Combustion Chapter 7 D.A.V School Science book

 A. Fill in the blanks.

1.A good fuel should have its ignition temperature above the room temperature.

2. Burning of cowdung cakes is an example of slow combustion.

3. The inner zone of a candle flame, is the coldest.

4. The non-luminous zone of a candle flame is the outer part of the flame.

5. During incomplete combustion of a fuel, CO2 gas is formed.

B. State true or false for the following statements.

1. Coal is an inflammable fuel.

Ans- False

2.The outermost part of a candle flame contains unburnt carbon particles.

Ans- False

3. The heat produced, by burning completely one kilogram of a given fuel, is known as the efficiency of that fuel.

Ans- True

4. All solid fuels have a higher calorific value than liquid and gaseous fuels.

Ans- False

5. Sulphur dioxide gas, produced during combustion of fossil fuels, causes acid rain.

Ans- True

C. Tick the correct option.

1. An example of a non-combustible substance is----

Ans- Iron

2. A fuel starts burning only when it is heated to----

Ans- Its ignition temperature

3. The highest temperature zone of a candle flame, is its----

Ans- Blue zone

4. The amount of heat produced, on complete burning of 10 kg of a given fuel, in pure oxygen, equals H kilojoule. The calorific fuel, of that fuel, would equal----

Ans- (0.1 H) kj/kg

5. The gas produced, due to incomplete combustion of carbon fuels, is----

Ans- Carbon dioxide

D. Answer the following questions in brief.

1. Define the term 'combustible material'? Give two examples of combustible material.

Ans- Those substances that burn in the presence of air to produce heat and light are known as combustible material. 

Example- Coal, wood

2. State the three conditions that are needed for combustion to take place.

Ans- The three conditions that are needed for combustion to take place are:-

i) There must be a combustible substance.

ii) Continuous supply of oxygen.

iii) The temperature should be above the ignition temperature of the combustible material.

3. State the condition under which 'slow combustion'  of a material takes place.

Ans- When there is an incomplete supply of oxygen, slow combustion of the material takes place.

4. Define 'calorific value of a fuel'.

Ans- The amount of heat energy produced when 1 kg of any fuel is burnt in the presence of air.

5. State any two characteristics of an ideal fuel.

Ans- Two characteristics of an ideal fuel are:- 

i) High calorific value.

ii) Easy to transport.

6. Why is water is not used in controlling electric fires.

Ans- We can't use water when an electric fire is there because the water is a good conductor of electricity. So, it may cause dangerous shocks.

E. Answer the following questions.

1. Draw the diagram showing the different zones of candle flame. Label the zones which contains:

(a) Unburnt vapours of wax.

(b) Unburnt carbon particles.

 Ans- 

2. Calorific value of wood is 18,000 kj/kg. How much of wood is required to produce 360,000 kg of heat energy?

Ans- Calorific value of wood= 18,000 kj/kg

          Therefore, the amount of wood required to produce 360,000 kg of heat energy = 360,000/18,000 = 20 kg

3. Why are gaseous fuels considered better than liquid or solid fuels.

Ans- Gaseous fuels considered better than liquid or solid fuels because:-

i) Gaseous fuels have higher calorific value.

ii) These produce the fewer amount of pollutants.

iii) It is easier to transport and store gaseous fuels.

4. Why do we say that 'burning of fuels' can cause 'health hazards'?

Ans- Burning of fuels causes air pollution and it also produces smog, carbon monoxide gas results into respiratory problems. Hence, it is said that the burning of fuels can cause health hazards.

Sources of Energy Chapter 6 D.A.V School Science

 A. Fill in the blanks.

1. Coal And petroleum are non-renewable sources of energy.

2. Solar energy is a major renewable, natural resource.

3. The process, in which coal is strongly heated in the absence of air, is known as destructive distillation.

4. In oil wells, natural gas is always found above the layer of petroleum.

5. Coal tar is a black viscous liquid, obtained by destructive distillation of coal.

B. State true or false for the following statements.

1. Fossil fuels are renewable natural resources.

Ans- False

2. Anthracite has higher carbon content than lignite.

Ans- True

3. Coke can be used to make fuel gases.

Ans- True

4. Natural gas is found below the petroleum layers.

Ans- False

5. Burning of fossil fuels is a major source of pollution.

Ans- True

C. Tick the correct option.

1. The highest grade of coal is known as----

Ans- Anthracite

2. Coke and coal tar are obtained from----

Ans- Coal

3. Different type of coal generally have the----

Ans- Different content of volatile material as well as different percentage of carbon.

4. A product, that is not obtained through the refining of petroleum is----

Ans-  Coal gas

5. Which of the following is a renewable source of energy?

Ans- Tidal energy

D. Answer the following questions in brief

1. Define the term 'fuel'.

Ans- Any substance which produces heat and light on burning, is known as fuel.

2. Name two renewable natural sources of energy.

Ans- Wind energy and tidal energy are two renewable natural sources of energy.

3. Define the term 'Carbonisation'.

Ans- Formation of coal is known as 'Carbonisation'.

4. Name the three main products obtained from destructive distillation of coal.

Ans- The three main products obtained from destructive distillation of coal are:-

i) Coke

ii) Coal tar

iii) Coal gas

5. State two uses each of the following:

(a) Asphalt

Ans- i) For making roads.

        ii) Coating of the underside of the electric poles.

(b) Paraffin wax

Ans- i) Used for making vaselines.

        ii) Used for making candles.

6. Write the full form of CNG, LPG and PNG.

Ans- The full form of CNG, LPG and PNG are:-

CNG- Compressed Natural Gas

LPG- Liquified Petroleum Gas

PNG- Piped Natural Gas

E. Answer the following questions.

1. Describe, in brief, the process of 'Coal formation'.

Ans- The remains of dead plants buried deep inside the earth, faces the action of heat from the earth core and the pressure of rocks over a long period of time, it gets converted into coal.

2. Differentiate between lignite and bituminous coal.

Ans- Lignite- i) It contains 38% of carbon.

                     ii) It is mainly used for power generation.

Bituminous- i) It contains 65% of carbon.

                     ii) It is used for power generation and for making coke.

3. How do petroleum and natural gas occur in nature?

Ans- Petroleum occurs in the rock formations as crude oil.

Natural gas is found in oil wells above the crude oil.

4. State the main advantages of using natural gas.

Ans-  Main advantages of using natural gas are:-

i) It is a clean fuel.

ii) It has a high calorific value.

iii) Natural gas is economical than petrol and diesel.

iv) It is easy to transport natural gas through pipelines.

5. Keeping in mind their availability in nature, explain the need of using coal and petroleum judiciously?

Ans- Coal, and Petroleum are non-renewable resources because it takes a long period of time to replenish it. Therefore, we should use alternative sources of energy like solar energy, wind energy, hydro energy, tidal energy, etc. Hence, their stock is going to be finished in near future.

Friction Chapter 5 D.A.V School Science book

 A. Fill in the blanks.

1. Friction always opposes any relative motion between two surfaces that are in contact with each other.

2. Static friction is always greater than sliding friction.

3. Sportsmen use shoes, fitted with spikes, to increase friction between their shoes and the ground.

4. Sprinkling of talcum powder, on the carrom-board, helps to decrease friction.

5. Frictional force, on an object moving in a fluid, depends on its viscosity.

6. The shape of an aeroplane is streamlined to reduce, the effects of friction, due to air.

B. State True or false for the following statements.

1. When a body slides over smooth and wet surfaces, the amount of interlocking of irregularities, of the two surfaces in contact, increases. 

Ans- False

2. If a car moves eastwards, the force of friction acts southwards.

Ans- False 

3. Friction depends on how hard the two surfaces press against each other.

Ans- True

4. The sole of shoes and the tyres of the vehicle are 'treaded' to decrease the effects of friction.

Ans- False

5. Lubricants can be liquid, semi-liquids or solids.

Ans- True

6. Friction can be increased by using ball bearings between the moving parts of machines.

Ans- False

C. Tick the correct option.

1. Suppose your writing desk is tilted to a position where a book kept on it just starts sliding down. The figure, showing the correct direction of frictional force acting on it, is----

Ans- D

2. Two boys are applying oppositely directed, and equal in magnitude, forces on a box as shown in the figure.

In such a case, the force of friction, that would exist between the lower end of the box and the ground, would be called----

Ans- Static friction

3. Four students were asked to arrange the (frictional) force, due to rolling, static, and sliding, in increasing order. Their arrangements are listed below. The correct arrangement is----

Ans- Rolling, sliding, static.

4. The energy, 'used up' in overcoming friction, gets converted mainly into----

Ans- Heat energy

5. Rahul rolls a ball on a wooden surface. The ball covers a certain distance before coming to rest. To make the same ball cover a (much) longer distance, before coming to rest, Rahul should----

Ans- Sprinkle talcum powder on the wooden surface.

6. A block is sliding on a horizontal surface. The force of friction between the two can be increased by----

 Ans- By putting a second identical block on top of the given block.

D. Answer the following question in brief.

1. Define the term (a) static friction (b) sliding friction.

Ans- a) Static friction- Force of friction acting between two surfaces in the address is called static friction.

        b) Sliding friction- Force of friction acting between two surfaces when one surface slides on another surface is called sliding friction.

2. State the meaning of the term (a) rolling friction (b) fluid friction.

Ans- a) Rolling friction- The force of friction acting between two surfaces when one surface or both surfaces roll on each other is called rolling friction.

        b) Fluid friction- The force of friction experienced by fluid or among the different layers of the fluid is called fluid friction.

3. State the likely causes of friction.

Ans- Interlocking between the two surfaces causes friction between them.

4. A box is resting on the floor. To move it, a (variable) force is applied as shown in the diagram below.

a) Give the (likely) value of the force of limiting friction.

Ans- 2F

b) Why does the box stay at rest in the cases corresponding to figure (a) and figure (b)?

Ans- Box stays at rest as the applied force is not being able to beat the frictional force between the block and the surface, which means that applied force in both cases is less than the static friction between the block and the surface.

(c) Mark the direction of frictional force, and mention the kind of frictional force that comes into play, in each case.

Ans- Direction of frictional force in all cases will be opposite of applied force.

i) Static friction

ii) Static friction

iii) Limiting friction

5. Name the kind of frictional friction, that comes into play, when a book, kept on a collection of cylindrical pencils, is moved by pushing.

Ans- Rolling friction

6. Why are objects given special shapes when they are moving through fluids? Write the names given to these special shapes.

Ans- Objects are given special shapes to reduce fluid friction.

The name given to these special shapes is streamlined shapes.

E. Answer the following questions.

1. Define the force of friction. List the factors affecting the force of friction. Explain with examples.

Ans- Friction is a contact force acting on two surfaces that oppose the relative motion between one another.

Factors affecting the force of friction----

i) Nature of the surfaces in contact.

ii) Force pressing or weight of the two surfaces acting together.

For example- When we rub our hand, friction is produced.

2. A ball is allowed to roll down an inclined wooden plane from a given height. At the foot of the inclined plane, it moves on a horizontal surface, differently 'covered', one by one, as shown in the following figures.

In which case, is the ball likely to move the longest distance? Give reason for your answer.

Ans- In the case of the plane glass sheet, the ball is likely to move the longest distance because the plane glass sheet has low friction.

3. Explain why sliding friction is less than static friction.

Ans- Frictions comes into play when irregularities present in the surfaces of two objects in contact get interlocked with each other. In sliding the time given for interlocking is very small. Hence, interlocking is not strong. Therefore, less force is required to overcome this interlocking. Because of this reason, sliding friction is less than static friction.

4. Give reason for the following.

(a) We tend to slip when we step on a banana peel.

Ans- The friction between the banana peel and the surface is very less so, when we step on a banana peel, no grip is provided by the surface and we slip down.

(b) It is easier to push a lighter box than a similar heavy box on the same floor.

Ans- It is easier to push a lighter box than a similar heavy box on the same floor because frictional force will be more in the case of a heavy box so, it is difficult to move a heavy box than a lightbox.

(c) The force, needed to start a cart, is (somewhat) greater than the force needed to keep it moving with a uniform speed.

Ans- The force, needed to start a cart, is (somewhat) greater than the force needed to keep it moving with a uniform speed because at first, the body remains in a state of rest. In order to brake its state of rest, a larger force is required. In the second case, the body acquires linear momentum. It allows it to gain a force there. So, it is easier to move the body once it is in motion.

(d) Sportsmen use shoes fitted with spikes.

Ans- Sportsmen use shoes fitted with spikes because they want grip and get grip from the friction created by the spikes.

(e) Ball bearing are used in machines.

Ans- Ball bearing are used in machines.

(f) Tyres of the vehicles needs to be changed regularly.

Ans- Tyres of the vehicles needs to be changed regularly because with passing time they get worn off and due to friction they become more smoother.

(g) Machine parts are frequently oiled or greased.

Ans- Machine parts are frequently oiled or greased to reduce friction and help in the smoother running of the machine.

(h) Sports cars, aeroplanes and boats are designed to have a streamlined shape.

Ans- Sports cars, aeroplanes and boats are designed to have a streamlined shape to reduce fluid friction.

(i) Metal chains are wrapped on tyres when they run on icy roads.

Ans- An ice is slippery and there is almost less friction, so tyres are wrapped with chains to create high friction. So, cars or trucks can move easily on them.

(j) Rollers are used for transporting luggage.

Ans- Rolling decreases friction and makes the movement of things easier. That's why luggage are fitted with rollers.

5. State and explain, with examples, how friction can help the cause motion in certain situations.

Ans- We can walk on the road or floor due to friction. Also, the vehicles run on the road due to friction between their tyres and the road. We slip and the vehicles skid in the absence of friction. Thus, friction can cause motion in these situations.

Force and Pressure Chapter 4 of D.A.V school Science book

 Fill in the blanks.

1. For a force to come into play, the two concerned bodies must interact with each other.

2. To draw water from a well, we have to pull the rope.

3. An unbalanced force, acting on a moving object, may change its speed and/or its distance.

4. In the game of cricket the 'bails' fall when the ball strikes them. This is an example of a/an force.

5. The force, responsible for raising our body hair, when we try to take off a synthetic (terylene or polyster) shirt in dry weather conditions, is an electric force.

6. The atmospheric pressure decreases as we move towards higher altitudes.

B. State true or false for the following statements.

1. The effect of the force may change by changing the direction of the applied force.

Ans- True

2. A force has to be specified both in terms of its magnitude as well as its direction.

Ans- True

3. Friction force is an example of a non-contact force.

Ans- False

4. A gas filled balloon moves up. The upward force acting on it is smaller than the force of gravity, i.e. (the downward acting force).

Ans- False

5. We can reduce the pressure of a given force by increasing the area over which force acts.

Ans- True

6. Inside a bottle filled with water, pressure is least at the bottom and the greatest at the surface of the water.

Ans-False

C. Tick the correct option.

1. When two forces, applied on an object, are equal and opposite, then these forces----

Ans- do not move the object but may cause a change in its shape.

2. The following are the names of some of the well-known forces

a. Gravitational force                    b. muscular force

c. magnetic force                            d. frictional force

Out of these, the 'contact force' are the force labelled as----

Ans- b and d

3. Rohini is pushing a box towards the west direction with a force of magnitude F. To help her move the box faster in the same direction, her friend should----

Ans- Push the box in the west direction with a force of any magnitude.

4. A container is filled with water as shown in the figure given below.

Which of the following statement is correct about the pressure of water in this container?

Ans- Pressure at C>Pressure at B>Pressure at A

5.  An empty metal bottle has to be placed on a table so that it exerts the maximum pressure on the surface of the table?

For this, the bottle need to be placed in the position(s) labelled as----

Ans- Position B

6. When we press the bulb of a dropper, with its nozzle kept underwater, air in the dropper is seen to escape in the form of bubbles. If we then release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to--- 

Ans- atmospheric pressure

7. The length, breadth, and height, of a given rectangular box, are 100cm, 50cm, and 20cm, respectively. This box is kept on ground in three different ways, one by one. Which of the following statement is the correct statement about the pressure exerted, by this box, on the ground?

Ans- the pressure exerted is maximum when the 'breadth' and 'height' sides form the base. 

D. Answer the following questions in brief.

1. In the following situations, identify the agent exerting the force. Also, state the effect of the force in each case.

(a) Squeezing a piece of lemon between the fingers to extract its juice.

Ans- Agent- Fingers, Effects of force- Change in shape.

(b) A person diving into a swimming pool.

Ans- Agent- Water, Effect of force- Change in state of motion.

(c) A labourer moving a loaded cart.

Ans- Agent- Labourer, Effect of force- Change in state of motion.

(d) A car coming to rest once its engine is switched off.

Ans- Agent- Friction from road, Effect of force- Change in motion.

(e) An athelete making a high jump to clear a bar kept at a certain height.

Ans-  Agent- Muscles, Effect of force- Change in motion

2. An object experiences a net non-zero force. Is it possible for the object to move with a constant speed along a straight line?

Ans- Yes, it is possible for the object to move within constant speed along a straight line as the value of opposing force is not experienced by the object.

3. Distinguish between:

(a) balanced and unbalanced force.

Ans- Balanced force- A force is said to be balanced if the resultant force acting on the object is 0. 

        Unbalanced force- A force is said to be unbalanced if the resultant force acting on the object is not 0. 

(b) contact and non-contact force

Ans- Contact force- Force is said to be contact if bodies are directly in physical contact with each other. 

Example- Muscular force and frictional force.

        Non-contact force- Force are said to be non-contact if bodies are not physically in contact with each other.

Example- Gravitational force, electrical force, etc.

4. When we throw a ball upwards, what happens to its speed while it is going up? Give reason for your answer.

Ans- When we throw a ball upwards, its speed gradually decreases because the earth produces a gravitational force that brings down everything.                                      

5. The figure shows a man with a parachute.

(a) Name the force which is responsible for his downward motion. Is it a contact force or a non-contact force?

Ans- Gravitational force. It is a non-contact force.

(b) Will the man come down with the same speed without the parachute? Explain.

Ans- The man will not come with the same speed without the parachute because the parachute has a large area that helps it to trap air below it and friction is generated.

6. How would the pressure (exerted by a force on an area) change if----

(a) the area is doubled keeping the thrust constant?

Ans- The pressure will be halved.

(b) thrust is doubled keeping the area constant?

Ans- The pressure will also be doubled.

 

7. When will a diver 'experience a greater pressure' --- 100cm above the surface of water or 200cm below the surface of water? Justify your answer.

Ans- At 200cm diver will experience greater pressure because pressure increases with an increase in depth.

E. Answer the following question.

1. Define force. Is it necessary for the two bodies to be in direct contact for a force to exists between them? Explain with examples.

Ans- Force is a push or pull which is due to the interaction that changes or tends to change in the object.

                                                                          It is not necessary for the bodies to be in direct contact for a force to exists between them as there are non-contact forces too like a magnetic force, gravitational force, etc.

2. State three effects forces. Give suitable examples.

Ans- i) Change in state of the object.

Example- Force applied to move a chair, etc.

         ii) Change in the shape and size of the object.

Example- During making a dough.

         iii) Change in direction of the object.

Example- When we hit a ball with a bat, it changes its direction.

3. Give reasons for the following statements----

a) 'Snowshoes' are more effective than ordinary shoes for walking on snow.

Ans- 'Snowshoes' are more effective than ordinary shoes for walking on snow because snowshoes apply less pressure than ordinary shoes.

b) Porters have a large round piece of cloth on their heads when they carry heavy loads.

Ans-  Porters have a large round piece of cloth on their heads when they carry heavy loads because the increase in the area reduces the pressure. 

c) A sharp knife cuts vegetables and fruits more effectively than a blunt knife.

Ans- A sharp knife cuts vegetables and fruits more effectively than a blunt knife because the sharp knife has a less surface area than the blunt knife so, it applies more pressure and it is easy to cut vegetables and fruits with a sharp knife.

d) School bags are provided with wide straps to carry them.

Ans- School bags are provided with wide straps to carry them because it reduces the pressure of books book and notebooks.

e) It is much easier to burst an inflated balloon with a needle than (directly) with the finger.

Ans- It is much easier to burst an inflated balloon with a needle than (directly) with the finger because a needle has a lower surface area as compared to finger.

f) Mountaineers may suffer from nose bleeding at high altitudes.

Ans- Mountaineers may suffer from nose bleeding at high altitudes because, at high altitude, the atmospheric pressure decreases. Since, the pressure of the blood inside the mountaineer increases.

g) Air-planes have pressurised cabins for passenger safety while flying high in the atmosphere.

Ans- Air-planes have pressurised cabins for passenger safety while flying high in the atmosphere because at very high altitude humans can't breathe well.

4. Two rods 'A' and 'B', of the same weight and length, have different thickness. A boy while playing with them on a beach, held them vertically on the surface of land as shown in the figure. Which one of them will sink less? Explain

.

Ans- Rod 'B' will sink less because it has more surface area and less pressure.

5. Three holes A, B and C are made in an empty can at a different level, one over the other, as shown in the figure. They are (temporarily) closed with adhesive tape. The can is now filled with water, what will you observe, when the tap (on all of them) is pulled out? Justify your answer.

Ans- We will observe that the water from the hole A goes the farthest, water from hole B goes at a middle or average but water from hole C travels the minimum distance. This happens because the pressure exerted by liquid increases with depth.

6. Make any two tiny holes, of the same size, at the equal heights from the bottom in a plastic bottle. Cover them and fill the water. Let the 'covers' be now removed. State the 'observations' and the resulting 'conclusions', based on this activity.

Ans- Observation- The water will pass in an equal amount through the holes.

         Conclusion- The water pressure is the same at that level.

7. Discuss, in brief, the variation in atmospheric pressure with altitude. Do changes in temperature also cause a change in atmospheric pressure?

Ans- As we move upwards through the atmosphere, the height of the air column would decrease. So, the pressure will decrease with higher altitude.

                                                       Yes, change in temperature also cause a change in atmospheric pressure.

Metals and non-metals Chapter 3 of D.A.V Science book

 A. Fill in the blanks.

1. The property due to which a metal can be hammered into thin sheets, is known as malleability.

2. Bronze is an alloy of copper and tin.

3. Gold is mixed with copper and/or silver to make it hard.

4. Iodine is the only non-metal to have a natural lustre.

5. Phosphorous is a non-metal which catches fire in the air.

6. The only metal, which exists in the liquid state at room temperature, is mercury.

B. Match the following.

1. Hardest substance- Diamond

2. Aluminium ore- Bauxite

3. A non-metal, normally, existing in the liquid state- Bromine

4. A good electrical conductor- Graphite

5. A metalloid- Arsenic

C. Tick the correct options.

1. The two most abundant metals, found in the earth's crust, are-----

Ans- aluminium and iron

2. The metals, used in making the alloy 'german silver', are----

Ans- Copper+zinc+nickel

3. When a metal reacts with oxygen, the resulting oxide of the metal -----

Ans- is a basic oxide

4. Out of the metals, gold, silver, copper and aluminium, the one, that is most ductile, is -----

Ans- gold

5. Two of the metals, that cannot be stored either in the air or underwater, are----

Ans- potassium and sodium

D. Answer the following questions in brief.

1. Name (i) one metal and (ii) one non-metal which normally exists in the liquid state.

Ans- (i) Mercury

       (ii) Bromine

2. State the fraction of gold present in an 18-carat gold piece.

Ans- 18/24=3/4parts

3. State the property of copper wires that make them useful for electrical fittings.

Ans- Copper wires are a good conductor of electricity. That's why they are useful for electrical fittings.

4. Define an alloy.

Ans- An ally is a homogenous mixture of two or more metals, and metal or a non-metal.

5. List any two uses of non-metals.

Ans- Following are two uses of non-metals---

      (i) Iodine is used as an antiseptic.

      (ii) Phosphorous is used in the matchbox industry and in fertilizers.

E. Answer the following questions.

1. Write the balanced chemical equations for the following reactions:

 Sodium reacts with oxygen

(b) Aluminium reacts with dilute hydrochloric acid 

Ans- (a) 4Na+O2----> 2Na2O2  

       (b) 2Al+6Hcl ----> 2AlCl3  +H2

2. Why are gold and platinum suitable for making jewellery?

Ans- Gold and platinum are the least reactive metals and they have their own lustre. That's why they are suitable for making jewellery.

3. Sodium and potassium are stored under kerosene. Give reason.

Ans- Sodium and potassium are stored under kerosene because when they come in contact with moisture present in the air they catch fire. So, in kerosene air is avoided.

4. Why is bronze preferred over copper metal for making statues?

Ans- Bronze is an alloy. Therefore, it is more stronger and harder than copper. It is corrosion resistant also.

Microorganisms: Friends or Foes Chapter 2 of D.A.V School Science Book

A. Fill in the blanks.

1. The study of microorganisms is known as microbiology.

2. The bread dough rises because of the production of Carbon dioxide.

3. Pathogens are the microorganisms that cause diseases.

4. Sodium Benzoate and Potassium metabisulfite are two chemical preservatives.

5. Aspergillus is a fungus that causes food poisoning.

B. Match the following.

 

1. Ringworm- Fungus

2. Clostridium- Food poisoning

3. Anthrax- Cattle

4. Lactobacillus- Curd

5. Methane- Biogas reactor

C. Tick the correct option.

1. The process, that helps the milk to last longer but does not kill all microbes present in it, is known as ----

Ans- Pasteurisation

2. Rust of wheel is caused by----

Ans- Fungus

3. Medicines, containing killed or weakened pathogens are used to prevent infectious diseases, are called----

Ans- Vaccines

4. Which of the following reproduces only inside a host cell----

Ans- Virus

5. A disease, caused by a virus, and spread by an insect is----

Ans- Dengue

D. Answer the following questions in brief.

1. Why are viruses considered as being at the 'borderline' between living and non-living things?

Ans-  The viruses considered as being at the 'borderline' between living and non-living things because, when it is prevented in the environment, it acts as non-living but, when it comes in contact with the living environment, it acts as living beings.

2. What is fermentation? How is the process useful in the food and beverage industries.

Ans- It is an anaerobic process through which carbohydrate gets converted into alcohol or acid and carbon dioxide by the yeast.

                                                        Due to the production of carbon dioxide and alcohol.

3. ' In the absence of microorganisms the Earth would become a heap of dead plants and animals. Justify this sentence.

Ans- Microorganisms are decomposers. So it decomposes dead plants and animals. But in absence of it, the earth would become a heap of dead plants and animals.

4. Munna observes that the yield of wheat, growing in his field, has reduced in the current year. He gets the soil tested and the report confirms that deficiency of one particular nutrient. Accordingly, he is advised to grow peas after harvesting wheat.

(i) Name the nutrient found insufficient.

Ans- Nitrogen found insufficient in the soil.

(ii) How Do you think growing peas will help in replenishing the soil?

Ans- Pea belongs to a leguminous family plant, which has root nodules, where nitrogen-fixing bacteria Rhizobium is present.

5. Why does it take less time to prepare curd in summers as compared to winters?

Ans- Growth of lactobacillus bacteria is more in summer than winter. So, it takes less time to prepare curd in summer than in winters.

6. How are the following disease transmitted:

(a) Malaria- Mosquito

(b) Common cold- Air

(c) Tetanus- Soil

(d) Typhoid- Contaminated water

7. What are antibiotics? How are they produced? Give two examples of these.

Ans-Antibiotics are the chemicals produced by microorganisms that kill or inhibit the growth of other harmful microorganisms.

                                                They are produced by bacteria and funguses. For ex- Streptomycin and Tetracycline.

E. Answer the following questions.

1. ' Microorganisms are very useful in manufacturing different food items.' Explain the above statement.

Ans- Microorganisms are very useful in manufacturing different food items----

(i) Curd and cheese formation- Lactobacillus helps in the formation of curd. Some other bacteria and fungi also help in making cheese.

(ii) In bakery product- Some fungi like yeast increased the volume of batter and make it fluffy and soft by the process of fermentation.

(iii) Alcoholic beverage- Yeast also converts carbohydrate into alcohol and help in manufacturing alcoholic beverages.

2. Give the reason for the following.

(a) Yeast is added to the batter used to make 'dosas'.

Ans- Yeast by fermentation process produced CO2 and make it fluffy and soft.

(b) It is important to brush one's teeth before going to bed.

Ans- Food particles after decomposition produces acid which causes teeth decay. So, it's important to brush your teeth before going to bed.

(c) Reducing the quantity of salt in the pickle can cause it to go bad soon.

Ans- Salt is a preservative item and it stops the growth of microorganisms and prevents pickle.

(d) When using frozen food items one should take only the required quantities; thawed food should never be refrozen.

Ans- Puffed food indicate spoilage of food which causes food poisoning.  Most bacterial spores and a large number of organisms survive and get revitalized, when the food is thawed.

3. How do communicable diseases spread? Suggest ways to prevent the following diseases;

a) Tuberculosis           

b) Athlete's foot

c) Cholera

Ans- Communicable diseases spread from one person to another through the air, water, food, and physical contact or insect.

a) Tuberculosis- Vaccination        

b) Athlete's foot- Maintaining good personal hygiene

c) Cholera- Proper disposal of waste and using disinfected water.

4. What are pathogens? Name two pathogens each that cause diseases in

(i) plants

(ii) animals

Ans- Disease causing microorganisms are called pathogens.

In plants----

i) Virus- Tobacco mosaic virus

ii) Bacteria- Citrus canker

In animals----

i) Bacteria- Anthrax

ii) Virus- Rabies

5. Mohan bought samosas from a road-side vendor and ate them. After some time he felt nausea and he started vomiting he had severe pain in the abdominal region and suffered from diarrhoea. What could be the reason for his condition? Was is it called? How could it be prevented?

Ans- Eating samosa from road-side vendors is the reason for this condition. It is called food poisoning.

It can be prevented by avoiding eating food from the road-side vendors. The food items must be properly prepared and stored. Always wash your hands and eat fresh food.

6. Which diseases the following children are most likely to suffer from?

(a) Ramu drinks water from a nearby lake. The water is neither boiled nor disinfected.

Ans- Cholera

(b) Ashu does not take a bath every day. He maintains poor personal hygiene.

Ans- Athlete's foot or ringworm

(c) Pulkit has been bitten by an infected street dog.

Ans- Rabies

(d) Sohan is living in an area where the population is very high. He does not use a mosquito net (while sleeping), or insect-repellent creams(while playing) in the open.

Ans- Malaria or dengue

(e) Mohan was with two of his friends who were coughing and sneezing (they were suffering from common cold). One of these friends did not keep a handkerchief in front of his mouth while coughing and sneezing.