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Question 1:

What is the time of sowing rabi crops?

Answer:

Rabi crops are sown from November to the month of April.

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Question 2:

What chemical substance is deposited in the secondary wall of sclerenchyma?

Answer:

The secondary wall of sclerenchyma is composed of lignin.

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Question 3:

State whether the speed is a scalar or a vector quantity. Give a reason for your choice.

Answer:

Speed is a scalar quantity as it can be described by the only magnitude, we do not need direction while describing it.

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Question 4:

What conclusion can be obtained from the observation that when the prongs of a sound making tuning fork touch the surface of the water in a beaker, the water gets splashed?

Answer:

When the prongs of a sound producing tuning fork touch the surface of the water in a beaker, then we would see disturbances produced in the water in the form of ripples and waves. This shows that they vibrate.

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Question 5:

Which organisms are called primitive and how are they different form so-called advanced organisms?

Answer:

A primitive organism has a relatively simpler body design and structure. The body design of these organisms have not changed since their evolution. A typical example of primitive organism is an Amoeba. Advanced organisms, on the other hand, have complex body design and an advanced structural organization. An example of advanced organism is Homo sapiens.



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Question 6:

State two characteristic properties each of:
​(a) a solid (b) a liquid (c) a gas

Answer:

Property Solid Liquid Gas
1. Packing of particles Particles are packed very close to each other. Particles are packed less close to each other. Particles are packed very far from each other.
2. Force of attraction between the particles Strongest.  Weaker than solids. Negligible.
3. Shape and volume Fixed shape and fixed volume. No fixed shape but fixed volume. Neither fixed shape nor fixed volume.

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Question 7:

State three reasons why you think air is a mixture and water is a compound.

Answer:

Air is a mixture and water is a compound because:

1. Air contains different gases mixed together, which do not react to form any new compound. Whereas water is formed due to the chemical reaction between hydrogen and oxygen.

2. Air has a variable composition of its constituents, which depends on place to place. Whereas constituents of water i.e. hydrogen and oxygen are always found in a fixed ratio.

3. Air shows the properties of its constituents but the properties of water are entirely different than its constituents i.e. hydrogen and oxygen.

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Question 8:

Sodium carbonate reacts with ethanoic acid to form sodium ethanoate, carbon dioxide and water. In an experiment, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid to form 8.2 g of sodium ethanoate, 2.2 g of carbon dioxide and 0.9 g of water. Show that this data verifies the law of conservation of mass.

Answer:

2CH3COOH6 g+Na2CO35.3 g 2CH3COONa8.2 g+CO22.2 g+H2O0.9 g

Total mass of reactants = 6 g + 5.3 g = 11.3 g
Total mass of products = 8.2 g + 2.2 g + 0.9 g = 11.3 g

The total mass of the reactants = Total mass of the products.

So, from this, we can verify the law of conservation of mass.

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Question 9:

Explain the meaning of the following equation: p = m × v where symbols have their usual meanings.

Answer:

In the given equation: p = m × v, 'p' is the momentum and 'm' and 'v' are the mass and velocity respectively.

This relation shows that the momentum of a body is given by the product of its mass and velocity.
 

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Question 10:

The mass of the earth is 6 × 1024 kg and that of the moon is 7.4 ×1022 kg. If the distance between the earth and the moon be 3.84 × 105 km, calculate the force exerted by the earth on the moon. (G = 6.7 × 10−11 Nm2 kg−2​)

Answer:

The gravitational force between two bodies of masses m1 and m2 separated by the distance r is given by, F=Gm1m2r2

Mass of the earth = 6 × 1024 kg
Mass of the moon = 7.4 ×1022 kg
Distance between the earth and the moon = 3.84 × 105 km
G = 6.7 × 10−11 Nm2 kg−2

Hence, the gravitational force between the earth and the moon,

 F=6.67×10-11 Nm2kg-2 ×6×1024 kg ×7.4×1022 kg(3.84×108 m)2F=2.08×1020 N
 

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Question 11:

State whether the following objects possess kinetic energy, potential energy, or both:
(a) A man climbing a hill
(b) A flying aeroplane
​(c) A bird running on the ground

Answer:

(a) A man climbing a hill posses only potential energy by virtue of his height with respect to the ground.

(b) An aeroplane flies at a great height from the ground with a super high speed, so we can say that a flying aeroplane has both the potential and kinetic energies.

(c) A bird running on the ground has only kinetic energy because of its motion. 

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Question 12:

Why is the cell called the structural and functional unit of life?

Answer:

A cell is considered as the structural unit of life because cell constitutes the basic structure of living organisms. Every living organism and life form is made up of cells. Cells are also defined as the functional unit of life because most of the fundamental and life processes required for life are performed by cells. The metabolic reactions performed by cells forms the basis for all life processes. Thus, cells form the basic structural and functional unit of life.

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Question 13:

How do poriferan animals differ from coelenterate animals?

Answer:

The differences between proiferan and coelentrate animals are as follows:
 

Porifera Coelentrate
1. Cellular level of organisation is present. 1. Tissue level of organisation is present. 
2. Intracellular digestion is present. 2. Intracellular as well as extracellular digestion is present.
3. Appendages are not present. 3. Appendages in the form of tentacles are present.
4. Muscles and nerve cells are not present. 4. Muscles as well as nerve cells are present in these organisms.
5. Large number of incurrent pores and a single excurrent pore is present in the bodies of these organisms. 5. The body of these organisms is composed of a single opening.

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Question 14:

What do you mean by disease symptoms? Explain giving two examples.

Answer:

Symptoms refer to a set of collective indications, which can be used to ascertain a particular disease. These generally appear as functional and structural changes in the body or a part of the body. Symptoms serve as a clue for a physician to identify the associated disease. Some of the examples of symptoms are as follows:
1. Jaundice is characterised by the symptoms of fever and yellowish coloration of skin.
2. Constipation, diarrhoea, abdominal pain and head ache are the symptoms associated with typhoid.

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Question 15:

What are the causes of 'water pollution'? Discuss how you can contribute in reducing water pollution.

Answer:

The different causes of water pollution are as follows:
1. The dumping of sewage and household wastes into water bodies is a major reason for water pollution.
2. Industrial waste, which is discharged from factories and processing plants also contributes to water pollution.
3. Agriculture runoff can introduce fertilizers and pesticides into the water, which leads to water pollution.

Water pollution can be reduced by proper waste disposal, minimising agricultural runoff and bathing or washing of clothes in rivers should be avoided.

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Question 16:

(a) What is a mixture? Give two examples of mixtures.
​(b) What is meant by (i) homogenous mixtures, and (ii) heterogeneous mixtures? Give two examples of homogeneous mixtures and two of heterogeneous mixtures.

Answer:

(a) A mixture is a combination of two or more substances, which do not react with each other. Examples: sugar and water, sugar and sand, etc.

(b) (i) Homogenous mixtures: When two or more substances combine physically in a fixed ratio or a uniform composition, it is known as a homogeneous mixture. The homogenous mixture has no visible boundaries of separation. For e.g. Salt and water, sugar and water, etc.

(ii) Heterogeneous mixtures: When two or more substances combine in a non-uniform proportion, it is known as a heterogeneous mixture. It has visible boundaries of separation. For e.g. sand and water, oil and water, etc.
 



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Question 17:

(a) Describe Thomson's model of the atom. Which subatomic particle was not present in Thomson's model of the atom?
​(b) The mass number of an element is 18. It contains 7 electrons. What is the number of protons and neutrons in it? What is the atomic number of the element?

Answer:

(a) Thomson's model of an atom is similar to the model of plum pudding or watermelon. He said that the positive charge in an atom is spread all over like the red edible part of the watermelon. Also, electrons are embedded in the positively charged sphere like the seeds in the watermelon.

Explanation of Thomson' model:
(i) An atom consists of a positively charged sphere with electrons embedded in it.
(ii) The negative and positive charges present inside an atom are equal in magnitude. Therefore, an atom as a whole is electrically neutral.

Thomson only explained about electrons and protons, he did not take neutrons into consideration.

(b) Mass number of element = 18
Number of electrons = 7

For an atom, number of electrons = number of protons

Number of protons = number electrons = 7

Number of neutrons = (Mass number)-(number of protons)
Number of neutrons = 18-7
Number of neutrons = 11

The atomic number of an element is defined as the number of protons present. Therefore, the atomic number of the given element is 7.

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Question 18:

A scooterist covers a distance of 3 kilometres in 5 minutes. Calculate his speed in:
(a) centimetres per second (cm/s)
(b) metres per second (m/s)
​(c) kilometres per hour (km/h)

Answer:

(a) Distance covered by the scooterist = 3 km = 3×105 cm

Time taken = 5 minutes = 300 seconds

Speed = DistanceTime=3×105 cm300 s=1000 cm/s

(b) Distance covered by the scooterist = 3 km = 3×103 m

Time taken = 5 minutes = 300 seconds

Speed = DistanceTime=3×103 cm300 s=10 m/s

(c)  Distance covered by the scooterist = 3 km 

Time taken = 5 minutes = 560 hours

Speed = DistanceTime=3 km560h=36 km/h

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Question 19:

(a) When do we say that work is done? Write the formula for the work done by a body in moving up against gravity. Give the meaning of each symbol which occurs in it.
​(b) How much work is done when a force of 2 N moves a body through a distance of 10 cm in the direction of force?

Answer:

(a) Work is said to be done when an object is displaced in the direction of applied force.  Work, W=F×s (Where 'F' is the applied force and 's' is the displacement in the direction of the force)

When a body moves against gravity, work is done by the body against the force of gravity. Let the body moves up a height of 'h' against the gravity, then work done by the body = F×s=(mg)×h=mgh (Where 'm' is the mass, 'g' is acceleration due to gravity)

(b) According to relation work done = Force×Displacement=2 N×(10×10-2) m=0.2 J

Hence, the work done by the given force is 0.2 J.

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Question 20:

Distinguish between fertilizer and manure. Give suitable examples. What are advantages and disadvantages of using fertilizer?

Answer:

The differences between fertilizer and manure have been summarised as follows:

Fertilizer Manure
1. Fertilizer is a synthetic compound  which can be inorganic or organic. 1. Manure is a natural compound formed by the decomposition of natural substances.
2. It has a relatively higher concentration of essential nutrients such as phosphorous, nitrogen and potassium. 2. The concentration of essential nutrients is comparatively lesser in manures.
3. They do not contribute to the  formation of humus. 3. They contribute to the formation of humus.
4. They are costly and are prepared in factories. 4. They are cheap and can be prepared in home or fields.
5. Examples of fertilizers are urea, ammonium nitrate and sulphate of potash. 5. Some of the examples of manure are vegetable waste and compost.

The advantages of using fertilizers are as follows:
1. High nutrient specificity
2. Readily absorbed by the plants

The disadvantages of using fertilizers are as follows:
1. Reduction of soil fertility
2. Adverse affects on the soil microbes

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Question 21:

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

Answer:

The fluid mosaic model of the plasma membrane can be represented as follows:


Figure.1. Fluid mosaic model of plasma membrane.

The fluid mosaic model is used to describe the structure of the plasma membrane. This model was proposed by Nicolson and Singer in 1972. This model suggests that the plasma membrane is composed of lipids and proteins primarily. However, small amounts of carbohydrates can also be found in the plasma membrane. The proteins of the plasma membrane can be integral or peripheral membrane proteins. These proteins   move through the lipid bilayer, which gives plasma membrane a typical fluidic nature. 
 

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Question 22:

When a crystal of potassium permanganate is placed in a beaker, its purple colour spreads throughout the water. What does this observation tell us about the nature of potassium permanganate and water?

Answer:

When we place potassium permanganate crystals into the water, it's purple colour spreads throughout the water. This shows the diffusion of potassium permanganate in the water. Potassium permanganate has tiny particles, which get into the space between the water molecules. That's how its purple colour spreads throughout the water.

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Question 23:

The ion of an element has 3 positive charges. The mass number of atom of this element is 27 and the number of neutrons is 14. What is the number of electrons in the ion?

Answer:

Mass number of atom = 27
Number of neutrons = 14
Number of protons = Mass number-Number of neutrons
Number of protons = 27-14
Number of protons = 13

As the number of protons = Number of electrons
So, Number of electrons = 13
But the element has 3 positive(+3) charge that means this element has the deficiency of 3 electrons.
So, Number of electrons = 13-3 =10

Hence, the number of electrons in the given ion is 10.

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Question 24:

A body is thrown vertically upwards. Its velocity goes on decreasing. What happens to its kinetic energy as its velocity becomes zero?

Answer:

When a body is thrown up, it's velocity goes on decreasing, but its potential energy goes on increasing. The kinetic energy of the body gradually changes into the potential energy of the body as soon as it goes up above the ground. At the highest point, the velocity of the body becomes zero and all of the kinetic energy gets converted into potential energy. 



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Question 25:

On holidays, Rahul used to go to morning walk with his grandfather and on the way he used to collect milk from milk man for his home. One day, the milkman told dadaji that he is going to purchase a Murrah breed buffalo as he is not able to fulfill the demand of his customers to supply good quality milk. Rahul asked his grandfather following questions:
(i) What are Murrah buffaloes?
(ii) What are the advantages of keeping them in diary?

Answer:

(i) Murrah is a breed of buffalo, which originally belongs to Punjab and Haryana. This breed is characterised by large body size and short-curved horns.

(ii) The advantages of keeping Murrah buffaloes in diary are as follows:
1. These buffaloes can produce a large amount of milk during their lactation period. Typically 1800-2500 llitres of milk can be produced by these buffaloes.
2. These buffaloes are disease resistant.

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Question 26:

Why is immune system essential for our health?

Answer:

The immune system is essential for health because of the following reasons:
1. It acts as a defensive system and prevents the harmful affects of pathogens.
2. It also ensures that the different physical and biological functions of the body are effectively carried out.

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Question 27:

How does the atmosphere act as a blanket?

Answer:

Atmosphere maintains the temperature of our planet in a steady situation, neither too much high nor too much low. This happens because of a gaseous layer present in our atmosphere which prevents the extra heating by sunlight and also too much cooling at night by absorbing the heat. The atmosphere also has a preventive layer of ozone which does not allow harmful radiations like UV rays to enter our environment. So, in this way atmosphere acts as a blanket for our planet.



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