CBSE Class VIII Science Preparation

   Microorganisms- A living organism that is very minute to be seen by the naked eye, especially a single celled organism, such as a bacterium is called microorganism. Microorganisms are classified into four major groups mainly bacteria, fungi, protozoa and some algae.

   Some of the microorganisms are unicellular like bacteria, while some have well developed, multi-cellular body like moulds.

   They can survive under different types of climatic environment, ranging from ice cold climate to hot summers and deserts to marshy, muddy lands. They are also found inside the bodies of animals including humans, air, water, soil, food and other things.

   Virus: You may be surprised to know that the viruses can be crystallized and stored like some non-living things, such as common salt and sugar. On the other hand, they multiply like living organisms when they are within a living body.

   Bacteria: Bacteria are single celled microorganisms. They are put under plant kingdom because they have rigid definite cell wall like plant cells. Bacteria can be seen under microscope which enlarges their image from a hundred to thousand times.

   Fungi: Fungi are non-green plants. They cannot synthesize their own food. They have to depend for their food on others. Most fungi take their food from dead organic matter. Some live on other organisms as parasites.

   Algae: Algae are green substances floating on the surface of a pond, lake, river, stagnant water, moist soil, stones. They tend to grow on wet surfaces. Therefore, they can synthesize their own food. They are found in water or in very moist places.

   Protozoa: Protozoa are unicellular animals. Some are free-living, others are parasites. Several parasitic protozoans cause diseases in human beings, domestic animals and plants. For example, Plasmodium, a protozoan, causes malaria.

   Microorganisms are commercially used for the large scale production of alcohol, wine and acetic acid (vinegar), while has medicinal uses too.

   Microorganisms can harmful too. Some of the microorganisms cause diseases in humans, plants as well as in animals. Such microorganisms which cause disease are known as pathogens. Some microorganisms spoil leather, food and clothing.

   Food Poisoning- Food poisoning can be caused as a result of consumption of food spoilt by some microorganisms. Microorganisms that grow on our food sometimes produce substances that are toxic in nature. These make the food poisonous and can cause serious illness to living organisms.

   Food Preservation- Microorganisms may grow on our food and spoil it. Spoiled food emits bad smell,bad taste and changed colour.

   Antibody- When a disease causing microbes enter our body, our internal defensive mechanisms produces substances called Antibodies to fight disease causing microbes.

   Vaccine- When a disease-carrying microbe enters our healthy body, the body produces antibodies, body fights and kills them by these antibodies. The body also remembers how to fight the microbe if it enters again. The antibodies remain in the body for a long time and protect us from the disease causing microbes. The substance which is injected into the body to trigger the body to initiate this entire process is called a vaccine.

   Pasteurization- this is a process in which milk is heated to about 70 degree Celsius for about 15 to 30 seconds and then suddenly chilled and stored. This process was discovered by Louis Pasteur.

   Nitrogen Cycle- Some bacteria and blue green algae present in the soil fix nitrogen from the atmosphere and convert into compounds of nitrogen. Once nitrogen is converted into these usable compounds, it can be utilised by plants from the soil through their root system. On the othe hand when plants and animals die, bacteria and fungi present in the soil convert the nitrogenous wastes into nitrogenous compounds to be used by plants again. Thus due to this Nitrogen Cycle, the percentage of nitrogen in the atmosphere remains more or less constant.

1.  Watering the crops is called:

      (a)   sowing

(b)   manuring

(c)   tilling

(d)   irrigation

1.  Spyrogyra is

      I.     An algae

      II.    A fungi

      III.   A protozoa

      IV.   A bacteria

2.  Vaccine for small pox is discorvered by

      I.      Louis Pasteur

      II.    Alexander Fleming

      III.   Edward Jenner

      IV.   John Mendal

3.  Amount of nitrogen in the atmosohere is

      I.      58%

      II.    68%

      III.   78%

      IV.   88%

4.  Mushroom belongs to

      I.      Algae

      II.    Virus

      III.   Fungi

      IV.   None of these

5.  Amoeba belongs to

      I.      Algae

      II.    Fungi

      III.   Protozoa

      IV.   Virus

6.  Scientist who discovered fermentation is

      I.      Alexander Fleming

      II.    Louis Pasteur

      III.   John Mendal

      IV.   Edward Jenner

7.  Rhizobium becteria

      I.      Help in digestion

      II.    Help in nitrogen fixation

      III.   Cause diseases

      IV.   All of the above

8.  Malaria Is caused by

      I.      Protozoa

      II.    Virus

      III.   Algae

      IV.   Bacteria

9.  Penicillium is a

      I.      Algae

      II.    Fungus

      III.   Bacteria

      IV.   Yeast

10.  Microorganisms are

      I.      Unicellular

      II.    Multi-cellular

      III.   Both

      IV.   None of these

      1)     II

      2)     III

      3)     III

      4)     III

      5)     III

      6)     II

      7)     II

      8)     I

      9)     II

      10)  II

Q1.  Fill in the blanks:

          (a)  Microorganisms can be seen with the help of a_______.

          (b)  Blue green algae fix _______ directly from, air to enhance fertility of soil.

          (c)  Alcohol is produced with the help of_______.

          (d)  Cholera is caused by_______.

Ans.   (a)   microscope       (b)   atmospheric nitrogen

             (c)   yeast                     (d)   bacteria.

Q.2.  Tick the correct answer:

            (a)   Yeast is used in the production of

            (i)   sugar

      (ii)   alcohol

            (iii)   hydrochloric acid

      (iv)   oxygen.

            (b)   The following is an antibiotic

            (i)   sodium bicarbonate

      (ii)   streptomycin

            (iii)   alcohol

      yeast.

            (c)   Carrier of malaria-causing protozoan is

            (i)   female Anopheles mosquito

      (ii)   cockroach

            (iii)   housefly

      butterfly.

            (d)   The most common carrier of communicable diseases is

            (i)   ant

      (ii)   housefly

            (iii)   dragonfly

      spider,

            (e)   (e) The bread or idli dough rises because of

            (i)   heat

      (ii)   grinding

            (iii)   growth of yeast cells

      kneading.

            (f)   The process of conversion of sugar into alcohol is called

            (i)   nitrogen fixation

      (ii)   moulding

            (iii)   fermentation

      infection

Ans. (a)  (ii)   alcohol      (b)   (ii)   Streptomycin

            (c)   (i)   female Anopheles mosquito         (d)   (ii)   housefly

            (e)   (iii)   growth of yeast cells         (f)   (iii) fermentation.

Q.3.  Match the organisms in Column A with their action in Column B.

Q.4.  Can microorganisms be seen with the naked eyes? If not how can they be seen?

Ans. Microorganisms cannot be seen with naked eyes. They can be seen with the help of a microscope.

Q.5.  What are the major groups of microorganisms?

Ans. There are following four major groups of microorganisms:

            (i)   Bacteria

      (ii)   Fungi

            (iii)   Protozoa

      Algae.

      In addition viruses are also considered as fifth group of microorganisms.

Q.6.  Name the microorganisms which can fix atmospheric nitrogen in the soil.

Ans. Bacteria like Rhizobium and Azotobacter and blue green algae can fix atmospheric nitrogen in soil.

Q.7.  Write 10 points on the usefulness of microorganisms in our lines:

Ans. Uses of microorganisms:

            (i)   Microorganisms help in the preparation of curd, bread, cake etc.

            (ii)   They are used to produce alcohol at large scale.

            (iii)   Yeast is used to prepare vinegar.

            (iv)   Microorganisms are used to make wines.

            (v)   They act as cleaning agent and decompose the waste products into manure.

            (vi)   They destroy the plant and animal dead bodies by decomposing them.

            (vii)   They increase soil fertility by fixing nitrogen of atmosphere.

            (viii)   They are used in making medicines like antibiotics and vaccines.

            (ix)   They are used as preservatives for food items.

            (x)   They help in various metabolic activities in our body.

Q.8.  Write a short paragraph on the harms caused by microorganisms.

Ans. Microorganisms are also very harmful to us. They cause a number of diseases inhuman as well as in other animals. Common cold, Tuberculosis, Measles, Chicken Pox, Polio, Cholera, Typhoid, Hepatitis B, Malaria, are some common human diseases caused by microorganisms. Anthrax is a serious disease in animals caused by microbes. They also make food items unfit for use by food poisoning. They also spoil clothes and leather products. They also cause diseases in plants like blights in potatoes, sugarcanes, oranges etc. They also reduce the crop production.

Q.9.  What are antibiotics? What precautions must be taken while taking antibiotics?

Ans. The medicines which kill or stop the growth of microorganisms in our body are called antibiotics. These are very useful to us as they prevent us from the effects of microorganisms. Antibiotics are made from bacteria and fungi. The penicillin is the first antibiotics which is discovered by Alexander Fleming in 1929. These days a number of antibiotics are used to cure various human and animal diseases. Streptomycin, Tetracycline, Erythromycin etc. are some common antibiotics. Precautions: We should take antibiotics only by the advice of a qualified doctor. Antibiotics should only be taken when needed. Otherwise, they may be harmful and become less effective in future.

1.  What are viruses? Name some common diseases in human caused by virus.

2.  Explain the formation of curd from the milk.

3.  Mention some beneficial effects of bacteria.

4.  Explain the discovery of Pencillin.

5.  How do microorganisms spoil food?

6.  What are carriers of disease causing microbes? Explain with the help of two examples.

7.  Explain nitrogen cycle and draw a schematic diagram of nitrogen cycle.

8.  Name some common plant diseases their causative microorganisms mode of transmission with the help of the figures.

9.  Explain the uses of Bacteria, Fungi and Algae.

10.  What are food preservatives? Explain some common food preservatives.

1.  What are food preservatives? Name some common food preservatives.

      2 marks

2.  Draw a systematic diagram of nitrogen cycle and explain it.

      4 marks

3.  Explain the process of Pasteurization in brief.

      3 marks

4.  Explain in detail how vaccination works?

      3 marks

5.  What are good microorganisms? Explain some of the uses of good microorganisms.

      2 marks

6.  Explain various types of bacteria.

      4 marks

7.  What are food poisoning and food preservation (short notes)?

      4 marks

8.  Explain the discovery of Penicillin.

      3 marks

9.  What are antibiotics? Explain with the help of examples.

      3 marks

10.  What are harmful microorganisms? Explain by giving the example of two diseasecarrying microbes.

          5 marks

11.  What are the indications required to detect spoilage in food?

          2 marks