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Karnataka State Syllabus Class 8 Science Important Questions Chapter 7 The World of Microbes
What are microorganisms?
Organisms which are too small to be seen with the naked eye and hence can be seen only under a microscope are called microorganisms. They are also called microbes.
Give examples for microorganisms.
Amoeba, paramecium, bacteria and algae are some examples of microorganisms.
Describe an activity to observe the microorganisms in pond water.
Take a drop of water collected from a pond on a microscopic slide. Add a drop of methyl cellulose to slow down the movement of microbes. Place a cover slip over the drop and remove excess of water using a blotting paper. Place and observe the slide under a powerful microscope. You will see many different types of tiny organisms which cannot be seen with the naked eye. These are microorganisms.
What is microbiology? Name the scientist who is considered as the father of microbiology.
The branch of science that deals with the study of microorganisms is called microbiology. Louis Pasteur is considered as the lather of microbiology.
What is fermentation? What did Pasteur establish with regard to fermentation?
A chemical reaction in w hich a substance is broken down into simpler substances and generally involving effervescence is known as fermentation. Louis Pasteur established that fermentation is caused by the activity of certain kinds of microbes called bacteria.
What is Pasteurization?
The process of destroying the microbes present in liquids such as milk by heating it to high temperature and suddenly cooling it is known as pasteurization.
What is spontaneous generation? Who propounded it?
The baseless belief that living organisms emerge from non-living matter is known as spontaneous generation. This theory was first advanced by Aristotle.
Who invented the vaccine for rabies?
Louis Pasteur invented the vaccine against rabies.
Describe Louis Pasteur’s swan neck experiment. What did this experiment establish?
The swan neck flask experiment was conducted by Louis Pasteur. He did his experiment in a special type of apparatus called as swan neck (S-shaped) flask. He took nutrient broth solution which contained bacteria in two such flasks. He boiled the broth to kill all the microorganisms present in them. Then he broke the neck of one of the flasks and exposed both flasks to air. Only air free from all the dust and microbes entered inside the flask while dust and microbes got trapped in the neck itself.
After a few days he examined the broth under a microscope. He found no microbes in the swan necked flask. However, they were present in the broken-necked flask. This established that the microbes had entered the flask through dust present in the air. This proved the fact that dust and other contaminants introduced microbes into food and water. Microbes do not appear as a result of spontaneous generation.
What did the swan neck flask experiment conducted by Louis Pasteur establish?
The swan neck flask experiment conducted by Louis Pasteur showed that life arises from pre-existing life.
What is biogenesis?
The principle that living organisms develop only from other living organisms and not from non-living matter is known as biogenesis.
List the contributions of Louis Pasteur to the field of microbiology.
Louis Pasteur’s work led to a greater understanding of human and animal diseases. He developed the methods of sterilization and pasteurization. He discovered the microbes that caused different kinds of fermentation.
He developed techniques to reduce the virulence of infectious organisms without eliminating their capacity to produce immunity. He developed techniques to prepare vaccines against microbial diseases. He developed vaccines against anthrax, cholera and rabies. He disproved the theory of spontaneous generation and established the theory of biogenesis.
Who isolated the bacilli that caused diseases such as anthrax and tuberculosis?
Robert Koch isolated the bacteria (bacilli) responsible for diseases such as anthrax and tuberculosis.
List Robert Koch’s postulates.
Robert Koch made four postulates to establish the relationship between microbe and the disease. These postulates are as follows;
The disease-causing agent must be present in abundance in an organism suffering from the disease, but absent in healthy organisms.
The microorganism can be isolated from a diseased organism and grown in laboratory environment.
The cultured microorganism will cause disease when introduced into a healthy organism.
The disease-causing agent can be recovered from an infected host.
For what work was Robert Koch given the Nobel Prize in 1905?
Robert Koch was awarded the Nobel Prize in 1905 for his work on tuberculosis.
Where do microorganisms live?
Microorganisms live in all kinds of environments including extreme hot and extreme cold conditions. They are found everywhere including in soil, fresh water, sea water, food items, body of organisms, plants etc.
List various types of microbes.
Three major types of microbes are bacteria, viruses and protozoa. Some fungi and algae are also microscopic organisms. Viruses are also microscopic entities which cannot be strictly classified under micro-organisms.
What are bacteria? To which kingdom do they belong?
Bacteria are prokaryotic single-celled microscopic organisms. They belong to the kingdom called monera.
Why are bacteria called prokaryotes?
Bacteria are single-celled organisms without a definitive nucleus. The genetic material is spread throughout the cell. They do not have a nuclear membrane that separates the nucleus from the rest of the cell. Therefore, bacteria are called prokaryotes.
Which are the major components of a typical bacterium?
A bacterial cell mainly consists of a cell wall, a cell membrane and the genetic material (DNA). In some bacterium, we find a whip-like extension from the cell body called flagella. This helps the bacterium to move. In some bacteria, the flagella are absent.
What is the name of the bacteria present in curds? Describe an activity for observing them.
Rod shaped bacteria called Lactobacilli are present in curds. Put a drop of curd on a glass slide. Spread the curd drop evenly and prepare a thin smear. Dry the smear carefully. Add methylene blue stain on the curd smear and leave it for a minute. Remove the excess of stain by washing the slide with water. Place the slide under a powerful microscope. We can see rod shaped bacteria present there and they are known as Lactobacilli.
Where do bacteria usually occur?
Bacteria occur everywhere in the biosphere. They live in air, water and land. Some of them are found in most hostile conditions.
How are bacteria classified on the basis of their shapes? Show by a diagram various kinds of bacteria.
Bacteria may be classified based on their shape as (i) spherical (cocci), rod-like (bacilli), spiral (spiralIi), or comma-shaped (vibrio).
What is the cell wall of bacteria made of?
The cell wall of bacterial cells is made up of a polymer called peptidoglycan. This is also known as murein. This polymer consists of sugars and amino acids. This substance forms a mesh-like layer of the cell wall outside the cell membrane of bacterial cell.
Draw a neat diagram of a typical bacillus bacterium and label the parts.
Explain the structure of a typical bacillus bacterium.
A bacillus is a bacterium that has a rod shaped structure. When seen under an electron microscope, a bacillus bacterium cell is seen to be bound by a cell wall similar to the cell wall in a plant cell. This is the outermost layer of the bacterium cell.
The cell wall is covered by an external layer called the capsule. The plasma membrane is located next to the cell wall which encloses the cytoplasm. Bacteria do not have a nucleus. However, the genetic material namely the DNA is centrally located. Some bacteria have a whip-like tail called flagellum. This helps the bacterium to move itself along.
Name any four human diseases caused by bacteria.
Bacteria can cause diseases in humans which include cholera, anthrax, leprosy and tuberculosis.
Which is the microbe that causes cholera? What are the symptoms of this disease?
Cholera is caused by a bacteria called Vibrio cholerae. The common symptoms of cholera are vomiting, diarrhoea, dehydration and stomach pain.
How does cholera spread? How can the transmission of this disease be prevented?
Cholera spreads through contaminated water and contaminated food. Cholera can be prevented by taking the following measures:
- Avoiding eating contaminated food and drinking contaminated water
- By taking vaccination against cholera.
What are viruses? What is the range of its size?
An ultramicroscopic infectious particle which can become active and replicate itself only in a host cell is called a virus. The size of viruses ranges from 20 to 300 nm. They arc much smaller than bacteria.
Give two examples for viruses.
Examples of viruses include bacteriophage and AIDS virus.
What is the genetic material of a virus?
The genetic material of a virus is either DNA or RNA. However, a virus cannot contain both DNA and RNA.
Describe briefly the structure of a virus.
Viruses are non-cellular entities. They show the characteristics of a living cell only when they are found in a host cell. A virus consists of a nucleic acid core which is made of either DNA or RNA. It is surrounded by a protein coal called capsid. The nucleic acid and capsid will together form nucleocapsid. This structure is either naked or surrounded by a loose membrane called envelope.
Do viruses infect plants? Explain.
Viruses infect all living organisms including plants, animals, humans and bacteria. However, a single virus does not infect all organisms. This is because, viruses are host-specific. Some viruses infect only plants, a few others infect only animals and a few others infect only humans. Others infect only bacteria.
What is a bacteriophage? Draw a neat labelled diagram of a bacteriophage.
Bacteriophage is a virus which infects bacteria. This type of virus can replicate itself inside a bacterial cell.
Explain briefly the structure of a bacteriophage.
A bacteriophage is a virus that attacks bacteria. A bacteriophage consists of a head which encloses the genetic material namely the DNA or RNA. The base of the head has a collar which extends into a tubular tail. The tail is a hollow tube.
The tail is surrounded by a contractile sheath. The tail ends in a base plate. One or more tail fibres are found attached to the base plate. The base plate and tail fibres are involved in binding the virus to the bacterial cell. However, the base plates and tail fibres may not be present in all bacteriophage.
List some of the unique characteristics of viruses.
- Viruses are non-cellular entities.
- Their genetic material consists of either DNA or RNA.
- They grow and multiply only inside a host organism. They are incapable of independent growth.
- They depend on the host cells for their energy.
- They can be seen only under an electron microscope.
Why are viruses called obligate intracellular parasites?
Viruses can grow and multiply only in animal or plant cells or in microorganisms. Hence they are
referred to as obligate intracellular parasites.
What is lysis of bacteria?
There are some viruses which attack bacteria and grow and multiply inside them. During this process they break down the membranes of the host cell. This is known as lysis.
Give an example of a virus that attacks a plant.
Tobacco Mosaic Virus (TMV) is an example of a plant virus.
Classify the following as DNA virus and RNA virus: HIV, Herpes Simplex Virus, Polio virus, Hepatitis B virus, Mumps virus, Varicella-zoster virus, Influenza virus.
- DNA Viruses: Hepatitis B virus, Varicella-zoster virus, Herpes simplex virus.
- RNA Viruses: HIV, Polio virus, Mumps virus, Influenza virus.
List the common symptoms of influenza. What is the causative agent of influenza?
The common symptoms of influenza are
- Chills with fever,
- Sore throat and cough,
- Muscle pain and severe headache.
Influenza is caused by a virus called influenza virus.
How is influenza virus transmittedfrom person to person? What measures can be taken to prevent this infection?
Influenza virus spreads through air and by sharing of infected handkerchiefs. The spread of this infection can be prevented by taking the following measures:
- Avoiding close contact with infected people.
- Avoiding the touch of nose and eyes with contaminated hands.
- Avoiding the sharing of infected handkerchiefs.
How is a bacteriophage different from AIDS virus?
A bacteriophage infects and replicates inside a bacterial cell. AIDS virus infects and replicates inside the body of human beings.
Classify the following as viruses and bacteria: TMV, Lactobacilli, HIV, Bacteriophage, Vibrio cholerae.
- Viruses: TMV, HIV. Bacteriophage
- Bacteria: Lactobacilli, Vibrio cholerae.
What are protozoans? To which kingdom do protozoans belong? Give two examples for protozoans.
Protozoans are eukaryotic unicellular microscopic organisms w ithout a cell wall. They have a true nucleus that encloses the genetic material. Protozoans belong to the kingdom Protista.
E.g. Amoeba, Euglena. Paramecium. Plasmodium etc.
Why are protozoa called eukaryotes?
Protozoans are single-celled organisms which har e a clear nucleus. Hence they are called eukaryotes.
Draw a neat labelled diagram of amoeba.
Distinguish between ectoplasm and endoplasm with reference to amoeba.
Amoeba is a unicellular organism consisting of cytoplasm enclosed by cell membrane.The cytoplasm has two parts namely the ectoplasm and the endoplasm. The ectoplasm is the outer, clear and transparent portion. The inner, viscous, translucent and granular portion is called the endoplasm.
Draw a neat labelled diagram of
Name two diseases caused by protozoans in human beings.
The diseases caused by protozoans in humans include malaria and amoebic dysentery.
What causes malaria? How does this disease spread from person to person?
Malaria is caused by a unicellular protozoan called Plasmodium vivax. This infection spreads from person to person through the bite of female anopheles mosquitoes.
What are the symptoms of malaria? Suggest measures to prevent the occurrence of malaria.
The symptoms of malaria are:
- Recurring fever and chills,
- Headache and muscle pain.
- Stomach pain
- Nausea and vomiting.
Malaria can be prevented by controlling mosquito population, use of mosquito curtains and mosquito repellents.
What are algae? Give two examples of microscopic algae.
Unicellular or multicellular eukaryotic plants which can carry out photosynthesis are called algae.
Examples of unicellular algae include Chlamydomonas and spirogyra.
Draw a neat labelled diagram of Chlamydomonas.
Describe briefly the structure of Chlamydomonas.
Chlamydomonas is a unicellular alga. It is oval or spherical in shape. The body cell is enclosed in a cell membrane which is in turn surrounded by a cell wall. The cell wall is made up of either cellulose or pectin. The cell contains cytoplasm and nucleus.
It also has cup-shaped chloroplast. There are two flagella situated in the anterior near the pointed end of the cell body and they originate from the basal granules. Each cell typically possesses two contractile vacuoles at the base of flagella. They have respiratory and excretory functions. An orange-red pigment spot called eye-spot is present. This structure is receptive to light.
What are fungi? Give two examples for microscopic fungi.
A group of saprophytic eukaryotic organisms are called fungi. Some fungi are microscopic and others are macroscopic organisms.
Examples of microscopic fungi include penicillium, aspergillus and yeasts.
Describe an activity to observe rliizopus (bread mold).
Keep a thin moist bread slice in a plastic bag for two to three days. You will sec the growth of fungi called rhizopus (also called bread mold) on the bread slice. Place a drop of lactophenol or cotton blue stain on a clean glass slide. Transfer a small bunch of rhizopus on to the slide. Gently squash the material. Place a cover slip and examine the slide under a powerful microscope. You will see filaments of rhizopus.
List the characteristics of fungi.
Fungi are eukaryotic organisms which are either unicellular or multicellular. Most fungi are however multicellular organisms. The cell is surrounded by a cell wall. They derive nutrition from dead and decaying matter and hence are called saprophytes. The fungi form characteristic filamentous tubes called hyphae. This structure helps to absorb nutrients. The collection of hyphae is called mycelium. Fungi reproduce by spore formation.
How do fungi reproduce?
Fungi reproduce with the help of spores.
What is chitin?
Fungi have cells that have a cell wall. The cell wall of fungi is made of a primary substance called chitin.
Why are fungi called saprophytes?
Fungi derive their nutrition by absorbing organic material from dead and decaying matter. This is why fungi are known as saprophytes.
Distinguish between hyphae and mycelium.
The vegetative part of a fungus consists of a network of fine white filaments called mycelium. Kach of the branching filaments of the mycelium of a fungus is called hyphae.
Describe an activity to observe yeast cells.
Make a suspension of yeast using yeast powder and water. Place a drop of this suspension and prepare a smear on a slide. Stain the smear with methylene blue. Place the slide under a powerful compound microscope and observe. You will see yeast cells.
Draw a neat diagram of a yeast cell and label the parts.
Describe briefly the structure of yeast cell.
The yeasts are unicellular fungi. The cells are eukaryotic and have an elliptical shape. The outermost cell wall is made of chitin. Inner to the cell wall, cell membrane is present. The other cell organelles include endoplasmic reticulum, ribosomes, mitochondria, vacuoles, golgi bodies and nucleus. These are enclosed in the cell membrane.
With the help of a neat diagram explain briefly the structure of aspergillus.
Aspergillus is a filamentous unicellular fungus. It is saprophytic fungi. The cell wall is made of hyphae. Hyphae are branched. The cells are either uni-nucleate or multinucleate. Most species have a characteristic pigment that gives them their colour.
Describe how we see yeast cells in a microscope.
Mix yeast powder in water taken in a bowl. Take a drop of this suspension and prepare a smear on a slide. Stain the smear with methylene blue. Observe the smear under a microscope. You can see yeast cells now.
Classify the following as algae and fungi: Diatoms, Rhizopus, Chlamydomonas, Yeast, Spirogyra, Aspergillum.
- Algae: Diatoms, Chlamydomonas, Spirogyra.
- Fungi: Rhizopus, Yeast, Aspergillum.
What is aspergillosis? How is it caused?
Aspergillosis is a fungal disease which causes cough, fever, chest pain and difficulty in breathing. It is caused by spores of a type of fungi called aspergillus niger.
How is aspergillosis spread? How can it be prevented?
Aspergillosis spreads by inhaling spores of aspergillus niger. It can be prevented by avoiding inhaling the spores which are usually present in dusty and unhygienic places.
What is meant by culturing of micro-organisms?
The growing of micro-organisms in artificial media under controlled laboratory conditions is known as culturing of microbes.
What is a culture medium?
A culture medium is an artificially controlled environment which supplies the ingredients necessary for the growth of an organism.
Name a suitable culture medium for the growth of
|1. Bacteria||Nutrient Agar|
|2. Fungi||Potato Dextrose Agar|
|3. Protozoans||Nutrient Broth media|
|4. Algae||Beneck’s media|
|5. Viruses||Chick embryo|
What are vaccines? Name any two commonly used vaccines.
Any biological preparation (made of weakened or killed microorganisms) that is administered to produce or artificially increase immunity to a particular disease is known as vaccine. Commonly known vaccines include Polio vaccine and DPT vaccine.
What are antibiotics? Give two examples.
Chemical substances produced by microorganisms which are used to kill or inhibit the growth of other microorganisms in the body of another organism are known as antibiotics.
E.g. Penicillin. Streptomycin, Nystatin, Amantadine etc.
Multiple Choice Questions
Which one of the following does not belong to the group?
(a) aspergillus niger
(d) vibrio cholerae
(d) vibrio cholerae
The locomotory structure in amoeba is called
Cholera is caused by a germ that belongs to the group
Which of the following types of microorganisms and its example is not correctly matched?
(a) Bacteria – prokaryotic
(b) Fungi – eukaryotic
(c) Algae – saprophytic
(d) Protozoa – unicellular animal
(c) Algae – saprophytic
Chlorophyll is present in
Which of the following is not a characteristic of bacteria?
(a) Most possess cell walls.
(b) All are unicellular,
(c) These are prokaryotic.
(d) All are pathogenic.
(d) All are pathogenic.
The carrier of malaria-causing protozoan is
(b) female anopheles mosquito
(b) female anopheles mosquito
Malaria caused by plasmodium vivax spreads from person to person through
(a) mosquito bites
(b) contaminated air
(c) polluted water
(d) All of the above.
(a) mosquito bites
Which one of the following is not an algae?
An example of a protozoan is
(b) Blue green algae
Fill In The Blanks
1. The scientist who is considered as father of microbiology is Louis Pasteur
2. The theory of biogenesis was established by Louis Pasteur
3. Malaria is caused by Plasmodium vivax
4. Vibrio bacteria are in the shape of comma
5. Bacteria, protozoa, some algae and fungi are all examples of microorganisms
6. A virus that attacks bacteria is known as bacteriophage
7. Spherical bacteria are called cocci
8. Yeast is a kind of fungi