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CBSE Questions for Class 8 Biology Microorganisms Friend And Foe Quiz 6 - MCQExams.com
CBSE
Class 8 Biology
Microorganisms Friend And Foe
Quiz 6
State whether the given statement is True or False:
Lightening can fix nitrogen.
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True
0%
False
Explanation
Other than some bacteria like Rhizobium, lightening can naturally fix nitrogen.
The given statement is True.
________ are disease-causing organisms that are so small you need a microscope to see them.
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Pathogens
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Humans
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Insects
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Both A and C
Explanation
A pathogen is an organism that can produce disease. It is also referred to as an infectious agent or a germ.
These include infectious microorganisms such as a virus, bacterium, protozoan, or fungus, which can be observed only under a microscope.
Thus, option A is correct.
Which of the following is not a fungus?
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Mould
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Yeast
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Rhizobium
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Mushroom
Explanation
Out of the given options, Rhizobium is not a fungus, but a bacterium, which help in nitrogen fixation for leguminous plants.
The rest, mould, yeast and mushroom are fungi.
The correct option is C.
________ can be passed to a person from another person, animal or object.
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Communicable diseases
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Non- communicable diseases
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Deficiency diseases
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Genetic diseases
Explanation
Communicable diseases can be passed to a person from another person, animal or object. Example- Viral fever, cholera and malaria.
Thus, option A is correct.
Nitrogen-fixing bacteria like Rhizobium live in the root ________ of the leguminous plants.
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hair
0%
tip
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nodules
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None of the above.
Explanation
Bacteria like Rhizobium live in the root nodules of leguminous plants and help in nitrogen fixation by forming a symbiotic relationship with the plant.
The correct option is C.
Pathogens like to attack humans because of the following reasons?
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Shelter
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Food source
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Place to multiply
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All of the above
Explanation
Pathogens are disease-causing organisms that attack humans (host) for shelter, food source, and for multiplying in their body and as a result spread the disease. Pathogen lives as endoparasite as well as ectoparasite, the food source is the cell of the host and the stored material. The pathogen undergoes asexual reproduction thus multiply vastly in a short period of time.
So, option D is correct.
Which of the following causes leaf rust of wheat?
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A bacterium
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A fungus
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A virus
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A protozoan
Explanation
Leaf rust of wheat is a fungal disease. Rust fungi are plant pathogens. They affect the
stem, leaves, and grains of
wheat, barley, and rye. On getting infected, dusty, reddish-orange, or reddish-brown lesions appear on the surface of leaves and stem, giving a rust-like appearance.
So, the correct answer is option B.
What are antibiotics?
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Medicines used against AIDS.
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Medicines used to kill or stop the growth of harmful or disease-causing microbes in the human body.
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Medicines used against viral infection.
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Medicines used against malaria.
Explanation
Correct option - B
Explanation for correct option -
In 1929, Alexander Flemming discovered the first antibiotic, penicillin.
Antibiotics such as streptomycin, erythromycin, tetracycline, etc. are commonly used drugs.
Antibiotics are medicines used to kill or stop the growth of harmful disease-causing microbes in the body.
They could be in the form of pills, capsules, or liquid. They work by killing the harmful microbes or they stop their spread.
Several microorganisms cause diseases in plants and reduce yield. Which of the following plant diseases is incorrectly matched with its causal microorganism?
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Citrus canker - Bacteria
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Tobacco mosaic - Virus
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Rust of wheat - Fungi
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Yellow vein mosaic of bhindi - Bacteria
Explanation
The causal agent for yellow vein mosaic of bhindi is the single-stranded DNA Bhendi yellow vein mosaic virus (BYVMV), which is associated with a $$\beta$$-satellite, both of which are required for infection. BYVMV belongs to the genus Begomovirus, family Geminiviridae.
So, the correct answer is option D.
What are the important products of yeast fermentation?
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Ethanol and acetic acid
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Butanol, glycerol and pyruvic acid
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Phenyl ethanol, amyl alcohol and caproic acid
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All of the above
Explanation
Ethanol forms an integral component of alcoholic beverages. It is produced by the fermentation of sugars by yeasts.
Acetic acid is a normal by-product of the alcoholic fermentation carried out by
Saccharomyces cerevisiae
.
So, the correct answer is option A.
Microorganisms are our friends and foes. Some of them are useful for us while some of them are harmful.
From the given list sort out useful and harmful actions of microorganisms.
Production of antibiotics, food spoiling, curd preparation, vaccine production, citrus canker.
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Useful: Curd preparation, citrus canker, production of antibiotics
Harmful: Food spoiling, vaccine production
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Useful: Production of antibiotics, curd preparation, vaccine production
Harmful: Food spoiling, citrus canker
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Useful: Citrus canker, vaccine production, curd preparation
Harmful: Food spoiling, production of antibiotics
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Useful: Vaccine production, curd preparation
Harmful: Food spoiling, citrus canker, production of antibiotics
Explanation
An
antibioti
c
is a chemical substance that inhibits the growth of bacteria. They hinder the reproductive cycle of the bacteria inside the body of the host.
Lactobacillus
is a genus of bacteria, which can convert sugars into lactic acid through fermentation.
A
vaccine
is a biological preparation that provides active acquired immunity to a particular disease. It has killed or weakened suspension of microorganisms which generates the immune response.
Citrus canker
is a disease affecting citrus species caused by the bacterium
Xanthomonas axopods
. The infection causes lesions on the leaves, stems, and fruit of citrus trees, including lime, oranges, and grapefruit.
Microorganisms like fungus release toxins that spoils the food.
So, the correct answer is option B.
Match column I with column II and select the correct option from the codes given below.
Column I
Column II
(a) Pathogens
(i) Pathogen-carrying organisms
(b) Vaccination
(ii) Prevents the growth of micro-organisms
(c) Pasteurization
(iii) Microbes that cause diseases
(d) Vectors
(iv) Gives immunity
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(a)- (ii), (b)- (i), (c)- (iii), (d)- (iv)
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(a)- (iii), (b)- (iv), (c)- (ii), (d)- (i)
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(a)- (i), (b)- (ii), (c)- (iii), (d)- (iv)
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(a)- (iv), (b)- (iii), (c)- (ii), (d)- (i)
Explanation
$$\textbf{Correct option:}$$
Option B
$$\textbf{Explanation for each component of the columns:}$$
a. Pathogens iii. Microbes that can cause disease
$$\bullet$$
A pathogen also referred to as an infectious agent, is a biological agent that is capable of causing a disease or illness in a healthy person.
$$\bullet$$
Bacteria, viruses, fungi, certain protozoans are referred to as pathogens as they cause diseases.
b
. Vaccination iv. Gives immunity
$$\bullet$$
Vaccination is the process of administering vaccines.
$$\bullet$$
A vaccine is the preparation of a killed or inactive disease-causing microbe that is injected into the body of a healthy person.
$$\bullet$$
This injection of vaccine stimulates the immune response of the body, wherein the body produces antibodies to fight the infectious agent whenever it is encountered in the future.
c. Pasteurization ii. Prevents the growth of micro-organisms
$$\bullet$$
Pasteurization is the process of heating the milk to a temperature of about 70-71 ºC for 15-30 seconds and then suddenly cooled to a temperature of about 4ºC.
$$\bullet$$
By doing so, the growth of microbes can be prevented and the milk becomes safe for consumption.
d. Vectors i. Pathogen-carrying organisms
$$\bullet$$
A vector is an organism that carries pathogens from a diseased person to a healthy person.
$$\bullet$$
Female
Anopheles
mosquitoes act as vectors as they carry the disease-causing malarian protozoan,
Plasmodium vivax
,
from a diseased person to a healthy person.
Match the items in column I with their preservation methods in column II and choose the correct
option from the codes given below.
Column I
Column II
(a) Amla
(i) Sodium benzoate
(b) Vegetables
(ii) Drying
(c) Squashes
(iii) Cooling
(d) Spices
(iv) Oil and vinegar
(e) Ketchups
(v) Sugar
(vi) Salts
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(a)- (i), (b)- (ii), (c)- (iii), (d)- (iv), (e)- (v)
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(a)- (vi), (b)- (iv), (c)- (v), (d)- (ii), (e)- (i)
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(a)- (ii), (b)- (i), (c)- (v), (d)- (vi), (e)- (iv)
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(a)- (iv), (b)- (iii), (c)- (i), (d)- (vi), (e)- (ii)
Explanation
Amla is a seasonal fruit, so we can preserve amla for 6 months in salt.
Typical pickling agents, including brine (high in salt), vinegar, alcohol, and vegetable oil, are added to preserve vegetables.
When making squashes, we make use of acetic acid and a lot of sugar for preservation.
Air-drying is a method to preserve herbs and spices.
Boric acid, benzoic acid, and sodium benzoate are used as preservatives to preserve ketchup.
All of these methods help in stopping the growth of microbes.
Thus, the correct answer is option B.
Viruses are useful in making breads.
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True
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False
Explanation
Yeast is used as a leavening agent in bread making. Yeast converts sugars present in the dough to carbon dioxide.
Due to this, the dough expands. When such dough is baked then air pockets formed due to carbon dioxide will give soft and spongy texture to the bread. The virus is not used for making bread as it lacks respiration.
Thus, the correct answer is option B.
Which disease among the following spread, if excreta from someone suffering from this disease get mixed with drinking water used by people living nearby?
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Pneumonia
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Cholera
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Tuberculosis
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Influenza
Explanation
Cholera is an infectious disease that causes severe watery diarrhoea. It is caused by eating food or drinking water contaminated with a bacterium called
Vibrio cholerae
.
Vibrio cholerae
, the bacterium that causes cholera, is usually found in food or water contaminated by feces from a person with the infection. When a person consumes the contaminated food or water, the bacteria release a toxin in the intestines that produces severe diarrhoea.
Which of the following are water-borne diseases ?
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Influenza
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Cholera
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Typhoid
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Tuberculosis
Explanation
Influenza is a viral infection that is mostly transmitted via airborne droplets or by contact with infected persons or objects.
Cholera is an acute diarrhoeal infection that is transmitted by contaminated drinking water and contaminated food. It is most likely to happen after a natural disaster that disables the sewage system.
Typhoid is a bacterial disease that is transmitted by contaminated food and water.
Tuberculosis is a potentially serious infectious disease that mainly affects the lungs and is transmitted by infected droplets.
So, the correct answer is 'Typhoid and Cholera'.
What is a communicable disease?
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It is a disease that can be spread to others and is contagious.
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It is a disease that cannot be spread and is caused by health habits and behaviours.
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It is a disease that is caused by bacteria in our environment.
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It is a disease that can be spread through food, animals, water, and the air.
Explanation
Explanation: Communicable diseases are infectious diseases that can spread from one organism to another by various ways. They include common cold, cholera, tuberculosis, AIDS, etc.
Hence the correct option is A.
State whether the given statement is True or False:
Rhizobium is a type of virus.
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True
0%
False
Explanation
Rhizobium is a type of bacterium and not a virus. Rhizobium helps leguminous plants in nitrogen fixation.
The given statement is False.
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