1. Tick the correct option:
1. The yeast multiply by a process called (a) Binary fission (b) Budding (c) Spore formation (d) None of the above 2. The example of protozoan is (a) Penicillium (b) Blue green algae (c) Amoeba (d) Bacillus 3. The most common carrier of communicable diseases is (a) Ant (b) Housefly (c) Dragonfly (d) Spider 4. The following is an antibiotics (a) Alcohol (b) Yeast (c) Sodium bicarbonate (d) Streptomycin 5. Yeast produces alcohol and carbon dioxide by a process called (a) Evaporation (b) Respiration (c) Fermentation (d) Digestion 6. The algae commonly used as fertilizers are called (a) Staphylococcus (b) Diatoms (c) Blue green algae (d) None of the above 7. Cholera is caused by (a) Bacteria (b) Virus (c) Protozoa (d) Fungi 8. Plant disease citrus canker is caused by (a) Virus (b) Fungi (c) Bacteria (d) None of these 9. The bread dough rises because of (a) Kneading (b) Heat (c) Grinding (d) Growth of yeast cells 10. Carrier of dengue virus is (a) House fly (b) Dragon fly (c) Female Aedes Mosquito (d) Butterfly 11. Yeast is used in the production of (a) Sugar (b) Alcohol (c) Hydrochloric acid (d) Oxygen 12. The vaccine for smallpox was discovered by (a) Robert Koch (b) Alexander Fleming (c) Sir Ronald Ross (d) Edward Jenner 13. Chickenpox is caused by (a) Virus (b) Fungi (c) Protozoa (d) Bacteria 14. The bacterium which promote the formation of curd (a) Rhizobium (b) Spirogyra (c) Bread mould (d) Lactobacillus 15.Plasmodium is a human parasite which causes (a) dysentery (b) Sleeping sickness (c) Malaria (d) All of the above 16. The bacterium Bacillus Anthracis was discovered by (a) Edward Jenner (b) Alexander Fleming (c) Louis Pasteur (d) Robert Koch 17. Carrier of malaria causing protozoan is (a) Butterfly (b) Housefly (c) Female Anopheles Mosquito (d) Cockroach 18. The process of conversion of sugar into alcohol is called (a) Infection (b) Moulding (c) Nitrogen fixation (d) Fermentation 19. Foot and mouth disease of cattle is caused by (a) Fungi (b) Virus (c) Algae (d) None of these 20. Which of the following is not a fungi (a) Paramecium (b) Bread mould (c) Penicillium (d) Aspergillus Answers: 1)b 2) c 3) b 4) d 5) c 6) c 7) a 8) c 9) d 10) c 11) b 12) d 13) a 14) d 15) c 16) d 17) c 18) d 19) b 20) a 2. Write the contributions of the following: A. Louis Pasteur B. Edward Jenner C. Alexander Fleming D. Robert Koch 3. Define: A. Microbes B. Pathogens C. Nitrogen Fixation D. Pasteurization E. Preservatives F. Carriers G. Fermentation 4. Give two uses of microorganisms in the following areas: i) Food Industry ii) Medicinal Use iii) Environment related 5. Give an activity to show the process of fermentation? 6. List few differences between Antibiotics and Antibodies? 7. Explain Nitrogen Cycle in detail with the help of a cyclic representation? 8. List some harmful effects of microorganism? 9. How can we control the spread of diseases caused by mosquitoes? 10. Why milk in polypacks does not get spoiled? 11.Why does sugar solution with yeast powder become alcoholic in taste? 12. Megha, a class VIII student was asked to submit a project report on mosquito transmitted diseases. She visited a nearby hospital where her aunt was staffed as a nurse. Her aunt took her to a patient suffering from malaria. Megha talked to the patient and asked him about his health and also took some flowers for him. (a) Name the mosquito that spreads malaria. (b) What is the name given to such organisms that transmit the diseases from infected to healthy persons? (c) How can we control the spread of diseases by mosquitoes? (d) Identify two important values as shown by Megha. 13. Kushal's family is happy as he became a proud father to a baby girl. Upon a routine visit to the hospital, the doctor advised him not to skip the vaccination schedule. While discussing the same at home, one of the family members suggested that vaccination is not necessary for a girl child. Kushal opposed this suggestion. (a) What is vaccination? (b) Name the scientist who prepared the first vaccine? (c) Critically comment upon Kushal's viewpoint. III Microorganisms-Friend and Foe Solved Questions Read Download CBSE 8th science: "Notes ands Questions Answers" Read Download You might also like: Chapter: VIII Microorganisms-Friend and Foe Microorganisms : Solved Questions Read Download Microorganisms- : Notes Read Download Microorganisms- : MCQ 's Read Download Microorganisms- : Test Paper-1 Read Download Microorganisms- : Test Paper -2 Read Download
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8th synthetic materials Þ Synthetic materials are kinds of materials obtained from the synthesis of chemicals. Þ The chemicals used for synthetic materials are obtained from petroleum and natural gas(methane) Þ Petroleum and natural gas is compound of hydrogen and oxygen called hydrocarbon. Þ Monomers are simple chemical molecules of hydrocarbon. Þ When monomers join end to end form a long chain of monomers called polymers. The process of the formation of polymers is called polymerization. Þ Cellulose [beet root] is polymers of glucose while Hemoglobin is polymers of amino acid. Þ Fibres are thin thread like materials used to prepared cloths. Þ Fibres obtained on mixing natural and synthetic fiber are called semi synthetic fibre. e.g. rayon Rayon Þ Rayon is synthetic fibres obtained from cellulose. Þ Rayon are of three types: Viscose Cupreammonium (cupro) and acetate rayons. Viscose Rayon Þ In industry cellulose dissolved in mixture of sodium hydroxide (NaOH) and CS2 (carbon disulphide) to get Viscous liquid [semi solid] called viscose. Þ Viscose is forced to spinnerets [an apparatus having small holes like shower] into an acid bath [through solution of acid like H2SO4] . Thus filaments of rayon are obtained which is spun into thread. Cupro Rayon Þ Cupro Rayon are obtained on dissolving cellulose into solution of CuSO4 and NH4 . The dissolve solutions forced to spinnerets into an acid bath to get filaments of cuprammonium rayon are obtained which is spun into thread. Acetate Rayon Þ Acetate Rayon is obtained on dissolving cellulose into solution of Acetate and H2SO4. Rayon in our daily life Þ Rayon mixed with cotton or silk to make smooth and silky cloth in textile industry. Þ Rayon mixed with wool to make carpet. Þ Rayon are also used for making reinforced tyre, bangles and surgical dressing Þ The name Nylon derived from the New York [NY] and London[LON] as Nylon was first produce in both places at same time. NYLON Þ Nylon (polyamides) was first prepared in 1935 chemically. Þ Nylon are prepared using cyclic hydrocarbon Benzene(C6H6) Þ Nylon has silk like texture and high tensile strength[Drawn into long thin straps] Nylon in our daily life Þ Nylon is mainly used for making ropes, woman’s wear, fishing net, sari socks and tie Polyster Þ Polyster is obtained from polymer of ethene. It has maximum stretchable strength. Þ Terylene, Dacron are kinds of Polyster used for dress, cloth and curtain. Þ Terylene mixed with cotton and wood to produce terycot and terry wool respectively. Þ Polysters are also used for making sail for sail boat and conveyor belts. Acrylics Þ Acrylics fibres are obtained on dissolving acetylene[C2H2] into suitable solvent like HCN and then forced to spinneret because acetylene decompose without melting. Acrylics in our daily life Þ They are light and soft like wool. The y are crimpy (wavy) and straight like Polyster thus appear to be bulky and look like wool. Þ They are resistant to weather as they are not easily acted upon by moisture. Advantages of synthetic fibres Þ Having long lasting luster and do not turn yellow with age Þ Easy to clean and dry up quickly Þ Durable and do not shrink on washing Þ They are less expensive than cotton Þ They do not depend on plants or animal like cotton Advantages of synthetic fibres Þ The get electrically charged in dry weather and cause skin irritation Þ The melt and form sticky beads on heating. There is always a risk of getting burn in kitchen Þ They are hydrophilic as do not absorb sweat and moisture thus uncomfortable to wear. Þ They are non bio degradable and cause pollution. Þ They are good absorber of radiant heat and not fit in summer. Good to more good To make make wide spread use of synthetic material it is mixed with natural fibre .There are called blend fibre. PLASTIC Þ Plastic : Any material which can be molded into any desirable shape on heating is called plastic Þ Petroleum product such that Ethane, propane, benzene ,toluene etc are used for manufacturing plastic. Plastic Thermoplastic Thermosetting Thermosetting Plastic Þ Thermosetting plastics are kind of plastic which once moulded cannot moulded again by heating. Þ Thermosetting plastics are kind of plastic whose polymers form highly cross linked chain on heating. Þ Bakellite , melanin, Formaldehyde are some of the examples of Thermosetting Plastic Thermoplastic Plastic Þ Thermoplastic are kind of plastic which can be moulded again and again by heating and easily reused. Þ PVS, Polysterine , nylon , polythine are some of the examples of Thermoplastic Plastic Þ Polymers of thermoplastic Plastic have long chain without cross linked to each other. Characteristics of plastic Þ Plastic has much less toughness as compared to metal Þ having light weight Þ It is not affected by acids and bases. Þ Plastic are non bio degradable as it is weather resistant Þ Plastic are bad conductor of heat and electricity Þ Plastic melts on heating Some of the common plastics are a. Polythene Þ it is obtained from polymerization of ethene. it is non bio degradable . Þ it is a kind of thermosetting plastic Þ it is insoluble in any solvent Þ it is light weight Þ it is anti corrosion and insulator Þ it is used for making bag ,adhesive tap, electric wire cover and can b. Polyvinyl chloride (PVC) Þ it is use for making sole of shoe Þ it is use for making covering of electric wire Þ it is use for making sanitary fittings c. Polysterine Þ It is a polymer of polythene . Þ it is a kind of thermosetting plastic Þ it is highly transparent Þ it is use for making cups of hot drink , toy etc. Þ it is use for safe packaging of expensive items Þ it is use for making Styrofoam[themocole] Þ it is use as insulating material in refrigerator d. Teflon Þ It is prepared by using tera- fluroethene. Þ Heat and chemical are not effective on Teflon Þ it is use for making non stick cooking were Þ it is use for making corrosive proof coating in industry e. Bakelite Þ it is a kind of thermosetting plastic Þ it is use for making electrical switches and plug Þ it is use for making gear wheel Þ it is use for making table top Þ it is use for making comb, pen bodies and photograph records f. Melanin Þ It is hard and highly polished polymers used for making unbreakable kitchen were. Study in Depth Trend Setter Synthetic Fibres and Plastics[CBSE 8th Science] Read and Download III Synthetic fiber and Plastic Read and download VIII Synthetic fiber and Plastic Read and download VIII Synthetic fiber and Plastic view video 8th Synthetic fiber and Plastic [Solved Questions] Download File Searches related to synthetic fibres synthetic fibres examples synthetic fibres list names of synthetic fibres synthetic fibres ppt synthetic fibres and plastics synthetic fibres and plastics class 8 properties of synthetic fibres advantages of synthetic fibres
The basic structural and functional unit of an organism The basic structural and functional unit of an organism is called cell. Cells are like bricks that are assembled to make a building. Similarly, cells are assembled to make the body of every organism. This is why cell are called the basic structural and functional unit of an organism. Discovery of cell: Robert Hooke in 1665 observed slices of cork (a part of the bark of a tree) under a simple magnifying device. He Robert Hooke observed under a microscope there are many partitioned boxes or compartments like a honeycomb. Hooke coined the term ‘cell’ for each box. A hen’s egg can be seen easily. Is it a cell or a group of cells? It is a single cell. A white blood cell (WBC) in human blood is another example of a single cell. How do scientists observe and study the living cells? Scientists used microscopes which magnify objects. Stains (dyes) are used to colour parts of the cell to study the detailed structure. Kinds of organism: Organisms which are made up of a single cell are called unicellular where as Organisms made up of more than one cell is called multicellular. Cell Theory : Cell Theory was elaborated by a German botanist Schleiden and Zoologist Schwann The Cell Theory states that: 1) All organisms are made up of one or more cells and the products of those cells. 2) All cells carry out life activities ( require energy, grow, have a limited size). 3) New cells arise only from other living cells by the process of cell division. Tissue: The group of cells that are similar in structure and functions is called tissue. like nervous tissue in animal and Vascular tissue in plant. Cells have different shape of Cells according to function they perform in body: Generally, cells are round, spherical or elongated (red blood) . Some cells are long and pointed at both ends. They exhibit spindle shape (muscle cells) . Cells sometimes are quite long. Some are branched like the nerve cell or a neuron. Guard cell in leaves are kidney shaped. White blood cells change their shape and move like amoeba. Which part of the cell gives it shape? Cell membrane provides shape to the cells of plants and animals. Cell wall is an additional covering over the cell membrane in plant cells. It gives shape and rigidity to cells. The size of cells in living organisms may vary . The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest cell measuring 170 mm ×130 mm, is the egg of an ostrich. Nerve cell is the longest cell and blood cells are the smallest cell in our body Cell Structure Protoplasm: The entire content of a living cell is known as protoplasm. It includes the cytoplasm and the nucleus. Protoplasm is called the living substance of the cell. Plasma membrane: The cytoplasm and nucleus are enclosed within the cell membrane together called the plasma membrane. Cell membrane: The outer boundary of the cell is the cell membrane. It is composed of proteins and carbohydrates. Functions of Cell membrane: The cell membrane gives shape to the cell. The cell membrane separates cells from one another and also the cell from the surrounding medium. The cell membrane is porous and allows the movement of substances or materials both inward and outward. This is why it is called selectively permeable membrane. Cell wall: There is also another thick additional covering of animal cell called the cell wall. This is because plant cell need protection against variations in temperature, high wind speed, atmospheric moisture, etc. Full E-Notes for CBSE & NCERT class 8th given below
Class VIII Mathematics [Click on links given below]
VIII Algebra VIII Commercial Maths VIII Geometry & Menstruation CBSE Class VIII Science Physics Chemistry Biology 8th Sample paper 8th Social Science Q1. Why does a plastic comb rubbed with dry hair attract tiny pieces of paper?
a) Charging by rubbing: Charging of an object by rubbing it with another object is calledcharging by rubbing. c) Charging by induction: Charging a neutral body by bringing it near a charged body is called charging by induction. If the divergence of the leaves increases, the body has similar charge that is the given body is also negatively charged. If the divergence of the leaves decreases, the body has unlike charge that is the given body is positively charged. Q11. What will you observe when the metal cap of an electroscope is touched with a plastic comb rubbed in dry hair? Give reason for your answer.
Ans:Tremors or vibrations caused by the earthquakes which travel in the form of waves within the earth or along the earth's surface, are called seismic waves. Seismograph is an instrument which records these waves.
Ans: Two places in India which are most threatened by earthquake are 1. Kashmir 2. Rann of kutch. Ans: The earth's lithosphere is fragmented into many pieces. Each fragment is called a plate, also called tectonic plate. These plates are in continuous motion i.e. they float over hot magma.
Ans: Lightning conductor is a device used to protect buildings from the damaging effects of lightning. It runs from the top to the bottom, along the outer wall of the buildings or any other object, which is to be protected. If lightning strikes the buildings or any other objects, then the lightning conductor provides an easy and direct path for the lighning bolt to pass to the ground without effecting them. Ans: The process of transferring of charge from a charged object to the earth is called earthing. For our safety, most of the electrical appliances and the mains of the house are connected to earth, so that we can be prevented from getting an electric shock.
23. We can easily charge non-metals like rubber, woollen clothes, plastics, etc. whereas we cannot charge a copper rod by rubbing easily. Why?
Ans: When the metallic rods like copper rod are rubbed, charges does not build on their surface because charges can escape through metals as they are conductors whereas when non-metals like rubber, woollen clothes, plastics, etc. are rubbed, charges will build up on their surface because charges are not conducted through them as they are insulators. Ans: During the development of thunderstorm, air currents move in the upward direction and the water droplets move in the downward direction. These movements causes the seperation of charges. Usually, the negative charges accumulate at the lower part of the clouds and the positive charges are accumulated at its upper part. The positive charges are also accumulated at the ground also. When the accumulation of charges becomes large, a high potential difference is set up between lower part of clouds and earth, which is sufficient to break the insulation of air. As a result, negative and positive charges meet, producing streaks of bright light and sound. This process is called an electric discharge. Ans: An electroscope is used to detect the charge on a body. A plastic comp is taken and it is rubbed on hair. Now, the plastic comb gets charged. The comb is touched with the electroscope plate. The static charges which are developed on the comb travels down the conducting wire and reach the two leaves of aluminium foil. Similar charges are acquired by both the leaves and as a result, they repel each other. Thus, the method of charging an uncharged body by bringing another charged body directly in contact is called charging by conduction. Hence, by this way, an electroscope can be charged through conduction.
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