Microorganisms: Friend and Foe - 8th science

Choose the correct option for the following questions

 

Question (1) What is microorganisms?

(a) Micro sized organisms which cannot be seen without unaided eyes.

(b) A type of microscope.

(c) A type of plant that is found in Himalaya

(d) A certain type of water

Answer: (a) Micro sized organisms which cannot be seen with unaided eye.

Explanation

Organisms having micro size and which cannot be seen without unaided eye are known as microorganisms. Microorganisms can be seen using a microscope.

Question (2) What is virus?

(a) An four footed animal

(b) An aquatic animal

(c) An microorganism

(d) An organism which is very useful to us

Answer: (c) An microorganism

Explanation

Virus is a type of microorganisms. Almost all virus are disease causing microorganisms. Small pox, chicken pox, hepatitis A, AIDS, etc. are name of some diseases cause due to virus. Vaccine is given to prevent from diseases caused by virus.

Question (3) What is bacteria?

(a) An useful microorganism

(b) A harmful microorganism

(c) Friendly or harmful microorganism

(d) Another name of algae

Answer (c) Friendly or harmful microorganism

Explanation

Bacteria are one of the types of microorganisms. Some bacteria are useful and some are harmful for us, such as rhizobium is useful to us as it fix nitrogen in the atmosphere. Whereas diseases like cholera and typhoid, etc. are caused by bacteria. Bacteria are single cell microorganisms. Staphylococcus, Vibrio cholera, Brucelleae, Caryophanaceae, etc. are examples of some bacteria.

(4) What is algae?

(a) Alage is a plant and generally found in stagnant water.

(b) Algae is a type of fish

(c) Alage is a disease causing animal

(d) Algae is an atmospheric gas

Answer (a) Alage is a plant and generally found in stagnant water.

Explanation

Algae is a type of microorganism and can be seen easily in stagnant water. Algae are considered as plant. Algae may be green and brown or reddish in color. Seaweeds are largest and most complex marine algae. Because of presence of chloroplast, algae perform photoshynthesis. Charophyta, Spirogyra, stoneworts, etc. are examples of some algae.

(5) What is fungi?

(a) A type of milch animal

(b) An microorganism which convert milk into curd.

(c) An microorganism which is cause of cholera

(d) An microorganism which is cause of spoilage of chlothes and article made of leather especially in the rainy season.

Answer: (d) An microorganism which is cause of spoilage of chlothes and article made of leather especially in the rainy season.

Explanation:

Fungi can be single cellular and multicellular both types. Fungi is considered an organism more than a plant. Mushroom, yeast, bread mould, etc. are examples of some fungi.

Fungi are heterotrophs, which reproduce and get their nutrition on decomposing organisms. Fungi are called natural decomposer. Fungi get their food by secreting digestive juice of over decaying materials, this digestive juice dissolve the molecules of decaying organism and then fungi absorb the dissolve molecules as their food.

Question (6) What is protozoan?

(a) A microorganisms cause for malaria

(b) A microorganism cause for AIDS

(c) A microorganism cause for Hepatitis A

(d) A microorganism cause for TB

Answer: (a) A microorganisms cause for malaria

Explanation

Protozoa are single cellular organisms. Amoeba, paramecium, etc. are some examplea of protozoa. Protozoa may live freely or as a parasite. Dysentery, malaria, etc. are some diseases caused because of protozoa.

Question (7) What is antibiotic?

(a) A medicine that acts on virus

(b) A medicine that act against bacteria

(c) A plant

(d) A type of virus

Answer (b) A medicine that act against bacteria

Explanation

The medicines produced with the help of microorganisms are called Antibiotics. These medicines, antibiotics destroy or stop the growth of infectious bacteria. Since these medicines act against bacteria, thus are called antibiotics (anti + bacteria). Antibiotics come in the form of tablets, syrup and injections, which are given according to need to the sick people. These days a number of antibiotics are available in the market. Steptomycin, tetracyclin, cloxacyclin, erythomycin, etc. are the name of some antibiotics available in the market.

Question (8) Where do microorganisms live?

(a) In hot water

(b) In the sea

(c) In the marshy lands

(d) All of these

Answer (d) All of these

Explanation

Microorganism is found everywhere and can survive in almost every condition. Microorganisms can be found ranging from ice cold climate to hot spring and desert to marshy lands. Microorganisms are found even inside the bodies of animals and can grow over the other organisms.

Many microorganisms exist freely in the environment. Many microorganisms, such as amoeba live alone while many, such as fungi and bacteria may live in colonies.

Question (9) How milk is converted into curd?

(a) Spoiled milk is automatically converted into curd

(b) A bacterium called Lactobacillus converts milk into curd

(c) It is heat which converts milk into curd

(d) Cheese produced using milk is called curd

Answer (b) A bacterium called Lactobacillus converts milk into curd

Explanation

Milk is converted into curd because of growth of a type of bacteria called Lactobacillus. Lactobacillus is found in curd. When a small amount of curd is added to lukewarm milk, the lactobacillus present in curd multiplies in milk and converts whole the milk into curd. This process takes about 5 to 6 hours in summer and some more hours in winter, because lactobacillus multiplies quickly in hot weather, i.e. in summer.

Question (10) What is fermentation?

(a) The conversion of alcohol into sugar

(b) The conversion of sugar into alcohol

(c) The conversion of bacteria into algae

(d) The conversion of algae into bacteria

Answer (b) The conversion of sugar into alcohol

Explanation The conversion of sugar juice into alcohol is known as fermetation. To convert sugar juice into alcohol, a small amount of yeast is added to it. Yeast multiplies and produces carbon dioxide in the course of respiration. This converts sugar juice into alcohol. The process of fermentation is used in making of wine, vinegar, alcohol, and making of dough prepared for cake soft.

(11) Who discovered the process of fermentation?

(a) Albert Einstein

(b) Thomas Edison

(c) Louis Pasteur

(d) Albert Ekka

Answer : (c) Louis Pasteur

Explanation

Louis Pasteur, who was a French Scientist, discovered fermentation in the year of 1857. Louis Pasteur discovered the process to preserve milk also. In his honour the process to preserver milk is called the Pasturisation.

(12) What is pasteurization?

(a) Conversion of sugar into alcohol

(b) Preservation of food

(c) Preservation of milk

(d) Conversion of hydrogen gas and oxygen gas into water

Answer: (c) Preservation of milk

Explanation:

Pasteurization is a method to keep milk usable for long time. In the process of Pasteurization milk is heated to about 70^o C for 15 to 30 second and suddenly chilled and stored. This process prevents the growth of microbes. Pasteurized milk can be consumed without boiling as it is free from harmful microbes.

Louis Pasteur, a French scientist, discovered the process of Pasteurization. This process got its name as Pasteurization in the honour of its discoverer.

Question (13) What is vaccine?

(a) A medicine which act against bacteria

(b) A food which is given to sick people

(c) A method to preserve food for long time

(d) A medicine which is given to healthy people to enable to fight against certain virus

Answer: (d) A medicine which is given to healthy people to enable to fight against certain virus

Explanation:

Whenever any harmful microorganism enter in our body, our body produce antibodies. These antibodies destroy and stop the growth of the foreign as well internal harmful microorganisms.

The body also remembers how to fight the microbe if it enters again. Based on this theory of mechanism of body vaccines are prepared. If dead or weakened microbes are introduced in a healthy body, the body fights and kills them by producing suitable antibodies. The antibodies so produced remain in the body and protect us from disease causing microbes.

Particular type of dead or weakened microbes are introduced in our body as a vaccine, as type of medicine, to enable us to protect from that particular disease.

Several diseases, including cholera, tuberculosis, smallpox, and hepatitis B, etc. can be prevented by vaccination.

Children are vaccinated to protect from many diseases. WHO (World Health Organisation), which is an international organization, made the world almost free from small pox and polio like deadly diseases after introducing vaccination campaign worldwide.

Question (14) How do microorganisms increase soil fertility?

(a) By fixing nitrogen in the soil

(b) By fixing water level in the soil

(c) By fixing level of oxygen in the soil

(d) By fixing the level of carbon dioxide in the soil which is absorbed by plants in the process of photosynthesis

Answer: (a) By fixing nitrogen in the soil

Explanation

Microorganisms also help to increase the fertility of soil. Some bacteria and blue green algae are able to fix nitrogen from the atmosphere to enrich soil with nitrogen and increase its fertility.

 

These microorganisms absorb nitrogen from atmosphere and made available in the soil in soluble form. Plants absorb this soluble nitrogen from soil and sythesise nutrition.

The process of making available of nitrogen in soluble form in the soil is called Nitrogen Fixation and microorganisms who are responsible for this are called Biological Nitrogen Fixers.

Question (15) How do microorganisms help in cleaning of environment?

(a) By fixing nitrogen in the soil

(b) By decomposing oxygen in the soil

(c) By decomposing dead and decaying animals and plants

(d) By making available oxygen to the environment

Answer : (c) By decomposing dead and decaying animals and plants

Explanation

Some microorganisms convert dead and decaying organisms into simple form of substances. Later plants use these converted simple substances accordingly.

Microorganisms are natural decomposer. This is the cause that dead animals and plants are disappeared after sometimes due to decomposing by microorganisms. Environment becomes clean after vanishing out of dead animals and plant after decomposing by microorganisms. This process of decomposing of dead animals and plants eventually replenishes nutrients back to the ecosystem, thereby, allowing the plants to grow.