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#### Question 1:

What is HYV? Give examples.

High Yielding Variety (HYV) of seeds commonly known as miracle seeds were developed by the Nobel Laureate Dr. Narman Barlauf in Mexico. These seeds are more productive and need regular and adequate irrigation facilities along with greater use of fertilisers and pesticides. Example: rice and wheat.

#### Question 2:

Name two factors on which shape of the cell depends.

The two factors on which shape of the cell depends are -

• functions performed by them
• contents inside the cell

#### Question 3:

Find the initial velocity of a car which is stopped in 10 seconds by applying brakes. The retardation due to brakes 2.5 m/s2.

Time taken by the car to stop = 10 seconds

Let the initial velocity of the car = u

Final velocity = 0

Retardation = 2.5 m/sor Acceleration = $-$2.5 m/s2

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

Hence, the initial velocity of the car is 25 m/s.

#### Question 4:

Write down the differences between diffusion and osmosis.

 Osmosis Diffusion In osmosis, the solvent moves from a less concentrated solution to a more concentrated solution through a semi-permeable membrane. In diffusion, the molecules of two or more substances mix spontaneously to form a homogeneous mixture. No semi-permeable membrane is present in this case. It takes place only in the case of liquids. It takes place in the case of liquids as well as gases. It can be stopped or reversed by applying pressure. It is a spontaneous process and cannot be stopped or reversed.

#### Question 5:

Explain the term 'amplitude' of a wave. Draw the diagram of a wave and mark its amplitude on it.

When a wave passes through a medium, then the particles of the medium oscillate about their mean position. The maximum displacement of the particles from their mean position is known as Amplitude of the wave. The amplitude of a wave is shown in the following figure:

#### Question 6:

Give the general characteristics of phylum Mollusca.

The general characteristics of phylum Mollusca are -
(You can write any 4-5 points)
• The body of a molluscs is unsegmented like those of an annelid and an arthropod.
• They have an organ system level of organization.
• They show bilateral symmetry.
• They have an open circulatory system and possesses kidney-like organs for excretion.
• They are triploblastic animals.
• The coelomic cavity (schizocoelom) is reduced to a cavity called haemocoel, through which the hemolymph (function similarly as blood of vertebrates) circulates.
• Their body is divided into an anterior head, a ventral muscular foot and a dorsal visceral mass.
• The soft body is covered by a hard shell.
• A mollusc has a distinct foot for moving around.
• Examples of molluscs: OctopusPila (freshwater snail)

#### Question 7:

(a) Define the term 'latent heat of fusion' of a solid. How much is the latent heat of fusion of ice?
(b) Draw a labelled diagram of the experimental set-up to study the latent heat of fusion of ice.

(a) Latent heat of fusion is defined as the amount of heat required to change 1 kg of a solid substance into the liquid state at the melting point of the substance.
For ice, the latent heat of fusion is 334 kJ kg-1. This means that 334 kJ of heat is required to convert 1 kg of ice at 0 $°$C into 1 kg of water at 0 $°$C.

(b) Experimental setup to study the latent heat of fusion of ice:

#### Question 8:

Define diarrhoea. Give an account of occurrence, symptoms, prevention and control of this ailment.

Diarrhoea is caused by a group of bacteria such as Staphylococcus, Clostridium, E. coli, Shigella etc. It is defined as an abnormal frequent discharge of semi-solid or fluid faecal matter.

Modes of transmission -

• through contaminated food, water, drinks etc.
Symptoms -
• abnormal frequent discharge of semi-solid or fluid faecal matter
• reduced appetite
• abdominal cramps, nausea and vomiting
Control -
• use of anti diarrheoal antibiotics
• use of ORS or saline drip to maintain the electrolyte balance
Prevention -
• use of disinfected water
• proper covering of eatables
• mantaining proper hygeine and personal health

#### Question 9:

Which organelle is the "power house" of eukaryotic cell? Write in brief its functions.

Mitochondria is called the "power house" of eukaryotic cell.

Functions of mitochondria are -

• produce  energy (in the form of ATP) required for the functioning of cells
• regulate free calcium ion concentration in cytosol
• participate in apoptosis or programmed cell death
• provide intermediates for the synthesis of various chemicals such as fatty acids, steroids and amino acids

#### Question 10:

Explain the direction of air movement during the day and night in coastal areas.

The air always from a region of high pressure to a region of low pressure. In coastal areas during the day, the land gets heated faster than water. So, there is low pressure on land and high pressure in the sea. Therefore, the wind flows from sea to land. This is known as the sea breeze. During the night, the land quickly radiates all the heat but the sea still has some heat. So, the sea has low pressure and land has high pressure during the night. Hence, the wind direction changes and becomes from land to sea. This is called the land breeze.

#### Question 11:

(a) Define gram molecular mass of a substance. How much is the gram molecular mass of oxygen?
(b) If sulphur exists as S8 Molecules, calculate the number of moles in 100 g of sulphur. (S = 32 u)

(a) Gram molecular mass is defined as the mass in grams of one mole of molecular substance or simply equal to the sum of all the atomic masses in the molecular formula of a compound in grams.

The atomic mass of oxygen atom(O) = 16

So, gram molecular mass of oxygen molecule(O2) = (2 ⅹ 16) = 32 g

(b) The atomic mass of sulphur(S) = 32 u

Molecular mass of sulphur(S8)= 8 ⅹ 32 = 256 u

Given mass of sulphur(S8) = 100 g

#### Question 12:

Define the terms 'frequency', 'wavelength' and 'velocity' of a sound wave. What is the relation between them?

When a wave travels through a medium, particles of the medium oscillate about their mean position. The number of oscillations per second is known as the frequency of the wave. SI unit of frequency is Hertz(Hz).

The distance between two consecutive crests or troughs is called wavelength of the wave. SI unit of wavelength is meter (m). It is denoted by symbol 'λ'.

When a wave travels through a medium, it creates a disturbance in the particles of the medium. As the disturbance moves along the direction of the wave, we say the wave is moving. The distance covered by that disturbance in one second is known as the velocity of the wave. It is given by the product of the wavelength and frequency of the wave.

Wavelength, frequency, and velocity of any wave are related according to the following relation,

$v\left(\mathrm{velocity}\right)=\lambda \left(\mathrm{wavelength}\right)×\nu \left(\mathrm{frequency}\right)$

#### Question 13:

(a) What are isotopes? Explain by giving an example.
(b) Give one similarity and one difference between a pair of isotopes.
(c) Give the number of protons, neutrons, and electrons per atom in the two isotopes of chlorine ${}_{17}{}^{35}\mathrm{Cl}$ and ${}_{17}{}^{37}\mathrm{Cl}$.

(a) Isotopes are defined as atoms having the same atomic number, but different mass numbers. These atoms contain an equal number of protons and electrons, but the different number of neutrons.
For eg. In nature, hydrogen is found in three forms with different mass numbers, namely .

(b) Similarity: Isotopes have a similar atomic number
Difference: Isotopes have a different mass number.

(c) For chlorine ${}_{17}{}^{35}\mathrm{Cl}$,
Atomic number = 17
Number of protons = Atomic number
Number of protons = 17
Number of protons = number of electrons
Number of electrons = 17
Number of neutrons = Mass number - Number of protons
Number of neutrons = 35$-$17
Number of neutrons = 18

For chlorine ${}_{17}{}^{37}\mathrm{Cl}$,
Atomic number = 17
Number of protons = Atomic number
Number of protons = 17
Number of protons = number of electrons
Number of electrons = 17
Number of neutrons = Mass number - Number of protons
Number of neutrons = 37$-$17
​Number of neutrons = 20

#### Question 14:

How much is the weight of an object on the moon as compared to its weight on the earth? Give a reason for your answer.

The weight of an object on the moon will be 1/6th of the weight of the object on earth. This is because the value of acceleration due to gravity on the moon is one-sixth of its value on the earth. The reason behind the difference in the gravitational pull on both the planets is the difference between the mass and radius of the moon and the earth. The mass and radius of the moon are less than that of the earth. That's why the acceleration due to gravity is less on the moon, which make an object feels lighter on the moon i.e. one-sixth of the weight on the earth.

#### Question 15:

(a) What do you understand by the kinetic energy of a body?
(b) A body is thrown vertically upwards. Its velocity goes on decreasing. What happens to its kinetic energy as its
velocity becomes zero?
(c) A horse and a dog are running with the same speed. If the weight of the horse is ten times that of the dog, what
is the ratio of their kinetic energies?

(a) Energy possesses by a body by virtue of its motion is known as the kinetic energy of the body.

(b) When a body is thrown upwards, it's velocity decreases and its kinetic energy gradually changes into potential energy. At the highest point, its velocity becomes zero and all of the kinetic energy gets converted into potential energy.

(c) The kinetic energy of a body is given by $\frac{1}{2}m{v}^{2}$.  Where 'm' is the mass of the body and 'v' is the velocity of the body.

In the given case, the velocity of dog and horse are the same, let's say 'v'. Then the ratio of their kinetic energies,

#### Question 16:

Iron powder and sulphur powder were mixed together and divided into two parts A and B. When part A was heated strongly over a burner, then a substance C was formed. The part B was, however, not heated at all. When dilute hydrochloric acid was added to substance C, then gas D was evolved and when dilute hydrochloric acid was added to part B the gas E was evolved.
(a) What type of substance Is B?
(b) What type of substance is C?
(c) Name the gas (i) D, and (ii) E?
(d) State once characteristic property of gas D.

When mixture A(Iron + sulphur) is heated strongly, substance C is formed.

$\underset{\mathrm{A}}{\underset{⏟}{\mathrm{Fe}+\mathrm{S}}}\stackrel{\mathrm{Heat}}{\to }\underset{\mathrm{C}}{\underset{⏟}{\mathrm{FeS}}}$

When C(iron sulphide) reacts with dilute hydrochloric acid, a foul-smelling hydrogen sulphide gas(D) is eliminated.

$\underset{\mathrm{C}}{\underset{⏟}{\mathrm{FeS}}}+2\mathrm{HCl}\to \underset{\mathrm{D}}{\underset{⏟}{{\mathrm{H}}_{2}\mathrm{S}}}+{\mathrm{FeCl}}_{2}$

When dilute hydrochloric acid is added in mixture B(iron + sulphur), then only iron powder reacts with dilute hydrochloric acid and a colourless and odourless hydrogen gas evolves. It burns with a pop-up sound. Sulphur being non-metal do not react with dilute hydrochloric acid.

$\underset{\mathrm{B}}{\underset{⏟}{2\mathrm{Fe}}}+6\mathrm{HCl}\to 2{\mathrm{FeCl}}_{3}+\underset{\mathrm{E}}{\underset{⏟}{3{\mathrm{H}}_{2}}}$

(a) B is a mixture of iron and sulphur.

(b) Substance C is a black coloured compound known as iron sulphide.

(c) (i) D is hydrogen sulphide gas eliminated from mixture A.
(ii)  E is hydrogen gas eliminated from mixture B.

(d) D(Hydrogen sulphide gas) smells like rotten eggs.

#### Question 17:

(a) What are the two ways in which the physical states of matter can be changed?
(b) Draw the 'states of matter triangle' to show the interconversion of states of matter.
(c) How can the evaporation of a liquid be made faster?

(a) The physical state of matter can be changed by:
(i) By altering the temperature.
(ii) By altering the pressure.

(b) Inter conversion of state of matter can be shown as:

(c) Evaporation of liquid can be made faster by following methods:

(i) By increasing the temperature.
(ii) By increasing the surface area.
(iii) By lowering the humidity.
(iv) By increasing the speed of the wind.

#### Question 18:

Draw a well labelled diagram of animal cell and mention one function of the main call organells.

• Nucleus - It controls all the activities of a cell and acts like the brain of a cell.
• Mitochondria - The energy required for various cellular activities is released by mitochondria in the form of ATP (adenosine triphosphate) molecules. Thus, mitochondria are referred to as the power houses of the cell.
• Endoplasmic reticulum - It is the site where many important chemical reactions take place, including the synthesis of important proteins, lipids and many other materials. It functions as a packaging system.
• Lysosome - They contain digestive hydrolytic enzymes such as acid hydrolase. With the help of these enzymes, they are able to digest a variety of substances including worn out organelles, proteins, nucleic acids, lipids and carbohydrates.
• Golgi apparatus - It is involved in the transport of lipids in cells.
• Vacuole -  They help in the removal of unwanted structural debris and maintaining the turgor pressure within cells.

#### Question 19:

The given graph shows how the speed of a car changes with time:

(a) What is the initial speed of the car?
(b) What is the maximum speed attained by the car?
(c) Which part of the graph shows zero acceleration?
(d) Which part of the graph shows varying retardation?
(e) Find the distance travelled in the first 8 hours.

(a) The initial speed of the car is 10 km/h at t=0.

(b) Speed of the car increases and attains a maximum speed of 35 km/h.

(c) Part BC of the graph shows zero acceleration because the velocity for that part is constant. As there is no change in velocity, so there is no acceleration.

(d) From point C to D, the velocity of the car is decreasing at a variable rate. So, the car has varying retardation from C to D.

(e) Distance travelled in first 8 hours will be the area under the speed-time graph from t = 0 to t = 8 h.

Distance travelled = Area under the trapezium (from t =  0 to t = 3) + Area under the rectangle (t = 3 to t = 8)

=

#### Question 20:

Give reasons for
(a) Meristematic cells have a prominent nucleus and dense cytoplasm but they lack vacuoles.
(b) Intercellular spaces are absent in sclerencymatous tissue.
(c) We get a crunchy and granular feeling when we chew pear fruit.
(d) Branches of a tree move and bend freely in high wind velocity
(e) It is difficult to pull out the husk of coconut.

(a) Meristematic cells are actively dividing cells. For a cell to divide, its volume: surface area ratio should be high. This triggers the process of cell division. As meristematic cells need to divide at rapid rate, they have dense cytoplasm and large nucleus. The role of the vacuoles in the cell is to store ergastic substances. Since meristematic cells are rapidly dividing cells, they do not have the need for storage. Hence, meristematic cells have no vacuoles.

(b) Sclerenchyma is made up of long, narrow, and thick-walled cells. The walls of these cells are thick because of the deposition of a chemical substance called lignin. Also, the cells with thick walls are arranged very tightly with no intercellular spaces. These factors make sclerenchyma a hard tissue. It is responsible for providing mechanical strength to plants.

(c) We get a crunchy and granular feeling when we chew pear fruit due to the presence of sclereids. Sclereids are sclerenchymatous cells which are short and have thick lignified walls. They may vary greatly in their size and shape.

(d) Branches of a tree move and bend freely in high wind velocity due to the presence of collenchyma tissue. This tissue provides flexiblity to the branches.

(e) Husk of coconut is made up of sclerenchyma and the sclerenchymatous fibers are closely packed. This makes it difficult to pull them apart.

#### Question 21:

(a) Define momentum of a body. On what factors does the momentum of a body depend?
(b) Calculate the change in momentum of a body weighing 5 kg when its velocity decreases from 20 m/s to 0.20 m/s.

(a) The momentum of a body is defined as the product of its mass and the velocity. It is a vector quantity and has direction same as the direction of velocity. From the definition of momentum, we can say that it depends on the mass and velocity of the body.

(b) Mass of the body = 5 kg

Initial velocity of the body = 20 m/s

The initial momentum of the body = 5 kg$×$20 m/s = 100 kg m/s

Final velocity of the body = 0.20 m/s

Final momentum of the body = 5 kg$×$0.20 m/s = 1 kg m/s

Change in momentum = 100 kg m/s - 1 kg m/s = 99 kg m/s

Hence, the change in momentum of the body is 99 kg m/s.

#### Question 22:

How can a karate player break a pile of tiles or a slab of ice with a single blow of his hand?

Karate player breaks a pile of tiles or a slab of ice with a single blow of his hand because he strikes the pile with his hand moving very fast. In doing so, the entire momentum of his hand becomes zero in a very short span of time. As the force is basically the rate of change of momentum. Therefore, by doing the fast action of his hand, he is able to apply a stronger force on the pile and hence the pile of tiles or slab of ice breaks by a single blow of his hand.

#### Question 23:

When water is cooled to a temperature x, it gets converted into ice at temperature x by a process called P, and when ice at temperature x is warmed, it gets reconverted into water at the same temperature x in a process called Q.
(a) What is the value of temperature x in Kelvin?
(b) What is the process P Known as?
(c) What is the name of energy released during process P?
(d) What is the process Q known as?
(e) What is the name of energy absorbed during process Q?

$\mathrm{Water}⇋\mathrm{Ice}$
(a) The temperature at which water converts to ice is 273 K. Therefore, the temperature x is 273 K.

(b) Process P is known as cooling.

(c) Latent heat of freezing is released during the cooling.

(d) Process Q is known as liquifaction.

(e) Latent heat of fusion is absorbed during the reaction.

#### Question 24:

Animals of colder region and fishes of cold water have thicker layer of subcutaneous fat. Describe why?

Animals and fishes which live in colder areas and colder water have a thick layer of sub cutaneous fat because it acts as an insulating layer.
It prevents the loss of heat and also serves as reserve food resource during periods of scarcity.

#### Question 25:

How would you confirm that a colourless liquid given to you is pure water?

Upon boiling the liquid at 100$°$C or 373 K, if it converts to gas then it is pure water.

#### Question 26:

A boy walks from his classroom to the bookshop along a straight corridor towards North. He covers a distance of 20 m in 25 seconds to reach the bookshop. After buying a book, he travels the same distance in the same time to reach back in the classroom.

Find (a) average speed and (b) average velocity of the boy.

(a) The average speed of the boy is given by the ratio of total distance travelled by the boy and the total time taken to cover it. During the complete trip from classroom to bookshop and bookshop to the classroom, the boy travels a total distance of 40 m in 50 seconds of time.

So, Average speed =

(b) The average velocity of the boy is given by the ratio of total displacement and the total time taken by the boy. The total displacement of the boy during the complete trip of 50 seconds from classroom to bookshop and bookshop to the classroom is zero.

So, Average Velocity =

#### Question 27:

Khushi wanted to eat rice and kidney bean (rajmah). She requested her mother to cook the same for lunch tomorrow. At night her mother took a cup of kidney bean and put them in a container having some water. She kept the container covered overnight. Next morning, she cooked rice and kidney beans for lunch. Khushi inquired her mother the following questions:
(a) Why did she soak kidney beans in water overnight?
(b) Name the scientific phenomenon involved in above process.
(c) Name at least one more food item that is cooked in this way.

(a) Kidney beans are quiet hard and cooking them in that stage requires more time and energy (fuel). On the other hand, soaking the kidney beans overnight, causes them to absorb water and swell up. These soaked kidney beans cook fast and do not require much fuel as well.

(b) The scientific phenomenon involved in the above process is osmosis.

(c) Grams or Choley/Chaney are also cooked in the same way.

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