation of the common edible mushroom are as below :
(i) Composting :
The compost is prepared by mixing the following in certain proportions.

  • Wheat or paddy straw,
  • Chicken manure
  • Some organic and inorganic fertilizer
    This compost is kept at about 50°C for a week.

(ii) Spawning :
“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.

(iii) Casting :
A thin layer of soil is spread over the compost to give support to the mushroom and provide humidity. It also prevents quick drying of the compost and helps to regulate temperature

(iv) Cropping and Harvesting :
The growth occurs in three stages :

  • Mycelium (a network of fibrous mass) grows within 2 to 6 weeks.
  • Tiny pin heads.
  • Button stage which grows bigger attaining marketable size. The full grown mushrooms are taken out.

(v) Preservation :
Mushrooms are highly perishable. Their shelf life is increased by a variety of processes :

  • Vacuum cooling
  • Giving gamma radiation and storing at 15°C
  • Freeze drying in a solution of citric acid, ascorbic acid and brine, etc.

Question 3.
Comment on the following :
(a) Dentrifying bacteria are a blessing as well as a curse to farmers.
(b) Yeast is used in bakeries and breweries.
Answer:
(a)(i) Bacteria as a blessings
Bacteria play an important role as chief decomposers and in soil fertility by nitrogen fixation and by maintaining the circulation of nitrogen in the soil.

Denitrifying bacteria are present in soil that act on dead and decaying plant and animal matter and decompose them & break the soil nitrates into nitrogen gas (N) that enters the atmosphere.They convert organic compounds to simple forms like nitrates, phosphates, sulphates etc. which can be utilisedby the green plants again.

It also helps in curing and ripening of tea and tobacco. After harvesting, crude tea and tobacco leaves are hung in . shade and permitted for the action of certain bacteria. This process is called as the curing of tea or tobacco leaves adds flavour and taste to tea and tobacco leaves, increasing their market value.

(ii) Bacteria as a curse
A few very common bacterial diseases in cattle are :

  • Anthrax : High fever, swelling on neck and different parts, loss of appetite & breathing, death within 2 days.
  • Tuberculosis : Infection of lungs & Other parts, fever and diarrhoea.

Few Diseases in plants are :

  • Blight of wheat and rye : XANTHOMONAS
    TRANSLUCENS causes yellow, brown stripes of leaves, shrivelled seeds and dwarfed shoots.
  • Soft rots of potato tuber : ERWIN CAROTOUORA causes decay of potato, showing as dark brown circular soft spots which may turn into chalky-white mass.

(b) Yeast is used as a raising agent in bread making and in bakery (cakes, pastries and other products). The only fermentation product needed here is carbon dioxide. Yeast produces carbon dioxide that makes bubbles in the breaddough. These bubbles make the dough rise and make it light in texture. It adds sponginess to cakes and breads.

The yeast is used in alcoholic fermentation of sugars in the brewing industry to product alcohol. Production of alcoholic bewarages like beer and wine dates back to thousands of years. In both beer and wine the fermentation is brought about by yeast, Saccharomyces cerevisiae. During, fermentation, yeast breaks down sugars into ethanol and carbon dioxide in the absence of oxygen.
C6H12O6 → 2C2H5OH + 2CO2

Extra Questions

Question 1.
Match the items in column A with those in column B.

Column A

Column B
(i) Penicillium (a) Bacteria occurring in chains.
(ii) Yeast (b) Antibiotic.
(iii) Diplococci (c) Bacteria occurring in pairs.
(iv) Streptococci (d) Budding.

Answer:
(i) – b
(ii) – d
(iii) – c
(iv) – a.

Question 2.
How would you distinguish Rhizopus from Mucor?
Answer:
Rhizopus –

  • Stolons are present.
  • Rhizoids are present.
  • Many sporangiophores arise from the node.
  • More common

Mucor –

  • Stolons are absent.
  • Rhizoids are inconspicuous.
  • Sporangiophores arise singly from the nodes.
  • Less common.

Question 3.
Describe the sexual reproduction in bread mould, if any.
Answer:
Sexual reproduction takes place through conjugation. Steps in sexual reproduction.

  • Each hypha in a conjugating pair, gives out a short lateral outgrowth which points towards the corresponding out growth from the other hypha. These outgrowths are called progametes.
  • Tips of two progametes get enlarged, nuclei and cytoplasm collect in the swollen tips which is cut-off by partition wall from the basal suspensor.
  • The wall separating two gametangia dissolves and contents fuse to form zygote.
  • Zygote enlarges and develops a thick black warty wall to produce a resting zygospore.
  • Nuclei fusion follows out of which, only one survives.
  • Fusion nucleus undergoes subsequent divisions.
  • After resting period, zygospore germinates.
  • The outer wall ruptures to give way to a new hypha the promycelium. The promycelium at its tip develops rounded sporangium containing numerous spores.
  • Sporangium ruptures – release spores,
  • Spores germinate on favourable conditions to produce mycelia.

Question 4.
Moulds respire aerobically and not anaerobically. Can you think of an experiment to prove it?
Answer:
Take two test tubes A and B. Close the tube A and let B be open. Put some moist bread in it.
Observe after few days. Mould will grow in the test tube B. This shows moulds respire aerobically
Note – In test tube A, vacuum is maintained.

Additional Questions

Question 1.
Match the description in column A with the appropriate term/phrase in column B.

A

B
(i) Method of sexual reproduction on paramecium. (a) Macronucicus
(ii) Protozoan with short, haiirlike structures used for movement. (b) Flagellum
(iii) Fingerlike projections of cytoplasm. (c) Cilia
(iv) Method of reproduction in amoeba. (d) Pseudopodia
(v) Controls sexual reproduction in the paramecium. (e) Eye-spot
(vi) Reacts to light. (f) Micronucleus
(vii) The paramecium ingest its food through this opening. (g) Contractile vacuole
(viii) Used for excretion of waste products. (h) Oral groove
(ix) Used for movement by euglena. (i) Fission
(x) Controls metabolism of a paramecium. (j) Conjugation

Answer:
(i) – (j)
(ii) – (c)
(iii) – (d)
(iv) – (i)
(v) – (f)
(vi) – (e)
(vii) – (h)
(viii) – (g)
(ix) – (b)
(x) – (a)

Question 2.
Explain why :
(i) Water should be boiled at increased pressure to completely destroy bacteria.
(ii) Certain acids are added to preserve tinned foods and squashes..
Answer:
(i) Boiled water kills only the bacteria and never the spores but water boiled at increased pressure kills both the bacteria and the spores.
(ii) Acidic medium is unfavourable for the growth of bacteria an$ hence preserve foods from their attack and increase their life.

Question 3.
Shown below are stages in the reproduction of two microorganism A and B.
ICSE Class 9 Biology Solutions Chapter 9 Economic Importance of Bacteria and Fungi 1
(i) Identify the organisms.
(ii) Name the type of reproduction taking place in each.
(iii) Is the mode of reproduction sexual or asexual?
Answer:
(i) A : Amoeba B : Yeast
(ii) A : Binary fission B : Budding
(iii) A : Asexual B : asexual

Question 4.
List three animal-like characteristics of euglena.
Answer:

  1. Can ingest solid food particles from surroundings.
  2. Exhibit cyst formation.
  3. When kept in dark, loses its chlorophyll and lead a saprophytic life.

Question 5.
List two characteristics of virus in which it resembles :
(a) Living organisms
(b) Non-living
Answer:
(a)

  • Has the power of multiplication and reproduce its own kind within host cell.
  • Core material contains DNA, which is an essential component of all living cells.

(b)

  • Lacks a cellular structure.
  • They can be crystallised and stored in containers for any length of time.

Question 6.
Write an essay on the beneficial aspects of microorganisms.
Answer:
Beneficial aspects of microorganisms.
1. The bacteria which lives in the large intestine of human beings help in the production of essential vitamins, such as vitamin B2, K, B12 and Riboflavin.

2. Bacteria help in the production of wines and beers by the fermentation of fruit juices, molasses, etc.
ICSE Class 9 Biology Solutions Chapter 9 Economic Importance of Bacteria and Fungi 2
3. Bacteria help in making meat soft by the breakdown of the hard muscle fibres.

4. The bacteria living in the intestine of herbivorous animals such as cows, buffaloes, etc., and help in the breakdown of the carbohydrate cellulose, thus helping in digestion.

5. The bacteria living in the nodules of leguminous plants help in fixing atmospheric nitrogen. In this process of nitrogen fixation the bacteria rhizobium converts the nitrogen available in the air to nitrates in the soil, thus leading to increased soil fertility.

6. Bacteria also help in the decomposition of plant and animal remains by releasing important nutrients in the soil.

Question 7.
Describe how microorganisms help in sewage treatment.
Answer:
During the sewage treatment, aerobic bacteria like bacillus, pseudomonas etc., are used. These bacteria are circulated around sewage in a large tank through which air is pumped. The bacteria bring about rapid decomposition of sewage within few hours due to the presence of sufficient oxygen.

The remaining sewage is then transferred to anaerobic tank where anaerobic bacteria carry out rapid decomposition and produce methane like gases. The mixture of gases – known as biogas is used as fuel and the sludge left is used as manure after drying because it is rich in nitrogen. Thus, the microorganisms help and take part actively in sewage treatment.

Question 8.
What do you understand by microorganisms? Describe their useful and harmful effects.
Answer:
Microorganisms “means very small living things.” Microorganisms are very tiny free living organisms.
Most of the microorganisms are too small to be seen without the aid of a magnifying glass or a microscope.

Useful effects of microbes.

  • Bacteria help in the production of wines and beers by the fermentation of fruit juices, molasses etc.
  • Bacteria help in making meat soft by the break down of the hard muscle fibres.
  • Bacteria help in the curding of milk. They also help in cheese formation, vinegar production and help the production of tea, coffee and cocoa.
  • Bacteria help in decomposition of plant and animal remains by releasing important nutrients in the soil.
  • Bacteria help in production of vitamins B2, K, B12 and Riboflavin in large intestine of human being.
  • Bacteria also help in purification of sewage.
  • Bacteria is used in manufacture of antibiotics such as streptomycin and vitamin B complex tablets.
  • Bacteria helps in breakdown of plant and animal waste in thp absence of O2 to produce biogas (methane) which is used as fuel for cooking.

Harmful effects of microbes.
Microbes cause a large number of diseases among plants, animals and in human being: such as blight disease in potato, bacterial wilt, mildews in wheat and grapes.

In human being and animals.
Diseases like amoebic dysentery, the ring worm fungal infection, athlete’s foot, typhoid, cholera, whooping cough and yellow fever are caused by microbes.

Question 9.
Describe some of the important landmarks in the study of microorganisms.
Answer:
Some important discoveries related to the study of micro-organisms have proved to be landmarks : For example

  • Development of electron microscope – the perception that all microorganisms are harmful and disease causing came to an end. Rather some bacteria are very useful to us.
  • Production of penicillin from fungus called penicillium notatum.
  • Tatanus bacillus was discovered to cause tetanus disease.
  • German theory of diseases.
  • Process of fermentation.

Question 10.
Describe the role of blue-green algae in fertility of soil.
Answer:
Blue-green algae can fix free nitrogen of atmosphere in usable compounds and hence increase the fertility of soil. Nostoc, anabaena and oscillatoria are examples of blue-green algae. They also help increase soil or pond fertility. The addition of blue-green algae to barren fields with poor fertility increases the nitrogen and humus content of the field. This improve the water holding capacity of soil and supports crop growth.

Question 11.
State any one useful effect of micro organisms in our life.
Answer:
Some soil bacteria (rhizobium) can fix atmospheric nitrogen, which is useful for plants.
Microorganisms help in the preparation of wines, pickles, vinegar, cheese and curds.

Question 12.
How can you culture micro-organisms? Describe the process in brief.
Answer:
We can culture microorganisms on a media suitable for their growth. This is called culture medium. A culture medium-potato dextrose agar (PDA), can be prepared easily . to culture the microorganisms.

Properly washed potato pieces (about 200 gms) are boiled till they become soft. They are crushed and allowed to cool. About 20 gms of glucose is added in this potato paste and the paste is well mixed in 500 ml of distilled water in a beaker. 20 gms of plain agar is boiled in another beaker containing 500 ml of water. Solution of both the beakers are mixed, covered and stored. This is the culture medium.

A small quantity of the culture medium is taken in a petridish. Petridish is kept open for few hours. Spores of bacteria and fungi present in air position themselves on this culture medium. Then the petridish is kept in a dark, warm and moist place for few days.

After few days, we observe some spots on the culture medium. These spots are the colonies of either bacteria or fungi. We can take a part of the colony and study it in a microscope.

ICSE Class 9 Biology Solutions

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