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#### Question 1:

How do substances such as carbon dioxide and water move in and out of the cell?

Carbon dioxide and water move in and out of the cell through diffusion and osmosis, respectively.

#### Question 2:

Name two egg laying mammals.

Egg laying mammals include platypus and the spiny ant eater (echidna).

#### Question 3:

State an important characteristic of uniform circular motion. Name the force which brings about uniform circular motion.

In a uniform circular motion, the speed is constant throughout the motion, but yet it is an accelerated motion. Because the direction of motion of an object undergoing uniform circular motion changes continuously. Due to that, it has a variable velocity, which results in an accelerated motion. The force responsible for changing the direction of motion of the body in a uniform circular motion is known as the centripetal force.

So, we can say that the centripetal force is the force, which brings about the uniform circular motion.

#### Question 4:

To take the boat away from the bank of a river, the boatman pushes the bank with an oar. Why?

According to Newton's third law of motion, when we apply a force on some object, then in return the object applied an equal and opposite reaction force on us. Following this law, the boatman pushes the bank with an oar. The pushing of the bank with an oar is an action force applied by the boatman in order to get an equal and opposite reaction force from the bank, which helps the boat to move forward.

#### Question 5:

Why do plants and animals possess different types of tissues?

Plant and animal tissues are different because plants tend to grow throughout their life, whereas animals grow up to a certain period. Moreover, plants do not show locomotion but animals show locomotion, which necessitates the presence of different types of tissues.

#### Question 6:

What is evaporation? State the various factors which affect evaporation.

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

#### Question 7:

(a) State the various postulates of Dalton's atomic theory of matter.
(b) Which postulate of Dalton's atomic theory can explain the law of conservation of mass?

(a) Postulates of Dalton's atomic theory:
(i) All matter is made up of very tiny indivisible particles called atoms.
(ii) All the atoms of a given element are identical in mass and chemical properties whereas those of different elements have different masses and chemical properties.
(iii) Atoms of different elements combine in a fixed whole number ratio to form compounds.
(iv) Chemical reactions involve reorganization of atoms. Atoms can neither be created nor be destroyed.

(b) Atoms can neither be created nor be destroyed in a chemical reaction, it can be changed from one form to another. So, this explains the law of conservation of mass.

#### Question 8:

An element Z contains two naturally occurring isotopes 35Z17 and 37Z17. If the average atomic mass of this element be 35.5 u, calculate the percentage of two isotopes.

Let the percentage of ${}_{17}{}^{35}\mathrm{Z}$ = X$0}{0}$
Then the percentage of ${}_{17}{}^{37}\mathrm{Z}$ = (100 $-$ X)$0}{0}$

The average atomic weight of Z = 35.5u

Now, the average atomic mass is given by,

$35.5=\frac{35.\mathrm{X}+37.\left(100-\mathrm{X}\right)}{100}\phantom{\rule{0ex}{0ex}}35.5=\frac{35\mathrm{X}+3700-37\mathrm{X}}{100}\phantom{\rule{0ex}{0ex}}35.5×100=3700-2\mathrm{X}\phantom{\rule{0ex}{0ex}}3550-3700=-2\mathrm{X}\phantom{\rule{0ex}{0ex}}-150=-2\mathrm{X}\phantom{\rule{0ex}{0ex}}\mathrm{X}=75$

Therefore, ${}_{17}{}^{35}\mathrm{Z}$ = 75%
And, ${}_{17}{}^{37}\mathrm{Z}$ = 100 - 75 = 25%

#### Question 9:

Can we apply Newton's third law to the gravitational force? Explain your answer.

Yes, Newton's third law can be applied to the gravitational forces. The gravitational forces are mutual too. The force applied by a planet on another planet is considered as an active force, in return, another planet also applies an equal and opposite force on the same planet. Which proofs Newton's third law.

#### Question 10:

Find the momentum of a body of mass 100 g having a kinetic energy of 20 J.

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

Mass of the body = 100 g

Kinetic energy = 20 J

Hence, the momentum of the body is 2 kg m/s.

#### Question 11:

Why cannot a sound be heard on the moon? How do astronauts talk to one another on the surface of the moon?

Sound waves need a medium to travel. As there is no atmosphere or medium on the moon, that's why no sound can be heard on the moon. Astronauts use radio waves while talking to one another on the surface of the moon.

#### Question 12:

Discuss why the pesticides are used in very accurate concentration and at very appropriate time.

Pesticides are chemical compounds which are used to kill the pests that destroy the crops. These chemical compounds are highly potent and toxic. These compounds should be used in a definite proportion because excessive concentration of pesticides can lead to the development of pesticide resistance. Moreover, the pesticides can contaminate water bodies through agricultural runoff, which increases during rainy season. Thus, it is essential to use pesticides at a specific time to minimise their harmful effects.

#### Question 13:

Draw a neat diagram of plant cell and label any three parts which differentiate it from animal cell.

The labelled diagram of a plant cell can be represented as follows: A typical plant cell differs from an animal cell in many respects. A plant cell is composed of cell wall, chloroplast and vacuole, which are not found in animal cells.

#### Question 14:

Why a person suffering from AIDS cannot fight even very small infections?

Acquired Immuno Deficiency Syndrome (AIDS) is a immunological syndrome which affects the immune system of an individual. This syndrome is caused due to Human Immunodeficiency Virus (HIV). This particular virus specifically attacks and destroys the immune cells (T-cells) of a person. The destruction of immune cells decreases the overall immunity of an individual and decreases the ability to fight small infections.

#### Question 15:

What is the greenhouse effect?

Greenhouse effect can be defined as the process of gradual increase in the temperature of Earth because of the presence of gases such as methane, carbon dioxide and water vapours. These gases do not allow infra-red radiations reflected by the surface of Earth to leave the Earth. This results in an increase in the global temperature called greenhouse effect.

#### Question 16:

(a) Differentiate between a saturated and an unsaturated solution. How will you test whether a given solution is saturated or not?
(b) How would you prepare a saturated solution of sodium chloride in water at 25° C? What will happen if this solution is cooled to 10° C?

(a)

 Saturated solution Unsaturated solution At a given temperature, the solution can no longer hold an additional quantity of solute. At a given temperature, the solution can hold an additional quantity of solute. They are considered as a concentrated solution, as the maximum amount of solute is dissolved in it. They are considered as dilute solutions, as an additional amount of solute can be added in it. To increase solubility, the temperature should be increased. They do no required rise of temperature to increase the solubility.

To test whether a given solution is saturated or not:
Add a single crystal of the solute.
(i) If the solution is unsaturated it will dissolve.
(ii)  If the solution is saturated it will not dissolve.

(b)  To prepare a saturated solution of sodium chloride in water at 25 °C, take 100 mL of water in a beaker and warm it up to 25 °C. Then add sodium chloride pinch by pinch at constant stirring and observe the point when no more sodium chloride is dissolving in water. At that point, the added sodium chloride will appear at the bottom of the beaker and your saturated solution is prepared.

On cooling, crystals of sodium chloride separate from the solution. This is a separation technique known as crystallization.

#### Question 17:

(a) Define atomic mass unit. What is its symbol?
(b) Define atomic mass of an element.
(c) What is meant by saying that 'the atomic mass of oxygen is 16'?

(a) Atomic mass unit is a unit of mass used to express atomic and molecular weights. 1 atomic mass unit is equal to one-twelfth of the mass of an atom of carbon-12. It is usually expressed as "amu".

(b) The atomic mass of an element is defined as the total number of protons and neutrons present in the nucleus of an atom.

(c) The atomic mass of oxygen is 16 which means that the total number of protons and neutrons present in oxygen are 16.

#### Question 18:

(a) State Newton's third law of motion and give two examples to illustrate the law.
​(b) Explain why, when a fireman directs a powerful stream of water on a fire from a hose pipe, the hosepipe tends to go backward.

(a) Newton's third law says that "For every action, there is an equal and opposite reaction". This can be understood by the two following examples:

(i) When we throw a ball to hit a wall in front of us, the ball comes back in our hands. This happens because, ball exerts a force on the wall but the wall exerts an equal and opposite force on the ball too, which brings the ball back in our hands.

(ii) Another example can be taken from walking of us on the ground. When we walk on the ground, we push the ground back by our feet, the ground applies an equal and opposite force in return that helps us to move forward.

(b) Newton's third law is applicable here. According to Newton's third law, for every action, there is an equal and opposite reaction. So, when the fireman directs the powerful stream of water, which is an action force, the hosepipe receives an equal and opposite reaction force. That's why hosepipe tends to move in a backward direction.

#### Question 19:

(a) What do you understand by the term 'acceleration due to gravity of earth'?
(b) What is the usual value of the acceleration due to gravity of earth?
​(c) State the SI unit of acceleration due to gravity.

(a) Due to gravitational forces, earth pulls other objects towards itself. The acceleration produced in a body due to the gravitational attraction of the earth is known as the acceleration due to gravity.

(b) The calculated value of acceleration due to gravity on earth is 9.8 m/s2.

(c) SI unit of acceleration due to gravity is the same as of the normal acceleration. i.e. m/s2.

#### Question 20:

Draw a well labelled diagram of eukaryotic nucleus. How is it different from nucleoid?

The diagram of a eukaryotic nucleus is as follows: A eukaroyic nucelus is different from a nucleoid in the following manner:

 Eukaryotic nucleus Nucleoid 1. Eukaryotic nucelus is a membrane enclosed cellular organelle, which is found in eukaryotes. 1. Nuceloid represents a non-membraneous compartment of the prokaryotic cell. 2. It is generally composed of multiple chromosomes. 2. It constitutes a single chromosome. 3. Nucleoplasm and nucleolus are found in eukaryotic nucleus. 3. Nucleoplasm and nucleolus are not found in nucleoid. 4. It is generally spherical in shape. 4. It has an irregular shape. 5.It has a well defined and organised structure. 5. The structure is poorly organised.

#### Question 21:

Explain the general characters of phylum Arthropoda. Give one example of following classes
​(i) Crustacea; (ii) Myriapoda; (iii) Insecta; (iv) Arachnida.

The general characteristics of phylum Arthropoda are as follows:
1. The animals of this phylum show bilateral symmetry, triploblastic origin and metameric segmentation.
2. The body segments are generally classified into two (cephalothorax and abdomen) or three (head, thorax and abdomen) regions.
3. Sexual dimorphism is observed in most of the organisms.

(i) Daphnia (water flea) belongs to the class Crustacea.

(ii) Julus (millipede) is an organism that belongs to the class Myriapoda.

(iii) Melanopus (grasshopper) has been classified under the class Insecta.

(iv) Sarcoptes (itch-mites) belong to the class Arachnida.

#### Question 22:

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?

The given chemical reaction can be written as: $2\mathrm{Ca}+{\mathrm{O}}_{2}\to 2\mathrm{CaO}$

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 = $\frac{5}{40}=0.125$

The number of moles of oxygen = $\frac{20}{32}=0.625$

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 =

Hence, the weight of the calcium oxide formed =

Law of conservation of mass is applicable to this equation.

#### Question 23:

The atomic number of an element X is 16.
(a) Write down the electronic configuration of X.
(b) What will be the valency of X?

(a) Electronic configuration of X = 2, 8, 6.

(b) Valency is the number of electrons participating in bond formation.
So, here X requires two electrons to attain noble gas configuration, so it will share 2 electrons with other elements and form a bond.

#### Question 24:

A stone and earth attract each other with an equal and opposite force. Why then we see only the stone falling towards the earth but not the earth rising towards the stone?

Stone and earth attract each other with an equal and opposite gravitational force. But, the mass of the earth is very large as compared to the mass of the stone. The gravitational force acting on the earth produces a negligible acceleration in the earth due to its high mass. Whereas mass of the stone is much smaller as compared to the earth, therefore, the same force produces a considerable acceleration in the stone. That's why we are able to see a stone moving towards earth but not earth moving towards the stone.

#### Question 25:

How does the kinetic energy of a moving body depend on its (i) speed, and (ii) mass?

(i) The kinetic energy of a body is directly proportional to the square of its velocity. i.e.

(ii) The kinetic energy of a body is directly proportional to its mass. i.e.

#### Question 26:

Name five economically important plant fibres derived from sclerenchyma. Why they differ in softness and durability?

Some of the economically important plant fibres are jute, ramie, hemp, flax and gelatinous fibre. These fibres differ in their softness and durability because of the difference in type of sclerenchyma cells from which these are obtained.

#### Question 27:

Write down four characters of mammals. Give two examples.