LECTURE -1 : CLASS VIII : SCIENCE : CHAPTER 8 : CELL STRUCTURE & FUNCTIONS

CLASS VIII   |    SCIENCE    |    CHAPTER 8

      notes prepared by subhankar Karmakar

Cell : Cells are the basic units of life. All the living things both plants and animals, are made from cells. Cells are tiny basic unit of structure and function of all living organisms. Cells are the building blocks of plants and animals. Therefore, we can say a cell is the smallest unit of life which has a definite structure and performs specific function.

Microscope: The instrument used to study cells is called microscope.

Discovery of cell: an English scientist named Robert hooke discovered cell in 1665.

In 1838, a German scientist Schleiden first suggested that all plants are made of cells. 

In 1839, another German scientist Schwann suggested that all animals are made of cells too. 

Cell division: all cells arise from pre-existing cells by a method which is called cell division.

Classification of cell: All cells are primarily categorised into two main types. Animal cells and plant cells. 

Structures of a cell: Each cell has a number of smaller parts or internal structures in it. Some of the structures are present in both animal and plant cells, while some structures are only present in plant cells, they are not present in animal cells. They are also called parts of a cell.

The parts of a cell present in both animal and plant cells: 

Cell membrane or plasma membrane, Cytoplasm, Nucleus and Mitochondria. These basic parts are present in in both animal as well as plant cells. 

.                  Parts of a cell

The parts of a cells present in plant cells only:

Cell wall, Chloroplasts, Large vacuole are present in plant cell only. 

.               Parts of a Plant Cell

1. Cell membrane or plasma membrane:

Every cell is covered by a thin sheet of skin which is called cell membrane or plasma membrane. The cytoplasm and nucleus are enclosed within the cell membrane. Therefore we can say, cell membrane encloses the living part of the cell which is known as protoplasm. 

The cell membrane protects the cell and also gives shape to the cell. The cell membrane has tiny pores in it. Through this pores, the cell membrane controls the movement of substances "into the cell" and "out of the cell" like the dissolved glucose and oxygen can enter into the cell whereas the waste products like carbon dioxide can go out from the cell through this pores of the cell membrane. 

Cell membrane separates the cell from other cells as well as from the surrounding medium. The cell membrane or plasma membrane is a living part of the cell.

2. Cytoplasm: 

Cytoplasm is a transparent jelly like material which fills the cell between nucleus and the cell membrane. It acts like a chemical factory of the cell. In cytoplasm, new substances are built from materials taken into the cell and energy is released and stored. It is a place where most of the chemical reactions which keep the cell alive take place. Cytoplasm has many internal structures which are known as organelles. The most prominent internal structure in the cytoplasm is nucleus. It also contains mitochondria, Golgi bodies, ribosomes etc. Cytoplasm for plant cells also contain chloroplast. Cytoplasm and the nucleus taken together is called protoplasm.

3. Nucleus:

Nucleus is a large spherical organelle present in all the cells. In animal cell, nucleus lies in the centre of the cell whereas in plant cells the nucleus maybe on the periphery of the cell.  Nucleus is separated from the cytoplasm by a membrane called nuclear membrane. Nucleus controls all the activities of cell. The transmission of characteristics from the parents to the offsprings is called inheritance and Nucleus plays a role in inheritance.  

Chromosome: Nucleus contains thread like structure called chromosome. The function of chromosomes is to transfer the characteristics from the parents to the offspring through the genes and it is called inheritance. 

Nucleolus: The nucleus also contains a tiny round structure called nucleolus. The nucleus containing chromosomes and nucleolus is bound by a membrane called nuclear membrane. Nuclear membrane has tiny pores for the exchange of materials with cytoplasm. Some cells like red blood cells do not have a nucleus.

Gene: Gene is a unit of inheritance in living organisms, which is transferred from parent to offspring during reproduction and determine some characteristic feature of the offspring. Thus genes control the transfer of hereditary characteristics from parents to offsprings. 

Protoplasm: All the living matter in a cell is called protoplasm. Protoplasm is a liquid substance which is present inside the cell membrane. Protoplasm includes cytoplasm, nucleus and other organelles. Most of the protoplasm is made up of compounds of only 4 elements Carbon, Hydrogen, Nitrogen and Oxygen. It also contains water, carbohydrates, proteins, nucleic acids, fats and mineral salts.

4. Mitochondria: 

Mitochondria are the tiny rod-shaped or spherical organelles which are found in all the cells. Mitochondria provide energy for all the activities of the cell. This energy is produced by the process of respiration in which food such as glucose is broken down by oxygen. Thus mitochondria use glucose and oxygen to produce energy. Mitochondria are found in large numbers in the cytoplasm in all the cells.

5. Cell wall: The plant cells have a thick cell wall around them outside the cell membrane. The cell wall is made of a tough material called cellulose. Cell wall gives shape and support to the plant cell. Cell walls also hold the plant cells together and give plants most of their strength. Plants need protection against high wind speed, variation in temperature and atmospheric moisture etc. Since plants are fixed at a place so they cannot move to protect themselves from the various changes in their surroundings. The tough cell wall present in plant cells provides protection to plants. Cell wall is not there in animal cells. The cell wall is a non living part of the plant cells.

6. Chloroplasts: Chloroplasts are the green coloured organelles present in the cytoplasm of plant cells. The process of food making by plants known as photosynthesis takes place in chloroplasts. The green colour of chloroplasts is due to the presence of a green pigment called chlorophyll in them. Chlorophyll can absorb sunlight energy. In the chloroplasts, carbon dioxide and water combine in the presence of sunlight energy to produce food such as glucose. And this process of food making is called photosynthesis. 

The organelles containing pigments or colour matter present in the cytoplasm of plant cells are called plastids. Plastids can be of many different colours. The plastids containing green pigment or chlorophyll are known as chloroplasts. Chloroplast are present in the cells of leaves. It makes the leaves green. The plastids are may be of different colour like red colours of tomatoes are due to red plastids. Different colours of flowers are also due to this plastids.

7. Large Vacoule: 

Vacoule is a space in the cytoplasm of a cell which is enclosed by a membrane and is usually contains substances dissolved in water. A vacoule appears as an empty space under the microscope. All the plant cells have a large vacoule. The vacuole is filled with a liquid called "cell sap" , which contains dissolve sugar and salts. The function of vacuole in a cell is to store various substances including waste products of the cell.

* In amoeba vacuoles contain food particles so they are called food vacuoles.

Lecture: 11 :CLASS VIII : SCIENCE : Chapter 2: QUESTIONS & ANSWERS

CHAPTER TWO: MICRO-ORGANISMS: FRIENDS AND FOE

Very Short Answer Type Questions

1. Question. Name the instrument (or device) which is needed to see the micro-organisms.

Answer. Microscope is needed to see the micro-organisms.

2. Question. What is the name of micro-organisms which reproduce only inside the living cells of other organisms ?

Answer. Viruses are the smallest micro-organisms which reproduce only inside the living cells of other organisms.

3. Question. What are the major groups of micro-organisms?

Answer. There are five major groups of micro-organisms. These are: Bacteria, viruses, Protozoa, some fungi and Algae.

4. Question. Name any two human diseases caused by bacteria.

Answer. Typhoid and Cholera are caused by bacteria in human beings.

5. Question. Name any two human diseases caused by viruses.

Answer. The human diseases such as common cold and influenza are caused by virus. 

6. Question. Name any two human diseases caused by protozoa.

Answer. The human diseases amoebic dysentery and malaria are caused by protozoans.

7. Question. Name any two human diseases caused by fungi.

Answer. Diseases athlete’s food and ring worm are caused by fungi.

8. Question. Which micro-organism is utilized in making curd from milk ?

Answer. Lactobacillus bacterium is utilized in making curd from milk.

9. Question. Name the -micro-organism which is used for the large scale production of alcohol.

Answer. Yeast is used for the large-scale production of alcohol.

10. Question. Name any two antibiotics.

Answer. Streptomycin and erythromycin are two commonly known antibiotics which are made from fungi and bacteria.

11. Question. Name an antibiotic extracted from fungus (mould). Name the fungus.

Answer. An antibiotic Penicillin was extracted from fungus (mould) by Alexander Fleming in 1929. This antibiotic was made from the fungus called penicillium.

12. Question. Name any four diseases which can be prevented by vaccination.

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

13. Question. Name the scientist who discovered the-vaccine for 'smallpox.

Answer. Edward Jenner discovered the vaccine for smallpox in 1978.

14. Question. Name the scientist who discovered 'penicillin'.

Answer. Alexander Fleming discovered the antibiotic “Penicillin” in 1929.

15. Question. State an important function performed by blue-green algae.

Answer. Blue green algae fix the atmospheric nitrogen to enrich soil with nitrogen and hence, increase soil fertility.

16. Question. Name one 'biological nitrogen-fixer'.

Answer. Blue green algae are known as 'biological nitrogen-fixer' as they fix the atmospheric nitrogen.

17. Question. Name two common insects which act as carriers of disease-causing micro-organisms (or disease-causing microbes).

Answer. The two common insects which act as carriers of disease-causing micro-organisms (or disease-causing microbes) are housefly and mosquito.

18. Question. Name any two diseases spread by housefly.

Answer. Diseases cholera and tuberculosis spread by housefly.

19. Question. Name the insect which is the carrier of parasite of malaria.

Answer. The carrier of parasite of malaria is Female Anopheles mosquito.

20. Question. Name the insect which carries dengue virus.

Answer. Female Aedes mosquito carries dengue virus.

21. Question. Which of the two spreads dengue: mosquito or housefly ?

Answer. Female Aedes mosquito acts as a carrier of dengue virus.

22. Question. Name two diseases spread by mosquitoes.

Answer. Malaria and dengue spread by mosquitoes.

23. Question. Name the microbe which causes malaria disease.

Answer. Protozoa Plasmodium causes malaria disease.

24. Question. Name one disease which spreads by breathing in air containing microorganisms.

Answer. Tuberculosis disease spreads by breathing in air containing micro-organisms.

25. Question. Name one disease which spreads through insect bites.

Answer. Malaria disease spreads through insect bites.

26. Question. Name one disease which spreads through infected food or water.

Answer. Cholera disease spreads through infected food or water.

27. Question. Name the causative micro-organisms of the following animal diseases:

(a) Foot and mouth disease 

(b) Anthrax

Answer. (a) Foot and mouth disease is caused by a virus.

(b) Anthrax disease is caused by a bacterium.

28. Question. Name two food materials which are preserved by sun-drying method in our homes.

Answer. Vegetables like methi leaves and spinach are preserved by sun-drying method in our homes.

29. Question. Name two food materials which are preserved by using common salt.

Answer. Meat and fish are preserved by using common salt.

30. Question. Name two food materials which can be preserved by using sugar.

Answer. Jams and jellies are preserved by using sugar.

31. Question. Name two food materials which are usually preserved by deep freezing.

Answer. Preservation by deep freezing means preservation of food material in the extreme cold. Low temperature inhibits the growth of micro-organisms completely. Food materials such meat and fish are usually preserved by deep freezing.

32. Question. Name some of the preservatives which are used in the preservation of fruits as jams arid jellies.

Answer. Sodium benzoate and sodium meta bisulphite are common preservatives which are used in the preservation of fruits as jams and jellies.

33. Question. Name some of the preservatives which are used in the preservation of fruits and vegetables as pickles.

Answer. Salt, oil and vinegar are some of the preservatives which are used in the preservation of fruits and vegetables as pickles.

34. Question. Name two food materials which can be preserved by using oil or vinegar.

Answer. Fish and meat are often preserved by using oil or vinegar.

35. Question. Name any two special chemicals which are used as food preservatives.

Answer. Sodium benzoate and sodium meta-bi-sulphite are common preservatives.

36. Question. Name the micro-organisms which can fix atmospheric nitrogen in the soil.

Answer. Certain bacteria and blue green algae present in the soil fix atmospheric nitrogen and convert it into compounds of nitrogen.

37. Question. What type of plants can ϐix nitrogen gas of the air into compounds of nitrogen?

Answer. Leguminous plants can fix atmospheric nitrogen into nitrogen compounds.

38. Question. Name the micro-organisms present in the soil and in the root nodules of leguminous plants which can fix atmospheric nitrogen. 

Answer. Some bacteria and blue green algae present in the soil and rhizobium present in the root nodules of leguminous plants can fix atmospheric nitrogen.

39. Question. Name two leguminous plants which can fix nitrogen.

Answer. Leguminous plants such as beans and peas can fix nitrogen.

40. Question. Fill in the following blanks with suitable words:

(a) Alcohol is produced with the help of ............

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

(c) Micro-organisms can be seen with help of a..........

(d) Cholera is caused by..............

(e) Common salt has been used to preserve............. and ............ for ages.

(f) The food material which is preserved by pasteurization is .................

(g) As a result of nitrogen cycle, the percentage of nitrogen in the atmosphere remains more or less…….

Answer. (a) yeast (b) nitrogen (c) microscope (d) bacteria (e) meat; fish (f) milk (g) constant

Short Answer Type Questions

41. Question. How do viruses differ from other micro-organisms such as bacteria?

Answer. Viruses differ from other micro-organisms because they are too much smaller in comparison to other micro-organisms. They do not show most of the characteristics of the living organisms like respiration. They just reproduce. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal. Hence, virues differ from other organisms.

42. Question. What are micro-organisms? Give any two examples of micro-organisms.

Answer. The organisms which are too small to be seen by the naked eyes and can be seen only though a microscope are called micro-organisms or microbes. Bacteria and viruses are examples of micro-organisms.

43. Question. Can micro-organisms be seen with the naked eye? If not, how can they be seen?

Answer. Micro-organisms are too much smaller that they cannot be seen with naked eye. They can be seen with a magnifying glass called microscope.

44 A. Question. How do houseflies carry disease-causing microbes-(or pathogens)?

Answer. The houseflies feed on garbage, animal excreta and dead organic matter. When the houseϐly sits on garbage and animal excreta for feeding, then the millions of disease-causing micro-organisms present in them sticking to the body of housefly. And when this housefly sits on uncovered food, they may transfer the pathogens and food gets contaminated. When this contaminated food is consumed by a person, pathogens enter into his body and causes various diseases.

44 B. Question. State any two ways of preventing diseases spread by houseflies.

Answer. The spreading of diseases by houseflies can be prevented by following ways:

(i) Food should always be kept covered. 

(ii) Proper sanitation should be maintained in the kitchen.

45A. Question. How do mosquitoes carry disease-causing micro-organisms and spread diseases?

Answer. Mosquito acts a carrier of disease causing micro-organism and spreads diseases from one person to another. They carry disease-causing micro-organisms (microbes) inside its body. Female Anopheles mosquito is a carrier of malarial parasite. When it bits a person suffering from malaria, it sucks the blood of that person which contains the malarial parasite microbes. When this infected mosquito bites a healthy person, it transfers the microbes into his blood stream, hence the healthy person also gets malarial disease.

45 B. Question. Mention any three ways of preventing diseases spread by mosquitoes.

Answer. The spreading of diseases by mosquitoes can be prevented by following ways: 

(i) We should not let water collect anywhere in the neighborhood.

(ii) We should keep our surrounding clean and dry.

(iii) Mosquito repellant creams should be applied on the exposed parts of the body.

46 A. Question. What is meant by fermentation? Name the scientist who discovered fermentation.

Answer. The process of conversation of sugar into alcohol is known as fermentation. Louis Pasteur discovered fermentation in 1857.

46 B. Question. Which micro-organism converts sugar into alcohol during fermentation?

Answer. Yeast converts sugar into alcohol during fermentation. Yeast is used for commercial production of alcohol and wine.

47 A. Question. How do micro-organisms help in increasing soil fertility?

Answer. Some bacteria like rhizobium and blue green algae like Nostoc and Anabaena present in the soil are able to fix nitrogen gas from the atmosphere to enrich soil with nitrogen and increase its fertility. These micro-organisms are commonly called biological nitrogen fixers.

47 B. Question. How do micro-organisms help in cleaning the environment?

Answer. Some micro-organisms decompose the organic matter of dead plants and animals and convert them into simple substances which mix up with the soil. These substances are again used by other plants and animals. Thus, micro-organisms decompose the harmful and smelly dead remains of plants and animals into harmless materials and thereby clean up the environment.

48. Question. What are antibiotics? What precautions must be taken while taking antibiotics?

Answer. Medicines which kill or stop the growth of the disease-causing microorganisms are called antibiotics. Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.

Some of the precautions should be taken while taking antibiotics which are as follows:

● Antibiotics should be taken only on the advice of a qualified doctor.

● A person must finish the full course of antibiotics prescribed by the doctor.

● Antibiotics should not be taken unnecessarily.

49. Question. Why are antibiotics not effective against 'common cold' and 'flu'?

Answer. Antibiotics are not effective against 'common cold' and 'flu' as these are caused by viruses. And the viruses do not have cells but live in the cells of living beings. And the working mechanism of the antibiotics is to break the cell wall and attack on the bacteria.

50. Question. What is the full form of HIV? Name the disease caused by HIV. 

Answer. The full form of HIV is Human Immunodeficiency Virus. HIV causes AIDS disease.

51. Question. Describe how, curd is made from milk. Name the bacterium which converts milk into curd:

Answer. Milk is turned into curd by bacteria. Milk contains many microorganisms. Of these, the bacterium Lactobacillus promotes the formation of curd. When a small amount of pre-made curd is added into warm milk, then lactobacillus bacterium present in curd multiplies in milk and converts it into curd. During this process, lactobacillus bacterium acts on lactose sugar present in milk and converts it into lactic acid. This lactic acid then converts milk into curd.

52. Question. Name the micro-organism used in bread-making which makes the bread-dough rise. How does it make the dough rise?

Answer. Yeast is used in baking industry for making bread. It increase the volume of dough. When yeast is mixed in dough for making bread, the yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume. This makes the dough rise. This is the basis of the use of yeast in the baking industry for making breads, pastries and cakes.

53. Question. What is food poisoning? How is food poisoning caused?

Answer. Microorganisms such bacteria and fungi that grow on our food items sometimes produce toxic substances. These make the food unfit for consumption. Consuming such food can cause a serious illness called food poisoning. Food hygiene is essential for preventing food poisoning.

54 A. Question. What is meant by food preservation? Name any five methods of preserving food.

Answer. Food preservation: Processing of food to prevent their spoilage and to retain their nutritive value for period is called food preservation. 

Food can be preserved using following methods:

(1) Preservation by Salt

(2) Preservation by Sugar

(3) Preservation by oil and vinegar

(4) Heat and cold treatment

(5) Storage and packing

54 B. Question. How do you preserve cooked food at home?

Answer. We preserve cooked food in the refrigerator at home. Low temperature inhibits the growth of micro-organisms. When cooked food is kept in a cold place, then the food does not get spoiled easily.

55 A. Question. Why should we not let water collect anywhere in the neighbourhood?

Answer. All mosquitoes breed in water . Hence, one should not let water collect anywhere, in coolers, tyres, flower pot etc.

55 B. Question.  Name one animal disease each caused: (i) by virus (ii) by bacteria (iii) by fungus.

Answer.  (i) Yellow vein mosaic of bhindi (Okra) (ii) Citrus canker (iii) Rust of wheat

56. Question. Where do Rhizobium bacteria live? What is their function?

Answer. Rhizobium bacterium is found in the soil. It lives in the root nodules of leguminous plants such as beans and peas, with which it has a symbiotic relationship. It is involved in the fixation of nitrogen in leguminous plants (pulses).

57. Question. Name any two

(a) bacteria

(b) viruses

(c) protozoa

(d) algae, and

(e) fungi.

Answer. (a) Bacteria – (I) Lactobacillus bacteria (II) Rhizobium bacteria

(b) Viruses – (I) HIV (II) Tobacco Mosaic virus (TMV)

(c) Protozoa – (I) Amoeba (II) Paramecium

(d) Algae – (I) Spirogyra (II) Chlamydomonas

(e) Fungi – (I) Penicillium (II) Aspergillus

58. Question. State the beneϐicial effects (or usefulness) of micro-organisms in our lives.

Answer. Microorganisms are used for various purposes such as:

● They are used in the preparation of curd, bread and cake.

● They are used in the preparation of alcohol, wine and acetic acid (vinegar).

● They are also used in cleaning up of the environment.

● In agriculture, they are used to increase soil fertility by fixing nitrogen.

● The antibiotics are manufactured by growing specific microorganisms and are used to cure a variety of diseases. Penicillin is an antibiotic made from Penicillium.

● Certain microbes are also used in the biological treatment of sewage and industrial effluents.

● Yeast is used in making idlis, bhaturas, bread, pastries and cakes.

59. Question. Describe the method of pasteurization for the preservation of milk.

Answer.  The process of pasteurization for the preservation of milk is discovered by

Louis Pasteur. In this process, milk is heated to about 70°C for 15 to 30 seconds to kill bacteria. Next it is chilled very fast to prevent bacteria from growing. It is finally stored at low temperature. This Pasteurized milk can be

consumed without boiling as it is free from harmful microbes.

60. Question.  Name one plant disease each caused:

(a) by fungi

(b) by virus

(c) by bacteria

Answer. (a) The plant disease, Rust of wheat is caused by fungi.

(b) Yellow vein Virus Insect mosaic of bhindi (Okra), a plant disease, is caused

by virus.

(c) Citrus canker is caused by bacteria.

61. Question. Which disease is spread by:

(a) female Anopheles mosquito?

(b female Aedes mosquito?

Answer. (a) female Anopheles mosquito carries the parasite of malaria.

(b) Female Aedes mosquito acts as carrier of dengue virus.

62. Question. Name two fruits which are preserved:

(a) in the form of pickles

(b) in the form of jams.

Answer. (a) The fruits which are preserved in the form of pickles by using oil and vinegar as preservative are raw mango and lemon.

(b) The fruits which are preserved in the form of jams by using sugar as preservative are mango and orange.

63. Question. What is the mode of transmission of the following diseases?

(a) Rust of wheat

(b) Citrus canker

(c) Yellow vein mosaic of bhindi (Okra)

Answer

64. Question.  Name any two animal diseases and two plant diseases caused by micro-organisms.

Answer. The following diseases are caused by the micro-organisms:

65. Question. State the causative micro-organisms and modes of transmission of the

following human diseases :

(i) Tuberculosis

(ii) Measles

(iii) Chickenpox

(iv) Polio

(v) Cholera

(vi) Typhoid

(vii) Hepatitis B

(viii) Malaria

(ix) Dengue.

Answer:

Long Answer Type Questions:

66 A. Question. What is meant by communicable diseases? Name any two communicable diseases.

Answer. Microbial diseases that can spread from an infected person to a healthy person through air, water, food or physical contact are called communicable diseases. Cholera and tuberculosis are examples of communicable diseases.

66 B. Question.  What are the various ways in which communicable diseases can occur and

spread?  

Answer. The communicable diseases can occur and spread in the following ways:

● Through air we breathe

● Through water we drink

● Through food we eat, and

● Through carriers such as mosquito.

67 A. Question. Name any five human diseases caused by micro-organisms. Also name the

causative micro-organisms and mode of transmission for each of these diseases.

Answer. 

67 B. Question. State the various ways of preventing the occurrence and spreading of

communicable diseases.

Answer. There are various ways of preventing the occurrence and spreading of communicable diseases. These are as follows:

● Maintain personal hygiene and good sanitary habits.

● Drink boiled drinking water.

● Spray insecticides and control breeding of mosquitoes by not allowing

water to collect in the surroundings.

● Keep the infected person separated from others & advice him/ her to keep

a handkerchief on the nose and mouth while sneezing.

● Timely vaccination against diseases should also be taken.

● Food must be kept covered.

68 A. Question. What is a vaccine? How does a vaccine work?

Answer. A vaccine is a special kind of preparation which provides immunity against a

particular disease. Vaccine consists dead and weakened microbes which are harmless and do not cause any disease. Vaccine works as follows:

● When the vaccine containing dead or weakened microbes is introduced

into the body of a healthy person, the body fights and kills the microbes by producing some substance called antibodies.

● Some of the antibodies remain in the body for a long time and protect it from any future attack of disease germs. Thus, a vaccine develops the immunity from a disease.

68 B. Question.  Why are children given vaccination ?

Answer. Vaccination is the process of giving a vaccine orally or by injection which gives protection against a particular disease. Vaccination protect the children from number of diseases. Several diseases, including cholera, tuberculosis, smallpox and hepatitis can be prevented by vaccination. Since the immune system of children is not strong and they are more likely to catch any disease very easily, so all the children should be vaccinated at the proper ages to provide them immunity from certain diseases.

69. Question.  What is meant by 'nitrogen fixation' ? State two ways in which nitrogen gas of the atmosphere can be 'fixed' in nature to get nitrogen compounds in the soil.

Answer.  The process of converting atmospheric nitrogen into compounds of nitrogen is called nitrogen fixation. The two ways in which in which nitrogen gas of the atmosphere can be 'fixed' in nature to get nitrogen compounds in the soil are:

(i) Nitrogen fixation by lightning: Lightning also helps in fixing atmospheric nitrogen into the soil. The temperature and pressure during

lightning convert atmospheric nitrogen into oxides of nitrogen. These nitrogen compounds combine with rainwater to form nitric and nitrous acid which mix with the soil.

(ii) Nitrogen fixation by certain bacteria and blue-green algae: Certain bacteria and blue-green algae present in the soil fix nitrogen from the atmosphere and convert it into compounds of nitrogen.

70. Question.  Draw a neat, labelled diagram of nitrogen cycle in nature. Which natural

phenomenon occurring in the sky is responsible for nitrogen fixation?

Answer. A neat, labelled diagram of the nitrogen cycle in nature is shown below:

Lightning is a natural phenomenon which occurs in the sky and responsible for nitrogen fixation. The temperature and pressure during lightning convert atmospheric nitrogen into oxides of nitrogen. These nitrogen compounds

combine with rain water to form nitric and nitrous acid which mix with the soil. These acids are utilized by various organisms.

Multiple Choice Questions (MCQs)

71. Question. The bread dough rises because of:

A. heat

B. grinding

C. growth of yeast cells

D. Kneading

Answer. C

Yeast is used in baking industry for making bread. It increases the volume of dough.

When yeast is mixed in dough for making bread, the yeast reproduces rapidly and produces carbon dioxide during respiration. Bubbles of the gas fill the dough and increase its volume.

72. Question. Yeast is used in the production of:

A. sugar

B. alcohol

C. hydrochloric acid

D. Oxygen

Answer. B

 Yeast is used for commercial production of alcohol and wine.

73. Question. The process of conversion of sugar into alcohol is called:

A. nitrogen fixation

B. moulding

C. fermentation

D. infection

Answer. C

The process of conversion of sugar into alcohol is known as fermentation. Louis Pasteur Discovered fermentation in 1857.

74. Question. Which of the following is an antibiotic?

A. sodium bicarbonate

B. streptomycein

C. alcohol

D. yeast

Answer. B

Streptomycin, tetracycline and erythromycin are some of the commonly known antibiotics which are made from fungi and bacteria.

75. Question. The most common carrier of communicable diseases is:

A. ant

B. housefly

C. dragonfly

D. spider

Answer. B

Housefly is most common carrier of communicable diseases. The houseflies

feed on garbage, animal excreta and dead organic matter. Diseases cholera and tuberculosis spread by housefly.

76. Question.  The carrier of malaria causing protozoan is:

A. female anopheles

B. cockroach

C. housefly

D. female aedes mosquito

Answer. A

The carrier of malaria causing protozoan called plasmodium is female anopheles mosquito.

77. Question. The vaccine for smallpox was discovered by:

A. Alexander Fleming

B. Edward jenner

C. Louis Pasteur

D. Rober coch

Answer.  B

Edward Jenner discovered the vaccine for smallpox in 1978.

78. Question.  Alcohol can be converted into vinegar by the action of micro-organisms

called:

A. viruses

B. yeast

C. protozoa

D. bacteria

Answer. D

The dilute solution of acetic acid is called vinegar. Alcohol can be converted

into vinegar by the action of micro-organisms called bacteria. In this process, first alcohol is produce by using yeast. The acetobacter bacteria is then added to alcohol. Acetobacter bacteria convert alcohol into acetic acid (or vinegar).

79. Question. 

The first antibiotic called penicillin was extracted from:

A. a bacterium

B. a protozoan

C. a fungus

D. an alga

Answer. C

An antibiotic Penicillin was extracted from fungus (mould) by Alexander

Fleming in 1929. This antibiotic was made from the fungus called penicillium.

80. Question. Which of the following is not a communicable disease?

A. cholera

B. cancer

C. chickenpox

D. malaria

Answer. B

Cholera, chickenpox and malaria are communicable disease while cancer is not a communicable disease.

81. Question. Which of the following increases the fertility of soil

(A) Lactobacillus bacteria

(B) Rhizobium bacteria

(C) Spirogyra algae

(D) Blue-green algae

A. A and B

B. B and C

C. A and D

D. B and D

Answer. B and D 

As these two organisms are able to fix nitrogen gas from atmosphere to enrich soil with nitrogen compounds hence increasing fertility of soil. 

82. Question. Which of the following cannot be used as a food preservative?

A. sodium metabisulphate

B. sodium hydroxide

C. sodium benzoate

D. citric acid

Answer B

sodium metabisulphate, sodium benzoate and citric acid are used as a food preservative whereas sodium hydroxide is not used as food preservative.

83. Question. Which of the following disease is not caused by bacteria?

A. cholera

B. typhoid

C. tuberculosis

D. measles

Answer. D

Cholera, typhoid and tuberculosis are caused by bacteria whereas measles is caused by a virus.

84. Question. The micro-organisms which can reproduce and multiply only cells of other

organisms are:

A. protozoa

B. fungi

C. bacteria

D. viruses

Answer. D

Viruses are too much smaller in comparison to other micro-organisms. They do not show most of the characteristics of the living organisms like respiration. They just reproduce. They, however, reproduce only inside the cells of the host organism, which may be a bacterium, plant or animal.

85. Question.  The dengue disease spread by Aedes mosquito is caused by:

A. bacteria

B. virus

C. protozoan

D. fungus

Answer. B

Dengue disease is caused by a virus. Female Aedes mosquito acts as carrier of dengue virus.

86. Question.  Which of the following disease is not caused by viruses?

A. measles

B. smallpox

C. cholera

D. polio

Answer C

Measles, smallpox and polio are caused by viruses while cholera is caused by a bacterium.

87. Question. The micro-organism which is capable of converting sugar into alcohol and

carbon dioxide is:

A. bacterium

B. fungus

C. alga

D. protozoan

Answer. B

Yeast, a fungus is capable of converting sugar into alcohol and carbon dioxide.

88. Question. Which of the following is not a use of micro-organisms?

A. preparation of medicines (or drugs)

B. preparation of food by photosynthesis

C. recycling of materials in nature

D. increasing the fertility of soil

Answer B

Some of the micro-organisms are used to preparation of medicines. Some of micro-organisms are used recycling of materials in nature and increasing the fertility of soil. The synthesis of food by photosynthesis takes place in leaves with the help of inorganic materi like carbon-dioxide and water in the presence of sunlight and chlorophyll.

89. Question. The malaria disease is caused by a:

A. virus

B. protozoan

C. bacterium

D. fungus

Answer. B

The malaria disease is caused by a protozoan called plasmodium.

90. Question

The parasite called Plasmodium causes a disease known as:

A. measles

B. polio

C. malaria

D. dengue

Answer . C

The parasite called Plasmodium causes a disease known as malaria. Female Anopheles mosquito carries the parasite of malaria.

Lecture: 10 :CLASS VIII : SCIENCE : Chapter 2: PRESERVATION OF FOOD & NITROGEN FIXATION

CLASS VIII   |    SCIENCE    |    CHAPTER 2

      notes prepared by subhankar Karmakar

Preservation of food:

The process in which the food materials are given a suitable physical or chemical treatment to prevent their spoilage is called food preservation. Some of the methods for preserving foods are: 

1. Sun drying or dehydration

2. Heating

3. Cooling or refrigeration

4. Deep freezing

5. Addition of common salt

6. Addition of sugar

7. Addition of mustard oil and vinegar

8. Use of special chemical preservatives like sodium meta-bi-sulphite, sodium benzoate and citric acid.

9. Pasteurisation

10. Packing food in airtight packets.

1. Preservation of food by sun drying or dehydration:

Water content of the food is removed by sun drying. It is also known as dehydration.

Vegetables like spinach, methi leaves, cauliflower, peas are preserved in our homes by the sun drying method.

2. Preservation of food by heating:

Microorganisms in the food can be killed by heating the food. We boil milk to prevent it from spoilage.

3. Preservation of food by cooling or refrigeration:

The growth of microorganisms can be inhibited by keeping low temperature. 

The food materials like milk, kneaded flour, cooked food, fresh fruits and vegetables are kept in a cool place like refrigerator to prevent their spoilage.

4. Preservation of food by deep freezing:

At sub zero (below zero degree centigrade) temperature the growth of microorganism are completely stopped. 

Deep freezing method is used for the preservation of foods like meat, fish and their products; fruits and vegetables.

5. Preservation of food by adding common salt:

common salt prevents the growth of food spoilage microorganisms due to which it is used to preserve a number of food materials. It is one of the oldest practice for preservation of food like meat and fish. 

common salt is also used to preserve fruits such as raw mangoes lemon and amla as well as tamarind.

6. Preservation of food by adding sugar:

Sugar is used as a preservative in making jams and jellies from fruits. The fruits which are preserved in the form of jams and jellies by using sugar as preservative are Apple, ripe mango, Orange, strawberry, pineapple and guava etc.

7. Preservation of food by mustard oil and vinegar: 

Mustard oil and vinegar are widely used as preservatives for the preservation of fruits and vegetables in the form of pickles.

Fruits like raw mango, amla and lemon are preserved using mustard oil and vinegar in the form of their pickles.

8. Preservation of food by using special chemicals as preservatives:

Sodium metabisulphite, sodium benzoate and citric acid are used as chemical preservatives. To preserve foods such as jams, jellies, juices and squashes sodium metabisulphite and sodium benzoate are used. To preserve confectionery citric acid is used as a preservative.

9. Preservation of food by pasteurisation:

Pasteurisation involves the process of heating followed by quick cooling. Packaged milk is always pasteurized.

10. Preservation of food by packing and air tight packets:

This days dry fruits and even vegetables are sold in sealed airtight packets to prevent the attack of microorganisms on them. This helps the dry fruits and vegetables to remained unspoiled for a longer time.

NITROGEN FIXATION:

The process of converting nitrogen gas of atmosphere or air into compounds of nitrogen which can be used by the plants is called nitrogen fixation.

The nitrogen gas of atmosphere or air can be fixed or converted into nitrogen compounds-

1. By certain nitrogen fixing bacteria present in the soil,

2. By Rhizobium bacteria present in the root nodules of leguminous plants,

3. Buy blue-green algae,

4. By lightning.

Rhizobium Bacteria:

The nitrogen fixing rhizobium bacteria live in in the root nodules of leguminous plants like peas, beans etc, also known as legumes.

Nitrogen fixation by lightning:

Nitrogen gas of atmosphere also gets fixed through the action of lightning in the sky. When lightning takes place in the sky during thunderstorm, a high temperature is produced in the atmosphere. At this high temperature, nitrogen gas of air combines with oxygen gas of air to form nitrogen compounds. These nitrogen compounds dissolve in rain water, fall to earth with rain water and go to the soil. Nitrogen of atmosphere can also be fixed by artificial methods.

THE NITROGEN CYCLE:

The circulation of nitrogen element through living things like plants and animals and non living environment like air soil and water, is called nitrogen cycle in nature.

"Nitrogen is required by both plants and animals for their growth and development. Nitrogen is an essential component of proteins, which make up the bodies of plant and animals. Nitrogen is also present in chlorophyll, nucleic acids and vitamins. The same nitrogen element is circulated again and again through living things like plants and animals and non living things like air soil and water. This whole process is known as nitrogen cycle."

                  Fig:  Nitrogen Cycle in nature    

The main steps of nitrogen cycle:

I. The atmosphere or air contains nitrogen gas. The nitrogen fixing bacteria present in the soil and in the root nodules of leguminous plants, blue green algae and lightning in the sky fix nitrogen gas from the atmosphere and convert it into compounds of nitrogen which go into soil.

II. The plant take compounds of nitrogen from the soil for their growth. The plants absorb the nitrogen compounds from the soil through their roots. The plants convert the compounds of nitrogen into plant proteins and other organic compounds which make up the body of plants.

III.  The plants are eaten by the animals as food. Animals convert plant proteins into animal proteins and other organic compounds which make up their body. Some animals also eat other animals to obtained nitrogen compound. Thus, animals obtain nitrogen compounds by eating plants as well as other animals.

IV.  When plants and animals die, the complex nitrogen compounds like proteins etc. present in their dead bodies are decomposed and converted into simple compounds of nitrogen by certain bacteria and fungi present in the soil. Animal excretions like urine etc. are also converted into simple compounds of nitrogen. All the simple compounds of nitrogen formed in this way go into the soil. In this way, the compounds of nitrogen which were taken by the plants from the soil during their growth are returned to the soil. From the soil these nitrogen compounds are again absorbed by the new plants for their growth and this part of nitrogen cycle is repeated endlessly.

V. Some of the compounds of nitrogen formed from the decay of dead plants and animals, are decomposed by denitrifying bacteria present in the soil to form nitrogen gas. This nitrogen gas goes back into the atmosphere from where it initially came. This process is the reverse of fixation of nitrogen. In this way the nitrogen gas which was removed from the atmosphere during fixation is put back into the atmosphere.

From the atmosphere nitrogen gas is used again during nitrogen fixation and the nitrogen cycle is repeated in nature again and again. As a result of nitrogen cycle in nature, the percentage of nitrogen gas in the atmosphere or their remains constant.

 

Lecture: 9 :CLASS VIII : SCIENCE : Chapter 2: BAD MICRO-ORGANISMS

CLASS VIII   |    SCIENCE    |    CHAPTER 2

      notes prepared by subhankar Karmakar

HARMFUL MICROORGANISMS:

Those microorganisms which cause diseases are harmful to us and called pathogens. Pathogens can be bacteria, viruses, protozoa, fungi etc.

Communicable diseases:

Those microbial diseases which can spread from an infected person to a healthy person through air, water, food or physical contact, etc are called communicable diseases.

Some of the examples of communicable diseases are: Common cold, Cholera, Chicken pox, Tuberculosis (TB), Malaria and AIDS. 

Different ways by which communicable diseases can occur and spread:

Any communicable diseases can occur and spread in the following ways:

1. By breathing of air containing microorganisms,

2. By taking infected food or water,

3. Through insect bites,

4. By sharing infected injection needles,

5. By physical contact with an infected person.

Prevention of communicable diseases: 

Methods for preventing the occurrence and spreading of communicable diseases are as follows: -

1. A person suffering from common cold or influenza should always cover his mouth and nose with a handkerchief while sneezing, so that microorganisms are not being released into the air. We must keep a social distancing too.

2. We should keep our food covered to protect it from getting infected by flies. You should also drink clean and safe water.

3. We should use mosquito nets to protect ourselves from mosquito bites

4. Disposable syringes and needles should we use for injection.

5. A person infected by a communicable disease should be quarantined.

6. We should follow proper vaccination at proper time.

Vectors or carriers of disease causing microorganisms:

The insects or other animals which transmit disease-causing microorganisms to humans without itself suffering from them are called vectors or carriers. 

The most common Carriers of disease causing microorganisms are:

1. Housefly and

2. Mosquito

A. Housefly as the vectors of diseases:

Some of the dangerous diseases spread by housefly are: cholera, tuberculosis (TB), typhoid and diarrhoea.

Prevention of diseases spread by housefly:

The spreading of diseases by houseflies can be prevented in the following ways:

1. Household garbage should be put in garbage bin which should be kept covered. This will prevent the house flies from breeding because they will not be able to lay their eggs on garbage.

2. The food should always be kept covered so that flies cannot sit on it.

3. We should avoid eating uncovered food items from the roadside stalls.

4. The flies should be killed by using insecticide spray.

5. We should take proper vaccination as some of the diseases spread by housefly can be prevented by vaccination.

B. Mosquitoes as the vectors of diseases:

Mosquito spread diseases by transmitting disease causing microorganisms through its bites.

The most common diseases spread by mosquitoes are malaria and dengue fever.

Prevention of diseases spread by mosquitoes:

The spreading of diseases by mosquitoes can be prevented in the following ways:

1. As the mosquitoes breed in stagnant water, we should avoid any pools of stagnant water around the houses and our surroundings should be clean and dry.

2. The windows and doors of the house should have fine iron wire mesh so that mosquitoes cannot enter our house.

3. Insecticides should be spread in houses periodically to kill mosquitoes.

4. Oil should be sprayed on the surface of water in dirty water drains to kill the larvae of mosquitoes.

5. Mosquito net should be used over beds while sleeping to prevent mosquito bites.

Some of the common diseases caused by bacteria:

Tuberculosis, Cholera, Typhoid etc.

Some of the common diseases caused by virus:

Measles, Chicken pox, Polio, Hepatitis B,  Dengue.

Disease causing microorganisms in animals:

Some of the example of diseases caused in animals by the microorganisms are: foot and mouth disease, anthrax, aspergillosis.

1. Foot and mouth disease of animals like cattle is caused by a virus.

2. Anthrax is a dangerous disease of animals like cattle which is caused by a bacterium, known as bacillus anthracis.

3. Aspergillosis is a disease of animals like poultry birds which is caused by fungus.

Disease causing microorganisms in plants:

Several microorganisms cause diseases in plants like Wheat, Rice, Potato, Orange, Apple and others. 

Some of the common plant diseases caused by microorganisms are: rust of wheat, citrus canker and yellow vein mosaic of bhindi.

Rust of wheat is caused by fungi.

Citrus canker is caused by bacteria.

Yellow vein mosaic of bhindi is caused by virus.

Food poisoning:

The disease caused due to the presence of a large number of microorganisms like bacteria and fungi in the food or due to the presence of toxic substances in food formed by the action of microorganisms is called food poisoning.

The major symptoms of food poisoning are: vomiting, diarrhoea, pain in abdomen, headache and fever.

The most common microorganisms which cause food poisoning are salmonella bacteria, clostridium botulinum bacteria and aspergillus fungus.