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#### Question 1:

Name the smallest and the largest cell.

Smallest cell is Mycoplasma and the largest cell is an egg cell of Ostrich.

#### Question 2:

Name two countries that are centres of megadiversity.

Countries that are centres of megadiversity are India and USA.

#### Question 3:

A bus increases its speed from 20 km/h to 50 km/h in 10 seconds. Its acceleration is:
(a) 30 m/s(b) 3 m/s2 (c) 18 m/s2 (d) 0.83 m/s2

Initial speed of the bus = 20 km/h =

Final speed of the bus = 50 km/h =

Time taken by the bus to change its speed = 10 seconds

Acceleration of the bus =

Hence, the correct answer is option D.

#### Question 4:

What will happen if all blood platelets are removed from blood?

Platelets are responsible for the clotting of blood. If all the platelets are removed, then the blood will not be able to clot in case of an injury.
This would result in uncontrolled bleeding and could eventually lead to death.

#### Question 5:

What will happen if all blood platelets are removed from blood?

Platelets are responsible for the clotting of blood. If all the platelets are removed from the blood, it would lose its ability to clot.
This means, in case of an injury, the blood will not clot and would lead to uncontrollable bleeding. This would eventually result in the death of the organism.

#### Question 6:

(a) What is sublimation? Name two substance (other than ammonium chloride) which undergo sublimation.
(b) Draw a labelled diagram of the experimental set-up to demonstrate the sublimation of ammonium chloride.

(a) Sublimation can be defined as the process in which the solid phase of the matter directly converts to the gaseous phase. For eg. camphor, naphthalene.

(b) Setup to demonstrate the sublimation of ammonium chloride:

#### Question 7:

Give the formulae of the compounds formed from the following sets of elements:
(a) calcium and fluorine (b) hydrogen ans sulphur (c) nitrogen and hydrogen (d) carbon and chlorine
(e) sodium and oxygen (f) carbon and oxygen

(a) CaF2
(b) H2S
(c) NaH
(d) CCl4
(e) Na2O
(f) CO2

#### Question 8:

Describe bohr's model of the atom. How did Niels Bohr explain the stability of atom?

Niels Bohr proposed the following postulates regarding the model of the atom:

(i) Only certain orbits known as discrete orbits of electrons are allowed inside the atom.
(ii) While revolving in these discrete orbits, the electrons do not radiate energy.

These discrete orbits or shells are shown in the following diagram:

Bohr explained the stability of atom by proposing that electrons revolve around the nucleus in the definite circular paths having fixed energy and while moving in the same orbit they do not lose or gain energy.

#### Question 9:

(a) Define mass of a body. What is the SI unit of mass?
(b) Define weight of a body. What is the SI unit of weight?
(c) What is the relation between mass and weight of a body?

(a) Mass of a body is defined as the quantity of matter(Solid, liquid or gas) contained in the given volume of the body. Mass is a scalar quantity. SI unit of mass is kilogram.

(b) The force felt by a body towards the center of the earth due to earth's gravitational attraction is known as the weight of the body. The SI unit of weight is Newton.

(c) We know that Force = (Mass)$×$(Acceleration).

The weight of a body is actually the gravitational force applied by the earth.

Hence, we can write, Weight = (Mass)$×$(Acceleration due to gravity) = m$×$= mg

So, the weight of a body is given by the product of its mass and acceleration due to gravity.

#### Question 10:

(a) What is the meaning of the symbol kWh? What quantity does it represent?
(b) How much electric energy in kWh is consumed by an electrical appliance of 1000 watts when it is switched on for 60 minutes?

(a) 'kWh' symbol means kilowatt hour. kWh is a unit of energy. 1 kWh means the energy consumed when 1-kilowatt is used for 1 hour.

(b) The electrical energy consumed  by the appliance = Power of the appliance $×$ Time

= 1000 W $×$ 60 $×$ 60 s

= 3.6 $×$ 10J

#### Question 11:

(a) What is an echo? How is echo formed?
(b) What is the minimum distance in the air required from a sound reflecting surface to hear an echo (at 20° C)?

(a) An echo is basically a reflection of a sound wave. When a sound wave gets reflected by a hard surface and comes back to the listener with a little delay, then the reflected sound heard by the listener is known as the echo of the original sound wave.

An echo is formed when a sound wave reflects back towards its source after reflecting from a hard surface.

(b) The velocity of the sound at 20° C is 343 m/s.

Let the minimum distance in the air required to perceive an echo is 'x'

Minimum time required to perceive a sound by human, t = 0.1 s

Then,

Hence, minimum distance in the air required from a sound reflecting surface to hear an echo is 17.2 m.

#### Question 12:

Define intercropping. How does it differ with mixed cropping?

The technique of growing crops with different nutritional requirements (e.g., soyabean and maize) in alternate rows, in a definite pattern, to ensure maximum utilisation of nutrients is called intercropping.

 Mixed cropping Inter cropping Two or more crops are grown simultaneously but not in a definite pattern. Two or more crops are grown simultaneously in a definite pattern. Competition exists between the growing crops. No competition exists between the crops. Seeds are mixed before sowing. Seeds are not mixed before sowing. Helps to reduce the risk of crop failures due to unfavorable climatic conditions. Helps to increase the productivity of crops.

#### Question 13:

Distinguish between the following:
(a) Chromoplast and chloroplast
(b) Ribosome and centrosome

(a)

 Chromoplast Chloroplast Mainly contains the pigments carotene and xanthophyll. Mainly contains the pigment chlorophyll. Found in petals of flowers, skin of fruits etc. Found in the mesophyll cells of leaf. Have a role in imparting colour to plants. Have an important role in photosynthesis.

(b)
 Ribosomes Centrosomes Found in both plant and animal cells. Found only in animal cells. Play an important role in photosynthesis. Play an important role in cell division. Found scattered through out the cell. Found only near the nucleus.

#### Question 14:

Explain various modes of transmission of infectious diseases.

Different modes of transmission of infectious diseases are -

(a) Through air − The microorganisms that cause diseases such as influenza, chicken pox, etc., are transmitted through air as and when the infected person sneezes or coughs.

(b) Through water − The microorganisms that cause diseases such cholera, typhoid, etc., spread through contaminated water containing the faeces of infected individuals.

(c) Blood to blood contact − This occurs during blood transfusion, pregnancy, etc. For example - AIDS.

(d) Animal vectors − Insects carry disease-causing microbes in their saliva and transmit them to the healthy individuals by biting them. Malaria and dengue are spread in this way

(e) Direct physical contact − AIDS and syphilis are sexually-transmitted diseases.

#### Question 15:

Why is air called breath of life? Enumerate functions of air or atmosphere.

Air is called breath of life because it contains oxygen which is essential for us to survive. We take in oxygen and use it for our vital life processes. Absence of oxygen can cause immediate death of an organism.

Air is a mixture of various other types of gases. Each of this gas plays an important role -

• oxygen is required by living organism to carry out their vital functions
• carbon dioxide is used by plants to produce their food
• air is used in the process of combustion

#### Question 16:

How is water purified on a large scale at water works? Explain with the help of a labelled diagram. Name the substance which is added to kill germs in the drinking water supply.

The water is purified at a large scale in water treatment plants:
Following three steps are involved for purification of water at large scale:
1. Sedimentation: In this process, all the large impurities are removed from the water.
2. Filtration: In this process, the water is filtered through different types of filters that trap the minute impurities present in the water.
3. Disinfection: In this process, the water is disinfected to remove the remaining microorganisms from the water.

Water purification on a large scale can be done as shown below:

Chlorine gas is passed through the water to kill germs in the drinking water supply.

#### Question 17:

Explain the formation of (i) sodium ion, and (ii) chloride ion, from their respective atoms giving the number of protons and number of protons and number of electrons in each one of them. What is the reason for positive charge on a sodium ion and a negative charge on a chloride ion?

(i) Electronic configuration of sodium(Na) is 2, 8, 1. To attain noble gas configuration sodium atom will lose one electron and form sodium ion. As sodium loses one electron due to which sodium gets a positive charge on it.

Na = 2, 8, 1
Number of protons = 11
Number of electrons = 11
Na$+$ = 2, 8
Number of protons = 11
Number of electrons = 10

(ii) Electronic configuration of chlorine(Cl) is 2, 8, 7. To attain noble gas configuration chlorine atom will gain one electron and form chloride ion. As chlorine gain one electron due to which chlorine gets a negative charge on it.

Cl = 2, 8, 7
Number of protons = 17
Number of electrons = 17
Cl$-$ = 2, 8, 8
​Number of protons = 17
Number of electrons = 18

#### Question 18:

(a) What do you understand by term "balanced forces" and "unbalanced forces"? Explain with examples.
(b) What type of forces - balanced or unbalanced - act on a rubber ball when we press it between our hands? What effect is produced in the ball?

(a) Balanced forces are those forces whose resultant is zero. Unbalanced forces are those whose resultant is not zero.

When we push a box and it moves, that means it has some unbalanced forces working on it, or the resultant forces working on the box is not zero, that's why the box moved in the direction of the resultant force.

But, if we push a box and someone pushes the same box back from the other side with an equal and opposite force, then in that condition the box will not move. Because, the resultant force on the box would be zero, or we can say the forces are balanced on the box. So, there is no movement of the box.

(b) When we press a rubber ball between our hand, then forces acting on it are balanced, because the ball does not move when we press it. By pressing the ball between our hands, the ball gets deformed.

#### Question 19:

State and explain kepler's laws of planetary motion. Draw diagrams to illustrate these laws.

First law: Kepler's first law states that the planets move in elliptical orbits around the sun, with the sun at two foci of the elliptical orbit.

This law means that the motion of the planets around the sun follows an elliptical path, not a circle. As an ellipse has two foci, according to this law, the sun is considered to be situated at one of the foci.

Second law: Kepler's second law states that each planet revolves around the sun in such a way that the line joining the plant to the sun sweeps the equal areas in equal intervals of time.

This law means that a planet while revolving around the sun situated at one of the foci of their elliptical orbit, travels faster when it's close to the sun and slower when it is away from the sun.

#### Question 20:

Write short note on the following:
(a) Golgi apparatus
(b) Mitochondria

Mitochondria -
Mitochondria are double membraned structures i.e. they are enclosed by double membranes. The outer membrane is porous while the inner membrane is deeply folded. These folds are called cristae. They have their own DNA and proteins and hence are semi-autonomous in nature. It performs various kinds of functions like -

• 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

Golgi apparatus -
It consists of a system of membrane-bound vesicles arranged approximately parallel to each other in stacks of cisternae. It is usually composed of five−eight stacks of cisternae. Vesicles leave the Golgi body from the end known as the cis face. The other end is known as the trans face. Plant cells contain many freely distributed subunits of the Golgi apparatus, called dictyosomes. It performes functions like
• transport of lipids in cells
• formation of lysosomes
• takes part in glycosylation and phosphorylation  of certain proteins

#### Question 21:

Explain general characteristics of phylum platyhelminthes and Nematoda. Give two examples of each.

Characteristic features of phylum Platyhelminthes:

• The body is bilaterally symmetrical and flattened.
• The members of this phylum lack a body cavity. They are acoelomates.
• The digestive tract lacks an anus; an excretory pore is present instead.
• The members are mostly parasitic.
• Example − Taenia soliumFasciola, etc.

Characteristic features of phylum Nematoda:

• They are parasitic animals which cause diseases such as elephantiasis (filarial worms) and usually live in the intestine.
• A nematode has a cylindrical body with tapering ends.
• Nematodes have an organ system level of organization, but no real organs are formed due to the absence of a true coelom.
• They are bilaterally symmetrical and triploblastic.
• A false body cavity or pseudocoelom is present.
• Examples of nematodes: AscarisWuchereria (filarial worm)

#### Question 22:

If 16 g of oxygen contain 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.

1 mole of oxygen = $6.022×{10}^{23}$ atoms of oxygen

Mass of 1 mole of oxygen atom = 16 g

#### Question 23:

All the gases form cathode rays and anode rays when electricity is passed through them.
(a) What does the formation of cathode rays tell us about the atoms?
(b) What does the formation of anode rays tell us about the atoms?

(a) When electricity is passed through gases, electrical energy pushes out some electrons from the atoms of the gas. These fast-moving electrons form cathode rays. Thus, the formation of cathode rays shows that one of the subatomic particle present in all the atoms is the negatively charged "electron".

(b) When electricity is passed through gases, electrical energy pushes out some electrons from the atoms of the gas and a positively charged particle proton is formed. These fast-moving protons form anode rays. Thus, the formation of anode rays shows that one of the subatomic particle present in all the atoms is the positively charged "proton".

#### Question 24:

State two applications of the universal law of gravitation.

Applications of the universal law of gravitation are as follows:

(1) We use the universal law of gravitation to calculate the force that binds us to the surface of the earth.

(2) We can also use this law to study the motion of planets around the sun or the motion of the moon around the earth.

#### Question 25:

In loading a truck, a man lifts boxes of 100 N each through a height of 1.5 m.
(a) How much work does he do in lifting one box?
(b) How much energy is transferred when one box is lifted?
(c) If the man lifts 4 boxes per minute, at what power is he working?
(g = 10 m s−2)

(a) While lifting the boxes to a height of 1.5 m, the work is done by the man against the gravitational pull of the earth.

Work done against the gravity is given by, . (Where 'm' is the mass of the body, 'g'  is the acceleration due to gravity and 'h' is height  up to which the body is taken)

In the given case, weight of one box = mg = 100 N

Height up to which the man lift the box = 1.5 m

Work done by the man = mgh = 100 N $×$ 1.5 m= 150 J

(b) The work done by the man is stored in the box as the potential energy of the box by virtue of its height with respect to ground. So, when one box is lifted the total work done of 150 J is transfered to the box in form of energy.

#### Question 26:

Which structure protects the plant body against the invasion of parasites? How?

Epidermis provides protection to plants against the invasion of parasites. It forms an outer covering of plant organs which remains in direct contact with the environment. This epidermis is further covered by a layer of fatty substance called cuticle. The epidermis is interrupted only at regions where stomata are present. Anything that enters the plant, has to first cross this epidermal layer.

#### Question 27:

A weed is growing on the border of your playing ground. How will you recognise it to be a dicot or monocot?