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Page No 290:

Question 1:

Name two biologically important compounds that contain both oxygen and nitrogen.

Answer:

Two biologically active compounds that contain both oxygen and nitrogen:
i) Amino acids
ii) DNA and RNA

Page No 290:

Question 2:

What is polyculture?

Answer:

Polyculture refers to the practice of growing more than one crop at the same time and in the same space. Intercropping is an example of polyculture.

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Question 3:

A snail covers a distance of 100 metres in 50 hours. Calculate the average speed of snail in km/h.

Answer:

Total distance travelled by snail = 100 m = 0.1 km

Total time taken = 50 h

Average speed of the snail = Total distance travelledTotal time taken=0.1 km50 h=0.002 km/h

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Question 4:

How is the complexity of cell structure and their number used in classification?

Answer:

On the basis of complexity of cell structure, the cells are classified as prokaryotes and eukaryotes. Prokaryotes have primitive cell structure whereas eukaryotes have advanced cell structure.

Eukaryotes are further divided into unicellular or multicellular organisms based on the number of cells they are composed of.

Page No 290:

Question 5:

Explain why, if we strike a table lightly, we hear a soft sound but if we hit the table hard, a loud sound is heard.

Answer:

When we hit the table lightly, we transfer a small amount of energy to the particles of the table, so they vibrate will a low amplitude and we listen a low or soft sound. However, if we hit the table hard, due to greater energy supplied, the table top vibrates with a large amplitude and a loud sound is heard.

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Question 6:

An elephant weighing 40,000 N stands on one foot of area 1000 cm2 whereas a girl weighing 400 N is standing on one 'stiletto' heel of area 1 cm2.
(a) Which of the two, elephant or girl, exerts a larger force on the ground and by how much?
(b) What pressure is exerted on the ground by the elephant standing on one foot?
(c) What pressure is exerted on the ground by the girl standing on one heel?
(d) Which of the two exerts larger pressure on the ground: elephant or girl?
(e) What is the ratio of pressure exerted by the girl to the pressure exerted by the elephant?

Answer:

(a) Weight of the elephant is greater than the weight of the girl so it would exert a large force on the ground.

Weight of the elephant = 40,000 N

Weight of the girl = 400 N

So, the elephant would exert an extra force = 40,000 N - 400 N = 39,600 N

(b) Pressure = ForceArea

The pressure exerted on the ground by the elephant on one foot = 40,000 N1000 ×(10-2)2 m2=4×105 Pa

(c) Pressure = ForceArea

The pressure exerted on the ground by the girl standing on one heel = 400 N1 ×(10-2)2 m2=4×106 Pa

(d) The girl exerts larger pressure on the ground.

(e) The pressure exerted by the girl on the ground = 4×106 Pa

The pressure exerted by the elephant on the ground = 4×105 Pa

The ratio of pressure exerted by the girl to the pressure exerted by the elephant = 4×106 Pa4×105 Pa=10 : 1

Page No 290:

Question 7:

What is evaporation? State the various factors which affect evaporation.
​(b) Why does evaporation cool a liquid?

Answer:

(a) The phenomenon of conversion of a liquid into its vapors at any temperature below its boiling point is known as evaporation.
Various factors which affect evaporation are:

(i) Velocity of wind
(ii) Humidity
(iii) Surface area
(iv) Temperature

(b) As we know that when a liquid evaporates it converts into liquid before its boiling point, so when it evaporates the particles at the surface of the liquid uses the heat of the liquid as energy to increase the kinetic energy so that they are able to overcome the force of attraction of the other particles of liquid and then directly convert into the gaseous state. That's why the temperature of the liquid gets reduced and it becomes cooler.

Page No 290:

Question 8:

What are differences between the following:
(a) Cartilaginous fishes and bony fishes
(b) Amphibia and Reptilia;
​(c) Aves and mammals.
 

Answer:

(a)

Cartilaginous fishes
Bony fishes
Their skeleton is made entirely of cartilage. Their skeleton is composed partly or wholly of bones.
E.g., torpedo, shark, etc. E.g., tuna, sea horse, etc.

(b) 
Amphibia Reptilia
They have dual mode of life − larva is aquatic, while the adult is terrestrial. They can be terrestrial or aquatic. The aquatic forms return to land in order to lay eggs.
Scales are absent. Body is covered with scales.
They lay eggs on water. They lay eggs on land.


(c) 
Aves Mammals
They lay eggs. They give birth to young ones.
They have feathers. They have fur or hair.
They feed their young ones by regurgitating
partially digested food.
They feed their young ones through mammary glands.

Page No 290:

Question 9:

Write short note on Pulse Polio Programme.

Answer:

Pulse Polio Programme was launched in 1995-1996 in order to eradicate the polio disease from the world. The aim of this programme was 

  • to immunise those children who are not earlier immunised or are partially immunised
  • to boost the immunity of children already immunised
  • to replace disease carrying wild virus by harmless vaccine virus in the environment
This programme involved simultaneous administration of polio drops to children under three years of age on a single day throughout the nation. Under this programme, 2 doses of vaccines are given 4-6 weeks apart. The days on which this programme is carried out are pre-fixed and are called National Immunisation Days.

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Question 10:

Diagrammatically show the difference in three types of muscle fibres.

Answer:

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Question 11:

Distinguish between prokaryotic and eukaryotic cells.

Answer:


Prokaryotes
 
Eukaryotes

Nuclear region is poorly developed and nuclear membrane is absent.
 
Nucleus is well defined and nuclear membrane is present.

Nucleolus is absent.
 
Nucleolus is present.

Membrane-bound organelles are absent.
 
Membrane-bound organelles are present.

Page No 290:

Question 12:

Describe the various steps involved in the separation of iodine, iron fillings and salt from a mixture.

Answer:

steps followed in the separation are as follows:
1. Dissolve the mixture of iodine, iron filing and salt in water. 
2. Salt will dissolve in the mixture.
3. Filter the above solution.
4. The filtrate will contain salt which can be obtained by evaporation.
5. Now, heat the residue, iodine can be collected by sublimation and iron fillings will be left behind.
 



Page No 291:

Question 13:

When 5 g of calcium is burnt in 2 g of oxygen, then 7 g of calcium oxide is produced. What mass of calcium oxide will be produced when 5 g of calcium is burnt in 20 g of oxygen? Which law of chemical combination will govern your answer?

Answer:

The given chemical reaction can be written as: 2Ca+O22CaO

From the equation, Number of moles of calcium oxide = 2×Number of moles of oxygen = Number of moles of calcium

From the given data, 

Given mass of calcium = 5 g
Given mass  of oxygen = 20 g

The number of moles of calcium = 540=0.125 

The number of moles of oxygen = 2032=0.625

Here, the number of moles of calcium is lesser than the number of moles of oxygen. So, calcium is the limiting reagent.

Number of moles of calcium oxide = Number of moles of calcium =  0.125

Hence, the weight of the calcium oxide formed = 0.125×56=7 g

Law of conservation of mass is applicable to this equation.
 


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Question 14:

The velocity of a body of mass 10 kg increases from 4 m/s to 8 m/s when a force acts on it for 2 s.
(a) What is the momentum before the force acts?
(b) What is the momentum after the force acts?
(c) What is the gain in momentum per second?
​(d) What is the value of the force?

Answer:

(a) Mass of the body = 10 kg

Velocity before the force acts = 4 m/s

Momentum before the force acts =  Mass × Velocity = 10 kg × 4 m/s = 40 kg m/s

(b) Mass of the body = 10 kg

Velocity after the force acts = 8 m/s

Momentum after the force acts =  Mass × Velocity = 10 kg × 8 m/s = 80 kg m/s

(c) Gain in momentum = Final momentum - Initial momentum = 80 kg m/s - 40 kg m/s = 40 kg m/s

Time taken = 2 s

The gain in momentum per second = 40 kg m/s2 s=20 kg m/s2

(d) Force is defined as the rate of change of momentum. Hence, force is equal to the change in momentum per second i.e. 20 N

Page No 291:

Question 15:

The hanging bob of a simple pendulum is displaced to one extreme position B and then released. It swings towards centre position A and then to the other extreme position C. In which position does the bob have:
(a) Maximum potential energy?
(b) Maximum kinetic energy?
​Give reason for your answer.

Answer:

A simple pendulum oscillates about its mean position. The mechanical energy throughout the motion remains conserved. At extremes positions, the velocity of the bob becomes zero and the energy becomes purely potential. At mean position, the energy becomes purely kinetic and potential energy becomes zero. Hence, we can conclude:

(a) Bob has the maximum potential energy at the extreme position.

(b) Bob has the maximum kinetic energy at the mean position,

Page No 291:

Question 16:

Describe with a diagram the fluid mosaic organisation of the plasma membrane.

Answer:

Singer and Nicolson proposed the fluid mosaic model for describing the structure of a cell membrane. According to this model, the cell membrane is made up of a lipid bilayer and proteins. These proteins are of two types - intrinsic and extrinsic proteins. The lipid bilayer forms the highly viscous fluid and these two types of proteins are arranged in it in mosaic manner.
The extrinsic proteins are present superficially while the intrinsic proteins are embedded in the lipid bilayer.

Page No 291:

Question 17:

(a) What is fractional distillation? What is the use of fractionating column in fractional distillation?
​(b) Draw a labelled diagram of the fractional distillation apparatus used for separating a mixture of alcohol and water.

Answer:

(a) Fractional distillation: It is a process of separation of a chemical mixture of two liquids whose components have different boiling points. This process is used for separating mixtures like water and ethanol, or in production of gasoline from crude oil. The fractionation column is used to separate the liquids according to the order of their vaporization so that they get separated as they are vaporized.

(b) Diagram of the fractional distillation used for separating a mixture of alcohol and water:

Page No 291:

Question 18:

Explain various types of irrigation systems in India. How can efficiency of applied water be increased in agriculture?

Answer:

Irrigation is the process through which water is supplied to the land or soil to grow agricultural crops, maintain vegetation, etc. The following are the various methods of irrigation:

(i) Dugwells and tube wells- In this method, wells are dug deep in soil so as to get water which is then used for irrigation purposes.

(ii) Surface irrigation- Herein, the earth's force of gravity is used to distribute water in the land area so as to saturate the crops.

(iii) Drip irrigation- Under this system, water from streams is tapped using bamboo pipes and used for irrigating the roots of the plants. Water flows through these pipes and is used directly at the site of the plant.

(iv) Micro sprinklers- In this method, water sprinklers are used wherein a set amount of water is sprayed over the crops through sprinklers which facilitates even flow of water throughout the land area.

(v) Canal system- In this type of irrigation, canals are formed in order to control and measure the water flow into the farmlands for irrigation purposes.

The efficiency of applied water in agriculture can be increased by the following ways -

  • suitable crop selection
  • proper irrigation scheduling
  • effective irrigation techniques
  • use of alternative sources of water for irrigation 

Page No 291:

Question 19:

(a) Define valency of an element. What valency will be shown by an element having atomic number 14?
​(b) What is the relation between the valency of an element and the number of valence electrons in its atoms? Explain with examples.

Answer:

(a) Valency of an element can be defined as the number of electrons present in the valence shell that is available for bonding.
Electronic configuration of the element having atomic number 14 is 2, 8, 4.
As this element has 4 electrons in its valence shell it's not possible to lose 4 electrons, so valency of this element is 4.

(b) Valency of an element is the number of electrons available for bond formation while valence electrons are electrons available in the outer most shell of the atoms.
For eg. Electronic configuration of chlorine is 2, 8, 7.
Valence electrons = 7
Valency of chlorine = 1
Electronic configuration of aluminium is 2, 8, 3.
Valence electons= 3
Valency of aluminium = 3



 

Page No 291:

Question 20:

A car is moving along a straight road at a steady speed. It travels 150 m in 5 seconds. 
(a) What is its average speed?
(b) How far does it travel in 1 second?
​(c) How far does it travel in 6 seconds?
(d) How long does it take to travel 240 m?

Answer:

(a) Total distance traveled by car = 150 m

Total time taken = 5 s

Average speed of the car = Total distance travelledTotal time taken=150 m5 s=30 m/s

(b) Distance traveled in 1 second = Average speed × time = 30 m/s × 1 s = 30 m

(c) Distance traveled in 6 seconds = Average speed × time = 30 m/s × 6 s = 180 m

(d) Time take by the car to travel 240 meters = DistanceSpeed= 240 m30 m/s=8 s

Page No 291:

Question 21:

(a) What do you understand by the term "transformation of energy"? Explain with an example.
(b) Explain the transformation of energy in the following cases:
(i) A ball is thrown upwards.
​(ii) A stone dropped from the roof of a building.

Answer:

(a) The transformation of energy means the conversion of energy from one form to another. Example: Electric energy is converted into mechanical energy by an electric motor. 

(b) (i) When a ball is thrown upwards, the kinetic energy of the ball gradually gets converted into potential energy and at the highest point, the whole of the kinetic energy transforms into potential energy of the ball. 

(ii) A stone at the roof of the building has some potential energy. When it is dropped from the roof, the potential energy possessed by the stone starts transforming into kinetic energy and at the bottom, it becomes purely kinetic. 

 



Page No 292:

Question 22:

An inflated balloon full of air goes down slowly (becomes smaller and smaller slowly) even though the knot at the mouth of the balloon is airtight. And after a week all the air has escaped from the balloon. Explain how the air particles got out of the balloon.

Answer:

This is due to the reason that balloons are not completely airtight. The air particles slowly diffuse through walls of the ballon or knot, due to the high pressure inside the balloon and the flux is operating outside. This is the reason it slowly reduces and after a week s all air goes out of the balloon.

Page No 292:

Question 23:

Few days back, our school organised health check-up camp. Eminent doctors (general physicians, opthalmologists, dentist, etc.). Doctor X, leader of the doctor's team, gave us tips about essential conditions of keeping good health, extrinsic and intrinsic causes of diseases as well as types of diseases.
Later, students of the school were examined by the doctors. Next day our class teacher asked us to answer the following questions:
(a) List at least three conditions essential for good health.
(b) How can we keep our surroundings clean? Mention at least two ways.
​(c) How would you define a disease?

Answer:

(a) Three conditions essential for good health are -

  • proper diet
  • clean surroundings and environment
  • regular exercise
(b) Our surroundings can be kept clean by taking small steps such as -
  • not throwing waste anywhere in the open and use dustbins for that
  • planting more trees
  • cleaning the leash of pets from pavements or roads 
(c) Disease is made up of the two words dis and ease. It is the state of the body when one feels uncomfortable and the normal functioning of the body is impaired.
 

Page No 292:

Question 24:

Composition of the nuclei of two atomic species A and B is given as under:

  A B
Protons: 18 20
Neutrons: 22 20
Give the mass numbers of A and B. What is the relation between the two species and which element or elements they represent?​

Answer:

The mass number of A = Number of proton + Number of neutrons
The mass number of A = 18 + 22
The mass number of A = 40
Number of electrons of A = 18

The mass number of B = Number of proton + Number of neutrons
The mass number of B = 20 + 20
The mass number of B = 40
Number of electrons of B = 20

There is no relation between the two species.
As specie A, represents argon.
As specie B, represents calcium.
Argon(A) is a noble gas element, argon does not form any molecule with calcium(B).
 

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Question 25:

Ramlal has been cultivating wheat crop year after year in the same field. Recently he has observed decline in the yield despite best inputs. Agriculture inspector of the area suggested him to sow legume crop (e.g., pea, chick pea or soyabean) for one or two years before again using the field for wheat crop. What is the logic behind this suggestion?

Answer:

Ramlal has been growing only wheat for several years. This has depleted the essential nutrients of the soil of its farms. It is suggested to him, to grow crops such as gram, pea etc as these are leguminous crops. They help in nitrogen fixation as they have nitrogen fixing bacteria in their root nodules. Legumes replenish the nitrogen of soil used by other plants during their growing session.

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Question 26:

A man wearing a bullet-proof vest stands still on roller stakes. The total mass is 80 kg. A bullet of mass 20 grams is fired at 400 m/s. It is stopped by the vest and falls to the ground. What is then the velocity of the man?

Answer:

The momentum of the bullet before hitting the vest of the man = 20×10-3 kg ×400 m/s=8 kg m/s

The momentum of the bullet after hitting the vest of the man = 0

Change in the momentum of the ball after hitting the vest = -8 kg m/s

The total momentum of the man initially = 0

By conservation of momentum, the man will also have the same change in momentum.

Final momentum of the man =  -8 kg m/s

The final velocity of the man = -8 kg m/s80 kg=-0.1 m/s

Hence, the man will recoil back with a velocity of 0.1 m/s.

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Question 27:

In an experiment to measure his power, a student records the time taken by him in running up a flight of steps on a staircase. Use the following data to calculate the power of the student:
Number of steps = 28
Height of each step = 20 cm
Time taken = 5.4 s
Mass of student = 55 kg
Acceleration due to gravity = 9.8 m s−2

Answer:

Power is energy consumed per unit time. 

When the student runs up on a staircase, his energy is consumed in doing work against the force of gravity.

Work done by the student against the force of gravity = mgh= 55 kg×9.8 ms-2×(28×20×10-2 m)=3018.4 J

Time taken by the student = 5.4 s

Power of the student = EnergyTime=3018.4 J5.4 s=559 J/s



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