Model Test Papers Class 8 Science

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 Fill in the blanks. (1×10 = 10)

 1.Winnowing is the process of separating grain from the chaff.

  1. The bacterium which promotes the formation of curd is Lactobacillus.
  1. Amoeba and Euglena are protozoans.
  1. The plastic that can be used for making pipe is Polyvinyl chloride.
  1. Metallic oxides are basic in nature.
  1. Diesel and petrol are fossil fuels.
  1. The most commonly used liquid fuel in Indian homes is LPG.
  1. Flora is the plants found in a particular area.
  2.  Cytoplasm is a jelly-like substance in the cell.
  1. Birds and reptiles are oviparous animals.

Match the following. (0.5×10 = 5)

 Column A Column B

  1. Asiatic lion   (a) plants
  2. Hydra            (b) used in thermometer
  3. Wheat           (c) produces sperms
  4. Neuron         (d) endangered species
  5. Ringworm    (e) rabi crop
  6. Cell wall        (f) hottest flame
  7. Testis            (g) fungi
  8. Non-luminous zone (h) blue flame
  9. LPG              (i) budding
  10. Mercury        (j) longest cell

Answer:

  1. d   2.i   3.e   4.j   5.g    6.a    7.c    8.f   9. h   10.b

Answer the following in one sentence: (1×5 = 5)

 1.What is the study of microorganisms called?

Ans. The study of microorganisms is called microbiology.

2.What are weeds? Give examples.

Ans. Weeds are unwanted plants that grow with the main crop and compete with the main crop plants for nutrients and space.

Example:

(i) Amaranthus (Chaulai)

(ii) Chenopodium (Bathua).

3.What are unicellular organisms?

Ans. Organisms that are made up of a single cell are called unicellular organisms.

4.Where does fertilisation take place in human beings?

Ans. Fertilisation is internal in human beings. It takes place in the fallopian tubes/oviducts.

5.Define ignition temperature of a substance.

Ans. The minimum temperature at which a particular substance burns in the presence of air is called Ignition Temperature.

(Based on Chapters – 1 to 10)

Marks: 50

Short answer questions: (1×5 = 5)

 1. Why is cell considered as a basic unit of life?

A cell is considered as a basic unit of life because cells unite to form tissues. Tissues group together to form organs. Various organs work simultaneously to form an organ system. An organism is with a different organ system.

Cell → Tissue → Organ → Organ system → organism

2.Mention any two ways in which bacteria are useful to us.

Ans. (a) They are used for cleaning up radioactive waste.

(b) Nitrifying bacteria convert ammonia to nitrates, the components that plants can use directly.

3.How are the twins born?

Ans. Generally, a woman gives birth to only one child at a time, but sometimes more than one is born. This type of birth is called multiple births.

4.What are the disadvantages of synthetic fibres?

Ans. Synthetic fibres burn more readily than natural.

 Prone to heat damage. Melt relatively easily.

 Prone to damage by hot washing.

 The more electrostatic charge is generated by rubbing.

 Not skin friendly, uncomfortable for long wearing.

 Allergic to some people.

 Non-biodegradable in comparison to natural fibres.

5.Why are sodium and potassium are stored in kerosene?

Ans. Sodium metal reacts with the oxygen of the air at room temperature to form sodium oxide. Hence sodium is stored under kerosene to prevent its reaction with oxygen, moisture and carbon dioxide.

Answer the following questions in 50-60 words: (3×5 = 15)

 Q1. Describe candle flame with a diagram.

A candle flame shows different (three) zones which as follows :

(i) The innermost zone of a flame is dark (or black)

The innermost zone of the flame is colder than the other zones and is dark too. It contains the fuel (wax) in the gaseous state. In this area, no oxygen is available for the burning to take place. If we place one end of a glass tube in the dark zone and hold a burning matchstick near the other end, the flames of the unburnt fuel coming out at the other end will burn.

(ii) The middle zone

It is the yellow coloured zone of a candle flame. It lies between the dark zone and the outermost non-luminous zone. In this part of the flame, the temperature is higher than in darker zone. Here the wax particles decompose to form carbon particles. Some of these carbon particles are oxidised.

(iii) The outermost zone

The outermost zone. It is the blue coloured zone, the non-luminous zone, of the flame is the hottest zone, with the highest temperature.

It gets enough supply of air and complete combustion takes place in this zone.

It does not supply light and produces carbon dioxide and water vapour after

complete combustion.

Q2. How does food get spoilt? In what ways, food can be preserved?

Ans. Microorganisms are responsible for the spoilage of food. When they grow on food, they produce toxic substances which are harmful. These toxic substances make food poisonous causing serious illness.

Food can be preserved by

Drying: Drying is one of the oldest techniques used to hamper the decomposition of food products. Vegetables and fruits are naturally dried by the sun and wind, Vegetables like cauliflower and mint leaves are preserved by drying.

  • Cooling: Cooling preserves food by slowing down the growth and reproduction of microorganism and the action of enzymes that cause food to rot. It makes the fruits, salads and dairy products to be stored safely for longer periods, particularly during warm weather. Meat and cooked food can be preserved by cooling.
  • Freezing: Freezing is also a commonly used process, both commercially and

domestically, for preserving a very wide range of foods. Cold stores provide large volume, long-term storage for strategic food stocks held in the case of national emergency in many countries.

  • Salting: Salt draws moisture from the food like meat through a process of osmosis. Meat is covered with salt or sugar, or a combination of both. Salting also helps to preserve tamarind, raw mangoes, etc.
  • Sugar: The earliest cultures have used sugar as a preservative; Sugar tends to reduce water from the food (plasmolysis). This process leaves the microbial cells dehydrated, thus killing them. In this way, the food will remain safe from microbial spoilage.
  • Smoking: Smoking is used to lengthen the life of perishable food items (Food that gets easily spoilt by microorganisms). It is one of the oldest food preservation methods, which probably arose after the development of cooking with fire. For example- Meat is smoked before storing.

Q3. How does the excessive use of plastics affect the environment?

Ans. Industrial practices in plastic manufacture can lead to polluting effluents and the use of toxic intermediates, the exposure to which can be hazardous. Most plastics are durable and degrade very slowly, the very chemical bonds that make them so durable tend to make them resistant to the most natural process of degradation. Sometimes we are very careless and throw

the wrappers of chips, biscuits and other eatables on the road in parks or picnic places. The polybags carelessly threw here and there are responsible for clogging the drains, too. In the process of eating the food waste animals such as cow swallow materials like polyethene bags and wrappers of food. The plastic material chokes the respiratory system of these animals, or

forms a lining in their stomachs and can be the cause of their death.

Q4. What is a displacement reaction? Explain with the help of an activity.

Ans. Displacement reaction is a chemical reaction in which a more reactive metal displaces a less reactive metal from its salt solution.

Activity

Dissolve some crystals of copper (II) sulphate (CuSO4. 5H2O, which is also called blue vitriol) in water. Place an iron nail in the solution. In a while, the portion of the nail which is the solution will become red. This is because a layer of copper gets deposited over the surface of the nail. The colour of the solution will slowly change from blue to green due to the formation of Iron (II) sulphate.

Fe + CuSO4                   Cu + FeSO4

Iron copper (II) sulphate Copper Iron (II) sulphate

(grey) (blue) (brown-red) (green)

You can repeat this activity using a piece of magnesium or aluminium instead of the iron nail. Copper will be deposited but the resulting solution will be colourless because magnesium sulphate and aluminium sulphate are colourless.

Q5. Human population is a threat to diversity. Justify.

Ans. Human population is a threat to diversity because of the following reasons:

(i) The increase in human population – The tremendous rise in human population

is one of the major cause for the loss of biodiversity. As the population increases the demand for construction of houses,

towns and cities also increase. This leads to clearing of forests for the availability of land. As a result, the animals lose their habitat.

(ii) Illegal hunting – Illegal hunting of animals for their skin, tusk, claws, meat, fur etc. is leading to loss of biodiversity, e.g. cheetah

and dodo bird became extinct due to illegal hunting.

(iii) Pollution – Pollution of soil, air and water is leading to oil spills in water, is killing the aquatic animals leading to loss of biodiversity.

(iv) Global warming – Due to global warming many organisms are not able to adapt to the changing environment due to which, they are dying.

(v) Natural disasters – Natural disasters like earthquakes, droughts, floods, forest fires etc. have contributed to the loss of biodiversity.

Draw diagram for each of the following. (1.5×2 = 3)

  1. Binary fission in amoeba
  2. Nerve cell

Multiple choice questions. (1×7 = 7)

  1. The process of loosening and turning the soil is called

(c) ploughing

  1. Which of the following is a bad conductor of heat?

(b) polythene

  1. Which of the following is a liquid at ordinary temperature?

(d) nitrogen

  1. Plasmodium is a human parasite which causes ……………………..

(b) malaria

  1. The shiny paper used to decorate sweets is made up of ………………………..

(d) silver

  1. Coal mainly contains ………………………….

(b) carbon

  1. Acid rain is caused by the burning of …………………………………

(c) coal

  

 

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