# CBSE Sample Papers for Class 10 Science Paper 7

## CBSE Sample Papers for Class 10 Science Paper 7

These Sample papers are part of CBSE Sample Papers for Class 10 Science. Here we have given CBSE Sample Papers for Class 10 Science Paper 7.

Time allowed: 3 hours
Maximum marks : 80

General Instructions

• The question paper comprises two sections, A and B. You are to attempt both the sections.
• All questions are compulsory.
• All questions of Section-A and B are to be attempted separately.
• There is an internal choice in two questions of three marks each and one question of five marks.
• Question numbers 1 and 2 in Section-A are one mark question. They are to be answered in one word or in one sentence.
• Question numbers 3 to 5 in Section-A are two marks questions. These are to be answered in 30 words each.
• Question numbers 6 to 15 in Section-A are three marks questions. These are to be answered in about 50 words each.
• Question numbers 16 to 21 in Section-A are 5 mark questions. These are to be answered in 70 words each.
• Question numbers 22 to 27 in Section-B are based on practical skills. Each question is a two marks question. These are to be answered in brief.

SECTION – A

Question. 1.
Look at the food chain : Plants → Sheep → Man. If plants had a total energy of 30000 joule what will be the amount of energy available to man ?

Question. 2.
How is the small intestine designed to absorb digested food ?

Question. 3.
Oil and fat containing food items are flushed with nitrogen. Why ?

Question. 4.
“A convex lens of focal length ‘ f ‘ can form a magnified, erect as well as inverted image.” Justify this statement stating the position of the object with respect to the lens in each case for obtaining these images.

Question. 5.
What are the smallest and thinnest blood vessels known as ? Why do they have such thin walls ?

Question. 6.
Define resistance. Write the SI unit of resistance and define it. Match the correct range of resistivity with the materials given.
(a) Conductors    (i) 10-6 Ωm
(b) Alloys             (ii) 1012 to 1017 Ωm
(c) Insulators       (iii) 10-6 to 10-8 Ωm
OR
The figure below shows three cylindrical copper conductors along with their face areas and lengths. Discuss in which geometrical shape the resistance will be highest.

Question. 7.
A circuit is shown in the diagram given below :

(a) Find the value of R.
(b) Find the reading of the ammeter.
(c) Find the potential difference across the terminals of the battery.

Question. 8.
(a) What is the importance of pH in everyday life ?
(b) How are sodium hydroxide and Cl2 gas are produced from common salt. What is this process called ?

Question. 9.
Define the terms :
(a) Mineral
(b) Ore
(c) Gangue.

Question. 10.
Distinguish between acquired trait and inherited trait giving an example of each.
OR
“Natural selection and speciation lead to evolution.” Is this statement correct justify it.

Question. 11.
Why are coal and petroleum categorised as natural resources. Why should they be used carefully ?

Question. 12.
A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located ?

Question. 13.
Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modem Periodic Table.
OR
Atomic number of a few elements are 10,20,7,14 :
(a) Identify the elements
(b) Identify the group number of these elements in the Periodic Table.
(c) Identify the periods of these elements in the Periodic Table.
(d) What would be the electronic configuration for each of these elements ?
(e) Determine the valency of these elements.

Question. 14.
What are unisexual and bisexual flowers ? What is pollination and the types of pollination ? Name the agents of pollination.

Question. 15.
What is a self-sustaining ecosystem ? Explain.

Question. 16.
A student fixes a sheet of white paper on a drawing board. He places a bar magnet at the centre of it. He sprinkles some iron filings uniformly around the bar magnet. Then he taps the board gently and observes that the iron filings arrange themselves in a particular pattern.
(a) Why do the iron filings arrange in a pattern ?
(b) What is indicated by the crowding of iron filings at the end of the magnet ?
(c) What do the lines along which the iron filings align represent ?
(d) Draw a neat diagram to show the magnetic field lines around a bar magnet.
(e) Write any two properties of magnetic field lines.

Question. 17.
Why are carbon compounds poor conductors of electricity and have low melting and boiling points ?
OR
What is the difference between the chemical composition of soaps and detergents ? State in brief the action of soaps in removing an oily spot from a shirt. Why are soaps not considered suitable for washing where water is hard ?

Question. 18.
What are reflex actions ? Give examples. Explain reflex arc by an example with labelled diagram ?

Question. 19.
You are given lenses with powers +10 D, + 5 D, – 5 D, – 20 D and -10 D. Taking a pair of lenses at a time, which two lenses will you select to have a combination of total focal length when the two lenses are kept in contact in each case.

(a) 20 cm
(b) – 10 cm
(c) – 20 cm
(d) $$\frac { 20 }{ 3 }$$ cm

Question. 20.
What is water of crystallisation ? Name some elements that have these water of crystallisation molecules.

Question. 21.
What are dams ? Give some examples of major dams in our country. State some benefits of constructing dams.
OR
What do you mean by watershed management ? What is its main aim ? What are the advantages of watershed management ?

SECTION – B

Question. 22.
When you add a pinch of sodium hydrogen carbonates to acetic acid in a test tube what happens ? Explain with a chemical equation.

Question. 23.
If we pour acetic acid on red litmus paper and blue litmus paper, what happens ?

(a) Red litmus remains red and blue litmus turns red.
(b) Red litmus turns blue and blue litmus remains blue.
(c) Red litmus turns blue and blue litmus turns red.
(d) Red litmus turns colourless and blue litmus remains blue.

Question. 24.
If you find coliform bacteria in a sample of potable water, what does it mean ? Explain.

Question. 25.
“The maximum concentration of harmful chemicals accumulates in human beings.” State the phenomenon involved and justify this statement.

Question. 26.
In an experiment to find the equivalent resistance of a series combination of two resistors R1 and R2, a student uses the circuit shown here. Will the circuit give the correct reading for current I and voltage V ? Justify your answer.

The given circuit diagram shows the experimental arrangement of different circuit components for determination of equivalent resistance of two resistors connected in series. Identify the components X, Y and Z shown in the circuit respectively.

Question. 27.
Study the ray diagram given below and answer the following questions :

(a) State the type of lens used in figure.
(b) List two properties of the image formed.
(c) In which position of the object will the magnification be – 1 ?

SECTION – A

We know that in a food chain only 10% of the energy moves to the next level. So by the 10% law, plants = 30,000 J, sheep will get 3,000 J energy, man will get 300 J energy.

Small intestine is the part in which maximum absorption of digested food occurs. It has numerous tiny finger like projections called villi which increases the surface area for maximum absorption of nutrients. The villi are richly supplied with blood vessels where nutrients are absorbed by the process of diffusion into the blood stream.

Oil and fat containing food items are flushed with nitrogen because it is an inert gas and does not easily react with these substances. On the other hand, oxygen reacts with food substances and makes them rancid. Thus, bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack. When oxygen is not present inside the pack, rancidity of oil and fat containing food items is avoided.

A convex lens of focal length’ f ‘ can form :

1. a magnified and erect image only, when the object is placed between the focus and the optical centre of the lens.
2. an inverted image, when the object is placed beyond the focus of the lens.

The smallest and thinnest blood vessels are known as capillaries. On reaching an organ or tissue, the artery divides into smaller and smaller vessels to bring the blood in contact with all individual cells. These small vessels are just one cell thick and are the capillaries. Their thin walls help in the exchange of material between the blood and the surrounding cells. The capillaries then join together to form the veins that carry blood away from the organ or tissue. They are in fact like a middle man between the arteries and the veins.

Resistance : The opposition offered by the material of a conducting wire to the flow of current through it is called resistance of the wire.

SI unit of resistance : Ohm (Ω), IΩ is defined as the resistance of a conductor which allows 1A of current through it when 1V potential difference is applied across its ends.

Matching :
(a) Conductors    (i) 10-6 Ωm
(b) Alloys            (iii) 10-6 to 10-8 Ωm
(c) Insulators       (ii) 1012 to 1017 Ωm
OR
For geometrical shape shown in :

Therefore, resistance of geometrical shape shown in figure (ii) will be highest.

(a) P.d. across 6 Ω = 12 V
∴ Current through 6 Ω, I = $$\frac { V }{ R } =\frac { 1 }{ 6 }$$ = 2 A
As R and 6 Ω are connected in series. So, the current through R is 2 A.
Using Ohm’s law, R = $$\frac { V }{ 1 } =\frac { 6 }{ 2 }$$ = 3 Ω
(b) Reading of ammeter = 2 A
(c) P.d. across the terminals of the battery
V = V1 + V2 = 6 + 12 = 18 V

(a) Our stomatch produces hydrochloric acid which helps in digestion of food. It has pH around 1.2. If excess acid is produced, it causes pain and irritation. It can be controlled by taking antacids which controls the pH in the stomach.
(b) Tooth enamel is the hardest substance in our body. It gets corroded slowly when pH in the mouth is below 5.5. Acid is produced in mouth due to degradation of food which is partially hydrolysed by saliva. But if excess acid is produced, it causes tooth decay.

(a) Mineral : It is naturally occurring substance from which metal may or may not be extracted profitably or economically, example, A1 cannot be extracted profitably from mica.
(b) Ore : A naturally occurring solid material from which a metal or valuable mineral can be extracted profitably. Example, Zinc blende is an ore of zinc from which zinc can be extraced profitably.
(c) Gangue: It is a rocky material which is present along with the mineral in the ore, example FeO is gangue in extraction of copper.

Acquired trait

1. These are traits that have been developed by the individual during his or her lifetime.
2. They are changes brought about in the non- reproductive tissues.
3. They cannot be inherited i.e. passed on to the progeny.
4. Some examples of acquired traits are muscular body, pierced ears etc.

Inherited trait

1. These are traits that have been inherited by the individual and so are present right from birth of the individual.
2. These are the result of changes that have happened intheDNA.
3. They are characters that will be transmitted to the progeny.
4. Some examples of inherited characters are skin colour, colour of the eyes, colour of the hair etc.

OR
Natural selection is the process by which nature selects those species which are most fit to survive in a given set of conditions. According to the theory of Natural Selection, there is a struggle for existence within the species of a population for the environmental resources and this struggle leads to the survival of the fit and capable organisms and the elimination of the less competent ones. During this struggle and competition some organisms may undergo genetic changes which helps them in their survival. These better adapted organisms would thus survive and pass on their traits to the next generation. After several generations, these changes would gradually lead to evolution. The formation of a new species from an existing one due to reproductive isolation of a part of its population is called speciation. Reproductive isolation can occur due to geographic isolation and with time  genetic drift will help accumulate different variations in each of the geographically isolated sub-populations. Ultimately individuals of these two groups will become reproductively isolated leading to the formation and evolution of a new species. Thus, we can say both natural selection and speciation lead to the evolution of a new species.

Natural resources are those living and non-living sources available in our environment which are exploited to meet the human requirements. Since coal and petroleum are actually the fossil remains of dead plants and animals respectively, they are considered as natural resources. Both coal and petroleum have been used as important sources of energy since a long time back. They were formed millions of years ago by the gradual degradation of biomass. Since these fossil fuels are non-renewable in nature and they have limited reserves, therefore, they need to be used judiciously or else they would get exhausted soon. That is why all human beings are repeatedly being asked to be careful in the use of these fossil fuels.

In this problem, we have been given magnification (m) and object distance (u). We are to find out the image distance (υ). Now,
Magnification, m = – 3 (Image is real)
Object distance, u = -10 cm (To the left of mirror)
Image distance, υ = ? (To be calculated)
Putting these values in the magnification formula for a mirror :

Thus, the image is located at a distance of 30 cm in front of the mirror (on its left side).

Mendeleev’s Periodic Table

1. Elements are arranged in the increasing order of their atomic masses.
2. There are a total of 7 groups and 6 periods.
3. Elements having similar properties were placed directly under one another.
4. Position of isotopes is not clear.
5. Electronic configuration cannot be predicted from the position of element

Modem Periodic Table

1. Elements are arranged in the increasing order of their atomic numbers.
2. There are a total of 18 groups and 7 periods.
3. Elements having the same valence shell are present in the same period while elements having the same number of valence electrons are present in the same group.
4. Position of isotopes is clear.
5. Electronic configuration can be predicted from the position of element.

OR

(a) Elements : Neon (Ne), Calcium (Ca), Nitrogen (N), Silicon (Si)
(b) Group : 18, 2, 15, 14
(c) Period : 2, 4, 2, 3
(d) Electronic configuration : (2,8) ; (2,8,8,2) ; (2,5) ; (2,8,4)
(e) Valency : 0, 2, 3, 4

Flowers may be unisexual or bisexual. Unisexual flowers may have either the male part calledstamen or the female part called the carpel. Some unisexual flowers are those of papaya, watermelon, pumpkin etc. Bisexual flowers have both the male part (stamen) and the female part (carpel). Some plants with bisexual flowers are hibiscus, mustard, clitoria, rose, sunflower etc.

The stamen consists of two parts, the slender filament and the anther on top. The anther contains the yellow colour pollen grains.

The carpel or pistil consists of three parts, stigma on top, style in the middle and the swollen ovary at the bottom.

The pollen grains contain the male gamete and once it lands on the stigma it develops a pollen tube through which the male gamete moves towards the female gamete which are the ovules in the ovary. Pollination is the process by which the pollen grains are transferred from the anther to the stigma of the flower which is sticky to hold the pollen grains.

When the pollen grains are transferred from the stamen to the stigma of the same flower it is called self-pollination.

When the pollen grains are transferred from one flower to the stigma of another flower it is called cross-pollination.

The agents of pollination are wind, water, insect animals,birds and even human beings

Living organisms like plants, animals, microorganisms and human beings as well as the physical surroundings interact with each other and maintain a balance in nature. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem. Thus, an ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, humidity, wind, soil and minerals. All the living organisms in an ecosystem interact with each other and their growth, reproduction and other activities are affected by the abiotic components of the ecosystem. We find this kind of healthy interaction both in the natural and artificial ecosystems.

In an ecosystem, organisms can be categorised as producers, consumers and decomposers depending on how they obtain their sustenance from the environment. Organisms depend on the producers either directly or indirectly for their sustenance. Consumers can be classified as herbivores, carnivores, omnivores and parasites.

Microorganisms have an important role to play in every ecosystem. Microorganisms like bacteria and fungi help to break down the dead remains of producers and consumers and convert them into simple inorganic substances that go back to the soil so that they can be used again by the plants. In this way there is a natural replenishment of the soil. This is how every ecosystem is said to be self- sustaining. However in the absence of these decomposers this replenishment process is affected. That is why it is very important that no part of the ecosystem is disturbed by our activities.

(a) When iron filings are placed in a magnetic field around a bar magnet they behaves likes a tiny magnet (by induction). The magnetic force experienced by these tiny magnets make them to rotate and align themselves along the direction of magnetic field lines. Thus, iron filling arrange themselves in a particular pattern.
(b) The crowding of iron filings at the end of the magnet indicates strong magnetic field at the ends of magnet.
(c) It represents the magnetic field lines around a bar magnet.
(d)

(e)
(i) The magnetic field lines never intersect each other.
(ii) Magnetic field lines are closed curve.

Carbon compounds are poor conductors of elctricity. Carbon has a valency of 4. To attain the stable configuration of noble gases, carbon atom needs to either gain or lose 4 electrons.

1. If it were to gain 4 electrons it would become C4- anion, but this makes it difficult to hold on to the 10 electrons.
2. If it were to lose 4 electrons it would become C4+ cation, but this means a lot of energy would be required to pull out the 4 electrons and leave the carbon atom with 6 protons and 2 electrons.

The easy way out is to share the 4 electrons with atoms of either carbon or other elements. The shared pair is then common to both the atoms. This bond formed by a sharing of electrons is called as covalent bond and such compounds are known as covalent compounds. As there are no charged particles available covalent compounds are poor conductors of electricity. They have low melting and boiling points also.
OR
Soaps are sodium or potassium salts of fatty acids having – COONa group whereas detergents are sodium or potassium salts of sulphonic acids having – SO3Na and – SO4Na group.
Cleansing action of soap: Soap molecules have two ends one is hydrophobic i.e., water repelling and other is water loving i.e., hydrophilic as shown in figure.

When a soap is dissolved in water, the molecules associate together as clusters called micelles in which water molecules, being polar in nature, surround the ions and the hydrocarbon part of the molecule attracts grease, oil and dirt.

Inside water, clusters of molecules are formed in which the hydrophobic tails are in the interior of the cluster and ionic ends are present on the surface of cluster. This formation is called micelle formation. To wash away the loosened dirt particles in the form of micelles from the surface of the cloth, it is either scrubbed mechanically, beaten or agitated in washing machine. In the form of a micelle, soap is able to clean, since the oily dirt is being collected in the centre of micelle.

Reflex action is a quick, automatic, involuntary, unconscious response in the body brought about by a stimulus. Examples of reflex action:

1. Withdrawal of hand suddenly on touching a hot plate.
2. Withdrawal of finger suddenly when pricked by a thorn.
3. Shivering of our body on feeling cold.
4. Sudden closure of our eyelids when bright light falls on our eye.

Reflex arc : It is the shortest route taken by impulse from receptor to effector.
Example : When we touch a hot plate by our finger, we instantly withdraw our hand. Here stimulus is touching a hot plate, receptors are our fingers. The specialized epithelial cells of our fingers respond to stimulus and convert into impulse. This impulse is carried by sensory neuron to spinal cord which generates a motor impulse. This impulse is carried by motor neuron to effector organ i.e., muscles of hand. Response is withdrawal of our hand.

Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt. When we heat the crystals, this water is removed and the salt turns white. 1 formula unit of CuSO4 has 5 water molecules so it is written as CuSO4.5H2O.

Gypsum is a salt which has water of crystallisation. It has 2 water molecules as water of crystallisation. When it is heated it loses the water molecules and becomes calcium sulphate hemihydrate (CaSO4.1/2H2O). This is called Plaster of Paris. It is a white powder and when mixed with water it changes again to gypsum which is a hard solid mass.

1. This substance is used as plaster for supporting fractured bones in the right position.
2. It is used for making toys, materials for decoration and for making smooth surfaces.

Dams are large water storage bodies built by government agencies to regulate the flow of water and utilize it for benefit of human beings. There are many dams constructed across major rivers in different parts of our country. For examples :

1. Bhakra dam across river Sutlej in Punj ab.
2. Tehri dam on river Ganga in Uttarakhand
3. Mettur dam on river Cauvery in Tamil Nadu.
4. Sardar Sarovar dam on river Narmada in Gujarat.
5. Hirakud dam on river Mahanadi in Odisha.

Some benefits of constructing dams are :

1. It stores adequate amount of water which can be used for irrigation.
2. Water can be supplied to villages and towns when there is shortage of water through pipelines.
3. It can be used to generate hydroelectricity.
4. It can be used for flood control.

OR
Watershed management is concerned with scientific soil and water conservation to increase the production of biomass.
Its main aim is to:

1. Develop land and water resources, to produce secondary resources of plants and animals without causing any ecological imbalance.
2. To implant the sustainable management of natural resources to improve the quality of living.
3. Improvement of quality of soil for better productivity.
4. Supplying clean and safe drinking water to all.

Advantages of watershed management are :

1. It enhances the life of downstream dam and reservoirs.
2. It minimizes the risk of droughts, landslides and floods.
3. It increases ground water level,
4. It increases crop production.
5. Various development activities like hydroelectric power generation, supply water for irrigation and other domestic uses.

SECTION – B

1. Brisk effervescence are evolved.
2. Evolution of a colourless and odourless gas.

The chemical equation for the reaction is :
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2

(a) Red litmus remains red and blue litmus turns red.

The presence of coliform bacteria in water indicates that water is contaminated by sewage as sewage contains human excreta. Human excreta contains a lot of disease causing microbes and when this sewage is dumped into rivers or lakes or ponds they get contaminated as coliforms from sewage will come into water.

Human beings are always placed at the top of a food chain. The harmful chemicals concentration (non-biodegradable substances) goes on increasing at every trophic level as a result as human beings are placed at the apex of every food chain so maximum concentration of harmful chemicals get accumulated in their body. This phenomenon is called biomagnification.

The circuit will give correct reading for current I but incorrect reading for voltage V. The voltmeter has to be put in parallel with the resistances being measured and not across the ammeter.
OR

• X represents the ammeter as it is connected in series.
• Y represents the voltmeter as it is connected in parallel.
• Z represents the rheostat (variable resistance).