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Page No 283:

Question 1:

Which type of body organisation is present in platyhelminthes?


Platyhelminthes show organ level of organisation.

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Question 2:

Differentiate between chromatin and chromosome.



These are thin, long, uncoiled structures.
These are thick, compact, ribbon like strcutures.

They are composed of nucleosomes.
They are condensed chromatin fibers.

They occur as single, unpaired fibers.
They exist in pairs.

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Question 3:

Describe components of phloem. Define translocation.


Components of phloem and their functions are as follows -

  1. Sieve tube − Transport food materials
  2. Companion cells − Carry out the cellular functions of the sieve tube elements
  3. Phloem parenchyma − Responsible for the storage of food
  4. Phloem fibres − Provide mechanical strength to the cells

The process of transport of food from the leaves to the other parts of a plant is known as translocation.

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Question 4:

A stone is dropped from a height of 20 m.
(a) How long will it take to reach the ground?
(b) What will be its speed when it hits the ground? (g = 10 m/s2)


(a) Distance travelled by the stone while falling from the height 20 m to the ground = 20 m

The initial velocity of the stone = 0

Acceleration of the stone = g

By using the second equation of  motion, we can write, s=ut+12gt2

Here, u = 0, s = 20 m, and 't'  is the time taken by the stone to reach the ground.


20 =0 + 12×g×t2t2=40g=4010=4t=4 s

(b) Using the first equation of motion, we can write, v = u + gt (Where 'v' is the speed of the stone when it hits the ground)

So, v = 0 + 10×4=40 m/s


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Question 5:

What is a soundboard? Explain the working of a soundboard with the help of a labelled diagram.


In big halls or auditoriums, the sound is absorbed by the walls, ceilings, and seats, that's why a curved board is placed behind the speaker such that the speaker is at the focus point of the curved surface. The curved surface or the board used for this purpose is known as a soundboard.

Soundboard makes the sound of the speaker louder and clear because after multiple reflections of the sound at the curved surface all the reflected rays distribute uniformly to the audience and sound is heard more clearly. As you can see in the figure, the source is always placed at the focus of the curved surface, and curved board is placed behind the source of the sound so that the sound gets reflected from the soundboard and distributed uniformly to the front.

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Question 6:

(a) What is meant by 'reflection of sound'? What type of surfaces are the best for reflecting sound?
(b) Name any two objects which are good reflectors of sound.
(c) State the laws of reflection sound.


(a) The sound waves bounced back after striking a hard surface are known as reflected rays and the phenomenon is known as the reflection of the sound. Sound is reflected well from hard surfaces like a wall, metal sheet or a hardwood. 

(b) Hard objects are the good reflectors of the sound, like steel and iron.

(c) There are two laws of reflections. 

(i) The incident ray, the normal and the reflected ray, all lie in the same plane.
(ii) The angle of incidence is always equal to the angle of reflection.

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Question 7:

Draw a plant cell and label the parts which
(a) determine function and development of the cell.
(b) provides resistance to microbes and to withstand hypotonic external medium without injury.
(c) packages materials coming from the endoplasmic reticulum.
(d) is a fluid contained inside the nucleus.
(e) is site for many biochemical reaction necessary to sustain life.


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Question 8:

Calculate the formula masses of the following compounds:
(a) Sodium oxide, Na2O
(b) Aluminium oxide, Al2O3
(Given: Atomic Masses: Na = 23 u; O = 16 u; Al = 27 u)


(a) The formula mass of sodium oxide,
Formula mass of Na2O= 2×atomic mass of Na+atomic mass of oxygenFormula mass of Na2O= 2×23+16Formula mass of Na2O= 62 u

(b) The formula mass of aluminum oxide,
Formula mass of Al2O3= 2×atomic mass of Al+3×atomic mass of oxygenFormula mass of Al2O3= 2×27+3×16Formula mass of Al2O3= 102 u

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Question 9:

It was diagnosed that the body of a patient has lost its power of fighting any infection. Name the disease he is suffering from. What type of microbe is responsible for this disease and how does it spread from one person to the other.


The person is suffering from AIDS. It is a disease which affects the immune system and lowers the immunity of the suffering individual. As a result of which the person becomes susceptible to all types of infections.
HIV (Human immuno virus) is the causal organism. It belongs to the category of viruses.

AIDS can spread by any one of the following ways-

(i) through sexual contact with the infected person

(ii) from the mother to her child, through the placenta

(iii) transfusion of infected blood to healthy individual.

(iv) by the use of infected syringe

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Question 10:

(a) What are forms of oxygen found in the atmosphere?
(b) "Forests influence the quality of our air, soil and water resources." Justify the statement.


(a) There are two forms of oxygen found in the atmosphere -

Elemental oxygen - It is usually found in diatomic state i.e. O2 in the lower part of atmosphere.
Ozone - Another form of oxygen is ozone, which exists in triatomic state i.e. O3 and is found in the stratosphere layer of atmosphere.

(b) Forests play an important role in various ways -

  • They maintain the carbon dioxide and oxygen balance. They use carbon dioxide and release oxygen into the atmosphere.
  • They play an important role in replenishing the water resources by maintaining the water cycle.
  • They prevent soil erosion by strongly holding onto the soil through their roots and preventing it from eroding.
  • They also check the speed of winds and running water.


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Question 11:

(a) Define velocity. What is the SI unit of velocity?
(b) What is the difference between speed and velocity?
(c) Convert a speed of 54 km/h into m/s.


(a) The rate of change of displacement is known as the velocity. It can be calculated by obtaining the ratio of displacement and the total time taken. The SI unit of velocity is 'm/s', same as of the speed. 

(b) Speed is the rate of change of distance travelled by a body whereas velocity is the rate of change of displacement by the body. Speed is a directionless quantity but the velocity is a vector quantity, we need magnitude as well as direction to describe it. 

(c) Given speed, = 54 km/h

1 km = 1000 m

1 h = 3600 s

So, v=54 kmh=54×1000 m3600 s=54036 m/s

 v =54 km/h = 15 m/s

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Question 12:

Define green revolution. What are the common objectives of crop improvement?


The Green Revolution refers to a period when technologically advanced methods were introduced in the field of agriculture for improving the yield. Green Revolution made its way into the Indian agricultural field in late 1960s. High Yielding Varieties (HYV) of seeds of wheat and rice were used by Indian farmers for increasing production. In addition, the use of fertilizers and pesticides greatly improved the overall yield and made India self-sufficient in food grain production.

The common objectives of crop improvemnt are -

1. Develop stable and high yielding varieties of both food and cash crops
2. Develop varieties with high nutritional value and good storage qualities
3. Conserve the germplasm of important crops
4. Develop appropriate production and management package for good agricultural production

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Question 13:

(a) When an incense stick (agarbatti) is lighted in one corner of a room, its fragrance
(b) A girl is cooking some food in the kitchen. The smell of food being cooked soon reaches her brother's room. Explain how the smell could have reached her brother's room.


(a) Atoms of incense stick when lighted get mixed with the particles of air. Then we are able to smell its fragrance.
This shows that atoms intermix with each other and the process is known as diffusion.

(b) Due to the diffusion of gases, particles of food cooking in the kitchen get mixed with air. Due to diffusion particles move from higher concentration to the lower concentration, so the smell of food reached her brother's room.

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Question 14:

Hydrogen has three isotopes written as:
H11, H12, H13
Explain Why:
(a) These isotopes have almost identical chemical properties.
(b) They are electrically neutral.


(a) The isotope of hydrogen is chemically similar because isotopes of the atom of the same element have the same atomic number but the different mass number. As the electronic configuration is the same. Due to this, there will be the same valence electrons and they have the same chemical properties.

(b) The isotopes of the hydrogen atom are electrically neutral because the number of protons and the number of electrons is equal. They both cancel out their charges resulting in the net charge zero.

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Question 15:

A car of mass 2400 kg moving with a velocity of 20 ms−1 is stopped in 10 seconds on applying brakes. Calculate the retardation and the retarding force.


The initial velocity of the car = 20 ms−1 

The final velocity of the car = 0

Time taken by the car to stop = 10 s

Using the first equation of motion, we can write, v = u + at

 0 = 20+ a×10

a =-2 ms-2

Hence, retardation is 2 ms-2

Retarding force = mass × retarding acceleration
                         = 2400 kg × 2 ms-2 
= 4800 kg ms-2
= 4800 N

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Question 16:

(a) write the symbols/formulae of two simple ions and two compound ions (or polyatomic ions).
(b) an element Y has a valency of 4. Write the formula for its:
(i) chloride (ii) oxide (iii) sulphate (iv) carbonate (v) nitrate


(a) Simple ion is formed due to gain or loss of electrons by a single atom of an element, For eg. Na+, K+, Mg+2, etc.
A compound ion is formed due to excess anions or cations in a compound. For eg. ammonium ions (NH4+), carbonate ions(CO3-2), etc.

(b) (i) As Y has four valence electrons, it will form four single bonds with a chlorine atom and form YCl4.
(ii) As Y has four valence electrons, it will form two double bonds with an oxygen atom and form YO2.
(iii) As Y has four valence electrons, it will form two double bonds with sulfate atom and form Y(SO3)2.
(iv) As Y has four valence electrons, it will form two double bonds with carbonate and form Y(CO3)2.
(v)  As Y has four valence electrons, it will form four single bonds with nitrate and form Y(NO3)4.

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Question 17:

(a) What are radioactive isotopes? Give two examples of radioactive isotopes.
(b) Give any two uses of radioactive isotopes.
(c) An element Z contains two naturally occurring isotopes Z1735 and Z1737. If the average atomic mass of this element be 35.5 u, calculate the percentage of two isotopes.


(a) Radioactive isotopes are those isotopes of an element which have an unstable nucleus. Because of this, the radioactive isotopes undergo radioactive decay by emitting alpha, beta, and gamma radiation to gain the stability of the nucleus. For eg, O15, Co60, etc.

(b) Uses of radioactive isotopes:
(i) Radioactive isotopes are used to determine the age of rocks and minerals.
(ii) It is used to treat cancer, detect blood clots and diagnose thyroid.

(c) Let the percentage of Z1735 = X
Then the percentage of Z1737 = 100 - X
Average atomic weight of Z = 35.5u

Therefore, Z1735 = 75% and, Z1737 = 100-75 = 25%

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Question 18:

Define pteridophytes. Compare between bryophytes and pteridophytes.


Pteridophytes belong to the phylum of plants. These are the first plants which show the presence of vascular tissues. They reproduce through spores instead of seeds.


They do not possess vascular tissues.
They possess vascular tissues.

Roots are absent and instead rhizoids are present which help in anchorage.
Roots are present.

They have haploid cells.
They have diploid cells.

Examples: liverworts, hornworts, mosses
Examples: ferns, horsetail

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Question 19:

Give an account of some important viral diseases of human beings.


Some important viral diseases of humans are - Hepatitis, Polio, Rabies and AIDS.

1. Hepatitis - 
Causal organism - Hepatitis virus
Mainly affects liver and usually results in jaundice.
There are different types of hepatitis - hepatitis A,  hepatitis B,  hepatitis C,  hepatitis D,  hepatitis E.

Mode of transmission -

  • Hepatitis A - spreads through contaminated food and water.
  • Hepatitis B - spreads through contact with infected person's secretions such as saliva, sweat, tears etc.

Symptoms -

  • Fever
  • Nausea and vomiting
  • Jaundice
  • Dark yellow urine
  • Itching of skin

Prevention -

  • Eating hygenic food and drinking disinfected water
  • Immunisation with hepatitis B and hepatitis A vaccines
  • Use of disposable syringes
  • Proper cleaning of hands after handling bed, clothes and utensils of the pateints

2. Polio
Causal organism - Polio virus
Mainly affects the children 

Modes of transmission -

  • Spreads through faecal-oral route

Symptoms -

  • Headache and fever
  • Stiffness of the neck and convulsions
  • Paralysis of limbs due to damage of motor nerve cells in the spinal cord
  • Respiratory failure

Prevention -

  • Immunization with oral polio vaccine

3. Rabies
Causal organism - Rabies virus named Lyssavirus.

Modes of transmission -

  • Spreads through the bite of an infected animal such as dogs or cats.

Symptoms -

  • Severe headache and high fever
  • Painful contractions of muscles of throat and chest
  • Hydrophobia, where an individual is afraid of water

Prevention -

  • Vaccination of pet dogs and cats
  • Cleaning the wound with soap and clean running water

4. AIDS -
Affects the immune system of the body

Causal organism - Human Immuno Virus (HIV)

Modes of Transmission -

  • By sharing infected needles while injecting drugs.
  • By having sexual contact with an infected person.
  • From an infected mother to the child through pregnancy or breast feeding.
Symptoms -
  • Weight loss
  • Prolonged fever
  • Prolonged diarrhoea
  • Kaposi’s sarcoma
  • Meningitis
  • Complete loss of immunity with infections like tuberculosis and pneumonia, etc.

Prevention -

  • Education about the disease
  • Use of disposable needles and syringes
  • Avoiding sharing of razors for shaving
  • Protected sexual intercourse using condoms

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Question 20:

The mass of a planet is 6×1024 kg and its diameter is 12.8 ×103 km. If the value of a gravitational constant is 6.7 ×10-11 Nm2/kg2, calculate the value of acceleration due to gravity on the surface of the planet. What planet could this be?


The value of acceleration due to gravity is given by the relation, g=GMR2 (Where 'M' is the mass and 'R' is the radius of the planet)

Mass of the planet = 6×1024 kg

The radius of the planet = Diameter2=12.8×103 km2=6.4×103 km

Gravitational constant = 6.7 ×10-11 Nm2/kg2

So, g=6.7×10-11 Nm2kg-2 × 6×1024 kg(6.4×103×103 m)2=9.8 ms-2

This planet could be earth because the value of acceleration due to gravity is the same on the planet earth.

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Question 21:

(a) Derive the relation between commercial unit of energy (kWh) and SI unit of energy (joule).
(b) A certain household consumes 650 units of electricity in a month. How much is this electricity in joules?


(a) Commercial unit of energy in 1 kWh. One kilowatt-hour is the amount of energy consumed in one hour at a constant rate of one kilowatt. SI unit of energy is joule.

1 kWh= 1 kW × 1 h = 1000 W × 1 h            =1000(Js) × 3600 s   ( 1 W = 1 Js)            = 3600000 J 1 kWh= 3.6×106 J

(b) Energy consumed by certain household = 650 units = 650 kWh

 1 kWh= 3.6×106 J

650 kWh= 650×3.6×106 J=2.34×109 J


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Question 22:

Tincture of iodine is a mixture of two materials X and Y. The material Y has a property that its solid form can be converted directly into vapours on heating by a process called Z.
(a) What could X be?
(b) What could Y be?
(c) Name the process Z.
(d) Which process would you use to recover both the components X and Y from tincture of iodine?
(e) Which process can be used to recover only component Y from tincture of iodine?


Tincture of iodine is prepared by dissloving proper amount of iodine(solid) in an alcohol solution.

(a) So X would be alcohol.

(b) So Y would be iodine.

(c) When the solid phase directly converts to gas phase on heating, it is known as sublimation. So process Z is sublimation.

(d) By fractional distillation method, we can easily separate both the components. As there is a difference in the boiling point of two solutions.

(e) By evaporation method, we can easily separate the component Y(Iodine) from the given sample.

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Question 23:

Seeing a bat flying over the roof of her house, Babita asked her father following questions:
(a) What is this night flying bird?
(b) How does it see during night?
(c) What does it eat and how does it obtain its food?


(a) First of all, bat is not a type of bird. It belongs to the category of mammals. It has patagia in the forelimbs which functions as wings and helps in the flight of bat.

(b) Bat is an animal which does not require sharp vision to see during night. It depends on ecowaves which it sends to interpret an obstacle (ecolocation).

(c) Bats feed nocturnal insects (insects which fly in night). Bats detect these insects based on sound waves produced by them. It is also one of the ways of biologically controlling the population of these insects.

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Question 24:

Why we are normally advised to take bland and nourishing food when we are sick?


When we are ill, our normal body functions get disturbed. In order to recover, we need a nutritious meal which is easily digestable and contains all the nutrients. So. it is advised to have bland and nourishing food.

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Question 25:

The formula of carbonate of a metal M is M2CO3.
(a) What will be the formula of its iodide?
(b) What will be the formula of its nitride?
(c) What will be the formula of its phosphate?


The formula of carbonate of a metal M is M2CO3.
Valency of carbonate is 2
As here two metals are present, 
So, the valency of metal, M is 1.

(a) Valency of iodide is 1.
So, the formula for iodide of metal M will be MI.

(b) Valency of nitrogen is 3.
So, the formula for nitride of metal M will be M3N.

(c) Valency of phosphate is 3.
So, the formula for the phosphate of metal M will be M3PO4.

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Question 26:

A coin and a piece of paper are dropped simultaneously from the same height. Which of the two will touch the ground first? What will happen if the coin and the piece of paper are dropped in a vacuum? Give reasons for your answer.


If a coin and a piece of paper are dropped simultaneously from the same height in the air, then the coin will touch the ground first and the paper will touch later. Because the paper will experience an air resistance due to its lightweight whereas coin has more weight, so air resistance won't affect coin.

But if the same coin and paper are dropped simultaneously in a vacuum then both the coin and the paper will reach the ground at the same time, because in a vacuum there will not be any kind of air resistance and gravity will take them both down at the same time.

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Question 27:

A ball falls to the ground as shown below:

(a) What is the kinetic energy of ball when it hits the ground?
(b) What is the potential energy of ball at B?
(c) Which law you have made use of in answering this question?


(a) In the given case, the mechanical energy of the ball will always remain conserved. Hence, the sum of the potential energy and the kinetic energy will always remain constant.

At the highest point A, total mechanical energy = Potential energy + Kinetic energy = 80 J + 0 J = 80 J

At the lowest point, total mechanical energy =  total mechanical energy at the highest point

So, at the lowest point, Potential energy + Kinetic energy  = 80 J = 0 + Kinetic energy

Hence, at the lowest point, kinetic energy is 80 J.

(b) As we know that mechanical energy is constant throughout the motion.

So, mechanical energy at point B = Mechanical energy at point A

Mechanical energy at point B  = Potential energy at point B + Kinetic energy at point B = 80 J

Potential energy at point B = 80 J - 48 J = 32 J

(c) The law of conservation of mechanical energy has been used while answering the above questions.

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