Class - VIII
TIME: 3 Hrs.
1. Attempt all the questions and follow the instructions given in each question.
2. Q.No. 1 is MCQs type; choose the correct option.
3. Q.No. 2 are Very Short Answer Type Questions, carry one mark each.
4. Q.No. 3 to Q.No. 9 are Short Answer Type Questions-I, carry 2 marks each.
5. Q.No. 10 to Q.No 19 are also Short Answer Type Questions-II, carry 3 marks each.
6. Q.No. 20 to Q.No 23 are Long Answer Type Questions, carry 5 marks each.
Q.1. Choose the correct options :
(i) Two objects repel each other. This repulsion could be due to
(a) frictional force only.
(b) electrostatic force only.
(c) magnetic force only.
(d) either a magnetic or an electrostatic force.
(ii) If we apply oil on door hinges, the friction will :
(c) disappear altogether
(d) will remain unchanged
(iii) The loudness of sound depends on :
(a) its amplitude
(b) its frequency
(c) its time period
(d) its speed.
(iv) Which of the following metals is used in electroplating to make objects appear shining?
(v) An electroscope is a device that is used to find an object that is
(c) free of cracks
(vi) Part of the eye which controls the light entering is called :
(vii) Ursa Major is not known as :
(a) Big Dipper
(b) Great Bear
(viii) Process of separating grain seeds from the chaff is called
(ix) Viruses reproduce only inside the cells of :
(a) Host organism
(c) Only surface of microbes
(x) Which is thermosetting plastic?
Q.2. (i) “Cells are the basic structural units of living organisms.” Explain.
(ii) What is the purpose of the tail in the sperm?
(iii) Which force is responsible for wearing out tyres of motor vehicles?
(iv) What is a drag?
(v) What is ultrasound?
(vi) Explain why a layer of zinc is coated over iron.
Ans: (i) Organisms in the living world differ from one another, but all are made up of cells. So, cells in living organisms are basic complex living structures.
(ii) The sperms swim in the oviduct with the help of their tails to reach the egg.
(iii) Tyres of motor vehicles wear out due to frictional force between tyres and the road.
(iv) The frictional force exerted by fluids is called drag.
(v) Sound frequencies higher than 20,000 Hz are called ultrasound.
(vi) Layer of zinc is coated over iron because zinc prevents it from rust and corrosion.
Q.3. Why are vaccines so important for children?
Ans: By introducing the vaccine in the body, the body fights and kills the bacteria by producing suitable antibodies. The antibodies remain in the body, and the child is protected from the disease-causing microbes.
Q.4. What are the characteristics of an ideal fuel?
Ans: Characteristics of an ideal fuel :
(i) It is readily available, cheap and can easily be transported.
(ii) It burns easily, has a higher calorific value and does not leave behind any residue.
Q.5. Compare between LPG and wood as fuel.
Ans: Differences between LPG and Wood are as follow :
Q.6. Explain how deforestation leads to reduced rainfall.
Ans: The plants need carbon dioxide for photosynthesis. Fewer trees would mean less carbon dioxide consumption and its increased amount in the atmosphere. This leads to global warming as carbon dioxide traps sun rays' heat. The increase in temperature on earth disturbs the water cycle and reduces rainfall. This causes drought.
Q.7. Why are wildlife sanctuaries important for the conservation of plants and animals?
Ans: In a wildlife sanctuary, killing and capturing wild animals is strictly prohibited. It does not allow any human activity which disturbs the wild animals in their habitat. So, animals live in the natural environment, protected from people in these areas. This is the reason that sanctuaries are important.
Q.8. Mention any two features seen in boys and girls each to distinguish them from each other at puberty.
Ans: Two features seen in boys at puberty are :
(i) Growth of facial hairs.
(ii) Voice becomes hoarse.
Two features seen in girls at puberty are :
(i) Development of breasts.
(ii) Region below the waist becomes wider.
Q.9. We should avoid taking medicines/drugs unless prescribed by a doctor. Give reasons.
Ans: We should avoid taking medicine/drugs unless prescribed by a doctor because :
(i) Several medicines have adverse side effects and have specific dosage levels that may harm the body if not followed.
(ii) Drugs can be addictive too, and can ruin our health and happiness.
Q.10. What is the cause of friction?
Ans: Friction is caused by the irregularities on the two surfaces in contact. Even those surfaces that appear smooth have many irregularities that lock each surface into one another.
Q.11. A ball rolling along the ground gradually slows down and finally comes to rest. Why does this happen? What is the effect of this force?
Ans: The force responsible for changing the state of motion of the ball is the force of friction. The ball will come to a rest position. This force causes wear and tear of the objects in motion.
Q.12. Complete the following chemical reaction: Carbon dioxide (CO2) + Water (H2O) →? Is it an acid or base?
It is acid.
Q.13. Give reason :
(i) LPG is a better domestic fuel than wood.
(ii) Differentiate between Flora and Fauna.
Ans: (i) Wood has less calorific value (17000-22000 kJ/kg) than the calorific value of LPG (55000 kJ/kg). It means that on combustion of 1 kg of LPG, 55000 kJ heat is generated while combustion of 1 kg of wood produces about 20000 kJ of heat only. So LPG is better domestic fuel than wood. Also, LPG does not leave any residue after combustion, which wood does.
Q.14. Once in a village, there was a fire in a hut. When a lot of dry powder of a substance, A was released over the fire, the fire got extinguished.
(i) Name the substance A.
(ii) How does the substance extinguish the fire?
(iii) Give another substance that behaves like substance A.
Ans: (i) A is sodium bicarbonate (NaHCO3).
(ii) The heat of fire decomposes sodium bicarbonate to produce carbon dioxide gas which covers the fire like a blanket. It cuts off the supply of fresh air to the burning substance. Thus, the fire gets extinguished.
(iii) Potassium hydrogen carbonate.
Q.15. Classify the following into friendly and harmful micro-organisms: Yeast, malaria parasite, Lactobacillus, bread mould, Rhizobium, Bacillus anthracis.
Q.16. List three sources of noise pollution in your locality.
Ans: The three sources of noise pollution in our locality are :
(ii) Television and music systems.
(iii) Transport, vehicles.
Q.17. A more reactive metal displaces the less reactive metal from its salt solution. What do you mean by this reaction?
Ans: In a chemical reaction, when a more reactive metal displaces the less reactive metal from its salt solution, it is called displacement reaction, e.g., zinc can displace copper from its copper sulphate solution zinc is more reactive than copper.
Less reactive metal cannot displace the more reactive metal from its salt solution. e.g., copper cannot displace zinc from its solution zinc sulphate as copper is less reactive than zinc.
Q.18. Draw structure of virus and amoeba.
Q.19. What are the advantages of using CNG and LPG as fuels?
Ans: CNG and LPG are essential fuels because they can easily transport them through pipes. CNG (Compressed natural gas) and LPG (Liquefied Petroleum gas) are used for power generations and non-polluting fuels. Its great advantages are that it can be used directly for burning in homes and factories.
Q.20. What do CFC’s stand for? Name some devices where CFC’s are used. Why are CFC’s considered pollutants?
Ans: CFCs stands for Chlorofluorocarbons. CFCs are used in refrigerators, air conditioners, aerosol sprays. CFCs are considered pollutants because they are depleting the upper atmosphere's useful ozone layer. This happens as follows :
CFCs released into the air go up and ultimately reach high into the atmosphere where the protective ozone layer exists. The chlorofluorocarbons react with the ozone gas of the ozone layer and destroy it gradually. This allows the sun's harmful ultraviolet rays to reach the earth and cause damage.
Q.21. What is the difference between revolution and rotation?
Ans: Difference between revolution and rotation :
Q.22. What are the major groups of micro-organisms?
Ans: Micro-organisms are divided into four major groups, which are as follows :
(i) Bacteria: These are single-celled organisms that are harmful, as they cause disease, and some of them may be useful as in vaccines.
(ii) Fungi: These are non-green plants that consume their food from the dead organic matter.
(iii) Protozoan: These are unicellular animals that cause diseases like malaria and dysentery.
(iv) Algae: These are photoautotrophic organisms that may be unicellular or multicellular. They play an important role in medicines, agriculture, industry and food.
Viruses are also considered micro-organisms but are actually the connecting links between non-living and living organisms.
Q.23. Write short notes on the following :
(ii) Nucleus of a cell
Ans: (i) Cytoplasm: It is a jelly-like substance present between the cell membrane and the nucleus. It encloses all tiny structures called cell organelles that perform different functions. It also contains water, sugar, proteins, minerals etc.
(ii) Nucleus of a Cell: It is a spherical component of a cell commonly located in the cell's centre. It is covered by a porous nuclear membrane and contains genetic material like RNA and DNA. It also contains thread-like structures called chromosomes, which carry genes. The nucleus controls various activities of the cell.