Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 7 World of Microbes offer valuable context and analysis.
WBBSE Class 8 Science Chapter 7 Question Answer – World of Microbes
Multiple Choice Questions & Answers : (1 mark for each question)
Microbes have survived in the earth over —
i) 5.8 billion years
ii) 2.8 billion years
iii) 8.8 billion years
iv) 3.5 billion years
iv) 3.5 billion years
Microbes grow better in —
i) darker place
ii) direct sunlight
i) darker place.
A protozal disease —
Microbes are of —
i) three types
ii) four types
iii) two types
iv) five types
ii) four types
Vaccine of hydrophobia was discovered by —
i) Robart Koch
ii) Louis Pasteur
ii) Louis Pasteur
Through sneezing spreads —
A fungal disease —
i) Ring worm
iv) Kaja azar
Microbes are found in —
If by mistake some one consumes colourful fungi, lie or she will suffer from —
iii) enteric disease
iii) enteric disease
Baoteria, Virus P, Fungus P can convert the alcohol to vinegar.
State whether True or False : (1 mark for each question)
1) Virus possess DNA or RNA surrounded by protein coat.
2) Tuberculosis is a water-borne disease.
3) Microbes cannot survive in direct sunlight.
4) Microbes can take food from hot foodstuff.
5) Virus is a microbe.
6) The microbes can grow better at 70° – 80°C temperature.
7) Algae can synthesise their own food.
8) Ringworm is a protozoal disease.
9) Some colourful fungi are poisonous.
10) Chlamydomonas is multicellular.
11) Dry places are ideal for growth and survival of the microbes,
2) All viruses are parasites and disease-causing agents.
Fill in the blanks : (1 mark for each question)
1) The living organisms that cannot be seen with naked eyes are called ……………
2) Microbes have survived over ……………years in the earth.
3) The total mass of microbes is …………… of the mass of all living organisms.
4) NearIy…………… of oxygen inhaled by us come into the atmosphere from the microbes.
5) Microbes cannot survive in direct ……………
6) Microbes collect their food from ………….. and ………….. organic substances.
7) The organisms that can produce their own food are ……………
8) The …………..bacteria can grow at 100°C.
9) …………… are structurally very simple and smallest among all living organisms.
10) In Bacteria ………….. is present instead of true nucleus.
11) The description of bacteria was given for the first time by ………….. in 1683.
12) The term bacteria was first used by ………….. in 1828.
13) Presently, bacteria are placed in kingdom ……………
14) Name of a colonial algae is …………..
15) From the research of ………….. we come to know the possible existence of a virus that causes small pox.
16) ………….. are acellular.
17) ………….. bacteria live in the intestine of humans for their food and shelter.
18) The interrelationship between host and microbes are called …………..
19) ………….. is prepared from sugar or starch by using yeast.
20) When a sample of warm milk at a temperature of ………….. is mixed with ………….. present in curds, vigorous growth of bacteria takes place.
2) 3.5 billion
6) dead, decaying
10) spiral DNA.
11) Antonyh von Leauwen hock,
15) Edward Jenner
17) E. coli
20) 37°C, Lactobacillus.
Match the following : (1 mark for each question)
a) Match the column A with column B.
2) Thermophilic bacteria
3) Louis Pasteur
5) Lactic acid
6) The term ‘virus’ means
8) Bacteria is placed in
|a) grow and survive at 100°C.
b) first used the term bacteria.
c) mosquito-borne disease
d) discovered vaccine of hydrophobia
f) present in curd
g) kingdom of Monera
1) Malaria, mosquito borne disease.
2) Thermophilic bacteria grow and survive at 100°C.
3) Louis Pasteur discovered vaccine of hydrophobia.
4) Ehrenberg first used the term bacteria.
5) Lactic acid present in curd.
6) The term virus means poison.
7) Multicelluar — Spirogyra.
8) Bacteria is placed in Kingdom of Monera.
Very Short Questions & Answers : (1 mark for each question)
What are microbes?
Besides plants and animals, many other living organisms remain scattered around us which are not seen with naked eyes, these are called microbes.
For how many years microbes are there in the earth?
Microbes have survived over 3.5 billion years in the earth.
How many microbes are there in the soil under our feet?
Near about 10 lakhs of microbes are there in the soil under our feet.
How many microbes are there in 1g of soil?
It is speculated that about 100 crore microbes are present in 1g of soil.
What type of place is ideal for the growth of microbes?
Damp and swampy places are ideal for the growth of microbes.
Name some microbes who find shelter in other organisms?
Microbes who find shelter in other organisms are virus, bacteria (Monera), fungi and protozoa etc.
Where can we find the thermophilic bacteria?
The thermophilic bacteria are found in hot springs and hydrothermal vent.
What is the shape of Bacteria?
Bacteria have various shapes — like a eamma, rod, spiral and rounded.
What is present in bacteria instead of true nucleus?
Spiral DNA (nucleoid) is present instead of true nucleus.
Who gave description of bacteria first time?
Anatomy von Leeuwen hock.
Who discovered vaccine of hydrophobia?
Louis Pastur, a French scientist discovered vaccine of hydrophobia.
Who discovered two human pathogens Cholera and Tuberculosis?
German Scientist Robert Koch.
Who first used the term bacteria?
The term bacteria was first used by Ehrenberg in 1828.
How many cells are there in Protozoa?
Protozoa are unicelluar.
Name the locomotary organs of protozoa.
Their locomotary organs are pseundopodia, whiplash flagella or hair-like cillia.
What is hyphnae?
The small filamentous part of a fungi is called hyphae.
When a mycelium is formed?
The large number of hyphae together form a mycelium.
Where Algae are found?
Algae are acquatic, they are found in marine and fresh water.
Why Algae can synthesist their own food?
Various types of chloroplasts are present in algae so they can synthesise their own food.
What the term ‘Virus’ means?
The term ‘ Virus’ is actually a Latin word which means poison.
Name a unicellular and a multicellular algae.
Chlamydomones is a unicellular algae and Sprigyra is a multicellular algae.
Who discovered the vaccine of small pox?
Write name of three Bacterial disease.
Tuberculosis, Whooping Cough, Cholera.
Write name of three virul diseases.
Influenza, Mumps, Pox.
Write name of three Protozoal diseases.
Amoebiasis, Malaria, Giardiasis.
Write name of three Fungal diseases.
Ringworm, Allergy, diseases of nose throat and lung.
Which crops increase nitrogen in soil?
Leguminous crops like pulses, pea etc increase nitrogen in soil.
Which vitamin helps to synthesise haemoglobin in RBC?
Which bacteria live in the nodule of the leguminous plant?
Symbiotic bacteria like Rhizobium live in the root nodules of the leguminous plants.
What is symbiosis?
Sometimes organisms live together for sharing their nutrition, this association is known as symbiosis.
How majority of the plants take nitrogen?
Majority of the plants take nitrogen in the form of NO3 or NH4.
Name some organisms which fix atmospheric nitrogen directly.
Clostridium, Azotobacter and a few cyanobacteria fix atmospheric nitrogen directly.
What is ammonification?
After the death of plants and animals, the protein components are broken down into ammonia, this process is called ammonification.
What is Nitrification?
Ammonia is converted into nitrate and nitrite by nitrifying bacteria, namely Nitrosomonas orNitrobacter, this process is called Nitrification.
How jute fibre can be separated?
The jute fibre can be separated easily by decomposing pectin which is present in the cell wall of jute.
Which bacteria is present in curd?
Who first discovered an antibiotics?
Alexander Flemming first discovered an antibiotic in the year 1928.
Name some antibiotics?
Penicillin, Streptomycin, Chloromycetin. Ampicillin etc.
Short Questions & Answers : (2 marks for each question)
What is Staining?
Sometimes to identify microbes under microscope we use various coloured substances for their identification, these coloured substances are known as stain and the process is called Staining.
What are parasitism?
Some of the microbes that enter our body through various agents finally reach inside the cell. This interrelationship between host and microbes are called parasitism.
What are antigens?
When any microbe (virus, bacteria) enters our body, many harmful compounds eminateu from their whole body or body surface and mix with our body fluids, they are called antigens.
What are antibody?
A type of compound gets synthesised in our body in order to destroy the antigens. The compounds are protein in nature and are referred to as antibody.
What is Immunity?
The power of resistance of any organism against infection is called Immunity.
What are antibioties?
Some organic compounds produced by some bacteria and fungi under the process of grotli of other bacteria or even kill them. Many life saving drugs manufactured through different processes of purification and chemical changes of these compounds, these life-saving drugs are called antibiotics.
What is symbiosis, define?
Sometimes organisms live together for sharing their nutrition. In the association of nodule-forming bacteria and root of leguminous plant in the association of E.ccoli and humans, both the bacteria never harm the host both are mutually benefited. This type of association is known as symbiosis
Long Questions & Answers : (3 marks for each question)
Write four characteristics of microbes.
- Microbes are found almost everywhere.
- Damp and swampy places are ideal for their growth and survival.
- They collect their food from dead and decaying organic substances, from different organs, tissues or cells of animals in which they take shelter. Some are able to synthesise their own food.
- Generally, the microbes can grow better at 25tvC to 38°C.
Write some characteristics of Bacteria.
- Bacteria are structurally very simple and smallest among all living organisms.
- They have various shapes – like a comma, rod, spiral and rounded.
- Spiral DNA (nucleoid) is present instead of true nucleus.
- Membraneless ceil organelle like ribosome is present.
Write some characteristics of Protozoa.
- Protozoa are unicellular and placed under protista having one or more nucleus.
- They are variously shaped
- They live freely as a single entity or in a colony, some live in the host body and cause disease.
- Their locomotory organs are pseudopodia, whiplash flagella or hair-like cilia.
Write some characteristics of Fungi.
- Body of Fungi is not differentiated into root, stem and leaves.
- They are unicellular or multicellular filamentous.
- They have cell wall, nucleus and other organelles but are devoid of chloroplast. Hence, they cannot synthesise their food.
- Cell wall is not similar to the cell wall of higher plants.
- They can survive in water, land either in presence or in absence of sunlight.
Write some characteristics of Algae.
- Body of Algae is not differentiated into root, stem and leaves.
- They are unicellular or multicellular.
- Their cell contains cell wall, nucleus, other organelles and chloropiasts, so they can synthesise their own food.
- They requere sunlight for their growth.
- All are acquatic (marine and fresh water).
Write some characteristic features of virus.
- Viruses are acellular.
- They have no boundary wall, cytoplasm or nucleus instead they possess a nucleic acid (DNA or RNA) surrounded by protein coat.
- All are parasites and disease-causing agents. They behave as inert particles, only when they enter the body of the host they behave like living being.
What is parasitism, define?
Some of the microbes that enter our body through various agents finally reach inside the cell. They cannot survive alone, they depend on the host, organ or cell for their food and shelter. When they grow inside the host cell, they inhibit the normal function of the cell and hamper the physiological process of the host. It may cause death of the host. This interrelationship between host and microbes are called parasitism.
What is saprophytism?
Many microbes grow’ on dead animals and help in the decay of organic matter. They decompose the organic mater into simpler compounds with the help of secreted enzymes. This helps plants consume these as nutrients. Numerous bacteria and fungi secrete digestive juices on the substratum, on which they grow end obtain their food. This process is known as saprophytism.
Suggest five ways in which we can preserve food?
- By keeping food products in airtight containers (Canning).
- By mixing salt with fish, meat and fruits (salting).
- Pieces of mango, lemon onion etc can be preserved by adding vinegar (Pickling)
- Food can be preserved by storing at low temperature (Refrigeration)
- Milk can be preserved by pasteurization.
What is vaccination or Innnunitsation? Name some diseases which can be prevented by Vaccinations.
Dead or weak but live microbe or weakly toxic substances released from the body of microbes are administred in a human being in a definite dose.
The defence mechanism become; activated in the individual against any particular infectious disease, in advance. This process is called Vaccination or Immunisation, it has been possible to control spreading of many diseases like typhoid, Tetanus, Polio and Diphtheria by the use Vaccines.
Explain some ways, of treatment of waste.
- Any untreated waste like human faeces or untie always bear some risk for human health. Some bacteria Living in less oxygenated atmospheres are able to break down these wastes to nitrate and phosphate. They reduce the chance of infection and also increase soil fertility.
- in countries like India and China, Methanogenic bacteria degrade human or animal faces, vegetable peels and produce methane gas. They act as substitutes for coal or Kerosene.
- Some algee are being used in space shuttles to clean the air.