ICSE Living Science Biology for Class 7 Solutions Chapter 9 Life Under a Microscope

Check Your Progress

Fill in the blanks.

Question 1.
………….. are spherical-shaped bacteria.
Answer:
Cocci are spherical-shaped bacteria.

Question 2.
……….. algae contain brown pigments along with chlorophyll.
Answer:
Brown algae contain brown pigments along with chlorophyll.

Question 3.
Kelps contain a gummy substance called ………..
Answer:
Kelps contain a gummy substance called algin.

Question 4.
An important product called ………….. is obtained from red algae.
Answer:
An important product called agar is obtained from tion

Question 5.
…………. are extensively used in making metal polish, toothpaste and porcelain.
Answer:
Diatoms are extensively used in making metal polish. toothpaste and porcelain.

Practice Question 1.
A …………… colony is a hollow sphere made of many identical cells.
Answer:
A Volvox colony is a hollow sphere made of many identical cells.

Check Your Progress

Question 1.
Bacteria are used in …………. of leather and …. ……..of fibres.
Answer:
Bacteria are used in tanning of leather and retting of fibres.

Question 2
…………… is prepared by fermentation of …………. by yeast.
Answer:
Alcohol is prepared by fermentation of cereals by yeast.

Question 3.
………… is a fungus used in the baking industry.
Answer:
Yeast is a fungus used in the baking industry.

Question 4.
…………. is used for the fermentation of sugar to manufacture alcohol.
Answer:
Yeast is used for the fermentation of sugar to manufacture alcohol.

Question 5.
Two diseases caused by viruses are ………….. and ………….
Answer:
Two diseases caused by viruses are polio and AIDS.

Question 6.
Imporperly canned food can cause a dangerous disease called …………..
Answer:
Imporperly canned food can cause a dangerous disease called botulism.

A. Tick the most appropriate answer.

Question 1.
What is the shape of vibrios bacteria ?
a. Rod-shaped bacteria
b. Spherical bacteria
c. Comma-shaped bacteria
d. Triangular bacteria
Answer:
c. Comma-shaped bacteria

Question 2.
Which type of bacteria can grow in the absence of oxygen ?
a. Saprophytic bacteria
b. Parasitic bacteria
c. Anaerobic bacteria
d. Aerobic bacteria
Answer:
c. Anaerobic bacteria

Question 3.
Which of these is a colonial alga ?
a. Chlamydomonas
b. Chlorella
c. Diatoms
d. Volvox
Answer:
d. Volvox

Question 4.
Laminaria and Fucus are examples of
a. red aglae
b. green algae
c. brown algae
d. blue-green algae
Answer:
c. brown algae

Question 5.
All organisms belonging to the group protozoa are –
a. unicellular
b. multicellular
c. colonial
d. filamentous
Answer:
a. unicellular

Question 6.
Pneumonia is caused by –
a. virus
b. Amoeba
c. bacteria
d. paramecium
Answer:
c. bacteria

Question 7.
Malaria is caused by –
a. Amoeba
b. Entamoeba
c. Plasmodium
d. giardia
Answer:
c. Plasmodium

Question 8.
Botulism and Tuberculosis are caused by –
a. bacteria
b. protozoa
c. fungi
d. viruses
Answer:
a. bacteria

B. Fill in the blanks.

Question 1.
The bacteria that need oxygen to grow are called ………………. bacteria.
Answer:
The bacteria that need oxygen to grow are called aerobic bacteria.

Question 2.
…………. are the simplest green plants that contain chlorophyll and usually live in water.
Answer:
Algae are the simplest green plants that contain chlorophyll and usually live in water.

Question 3
………….. are on the borderline of the living and non – living worlds.
Answer:
Viruses are on the borderline of the living and non-living worlds.

Question 4
…………… are the microrganisms without chlorophyll.
Answer:
Bacteria are the microrganisms without chlorophyll.

Question 5.
…………… is a bread mould.
Answer:
Rhizopus is a bread mould.

Question 6.
…………… is also used to ferment skimmed milk to butter milk.
Answer:
Lactobacillus (bacteria) is also used to ferment skimmed milk to butter milk.

Question 7.
The process of treating animal skin to produce leather is called ………….
Answer:
The process of treating animal skin to produce leather is called tanning.

C. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
Microorganisms live in extremely dry conditions.
Answer:
False. Microorganisms live in warm and humid weather.

Question 2.
The mushrooms that we eat are a type of bacteria.
Answer:
False. The mushrooms that we eat are a type of fungus.

Question 3.
Red algae do not have chlorophyll
Answer:
False. Red algae contain chlorophyll as well as red and blue pigments.

Question 4.
Algae are nature’s scavengers.
Answer:
False. Saprophytic bacteria are nature’s scavengers.

Question 5.
A spore-forming organism that lacks chlorophyll and absorbs food substances made by other organisms is an alga.
Answer:
False. A spore forming organism that lacks chlorophyll and absorbs food substances made by other organisms is a bacteria.

Match the following :

Column A Column B
1. typhoid a. virus
2. polio b. bacteria
3. ringworm c. protozoa
4. diarrhoea d. fungus

Answer:

Column A Column B
1. typhoid b. bacteria
2. polio a. virus
3. ringworm d. fungus
4. diarrhoea c. protozoa

E. Find the odd one out. Give reasons.

  1. Clilamydomonas, Spirogyra, Volvox, Mucor
  2. Spirogyra, Ulothrix, Volvox
  3. Amoeba, Chlamydomonas, Paramecium, Euglena
  4. Giardia, mushroom, bread mould, Penicillium

Answer:

  1. Mucor – It is a fungus while rest all are types of algae.
  2. Volvox – It is a colonial alga while the rest two are filamentous algae.
  3. Chlamydomonas – It is an alga while the rest all are protozoa.
  4. Giardia – It is a protozoa while rest all are fungi.

F. Answer the following in short.

Question 1.
Write two examples of filamentous algae.
Answer:
Spirogyra and Ulothrix.

Question 2.
What are bacteriophages ?
Answer:
Viruses which attack bacteria and infect bacterial cells are known as bacteriophages.

Question 3.
Name the bacterium which causes cholera in human beings.
Answer:
Vibrio cholerae causes cholera in human beings.

Question 4.
Why are bacteria and fungi called nature’s scavengers?
Answer:
Bacteria and fungi are called nature’s scavengers because they help in cleaning the earth. They decompose excretory products and dead remains of plants and animals into simple substances. Thus, they clear the earth of all the wastes.

Question 5.
What is retting of fibres ?
Answer:
Separation of fibres from the long lasting line stem of fibre plants, such as flax and jute is called retting of fibres. This is brought about by the action of bacteria on plant parts submerged in water.

Question 6.
Name the bacteria that helps in the formation of curd.
Answer:
Lactobacillus

H. Answer the following in detail.

Question 1.
What are the conditions that facilitate the growth of bacteria ?
Answer:
Conditions which facilitate the growth of bacteria are :
a. Most bacteria grow best in the range of temperature between 25°C to 40°C. Some bacteria can grow at a very high or low temperature.
b. Bacteria grow best in darkness. Sunlight kills many kinds of bacteria. ,
c. They become active in moisture otherwise become inactive.
d. Most of the bacteria can survive under extreme harsh conditions due to formation of hard protective covering around them called a cyst or a spore. They remain inactive in the cyst during unfavourable conditions.
e. They are also affected by the presence or absence of oxygen.

Question 2.
How do bacteria obtain their nutrition ? How do bacteria survive harsh conditions ?
Answer:
Bacteria lack chlorophyll and hence cannot prepare their own food. They depend on other sources for their food. They may be saprophytes i.e. derive their food from dead and decaying matter or they may be parasites i.e. obtain their food by living on or inside the body of other organisms. Thus most of the bacteria are heterotrophs. However, there are some bacteria which are autotrophic and are able to synthesise their own food.

Bacteria can survive under harsh conditions due to the formation of a hard protective covering around them called a cyst or a spore. They remain inactive in the cyst during unfavourable conditions. The hard protective covering protect it from the unfavourable conditions and it becomes active during favourable conditions by breaking the cyst wall.

Question 3.
Name the three groups of algae. How are they different from each other ?
Answer:
The three groups of algae are :
(i) Red algae
(ii) Green algae
(iii) Brown algae
Living Science Biology Class 7 ICSE Solutions Chapter 9 Life Under a Microscope - 1 - Copy

Question 4.
List five ways in which algae are useful.
Answer:
Algae are useful in the following ways :

  • They are the major sources of food for organisms that cannot make their own food and live in water.
  • They also release and large amount of oxygen during photosynthesis.
  • Algin, used for preparing ice- cream and toothpaste is obtained from kelp, an. alga.
  • Agar obtained from red algae is used in the laboratory for various experiments.
  • Some red algae are also used as food since they are a rich source of proteins, vitamins and minerals.
  • The cell wall of diatoms contains silica and are extensively used in making metal polish, toothpaste and porcelain.

Question 5.
List five ways in which bacteria are useful on the commercial basis.
Answer:
Bacteria are useful on the commercial basis
There uses are :

  • They are used in the manufacture of vinegar, curd and cheese.
  • They are also used in the production of tea coffee and cocoa.
  • Lactic acid, citric acid and alcohol are also obtained by the action of bacteria.
  • Bacteria are also involved in tanning of leather.
  • Retting of fibres is also brought about by the action of bacteria.
  • Bacteria also help in generating biogas.
  • Certain medicines like antibiotics and vitamin B complex are manufactured with the help of bacteria

Question 6.
How are bacteria harmful to human beings?
Answer:
Bacteria are harmful to the human beings in the following :
(i) Certain bacteria can cause diseases in human beings. Tuberculosis, tetanus, whooping cough, cholera, plaque,
leprosy, diphtheria and pneumonia are bacterial diseases. Bacteria also causes diseases to plants.

(ii) Spoilage of food, rotting of fruits, vegetables meat is also caused by bacteria. Improperly canned food items sometimes have certain anaerobic bacteria which release certain toxic substances causing a dangerous disease called botulism. Poultry products also carry disease-causing germs which may cause stomach infection, a kind of food poisoning.

(iii) Gastroenteritis, urinary tract infections are also caused by bacteria- Escherichia coli. Typhoid and food poisoning are caused by salmonella. Tuberculosis, a lung disease is caused by Mycobacterium tuberculosis.

Question 7.
Give four ways of protecting food stuff from spoilage by fungi and bacteria.
Answer:
Food stuffs may be protected from the attack of fungi and bacteria by the following ways.

  • Dry the food, this prevents microorganisms to multiply. Cereals and pulses are dried under the sun before storage.
  • Fungicides can be sprayed on standing crops from being destroyed.
  • Keep the food at low temperature in the refrigerator prevents spoilage of food. As fungus does not multiply in cold conditions.
  • Using of salt, sugar or other chemical preservatives prevents the growth of fungus.

H. Give reasons.

Question 1.
Your mother dries certain vegetables and stores them in airtight containers.
Answer:
Vegetables are dried to prevent the growth of microorganisms as they require moisture for their growth. They are stored in air tight containers so that microorganisms may not enter from the air.

Question 2.
Surgical instruments are boiled in water before using them for an operation.
Answer:
Surgical instruments are boiled in water before using them for an operation because boiling kills the microorganisms.

Question 3.
The dough prepared for making idli rises when kept overnight.
Answer:
Dough prepared for making idli rises when kept overnight due to the action of yeast. It becomes light, fluffy and sour. Yeast multiplies and produces carbondioxide which raises the dough.

I. Draw the following.

Question 1.
Different shapes of bacteria
Answer:
Living Science Biology Class 7 ICSE Solutions Chapter 9 Life Under a Microscope - 2

Question 2.
Chlamydomonas
Answer:
Living Science Biology Class 7 ICSE Solutions Chapter 9 Life Under a Microscope - 3

Question 3.
Bread mould
Answer:
Living Science Biology Class 7 ICSE Solutions Chapter 9 Life Under a Microscope - 4

J. Identify the following microorganisms. Write one unique feature of each.
Answer:
Living Science Biology Class 7 ICSE Solutions Chapter 9 Life Under a Microscope - 5
Living Science Biology Class 7 ICSE Solutions

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