DAV Solutions

The DAV Class 8 Science Book Solutions and DAV Class 8 Science Chapter 8 Question Answer – Conservation of Plants and Animals are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 8 Question Answer – Conservation of Plants and Animals

DAV Class 8 Science Ch 8 Solutions – Conservation of Plants and Animals

Something To Know

A. Fill in the blanks:

Question 1.
International Day for biological diversity is observed on ________ .
Answer:
May 22

Question 2.
A group of organisms, capable of interbreeding under natural conditions, is known as a ________ .
Answer:
species

Question 3.
________ species are the species that are found only in a particular area.
Answer:
endemic

Question 4.
________ is an important reserve for Project Tiger.
Answer:
Sunderbans Biosphere Reserve

Question 5.
________ sanctuary in Odisha is the breeding ground for the ‘giant olive ridley turtle’ which migrate here from the Pacific Ocean.
Answer:
Gahirmatha Turtle Sanctuary

B. Match the following:

Column I	Column II
(1) Rhinoceros	(a) Vulnerable
(2) Giant Panda	(b) Kaziranga National Park
(3) Flamingos	(c) Extinct
(4) Cheetah	(d) Endangered
(5) Passenger pigeon	(e) Migration

Answer:

Column I	Column II
(1) Rhinoceros	(b) Kaziranga National Park
(2) Giant Panda	(d) Endangered
(3) Flamingos	(e) Migration
(4) Cheetah	(a) Vulnerable
(5) Passenger pigeon	(c) Extinct

C. Tick (✓) the correct option:

Question 1.
Protection, and preservation of wildlife and natural resources is known as-
(a) Afforestation
(b) Preservation
(c) Deforestation
(d) Conservation
Answer:
(d) Conservation

Question 2.
The cheetah is a vulnerable species because-
(a) It is found in selected areas.
(b) It will be ‘extinct’ soon.
(c) It will be ‘endangered’ soon.
(d) Its hunting is banned.
Answer:
(c) It will be ‘endangered’ soon.

Question 3.
Plants found in a particular area are referred to as-
(a) Species
(b) Forest
(c) Flora
(d) Fauna
Answer:
(c) Flora

Question 4.
Which one of the following is not an outcome of deforestation in an area?
(a) Increased rainfall
(b) Increased temperature
(c) Decreased rainfall
(d) Decreased soil erosion
Answer:
(d) Decreased soil erosion

Question 5.
A region in which ‘conservation of biodiversity’ in its natural habitat is practiced is known as a—
(a) Botanical garden
(b) National park
(c) Aquarium
(d) Zoo
Answer:
(b) National Park

D. Answer the following questions in brief:

Question 1.
How have ‘urbanisation and industrialisation’ led to a large scale deforestation?
Answer:
Large areas of forest have been cleared to make way for urbanization and industrialization. Thus, urbanization and industrialization have led to a large scale deforestation.

Question 2.
A new species X is introduced in a forest. How is it likely to affect the local species of the area?
Answer:
The new species may prey on, or compete for resources with the existing species. Thus, introduction of a new species is generally harmful for the ecosystem of a forest.

Question 3.
What is a Biosphere Reserve? Name two biosphere reserves in India.
Answer:
Biosphere reserve is an international conservation designation given by the UNESCO under its programme on ‘Man and the Biosphere (MAB)’.
Two examples of biosphere reserves in India are: Nilgiri Biosphere Reserve and Nanda Devi Biosphere Reserve.

Question 4.
How does the ‘Red Data Book’ help in protecting biodiversity?
Answer:
Red Data Book provides the list of animals and plants whose continued existence is under threat. Thus, it helps in identifying the species at risk. Tirriely corrective measures can be taken to protect such species.

Question 5.
Why do some birds and animals migrate?
Answer:
Some birds and animals need to migrate in search of food and breeding places when conditions at a particular place become too harsh to continue living there.

Question 6.
How do birds ‘get helped’ in navigation while undertaking long distance flights?
Answer:
The precise methods by which animals and birds navigate are still obscure. But it appears that the birds and animals take the help of the Sun and stars, and possibly the earth’s magnetic field. This is achieved through an inbuilt ‘magnetic compass’, which is a tiny mass of tissue, between the eye and the brain in birds.

Question 7.
Distinguish between a National Park and a Wildlife Sanctuary.
Answer:
Most of the human activities are prohibited in a National Park. It is profected from human development and pollution. Whereas some human activities are permitted in a Wildlife Sanctuary. Hunting, killing or capturing of animals is prohibited in Wildlife Sanctuary.

E. Answer the following questions:

Question 1.
Explain how deforestation can result in droughts and floods.
Answer:
Trees help in reducing the flow of water. Thus, trees help in preventing soil erosion. Trees also help in rains by making immense contribution to atmospheric moisture by way of transpiration. Deforestation results in reduced and erratic rainfall which often results in droughts. Absence of obstruction from trees also results in excess water flow causing flood.

Question 2.
‘Extinction of tiger can destabilize the entire forest ecosystem and result in a large scale loss of biodiversity. ’ Justify this statement.
Answer:
Tigers are important components of an ecosystem. Being at the top of the food pyramid, tigers check the population of herbivores. This helps in preventing the green plants from being wiped out. Absence of tigers from the ecosystem would result in population explosion of herbivores. This will have disastrous consequences on the ecosystem.

Question 3.
Why are endemic species at a greater risk of becoming extinct? List the “human action related causes’ that are responsible for their extinction.
Answer:
Endemic species are adapted to live in limited areas. Any disturbance to their natural habitat can prove to be dangerous for their existence. Hence, they are at a greater risk of becoming extinct. Human related actions that are responsible for the extinction of endemic species are:

• Farming
• Deforestation
• Overgrazing
• Construction activities

Question 4.
The growing human population poses a grave threat to biodiversity.’ Justify this statement.
Answer:
Growing human population means that more land is required for farming, for making new houses and for making roads and industries. This necessitates deforestation. This also increases industrial activities which result in increased levels of environmental pollution. Thus, it destroys the biodiversity in the long run. Hence, it can be said that growing human population poses a grave threat to biodiversity.

Extinct species	Endangered species	Vulnerable species
These species do not longer exist on the earth.	These species face high risk of extinction in near future.	These species face high risk of extinction in medium term.
Examples: Dodo, passenger pigeon	Examples: Giant panda, Snow leopard	Examples: Cheetah, sloth bear

Question 6.
List five ways in which you, as an individual, can contribute to conserving forests and wildlife.
Answer:
The five ways by which one can contribute to conserving forests and wildlife are:

• Reducing the consumption of various items.
• Reusing old items.
• Recycling discarded items.
• By using public transport.
• By using bicycle wherever possible.

Value Based Question

Anil went to the house of his friend Rohan. They decided to draw a picture of their choice on a sheet of white paper. Not happy with their efforts, they crossed many sheets and threw them around. When Rohan’s elder sister saw them wasting paper, she, in a sweet voice, told them that they should not waste paper, just like that. She not only helped them to draw good pictures but also guided them to make interesting toys from the sheets they had thrown around. She explained to them how, by recycling and reusing paper, they can help in conserving/improving our ecosystem.

Question 1.
State the values displayed by Rohan’s elder sister.
Answer:
Rohan’s sister is polite, helpful and possess knowledge about the judicious use of resources.

Question 2.
Why do we say that wasting paper can damage our ecosystem?
Answer:
Paper is made from wood pulp. Trees need to be cut to make paper. So, wasting paper results in deforestation which harms the ecosystem. Hence, it is said that wasting paper can damage our ecosystem.

Question 3.
Have a group discussion in which each student gives his/her suggestions on recycling/reusing waste paper.
Answer:
Do it yourself

Something To Do

Question 1.
Find out about the different zones of a Biosphere Reserve and their significance. Also, prepare a list of all the Biosphere Reserves in India.
Answer:
Do it yourself

Question 2.
Collect information about ‘Hotspots of Biodiversity’. Find out about the flora and fauna of the ones in India and locate them on the map.
Answer:
Do it yourself

Question 3.
Prepare and present a photo essay on any one of the following topics:
(a) Medicinal plants: Preserving traditional Indian Wisdom.
(b) No good air to inhale: Deteriorating air quality of my city.
(c) Living in harmony; Reducing carbon footprints.
Answer:
Do it yourself

Question 4.
Project Tiger has been taken up on a massive scale by the Indian Government. Visit the website http://www.projecttiger.nic.in to find out what you can do to protect the tiger.
Answer:
Do it yourself

Question 5.
Visit the website http://www.wwfindia.org/help/greenliving_tips/ to gather more information about conservation of plants and animals.
Answer:
Do it yourself

DAV Class 8 Science Chapter 8 Solutions – Conservation of Plants and Animals Important Questions and Answers

I. Fill in the blanks:

1. Trees help in recharge of ________ .
Answer:
Groundwater

2. Greenhouse gases result in ________ .
Answer:
Global warming

3. Olive Ridley turtle is found in the state of ________ .
Answer:
Odisha

4. One-horned rhinoceros is found in the state of ________ .
Answer:
Assam

5. Gir National Park is the home of Asiatic ________ .
Answer:
Lions

II. Tick the correct answer:

Question 1.
Which of these is an extinct species?
(a) Dodo
(b) Blue whale
(c) Lion tailed macaque
(d) Asiatic lion
Answer:
(a) Dodo

Question 2.
Which of these is an endangered species?
(a) Blue whale
(b) Giant panda
(c) Snow leopard
(d) All of these
Answer:
(d) All of these

Question 3.
Which of these is an example of endemic species?
(a) Tiger
(b) Lion
(c) Elephant
(d) Kangaroo
Answer:
(d) Kangaroo

Question 4.
Red Data Book is mainly published by which organization?
(a) WWF
(b) UNESCO
(c) IUCN
(d) Department of Forest and Wildlife
Answer:
(c) IUCN

III. Answer the following questions:

Question 1.
What is an ecosystem?
Answer:
A natural unit consisting of all biotic and abiotic factors in an area is called ecosystem.

Question 2.
What do you understand by conservation?
Answer:
The protection, preservation, management or restoration of wildlife resources is known as conservation.

Question 3.
What is a national park?
Answer:
A national park is a reserve of land which is usually declared and owned by the national government. It is protected from most human development and pollution.

Question 4.
What is a wildlife sanctuary?
Answer:
A wildlife sanctuary is an officially designated territory, which provides protection and sustainable living conditions for wild animals. Hunting, killing or capturing of animals is strictly prohibited in such areas.

Question 5.
What is the difference between endangered species and vulnerable species?
Answer:
An endangered species is at the risk of extinction in near future, while a vulnerable species is at the risk of extinction in the middle term.

IV. Projects:

Question 1.
Find the name of national park or wildlife sanctuary in your state. Make a list of protected animal in this.
Answer:
Do it yourself

Question 2.
Make a project report about roles of WWF (World Wide Fund for Nature).
Answer:
Do it yourself

The DAV Class 8 Science Book Solutions Pdf and DAV Class 8 Science Chapter 7 Question Answer – Combustion are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 7 Question Answer – Combustion

DAV Class 8 Science Ch 7 Solutions – Combustion

Something To Know

A. Fill in the blanks:

Question 1.
A good fuel should have its ignition temperature ________ the room temperature.
Answer:
more than

Question 2.
Burning of cowdung cakes is an example of ________ combustion.
Answer:
slow

Question 3.
The ________ zone of a candle flame, is the coldest.
Answer:
innermost

Question 4.
The non-luminous zone of a candle flame is the ________ part of the flame.
Answer:
hottest

Question 5.
During incomplete combustion of a fuel, ________ gas is formed.
Answer:
carbon monoxide

B. State True or False for the following statements:

1. Coal is an inflammable fuel.
Answer:
False

2. The outermost part of a candle flame contains unburnt carbon particles.
Answer:
False

3. The heat produced, by burning completely one kilogram of a given fuel, is known as the efficiency of that fuel.
Answer:
True

4. All solid fuels have a higher calorific value than liquid and gaseous fluids.
Answer:
False

5. Sulphur dioxide gas, produced during combustion of fossil fuels, causes acid rain.
Answer:
True

C. Tick the correct option:

Question 1.
An example of a non-combustible substance is-
(a) Petrol
(b) Coal
(c) Wood
(d) Iron
Answer:
(d) Iron

Question 2.
A fuel starts burning only when it is heated to-
(a) Its boiling point
(b) Its ignition temperature
(c) Its melting point
(d) A temperature double of the room temperature
Answer:
(b) Its ignition temperature

Question 3.
The highest temperature zone of a candle flame, is its-
(a) Yellow zone
(b) Red zone
(c) Blue zone
(d) Orange zone
Answer:
(c) Blue zone

Question 4.
The amount of heat produced, on complete burning of 10 kg of a given fuel, in pure oxygen, equals H kilojoule. The calorific value, of that fuel, would equal-
(a) (0.1 H) kJ/kg
(b) (10 H) kJ/kg
(c) (H + 10) kJ/kg
(d) (H – 10) kJ/kg
Answer:
(a) (0.1 H) kJ/kg

Question 5.
The gas produced, due to incomplete combustion of carbon fuels, is-
(a) Carbon dioxide
(b) Carbon monoxide
(c) Sulphur dioxide
(d) Nitrogen dioxide
Answer:
(b) Carbon monoxide

D. Answer the following questions in brief:

Question 1.
Define the term ‘combustible material’? Give two examples of combustible materials.
Answer:
A material which can undergo combustion is called a combustible material.
Examples: Wood, coal

Question 2.
State the three conditions that are needed for combustion to take place.
Answer:
Following are the three conditions needed for combustion:

• A combustible substance
• Temperature should be more than ignition temperature
• Oxygen

Question 3.
State the condition under which ‘slow combustion’ of a material takes place.
Answer:
Slow combustion takes place in insufficient supply of air.

Question 4.
Define ‘calorific value of a fuel’.
Answer:
The amount of heat energy produced on burning 1 kg of a fuel is called the calorific value of a fuel.

Question 5.
State any two characteristics of an ideal fuel.
Answer:
The two characteristics of an ideal fuel are:

• It should have high calorific value.
• It should be cheap and easily available.

Question 6.
Why is water not used in controlling electrical fires?
Answer:
Normal water is a good conductor of electricity because it contains some dissolved salt. Using water against electrical fire has the risk of getting electric shock. Hence, water is not used in controlling electrical fires.

E. Answer the following questions:

Question 1.
Draw a diagram showing different zones of candle flame. Label the zone which contains:
(a) Unburnt vapours of wax
(b) Unburnt carbon particles
Answer:

Question 2.
Calorific value of wood is 18,000 kJ/kg. How much of wood is required to produce 360,000 kJ of heat energy?
Answer:
Calorific value of wood = 18,000 kJ/kg
∴ Amount of wood needed to produce 360,000 kJ of heat energy = \(\frac{3,60,000}{18,000}\) = 20 kg

Question 3.
Why are gaseous fuels considered better than liquid or solid fuels?
Answer:
Gaseous fuels are better than liquid or solid fuels because:

1. Gaseous fuels have higher calorific value.
2. These produce less amount of pollutants.
3. It is easier to transport and store gaseous fuels.

Question 4.
Why do we say that ‘burning of fuels’ can cause ‘health hazards’?
Answer:
Burning of fuels causes air pollution. Air pollution is detrimental to our health. Hence, it can be said that burning of fuels can cause health hazards.

Value Based Question

Ameeta was upset because she could not find hear black pencil and her coloured pencils set for completing her painting. Her elder sister, Suneeta helped her to locate them and guided her in colouring her painting. She then told her that we need to be careful as we often need to fulfill a number of conditions for completing our tasks. She gave the example of the phenomenon of ‘combustion’ and told her that combustion can be started and sustained, only if three conditions are simultaneously satisfied.

Question 1.
State the values displayed by Suneeta.
Answer:
Suneeta is helpful and intellectual.

Question 2.
State the three conditions that need to be simultaneously satisfied for starting and sustaining combustion.
Answer:
The three conditions which must be satisfied for starting and sustaining combustion are:
(i) A combustible substance
(ii) Temperature should be more than ignition temperature
(iii) Supply of oxygen or air

Question 3.
Ask the students to think of situations/tasks which need two or more conditions for their completion.
Answer:
Do it yourself

Something To Do

Question 1.
Conduct a survey of houses in your locality and find their average monthly consumption of LPG/PNG.
Answer:
One cylinder is generally sufficient for a household for a month. Students should <A» tkss.

Question 2.
Prepare a report on the precautions that should be taken while using CNG fuel in vehicles.
Answer:
Precautions that should be taken while using CNG fuel in vehicles are:
(i) Do not allow anybody to smoke near the CNG storage unit.
(ii) Do not burn firecrackers near CNG pumps.

Question 3.
Wastes’ have been traditionally disposed off by burning them. Waste combustors’ are used to dispose off hospital and industrial waste. Find out how these combustors work and their effects on the environment.
Answer:
Do it yourself

Question 4.
Find out about the different types of fire extinguishers. Write the type and locations of the fire extinguishers kept in your school.
Answer:
The different types of fire extinguishers are:

• Class A – fires involving solid materials such as wood, paper or textiles.
• Class B – fires involving flammable liquids such as petrol, diesel or oils.
• Class C – fires involving gases.
• Class D – fires involving metals.
• Class E – fires involving live electrical apparatus

DAV Class 8 Science Chapter 7 Solutions – Combustion Important Questions and Answers

I. Fill in the blanks:

1. Petrol is a highly ________ material.
Answer:
inflammable

2. Coal is capable of ________ combustion.
Answer:
slow

3. Spirit is capable of ________ combustion.
Answer:
rapid

4. Phosphorus is capable of ________ combustion.
Answer:
spontaneous

5. Calorific value of LPG is ________ than the calorific value of firewood.
Answer:
higher

II. Tick the correct answer:

Question 1.
Which of these is not required for combustion?
(a) Oxygen
(b) Combustible substance
(c) Carbon dioxide
(d) Ignition temperature
Answer:
(c) Carbon dioxide

Question 2.
Which of these shows spontaneous combustion?
(a) CNG
(b) LPG
(c) Diesel
(d) Sodium
Answer:
(d) Sodium

Question 3.
Which of these shows slow combustion?
(a) Firewood
(b) Petrol
(c) Kerosene
(d) LPG
Answer:
(a) Firewood

Question 4.
Which of these gases is evolved on incomplete combustion of a fuel?
(a) Sulphur dioxide
(b) Nitrogen oxide
(c) Carbon monoxide
(d) Hydrogen
Answer:
(c) Carbon monoxide

Question 5.
What is the colour of the innermost zone of a flame?
(a) Dark black
(b) Blue
(c) Yellow
(d) Red
Answer:
(a) Dark black

III. Answer the following questions:

Question 1.
What is ignition temperature?
Answer:
The lowest temperature at which a substance starts burning is called its ignition temperature.

Question 2.
What is slow combustion?
Answer:
When a combustive material burns at slow or moderate rate, it is called slow combustion. Examples: burning of cowdung cakes, wood, etc.

Question 3.
What is rapid combustion?
Answer:
When a combustible material burns at fast rate, it is called rapid combustion. Examples: burning of petrol and LPG.

Question 4.
What is spontaneous combustion?
Answer:
When a combustible material starts burning at room temperature, it is called spontaneous combustion. Example: Sodium and phosphorus catch fire at room temperature instantaneously.

Question 5.
What is explosive combustion?
Answer:
When a combustible substance completely burns in a very short period of time and releases lot of heat, light and gases, it is called explosive combustion. Examples: burning of firecrackers, gunpowder, etc.

IV. Projects:

Question 1.
Make a list of five combustible substances and five non-combustible substances in your household.
Answer:
Do it yourself

Question 2.
Look for items in your home which have warning sign of inflammable material on their packs. Make their list.
Answer:
Do it yourself

The DAV Class 8 Science Book Solutions Pdf and DAV Class 8 Science Chapter 6 Question Answer – Sources of Energy are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 6 Question Answer – Sources of Energy

DAV Class 8 Science Ch 6 Solutions – Sources of Energy

Something To Know

A. Fill in the blanks:

Question 1.
________ and ________ are non-renewable sources of energy.
Answer:
coal, petroleum

Question 2.
________ is a major renewable, natural resource.
Answer:
water

Question 3.
The process in which coal is strongly heated in the absence of air is known as ________ .
Answer:
destructive distillation

Question 4.
In oil wells ________ is always found above the layer of petroleum.
Answer:
natural gas

Question 5.
________ is a black viscous liquid, obtained by destructive distillation of coal.
Answer:
coal tar

B. State True or False for the following statements:

1. Fossil fuels are renewable natural resources.
Answer:
False

2. Anthracite has higher carbon content than lignite.
Answer:
True

3. Coke can be used to make fuel gases.
Answer:
True

4. Natural gas is found below the petroleum layers.
Answer:
False

5. Burning of fossil fuels is a major source of pollution.
Answer:
True

C. Tick (✓) the correct option:

Question 1.
The highest grade of coal is known as-
(a) Lignite
(b) Bitumen
(c) Anthracite
(d) Peat
Answer:
(c) Anthracite

Question 2.
Coke and coal tar are obtained from-
(a) Petroleum
(b) Coal
(c) Natural gas
(d) Diesel
Answer:
(b) Coal

Question 3.
Different types of coal generally have the-
(a) Same content of volatile material and same percentage of carbon
(b) Same content of volatile material but different percentage of carbon
(c) Different content of volatile material but same percentage of carbon
(d) Different content of volatile material as well as different percentage of carbon
Answer:
(d) Different content of volatile material as well as different percentage of carbon

Question 4.
A product, that is not obtained through the refining of petroleum, is
(a) Diesel
(b) Kerosene
(c) Coal gas
(d) Petrol
Answer:
(c) Coal gas

Question 5.
Which of the following is a renewable source of energy?
(a) Tidal energy
(b) Coal
(c) Diesel
(d) Petrol
Answer:
Tidal energy

D. Answer the following questions in brief:

Question 1.
Define the term ‘fuel’.
Answer:
A substance which produces heat on burning in air is called fuel.

Question 2.
Name any two renewable natural sources of energy.
Answer:
Wind energy, Solar energy

Question 3.
Define the term ‘carbonisation’.
Answer:
The process of conversion of dead plant materials into coal is called carbonization.

Question 4.
Name the three main products obtained from destructive distillation of coal.
Answer:
Petrol, diesel and kerosene

Question 5.
State two uses of each of the following:
(a) Asphalt
Answer:
Asphalt is used for making road and painting the underside of electric pole.

(b) Paraffin wax
Answer:
For making ointments and candles

Question 6.
Write the full forms of CNG, LPG and PNG.
Answer:
CNG: Compressed Natural Gas
LPG: Liquefied Petroleum Gas
PNG: Piped Natural Gas

E. Answer the following questions:

Question 1.
Describe, in brief, the process of ‘coal formation.
Answer:
Millions of years ago, plants got buried under the earth’s crust. In due course of time, those dead remains of plants got converted into coal due intense pressure and temperature inside the earth. The process of conversion of remains of plants into coal is called carbonization.

Question 2.
Differentiate between lignite and bituminous coal.
Answer:

Lignite	Bituminous coal
It contains about 38% carbon.	It contains about 65% carbon.
It is mainly used for power generation.	It is used for power generation and for making coke.

Question 3.
How do petroleum and natural gas occur in nature?
Answer:
Petroleum occurs in rock formations as crude oil. Crude oil is a dark, viscous and foul smelling liquid. Natural gas is found in oil wells above the crude oil.

Question 4.
State the main advantages of using natural gas.
Answer:
Advantages of using natural gas:

• It is a clean fuel.
• It is easy to transport natural gas through pipelines.
• Natural gas is economical than petrol and diesel.

Question 5.
Keeping in mind their availability in nature, explain the need of using coal and petroleum judiciously.
Answer:
Coal and petroleum are non-renewable resources. Their stock is going to be finished in near future. Hence, it is necessary to use them judiciously.

Value Based Question

The chemistry teacher, explained to her students that when petroleum, a naturally occurring fossil fuel, is separated into its different components, each of these components is useful in one way or the other. She then told her students that our daily life too can be thought of as ‘made up’ of a number of activities, actions and tasks. She suggested that ‘all of us’ should try to ensure and aim that all these ‘components’ of our daily life, are useful/helpful to the society at large.

Question 1.
State the values that you think are contained in the teacher’s talk and suggestions.
Answer:
Positive contribution of our activities to the society.

Question 2.
Name any three components, obtained from petroleum, and state any one use of each of them.
Answer:
Three components obtained from petroleum and their uses are as follows:

• Petrol: As fuel in cars.
• Diesel: As fuel in buses.
• Asphalt: For making road surface.

Question 3.
Have a ‘group discussion’ in which different students suggest “ways and means’ of making their different daily life actions and activities, useful to the society at large.
Answer:
Do it yourself

Something To Do

Question 1.
Make a report on ‘electricity consumption’ in your house. Suggest some ways that can help to reduce the consumption.
Answer:
Make the report yourself. Some ways to reduce electricity consumption are as follows:

• Switch off lights and fans when not in use.
• Do not use airconditioner until it is absolutely necessary.
• Use LED or CFL instead of incandescent bulbs.
• Use appliances with good energy rating.

Question 2.
Unlike thermal power plants, which burn fossil fuels and emit large amounts of carbon dioxide (a greenhouse gas) into the atmosphere, nuclear power plants use uranium (a metal) to produce huge amounts of energy from very small amount o fuel. However, they release harmful radiations that can pose a high risk to the population.
Do you think nuclear energy can be an answer to the problems caused by the use of fossil fuels? Try to prepare a report, listing points that suggest that nuclear power could be/could not be a better way of generating electricity as compared to fossil fuels.
Answer:
Replacing fossil fuels with nuclear energy can indeed help in reducing air pollution. But long term harms by potential leak of radiation is too costly for human life. Hence, nuclear energy cannot be a better way of generating electricity as compared to fossil fuels. We need to adapt other approaches for this; such as solar energy and hydel energy.

Question 3.
Try to find out information about the places/activities for which solar energy or wind energy is being put to use in place of conventional fossil fuel based energy sources.
Answer:
India has progressed significantly in the fields of solar energy and wind energy. Many solar power plants have come up in Rajasthan. Similarly, Tamil Nadu is the leading state in terms of wind energy.

DAV Class 8 Science Chapter 6 Solutions – Sources of Energy Important Questions and Answers

I. Fill in the blanks:

1. Battery is a ________ source of energy.
Answer:
Man-made

2. Firewood is used as ________ fuel in rural areas.
Answer:
Kitchen

3. LPG is used as ________ fuel.
Answer:
Domestic

4. CNG is used as fuel for ________ .
Answer:
Automobiles

5. Coal is a type ________ of rock.
Answer:
Sedimentary

II. Tick (✓) the correct answer:

Question 1.
Which of these is a man-made source of energy?
(a) Petrol
(b) Diesel
(c) Battery
(d) Wind energy
Answer:
(c) Battery

Question 2.
Which of these is non-renewable source of energy?
(a) Coal
(b) Hydel energy
(c) Solar energy
(d) Wind energy
Answer:
(a) Coal

Question 3.
Which of these produces lot of polluting gases on burning?
(a) LPG
(b) CNG
(c) Diesel
(d) All of these
Answer:
(c) Diesel

Question 4.
Coal mines are located at which of these places?
(a) Krishna Godavari Basin
(b) Bombay High
(c) Digboi
(d) Jharia
Answer:
(d) Jharia

Question 5.
A petroleum refinery is located at which of these places?
(a) Mathura
(b) Bokaro
(c) Bhilai
(d) Durgapur
Answer:
(a) Mathura

III. Answer the following questions:

Question 1.
What do you understand by non-renewable sources of energy?
Answer:
A source of energy which gets used up and cannot be recreated in a short period of time is called non-renewable source of energy. These are also called exhaustible source of energy, e.g. fossil fuels.

Question 2.
What is a fossil fuel?
Answer:
The fuels which were formed from dead remains of plants and animals are called fossil fuels.

Question 3.
What are the different types of coal?
Answer:
Peat, lignite, bituminous and anthracite are different types of coal.

Question 4.
What are the uses of coal gas?
Answer:
Uses of coal gas:

• It is used as domestic fuel.
• It is used as industrial fuel in those industries which are located near coal processing units.

Question 5.
Write a brief note on processing of coal.
Answer:
Coal is processed through destructive distillation. This is done by strong heating of coal in the absence of air. This helps in retaining useful contents of coal and removing unwanted components so that coal can produce optimum amount of energy. Coke, coal tar, and coal gas are also obtained during destructive distillation of coal.

IV. Projects:

Question 1.
Using a basket and aluminium foil, make a solar cooker. Demonstrate its working in your school.
Answer:
Do it yourself

Question 2.
What changes would you bring in your daily life to reduce environmental pollution? Make a project report.
Answer:
Do it yourself

These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 1 Notes – The Cell Its Structure and Functions act as excellent revision resources, particularly in preparation for board exams.

The Cell Its Structure and Functions Class 8 DAV Notes

→ Cell: The basic structural and functional unit of living organisms is called cell.

→ Discovery of Cell: Robert Hooke was the first scientist who observed thin slices of cork with the help of his self-designed microscope. He observed honeycomb-like structure and called the compartments as cell.

→ Celi Number: Some organisms are composed of a single cell. These are called unicellular organisms. Some organisms are composed of more than one cell. These are called multicellular organisms.

→ Cell Shape: The shape of cells differs in different organisms, as well as in different organs of the same organism. A cell may be oval, spherical, cuboidal, fibre-like or polygonal. The shape of a cell is influenced by its location and the function it serves.

→ Cell Size: The size of cells varies from 0.1 micron to 170 mm. Mycoplasma is a unicellular organism which is 0.1 micron in size. An egg of ostrich is the largest known living cell and is 170 mm in diameter.

→ Parts of a Cell: A cell is composed of protoplasm which is surrounded by a cell membrane. The protoplasm consists of cytoplasm and nucleus. There are a number of cell organelles in the cytoplasm and nucleus.

→ Cell Membrane: All living cells are bound by a thin membrane called plasma membrane or cell membrane. The cell membrane provides protection to the contents of the cell and controls the entry and exit of various substances as per a cell’s requirement.

→ Cell Wall: In plants, fungi and bacteria, the cell is surrounded by a cell wall in addition of the cell membrane also. Cell wall provides additional rigidity to the cell.

→ Cytoplasm: The part of the protoplasm which lies between the cell membrane and nucleus is called cytoplasm. It acts like a matrix for various cell organelles. It is made up of carbohydrates, proteins, fats, minerals, vitamins and water.

→ Nucleus: The nucleus lies in the centre of the cell. It controls all the activities of the cell. The protoplasm of the nucleus is called nucleoplasm. Nucleus is surrounded by a nuclear membrane. The nucleus has thread-like network called chromatin. The chromatin network is composed of chromosomes which become visible during cell division. Chromosomes are responsible for inheritance of characters.

→ Plastids: These are found in plant cells only. They are large and capsule-shaped. Plastids are in many colours. The green coloured plastids are called chloropiasts. Photosynthesis happens in chloroplast. Plastids are responsible for imparting colour to a plant part.

→ Mitochondria: Mitochondria are capsule-shaped structures. Cellular respiration takes place in mitochondria and energy is generated. Due to this, mitochondria are also called the powerhouse of the cell.

→ Endoplasmic Reticulum: It is a network of tube-like structures. It provides a skeletal framework to the cell and also facilitates transportation of substances.

→ Golgi Complex: These are sac-like structures stacked over one another. They store materials which are produced by cells. Due to this, Golgi complex is also called the store house of the cell.

→ Vacuole: These are fluid filled spaces inside cells. Vacuoles are very large in plant cells. Excess water and waste products are held in vacuoles. Food vacuoles are present in Amoeba.

→ Ribosomes: These are tiny granules which lie scattered in the cytoplasm. Ribosomes help in protein synthesis.

→ Cilia and Flagella: Some cells have special structures on them for locomotion. Paramecium has cilia, while Euglena has flagella.

Levels of Organisation in Organisms

→ Cellular Level: This level of organization is found in unicellular and in some simple multicellular organisms. In such organisms, a single cell is responsible for all life functions.

→ Tissue Level: This level of organization is found in some simple multicellular organisms in which a group of cells, i.e. tissue is responsible for all life functions.

→ Organ Level: Organisms; like hookworm and roundworm show organ level of organization.

→ Organ System Level: Many organs group together to form an organ system. Complex organisms show organ system level of organization.

→ Organism: An organism is an independent entity which can live on its own.

→ Cell : The basic structural and functional unit of living beings.

→ Cytology : The branch of biology in which we study about cells.

→ Protoplasm : The jelly like substance inside the cell.

→ Cytoplasm : The protoplasm which is present between cell membrane and nuclear membrane.

→ Nucleoplasm : The protoplasm which is present inside the nucleus.

→ Chromosomes : Rod-like stwctures inside nucleus which are responsible for transmission of genetic traits.

Comparison between plant cell and animal cell

Cell components	Plant cell	Animal cell
Cell wall	Present	Absent
Cell membrane	Present	Present
Plastids	Present	Absent
Mitochondria	Present	Present
Nucleus	Present	Present
Vacuoles	Large in size and more in number	Small in size and may be absent

The DAV Class 8 Science Book Solutions Pdf and DAV Class 8 Science Chapter 5 Question Answer – Friction are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 5 Question Answer – Friction

DAV Class 8 Science Ch 5 Solutions – Friction

Something To Know

A. Fill in the blanks:

Question 1.
Friction always ________ any relative motion between the two surfaces that are in contact with each other.
Answer:
opposes

Question 2.
Static friction is always ________ than sliding friction.
Answer:
greater

Question 3.
Sportsmen use shoes, fitted with spikes, to ________ friction between their shoes and the ground.
Answer:
increase

Question 4.
Sprinkling of talcum powder, on the carom-board , helps to ________ friction.
Answer:
decrease

Question 5.
Frictional force, on an object moving in a fluid, depends on its ________
Answer:
viscosity

Question 6.
The shape of an aeroplane is ________ to reduce, the effects of friction, due to air.
Answer:
streamlined

B. State True or False for the following statements:

1. When a body slides over smooth and wet surfaces, the amount of interlocking of irregularities, of the two surfaces in contact, increases.
Answer:
Flase

2. If a car moves eastwards, the force of friction acts southwards.
Answer:
Flase

3. Friction depends on how hard the two surfaces press against each other.
Answer:
True

4. The sole of shoes and the tyres of the vehicles are ‘treaded’ to decrease the effects of friction.
Answer:
Flase

5. Lubricants can be liquids, semi-liquids or solids.
Answer:
True

6. Friction can be increased by using ball bearings between the moving parts of machines.
Answer:
Flase

7. Fluid friction can be minimized by giving suitable shapes to the objects moving through the fluid.
Answer:
True

C. Tick (✓) the correct option:

Question 1.
Suppose your writing desk is tilted to a position where a book kept on it just starts sliding down. The figure, showing the correct direction of friction force acting on it is-

Answer:

Question 2.
Two boys are applying oppositely directed, and equal in magnitude, forces on a box as shown in the figure.

In such a case, the force of friction, that would exist between the lower end of the box and the ground, would be called-
(a) Sliding friction
(b) Fluid friction
(c) Static friction
(d) rolling friction
Answer:
Static friction

Question 3.
Four students were asked to arrange the (frictional) forces, due to rolling, static and sliding friction, in an increasing order. Their arrangements are listed below. The correct arrangement is-
(a) Rolling, static, sliding
(b) Rolling, sliding, static
(c) Static, sliding, rolling
(d) Static rolling, sliding
Answer:
(b) Rolling, sliding, static

Question 4.
The energy, ‘used up’ in overcoming friction, gets converted mainly into-
(a) Sound energy
(b) Heat energy
(c) Light energy
(d) Chemical energy
Answer:
(b) Heat energy

Question 5.
Rahul rolls a ball on a wooden surface. The ball covers a certain distance before coming to rest. To make the same ball cover a (much) longer distance, before coming to rest, Rahul should-
(a) Spread a newspaper on the wooden surface
(b) Spread a towel on the wooden surface
(c) Sprinkle talcum powder on the wooden surface
(d) Spread a jute bag on the wooden surface
Answer:
(c) Sprinkle talcum powder on the wooden surface

Question 6.
A block is sliding on a horizontal surface. The force of friction between the two can be increased by-
(a) Decreasing the area of contact of the block with the surface.
(b) applying a layer of some lubricant on the surface.
(c) By polishing the surface.
(d) By putting a second identical block on top of the given block.
Answer:
(d) By putting a second identical block on top of the given block.

D. Answer the following questions in brief:

Question 1.
Define the terms (a) static friction (b) sliding friction.
Answer:
When a force is applied on an object to move it over a surface, the counter force which opposes the applied force to prevent the motion is called static friction. When one surface is moving over another surface, the frictional force between them is called sliding friction.

Question 2.
State the meanings of the terms (a) rolling friction (b) fluid friction.
Answer:
When an object is rolling over a surface, the force of friction opposing this motion is called rolling friction.
When an object is moving through a fluid, the frictional force due to the fluid is called fluid friction.

Question 3.
State the likely cause of friction.
Answer:
The causes of friction are:

• Nature of the two surfaces in contact
• Force pressing the two surfaces towards each other

Question 4.
A box is resting on the floor. To move it, a (variable) force is applied as shown in the diagram below.

(a) Give the (likely) value of the force of limiting friction.
Answer:
2F

(b) Why does the box stay at rest in the cases corresponding to Fig (a) and Fig (b)?
Answer:
In these situations, static friction is equal to or greater than the applied force. Hence, the box stays at rest in these cases.

(c) Mark the direction of frictional force, and mention the kind of frictional force that comes into play, in each case.
Answer:
In all the cases, direction of applied force is towards right. Hence, the direction of frictional force is opposite to this, i.e. towards left.

Question 5.
Name the kind of frictional force, that comes into play, when a book, kept on a collection of cylindrical pencils, is moved by pushing it.
Answer:
Rolling friction

Question 6.
Why are objects given special shapes when they are moving through fluids? Write the name given to these special shapes.
Answer:
A streamlined shape helps in overcoming the fluid friction. Hence, object that are moving through fluids are given special shapes.

E. Answer the following questions:

Question 1.
Define force of friction. List the factors affecting the force of friction. Explain with examples.
Answer:
When two surfaces are in contact and one of them is moving in relation to the other, a counter force opposes this motion. This force is called force of friction. Following factors affect the force of friction:

• Nature of the two surfaces in contact
• Force pressing the two surfaces towards each other

It is difficult to walk over a path which is covered with pebbles. But it is easier to walk over a smooth road. This happens because rough surface gives more friction than a smooth surface. It is easier to slide a light box compared to a heavier box. This shows that the force pressing the two surfaces towards each other affects the friction.

Question 2.
A ball is moved to roll down an inclined wooden plane from a given height. At the foot of the inclined plane, it moves on a horizontal surface, differently ‘covered’, one by one, as shown in the following figures.

In which case, is the ball likely to move the longest distance? Give reason for your answer.
Answer:
The ball is likely to move the longest distance in case ‘C” because of the plane glass sheet. A glass sheet is highly smooth compared to a woollen cloth or a newspaper. So, the glass sheet would offer the least amount of friction.

Question 3.
Explain why sliding friction is slightly less than static friction.
Answer:
Once an object begins to move over a surface, the interlocking between the two surfaces gets removed. Due to this, sliding friction is slightly less than static friction.

Question 4.
Give reasons for the following:
(a) We tend to slip when we step on a banana peel.
Answer:
A banana peel provides very low amount of friction. Due to this, it can easily move over a surface. Hence, we tend to slip when we step on a banana peel.

(b) It is easier to push a lighter box than a similar heavy box on the same floor.
Answer:
A lighter box results in less amount of force that is pressing the box against a surface. On the other hand, a heavier box results in more amount of force pressing the box against a surface. So, it is easier to push a lighter box than a similar heavy box on the same floor.

(c) The force, needed to start a car, is (somewhat) greater than the force needed to keep it moving with a uniform speed.
Answer:
When a car is static and is about to move, static friction comes into play. When a car is moving, sliding friction comes into play. We know that static friction is more than sliding friction. Due to this, the force needed to start a car is somewhat greater than the force needed to keep it moving with a uniform speed.

(d) Sportsmen use shoes fitted with spikes.
Answer:
Spikes help in increasing the friction by creating more interlocking with the surface. This helps a sportsman to get better grip while running. Hence, sportsmen use shoes fitted with spikes.

(e) Ball bearings are used in machines.
Answer:
Ball bearings change sliding friction into rolling friction. Rolling friction is less than sliding friction. Hence, ball bearings are used in machines to reduce the amount of friction.

(f) Tyres of the vehicles need to be changed regularly.
Answer:
Tyres of vehicles wear off in the long run due to friction. Thus, tyres’ surface becomes smooth after prolonged use; which is not good for driving. Hence, tyres of the vehicles need to be changed regularly.

(g) Machine parts are frequently oiled or greased.
Answer:
Oil or grease helps in reducing friction. This helps in smooth running of the machine parts. This also prevents wear and tear of machine parts. Hence, machine parts are frequently oiled or greased.

(h) Sports cars, aeroplanes and boats are designed to have a streamlined shape.
Answer:
Streamlined shape helps in reducing fluid friction. This helps in increasing the performance of sports cars, aeroplanes and boats. Hence, sports cars, aeroplanes and boats are designed to have a streamlined shape.

(i) Metal chains are wrapped on tyres when they run on icy roads.
Answer:
Icy surface offers least amount of friction. It is very difficult to drive over an icy surface. Metal chains are wrapped on tyres to increase friction. This helps in better control on vehicle while driving on icy roads.

(j) Rollers are used for transporting luggage.
Answer:
We know that rolling friction is less than sliding friction. Rollers help in converting sliding friction into rolling friction. This makes it easier to move heavy luggage. Hence, rollers are used for transporting luggage.

Question 5.
State and explain, with examples, how friction can help the cause of motion in certain situations.
Answer:
Walking on a frictionless surface is almost impossible. Road’s surface is always made rough so that walking or driving becomes easier. Writing on a smooth and shiny surface is very difficult. But writing on a rough surface is quite easy. These examples show that friction is the cause of motion in certain situations.

Value Based Question

Ramit and Kush, both students of Class VIII, would often strongly argue with each other about the different aspects of their day to day school life. However, they made a very good ‘double team’, of their school, for the interschool badminton tournaments. When playing together, they would forget all their differences and play as a ‘team’ to ensure their school’s victory.
Their science teacher, who was also their badminton coach, would quote their example. He would explain to his students how the force of friction can be a ‘good friend’ and ‘a source of help’ even though it was usually viewed only as a ‘trouble maker’.

Question 1.
State the values displayed by Ramit and Kush.
Answer:
Team work, and overcoming difference of opinions.

Question 2.
Give two examples of situations in which the force of friction is a ‘source of help’.
Answer:
Opening a bottle of pickle can be difficult because of the layer of oil on bottle cap. But holding the cap with a rough towel helps in opening the bottle. The towel helps in increasing the friction, and thus helps in opening the bottle cap.

Treads of tyres of a tractor are very large. A tractor needs to traverse through muddy fields where lot of friction is required for smooth movement of tractor. This example shows that a friction can be a source of help.

Question 3.
Stage a play in which different members of two teams give examples to show that the force of friction is (i) a friend (ii) a foe.
Answer:
Do it yourself.

Something To Do

Question 1.
Imagine that friction force vanish suddenly. Write a short story/play on how would our lives be affected.
Answer:
Do it yourself

Question 2.
List some sports/games where friction is a ‘help’ or ‘a source of trouble’. Discuss your list with your friends with some supporting picture.
Answer:
Do it yourself

Question 3.
In the Activity 1 of this chapter, what is likely to happen if you change the angle which the tray makes with the table top? Does the angle, made by the inclined plane with respect to horizontal, affect the sliding? Discuss your findings with your teacher. Does the angle (at which sliding just starts) depend on the nature of the two surfaces in contact? Find the answer using different materials/toy cars and so on.
Answer:
Do it yourself

DAV Class 8 Science Chapter 5 Solutions – Friction Important Questions and Answers

I. Fill in the blanks:

1. Friction works in ________ direction of motion.
Answer:
opposite

2. In case of ________ friction, the two surfaces are not in relative motion.
Answer:
static

3. In case of ________ friction, the two surfaces are in relative motion.
Answer:
sliding

4. The motion of a wheel has to encounter ________ friction.
Answer:
rolling

5. A fish has ________ body shape.
Answer:
streamlined

II. Tick (✓) the correct answer:

Question 1.
Which of these surfaces would offer the least friction?
(a) Sand paper
(b) Velvet paper
(c) Wax paper
(d) Normal paper
Answer:
(c) Wax paper

Question 2.
Which of these vehicles runs on an air cushion?
(a) Metro rail
(b) Hovercraft
(c) Helicopter
(d) Aeroplane
Answer:
(b) Hovercraft

Question 3.
Which of these can be a good lubricant?
(a) Oil
(b) Grease
(c) Air cushion
(d) All of these
Answer:
(d) All of these

Question 4.
Which of the following surfaces is safe to walk on?
(a) Marble floor
(b) Paved footpath
(c) Ice skating ring
(d) Wet floor
Answer:
(b) Paved footpath

III. Answer the following questions:

Question 1.
Name the factors which affect friction.
Answer:
Factors affecting friction are:

• Nature of two surfaces in contact.
• Forces pressing the two surfaces together.

Question 2.
What is rolling friction?
Answer:
When a body rolls over a surface, the force of friction which comes into play is called rolling friction.

Question 3.
How can we say that friction is a necessaiy evil?
Answer:
Friction leads to wear and tear of many things and decreases efficiency. So, friction is an evil. Due to this, friction is called a necessary evil.

Question 4.
What is fluid friction?
Answer:
When an object moves through a fluid (liquid or gas), the friction offered by the fluid is called fluid friction. Fluid friction is also known as drag.

Question 5.
What do you understand by streamlined bodies?
Answer:
A body which is spindle-shaped is called streamlined. A streamlined body has to encounter least amount of friction, while moving through a fluid. Birds and fishes have streamlined bodies. Similarly, aeroplanes, boats and ships have streamlined bodies.

IV. Projects:

Question 1.
Take four marbles. Wrap one marble with chocolate wrap, second one with aluminium foil and the third one with sandpaper. Leave the fourth marble without a wrap. Now, roll these marbles on a smooth surface and measure the time they take to cross a certain distance. Note down your findings and correlate them with friction.
Answer:
Do it yourself

Question 2.
Name five daily activities in which friction helps you in completing a task.
Answer:
Do it yourself

The DAV Class 8 Science Book Solutions Pdf and DAV Class 8 Science Chapter 4 Question Answer – Force and Pressure are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 4 Question Answer – Force and Pressure

DAV Class 8 Science Ch 4 Solutions – Force and Pressure

Something To Know

A. Fill in the blanks:

Question 1.
For a force to come into play, two concerned bodies must ________ with each other.
Answer:
interact

Question 2.
To draw water from a well, we have to ________ the rope.
Answer:
pull

Question 3.
An unbalanced force, acting on a moving object, may change its ________ and/ or its ________.
Answer:
velocity, direction

Question 4.
In the game of cricket, the hails’ fall when the ball strikes them. This is an example of a/an ________ force.
Answer:
electrostatic

Question 5.
The force, responsible for raising our body hair, when we try to take off a synthetic (terylene or polyster) shirt in dry weather conditions, is an ________ force.
Answer:
unbalanced

Question 6.
The atmospheric pressure ________ as we move towards higher altitudes.
Answer:
decreases

B. State True or False for the following statements:

1. The effect of a force may change by changing the direction of the applied force.
Answer:
True

2. A force has to be specified both in terms of its magnitude as well as its direction.
Answer:
True

3. Frictional force is an example of a non-contact force.
Answer:
False

4. A gas filled balloon moves up. The upward force, acting on it is smaller than the force of gravity, i. e. the downward acting force.
Answer:
False

5. We can reduce the pressure of a given force by increasing the area over which the force acts.
Answer:
True

6. Inside a bottle filled with water, pressure is least at the bottom and the greatest at the surface of water.
Answer:
False

C. Tick the correct option

Question 1.
When two forces, applied on an object, are equal and opposite, then the forces-
(a) May move the object
(b) May stop a moving object
(c) May move the object and also cause a change in its shape.
(d) Do not move the object but may cause a change in its shape.
Answer:
(d) Do not move the object but may cause a change in its shape.

Question 2.
The following are the names of the well known force
A. Gravitational force
B. Muscular force
C. Magnetic force
D. Frictional force
Out of these, the ‘contact forces’ are the forces labelled as:
(a) A and B
(b) B and C
(c) B and D
(d) C and D
Answer:
(c) B and D

Question 3.
Rohini is pushing a box towards the west direction with a force of magnitude F.
To help her move the box faster in the same direction, her friend should-
(a) Push the box in the east direction with a force of magnitude F.
(b) Pull the box in the west direction with a force of magnitude F.
(c) Push the box in the west direction with a force of any magnitude.
(d) Push the box in the east direction with a force of any magnitude.
Answer:
(c) Push the box in the west direction with a force of any magnitude.

Question 4.
A container is filled with water as shown in the figure below.

Which of the following statements is correct about the pressure of water in the container?
(a) Pressure at A > pressure at B > pressure at C
(b) Pressure at C > pressure at B > pressure at A
(c) Pressure at A = pressure at B = pressure at C
(d) Pressure at A < pressure at B > pressure at C
Answer:
(b) Pressure at C > pressure at B > pressure at A

Question 5.
An empty metal bottle has a to be placed on a table so that is exerts the maximum pressure on the surface of table?

For this, the bottle needs to be placed in the position (s) labelled as:
(a) Position A
(b) Position B
(c) Position C
(d) Position A and C
Answer:
(b) Position B

Question 6.
When we press the bulb of a dropper, with its nozzle kept under water, air in the dropper is seen to escape in the form of bubbles. If we then release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to:
(a) Pressure of water in the container
(b) Weight of the bulb
(c) Gravity of the earth
(d) Atmospheric pressure
Answer:
(d) Atmospheric pressure

Question 7.
The length, breadth and height, of a given rectangular box, are 100 cm, 50 cm and 20 cm respectively. This box is kept on ground in three different ways, one by one. Which of the following statements is correct about the pressure exerted by this box on the ground?
(a) The pressure exerted is maximum when the ‘length’ and ‘height’ sides form the base.
(b) The pressure exerted is maximum when the ‘length’ and ‘breadth’ sides form the base.
(c) The pressure exerted is maximum when the “breadth’ and ‘height’ sides form the base.
(d) The pressure exerted remains the same irrespective of which of its ‘sides’ form the base.
Answer:
(c) The pressure exerted is maximum when the “breadth’ and ‘height’ sides form the base.

D. Answer the following questions in brief:

Question 1.
In the following situations, identify the agent exerting the force. Also, state the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to extract its juice.
Answer:
Agent of force: fingers, Effect: change in shape

(b) A person diving into a swimming pool.
Answer:
Agent of force: Person’s muscles, Effect: change in motion

(c) A labourer moving a loaded cart.
Answer:
Agent of force: Labourer, Effect: change in motion of cart

(d) A car coming to rest once its engine is switched off.
Answer:
Agent of force: Friction from road, Effect: change in motion

(e) An athlete making a high jump to clear a bar kept at a certain height.
Answer:
Agent of force: Muscles, Effect: change in motion

Question 2.
An object experiences a net non-zero force. Is it possible for the object to move with a constant speed along a straight line?
Answer:
When an object experiences a net non-zero force, it is not possible for the object to move with a constant speed along a straight line.

Question 3.
Distinguish between
(a) Balanced and unbalanced forces.
Answer:
When net force on an object is zero then it is called balanced force. When the net force on an object is non-zero, it is called unbalanced force.

(b) Contact and non-contact forces.
Answer:
When a force needs to contact an object to exert its influence it is called contact force. When a force can exert its influence without touching or contacting with the object, it is called non-contact force. Muscular force is an example of contact force. Magnetic force is an example of non-contact force.

Question 4.
When we throw a ball upwards, what happens to its speed while it is going up? Give reason for your answer.
Answer:
When we throw a ball upwards, its speed gradually decreases. It happens because of force of gravity is working in opposite direction of the motion of the ball.

Question 5.
The figure shows a man with a parachute.

(a) Name the force which is responsible for his downward motion. Is it a contact force or a non-contact force?
Answer:
Force of gravity. It is a non-contact force.

(b) Will the man come down with the same speed without the parachute? Explain.
Answer:
Without a parachute, the man will come down with faster speed. Air drag works in presence of parachute, and reduces the speed. But negligible air drag works in absence of parachute.

Question 6.
How would the pressure (exerted by a force on an area) change if
(a) The area is doubled keeping the thrust constant?
Answer:
Pressure will become half.

(b) Thrust is doubled keeping the area constant?
Answer:
Pressure will become double.

Question 7.
When will a diver ‘experience a greater pressure’; 100 cm below the surface of water or 200 cm below the surface of water? Justify your answer.
Answer:
Pressure of fluid increases with increase in depth. Hence, the diver will experience a greater pressure at 200 cm below the surface of water.

E. Answer the following questions:

Question 1.
Define force. Is it necessary for the two bodies to be in direct contact for a force to exist between them? Explain with examples.
Ans. A push or a pull is called force. Contact (direct or indirect) between two bodies is necessary for contact force to exist between them. No contact is necessary for non-contact force to act between them. A horse makes a contact with the cart by means of harness; to apply muscular force on the cart. A magnet can pull iron nail even from a distance.

Question 2.
State three effects of a force. Give suitable examples.
Answer:
Three effects of force are as follows:
Force can change the state of motion: When you kick a football, the football comes into motion.
Force can change the direction of motion: When a batsman hits a ball, direction of motion of the ball changes.
Force can change shape: Dough is changed into chapatti because of force applied by a rolling pin.

Question 3.
Give reasons for the following statements:
(a) ‘Snow shoes’ are more effective than ordinary shoes for walking on snow.
Answer:
Snow shoes have very wide base and thus a larger area on which force is being applied by the feet. Greater area results in less pressure. Hence, a snow shoe is more effective than ordinary shoes for walking on snow.

(b) Porters place a large round piece of cloth on their heads when they carry heavy loads.
Answer:
The round piece of cloth helps in increasing the area on which force acts. This helps in reducing pressure. It makes it easier to carry the load on the head.

(c) A sharp knife cuts vegetables and fruits more effectively than a blunt knife.
Answer:
A sharp knife provides smaller area on which the thrust works. This creates more pressure. Hence, it is easier to cut vegetables and fruits with a sharp knife rather than with a blunt knife.

(d) School bags are provided with wide straps to carry them.
Answer:
Wide straps provide more area. This helps in reducing pressure on shoulder. It becomes comfortable to carry the school bag. Hence, school bags are provided with wide straps.

(e) It is much easier to burst an inflated balloon with a needle than (directly) with the finger.
Answer:
The tip of the needle has much smellier area than the tip of a finger. So, the tip of the needle creates more pressure than finger. Hence, it is much easier to burst an inflated balloon with a needle than directly with the finger.

(f) Mountaineers may suffer from nose bleeding at high altitudes.
Answer:
Air pressure reduces as we go to higher altitudes. At higher altitudes, air pressure is less than blood pressure. Due to this, blood starts oozing out of the capillaries in nose.

(g) Airplanes have pressurized cabins for passengers’ safety while flying high in the atmosphere.
Answer:
Air pressure reduces as we go to higher altitudes. Low air pressure can be highly uncomfortable for air travellers. Hence, airplanes have pressurized cabins for passengers’ safety while flying high in the atmosphere.

Question 4.
Two rods ‘A’ and ‘B’, of the same weight and equal length have different thicknesses. A boy, while playing with them on a beach, held them vertically on the surface of sand as shown in the figure. Which one of them will sink less? Explain.

Answer:
We know that pressure varies directly with thrust and inversely with area on which force is applied. For equal amount of force, a smaller area would result in greater pressure. Hence, rod A will sink more while rod B will sink less.

Question 5.
Three holes, A, B and C, are made in an empty can at different levels, one over the other, as shown in the figure. They are (temporarily) closed with an adhesive tape. The can is now filled with water. What will you observe, when the tape (on all of them) is pulled out? Justify your answer.

Answer:
Water will start to gush out of three holes. Water from hole A will go to maximum distance because pressure is highest at bottom. Water from hole C will go to the least distance because of the least pressure.

Question 6.
Make two tiny holes of the same size, at equal heights from the bottom in a plastic bottle. Cover them and fill the bottle with water. Let the covers be now removed. State the observations, and the resulting conclusions based on this activity.

Answer:
Water will start gushing out of two holes. As the holes are at the same height so water will reach same distance. This happens because of same pressure.

Question 7.
Discuss in brief the variation in atmospheric pressure with altitude. Do changes in temperature also cause a change in atmospheric pressure?
Answer:
Atmospheric pressure decreases with increase in altitude. For constant volume, pressure increases with increase in temperature. In other words, at constant volume, pressure is directly proportional to temperature.

Value Based Question

On coming back from school, Anudit asked his mother to explain to him the concepts related to the addition/subtraction of forces acting along the same line. Mother explained to him the reason for adding such forces when they act along the same direction and of subtracting, one from the other, when they act along mutually opposite directions. She went on to say that, in a similar manner, we get an ‘added up and enhanced effect’, when we use our strength, hard work and attention together, for achieving our desired goal.

Question 1.
State the Values’ conveyed by Anudit’s mother.
Answer:
Combined effect of strength, hard work and focus.

Question 2.
Write down the magnitude and direction of the net force in the following situations:
(a) In tug of war, Team A is applying a force of 100 N along the east direction and Team B is applying a force of 200 N along the west direction.
Answer:
100 N along west direction

(b) A boy is pushing a box with a force of 100 N towards left by overcoming a force of friction that has a magnitude of 50 N.
Answer:
50 N towards left

(c) Have a group discussion in which students give examples of ‘combined’ and ‘similarly directed efforts’ of a number of individuals, producing enhanced/better ‘positive results’.
Answer:
Do it yourself

Something To Do

Question 1.
Design your own barometer to predict weather.
(Use an empty jar, a long necked bottle, coloured water and a marker pen.)
Note the changes in the marked level over a period of a few weeks and ‘predict weather’ on the basis of your observations.
Hint: Higher marked level indicates high air pressure and fine weather, lower marked level indicates low air pressure; this may cause a stormy weather.
Answer:
Do it yourself

Question 2.
How is pressure related to force and area?
Design an experiment/activity to explain how this inverse relationship, between pressure (due to a given force) and area, is used in daily life.
Answer:
Do it yourself

Question 3.
Force and pressure are two different concepts though at times we tend to use these two words interchangeably. Collect some pictures, or draw cartoons, to bring out the difference between the two.
Answer:
Do it yourself

DAV Class 8 Science Chapter 4 Solutions – Force and Pressure Important Questions and Answers

I. Fill in the blanks:

1. A ________ or ________ is called force.
Answer:
Push, pull

2. The SI unit of force is ________ .
Answer:
Newton

3. The unit of pressure is ________ .
Answer:
Pascal

4. Force of friction acts in ________ direction to the direction of motion.
Answer:
Opposite

5. The earth attracts everything towards itself because of force of ________ .
Answer:
Gravitation

II. Tick the correct answer:

Question 1.
In which of the following cases, the net of two forces would be non-zero?
(a) When forces are acting in the same direction
(b) When forces are acting in opposite directions
(c) Both ‘a’ and ‘b’
(d) None of these
Answer:
(c) Both ‘a’ and ‘b’

Question 2.
Which of the following is an example of contact force?
(a) Force applied by a magnet
(b) Force applied by a charged body
(c) Gravitational force
(d) Force applied by a horse on a cart
Answer:
(d) Force applied by a horse on a cart

Question 3.
Which device is used for measuring atmospheric pressure?
(a) Barometer
(b) Thermometer
(c) Milemeter
(d) Speedometer
Answer:
(a) Barometer

Question 4.
In case of which of these, the atmospheric pressure would be very low?
(a) On a hot sunny day
(b) On a cold day
(c) On a stormy day
(d) During night
Answer:
(c) On a stormy day

Question 5.
In which of the following cases, the direction of motion can change?
(a) When force is being applied in the direction of motion
(b) When force is being applied at an angle to the direction of motion
(c) When force is being applied parallel to the direction of motion
(d) All of these
Answer:
(b) When force is being applied at an angle to the direction of motion

III. Answer the following questions:

Question 1.
What are the effects of force on state of motion?
Ans. Force can change the state of motion of an object. If an object is in the state of rest, it can be changed into state of motion by force. If an object is in the state of motion, it can be changed into state of rest by force. Force also changes the direction of motion and rate of motion.

• If a force is applied on a body in the direction of motion, it increases the speed.
• If a force is applied on a body in the opposite direction of motion, it decreases the speed.
• If a force acts at an angle to the direction of motion, it changes the direction of motion.

Question 2.
What do you understand by balanced forces?
Answer:
When the net of different forces acting on a body is zero they are called balanced forces.

Question 3.
What do you understand by unbalanced forces?
Answer:
When the net of different forces acting on a body is not zero they are called unbalanced forces.

Question 4.
Explain contact forces and their types.
Answer:
When a force can be applied only through physical contact with a body it is called contact force. Following are some examples of contact forces:

• Muscular Force: Force applied by the muscles of humans or animals is called muscular force. When a horse is pulling a cart, it is applying muscular force.
• Frictional Force: When two surfaces are in motion in relation to each other, a force acts between them and opposes the motion. This force is called force of friction or frictional force. The direction of force of friction is opposite to the direction of motion.

Question 5.
What do you understand by pressure?
Answer:
When a force is applied perpendicular to a given surface area, this force is called thrust. Thrust acting on a unit area of a surface is called pressure.
Pressure = \(\frac{\text { Thrust }}{\text { Surface area over which it acts }}\)
A bigger surface area means less pressure for the given thrust, compared to a smaller surface area.

IV. Projects:

Question 1.
Make a list of five activities in daily life in which you need to increase pressure for accomplishing a task.
Answer:
Do it yourself.

Question 2.
Make a list of five activities in daily life in which you need to decrease pressure for accomplishing a task.
Answer:
Do it yourself.

The DAV Class 8 Science Book Solutions Pdf and DAV Class 8 Science Chapter 3 Question Answer – Metals and Non-metals are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 3 Question Answer – Metals and Non-metals

DAV Class 8 Science Ch 3 Solutions – Metals and Non-metals

Something To Know

A. Fill in the blanks:

Question 1.
The property, due to which a metal piece can be hammered into thin sheet, is known as ________ .
Answer:
Malleability

Question 2.
Bronze is an alloy of ________ and ________.
Answer:
copper, tin

Question 3.
Gold is mixed with ________ and/or ________ to make it hard.
Answer:
copper, silver

Question 4
________ the only non-metal to have a natural lustre.
Answer:
graphite

Question 5
________ is a non-metal which catches fire in air.
Answer:
phosphorus

Question 6.
The only metal, which exists in the liquid state at room temperature is ________.
Answer:
mercury

B. Match the following:

Column I	Column II
(1) Hardest substance	(a) Bromine
(2) Aluminium ore	(b) Graphite
(3) A non-metal, normally, existing in liquid state	(c) Bauxite
(4) A good electrical conductor	(d) Diamond
(5) A metalloid	(e) Arsenic

Answer:

Column I	Column II
(1) Hardest substance	(d) Diamond
(2) Aluminium ore	(c) Bauxite
(3) A non-metal, normally, existing in liquid state	(a) Bromine
(4) A good electrical conductor	(b) Graphite
(5) A metalloid	(e) Arsenic

C. Tick (✓) the correct option:

Question 1.
The two most abundant metals, found in the earth’s crust, are-
(a) Aluminium and copper
(b) Aluminium and iron
(c) Iron and copper
(d) Iron and silver
Answer:
(b) Aluminium and iron

Question 2.
The metals, used in making the alloy ‘german silver’, are-
(a) Copper + zinc + tin
(b) Copper + zinc + nickel
(c) Copper + nickel + tin
(d) Copper + nickel + cobalt
Answer:
(b) Copper + zinc + nickel

Question 3.
When a metal reacts with oxygen, the resulting oxide of the metal-
(a) Is a neutral oxide
(b) Turns blue litmus red
(c) Is an acidic oxide
(d) Is a basic oxide
Answer:
(d) Is a basic oxide

Question 4.
Out of the metals, gold, silver, copper and aluminium, the one, that is most ductile is-
(a) Gold
(b) Silver
(c) Aluminium
(d) Copper
Answer:
(a) Gold

Question 5.
Two of the metals, that cannot be stored either in air, or under water, are-
(a) Sodium and magnesium
(b) Magnesium and calcium
(c) Calcium and potassium
(d) Potassium and sodium
Answer:
Potassium and sodium

D. Answer the following questions in brief:

Question 1.
Name (i) one metal and (ii) one non-metal which normally exist in the liquid state.
Answer:
Mercury (metal) and Bromine (non-metal) exist in liquid state.

Question 2.
State the fraction of gold present in an 18 carat gold piece.
Answer:
Fraction of gold in 18 carat gold = 18/24 = 3/4

Question 3.
State the property of copper wires that makes them useful for electrical fittings.
Answer:
Copper is a good conductor of electricity, and it is highly ductile. Moreover, copper is economical too. Due to this, copper is ideal for electrical fittings.

Question 4.
Define an alloy.
Answer:
A homogenous mixture of two or more metals or a metal and non-metal is called alloy.

Question 5.
List any two uses of non-metals.
Answer:
Following are the two uses of non-metals:
(i) Phosphorus is used for making matchsticks.
(ii) Diamond is used for cutting glass sheets.

E. Answer the following questions:

Question 1.
Write the balanced equations for the following reactions:

(a) Sodium reacts with oxygen
Answer:
4Na + O₂ → 2Na₂0

(b) Aluminium reacts with dilute hydrochloric acid
Answer:
2Al + 6HCl → 2AlCl₃ + 3H₂

Question 2.
Why are gold and platinum suitable for making jewellery?
Answer:
Gold and platinum are highly malleable. They are noble metals; which means they do not lose lustre in the long run. Hence, gold and platinum are suitable for making jewellery.

Question 3.
‘Sodium and potassium is stored under kerosene’. Give reason.
Answer:
Sodium and potassium are highly reactive metals. They readily react with oxygen in air or in water. The reaction is highly exothermic. The reaction mixture quickly catches fire. Sodium and potassium are stored under kerosene to prevent their reaction with oxygen.

Question 4.
Why is bronze preferred over copper metal for making statues?
Answer:
Bronze is harder, stronger and more resistant to corrosion than copper. Hence, bronze is preferred over copper for making statues.

Value Based Question

The chemistry teacher, while teaching her students, explained to them the differences between ‘metals’ and ‘non-metals’. She told them that both of them react with the same gas; oxygen but their resulting oxides are ‘opposite’ in nature.
She then went on to say that, in a somewhat similar way, we could use our stay in the school either.
(a) To gain knowledge learn good manners and develop, and tone up, different skills or
(b) To indulge in idle gossip and other frivolous and irrelevant activities.

Question 1.
State two of the Values’ that the teacher conveyed to her students.
Answer:
Good manners and learning new skills

Question 2.
Give one example each of the reaction of a (i) metal, (ii) non-metal, with oxygen to explain the ‘opposite nature’ of the oxides formed in the two cases.
Answer:
Magnesium ribbon burns in air to produce dazzling white light. Magnesium oxide is formed in this reaction. Magnesium oxide is basic in nature.
Carbon burns in air to produce carbon dioxide. Carbon dioxide is acidic in nature. Acidic or basic nature of these oxides can be shown by brining wet litmus papers near them. Magnesium oxide will turn the red litmus blue. Carbon dioxide will turn the blue litmus red.

Question 3.
Let the students form two teams: M (metals) and N (non-metals); let the two teams form ‘pairs’ to explain the differences between their properties.
Answer:
Do it yourself

Something To Do

Question 1.
Find out the names of places in India where mines of gold, copper and iron are located. Also, write the names of the places where major steel plants are located.
Answer:

• Gold Mine: Kolar
• Copper Mines: Jharsugora
• Iron mines: Jamshedpur
• Steel Plants: Bokaro, Jamshedpur, Bhilai

Question 2.
The study of extracting metals from their ore is called metallurgy. Centuries ago, India was far ahead in metallurgy. Refer to books in library and find out the history of metallurgy in India.
Answer:
Do it yourself

Question 3.
Make a list of five articles used at home and school, which are made up of metals or alloys. Write their composition in a tabular form.
Answer:
Do it yourself

DAV Class 8 Science Chapter 3 Solutions – Metals and Non-metals Important Questions and Answers

I. Fill in the blanks:

1. Most of the metals have very ________ boiling point.
Answer:
High
2. ________ is the only metal which is present in liquid state at room temperature.
Answer:
Mercury

3. ________ and ________ are normally used for making electrical wires.
Answer:
Aluminium, copper

4. For making steel, ________ is added to iron.
Answer:
Carbon

5. ________ is an alloy of iron, chromium and nickel.
Answer:
Stainless steel

II. Tick the correct answer:

Question 1.
Which of the following is the hardest substance?
(a) Iron
(b) Platinum
(c) Diamond
(d) Charcoal
Answer:
(c) Diamond

Question 2.
Which of the following is the most reactive metal?
(a) Potassium
(b) Sodium
(c) Zinc
(d) Calcium
Answer:
(a) Potassium

Question 3.
Which of the following is a noble metal?
(a) Gold
(b) Silver
(c) Platinum
(d) All of these
Answer:
(d) All of these

Question 4.
Oxide of which of the following is basic in nature?
(a) Iron
(b) Carbon
(c) Phosphorus
(d) Sulphur
Answer:
(a) Iron

Question 5.
Which gas is evolved when a metal reacts with dilute acid?
(a) Oxygen
(b) Carbon dioxide
(c) Hydrogen
(d) Nitrogen
Answer:
(c) Hydrogen

III. Answer the following questions:

Question 1.
Write a brief note on occurrence of metals.
Answer:
Metals are present in the earth’s crust in abundance. Aluminium is the most abundant metal and iron is the next. Highly reactive metals are found in the form of their oxides, sulphides and carbonates, e.g. sodium, potassium, aluminium and zinc. Less reactive metals are found in their elemental or native state, e.g. gold, silver and platinum.

Question 2.
What is a mineral?
Answer:
A naturally occurring inorganic substance found deep under the surface of the earth is called mineral.

Question 3.
What is an ore?
Answer:
A mineral from which one or more metals can be profitably extracted is called ore.

Question 4.
What do you understand by malleability?
Answer:
Metals can be beaten into thin sheets. This property of metals is called malleability. Non-metals are non-malleable.

Question 5.
What do you understand by ductility?
Answer:
Metals can be drawn into thin wires. This property of metals is called ductility. Non-metals are non-ductile.

Question 6.
What are metalloids? Give some examples of metalloids.
Answer:
Some elements show properties of metals as well as non-metals. These Eire called metalloids. Silicon, germanium, arsenic, etc. are examples of metalloid.

Question 7.
How does a metal react with oxygen? Explain with suitable example.
Answer:
Metals react with oxygen to form metallic oxides. Metallic oxides are basic in nature:
Metal + Oxygen → Metal Oxide

When magnesium ribbon is burnt, it reacts with oxygen to make magnesium oxide.
2Mg + O₂ → 2MgO
(Magnesium) (Oxygen) → (Magnesium Oxide)

IV. Projects:

Question 1.
Show the comparison between metals and non-metals in a tabular form. Stick to physical properties only, while showing this comparison.
Answer:
Do it yourself

Question 2.
Ask your teacher to demonstrate the reaction of sodium with water.
Answer:
Do it yourself

Question 3.
Make a flow chart to show different steps of metallurgy.
Answer:
Do it yourself

The DAV Class 8 Science Book Solutions Pdf and DAV Class 8 Science Chapter 2 Question Answer – Microorganisms: Friends or Foes are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 2 Question Answer – Microorganisms: Friends or Foes

DAV Class 8 Science Ch 2 Solutions – Microorganisms: Friends or Foes

Something To Know

A. Fill in the blanks:

Question 1.
The study of microorganisms is known as ________ .
Answer:
microbiology

Question 2.
The bread dough rises because of the production of ________ .
Answer:
carbon dioxide

Question 3.
________ are the microorganisms that cause diseases.
Answer:
pathogens

Question 4.
________ and ________ are two chemical preservatives.
Answer:
sodium benzoate and potassium metabisulphite

Question 5.
________is a fungus that causes food poisoning.
Answer:
Aspergillus

B. Match the following:

Column I	Column II
(1) Ringworm	(a) Food poisoning
(2) Clostridium	(b) Biogas reactor
(3) Anthrax	(c) Fungus
(4) Lactobacillus	(d) Column I
(5) Methane	(e) Curd

Answer:

Column I	Column II
(1) Ringworm	(c) Fungus
(2) Clostridium	(a) Food poisoning
(3) Anthrax	(d) Column I
(4) Lactobacillus	(e) Curd
(5) Methane	(b) Biogas reactor

C. Tick (✓) the correct option:

Question 1.
The process, that helps milk to last longer but does not kill all microbes in it, is known as—
(a) Vaccination
(b) Pasteurization
(c) Bioaugmentation
(d) Fermentation
Answer:
(b) Pasteurization (✓)

Question 2.
Rust of wheat is caused by-
(a) Fungus
(b) Virus
(c) Bacteria
(d) Protozoa
Answer:
(a) Fungus (✓)

Question 3.
Medicines, containing killed or weakened pathogens, and used to prevent infectious diseases, are called-
(a) Disinfectants
(b) Antibodies
(c) Antibiotics
(d) Vaccines
Answer:
(d) Vaccines (✓)

Question 4.
Which of the following reproduces only inside a host cell?
(a) Virus
(b) Alga
(c) Protozoan
(d) Bacteria
Answer:
(a) Virus (✓)

Question 5.
A disease, caused by a virus, and spread by an insect, is-
(a) Polio
(b) Dengue
(c) Rabies
(d) Mumps
Answer:
(b) Dengue (✓)

D. Answer the following questions in brief:

Question 1.
Why are viruses considered as being at the ‘borderline’ between living and non-living things?
Answer:
A virus behaves like a non-living when it is outside a host cell. Once a virus enters a host cell, it starts to behave like a living being. Due to this, viruses are considered as the borderline between living and non-living.

Question 2.
What is fermentation? How is this process useful in the food and beverage industries?
Answer:
An anaerobic process through which sugars are converted into alcohol or acids and carbon dioxide by the action of microbes is called fermentation. Fermentation is useful in the food and beverages industries in various ways. Some examples are as follows:

• Fermentation in batter helps in making tasty dosa.
• Fermentation in dough helps in raising the dough while making bread and cake.
• Fermentation of fruit juice helps in making wine.

Question 3.
‘In the absence of microorganisms the earth would become a heap of dead plants and animals.’ Justify this statement.
Answer:
When a plant or animal dies, its remains are decomposed by microorganisms. Decomposition is the process through which all constituent materials of a living being are sent back to the environment. Had there been no microorganisms, dead remains of plants and animals would be keeping on accumulating all around us. So, it can be said that in the absence of microorganisms the earth would become a heap of dead plants and animals.

Question 4.
Munna observes that the yield of wheat, growing in his field, has reduced in the current year. He gets the soil tested and the report confirms the deficiency of one particular nutrient. Accordingly, he is advised to grow peas after harvesting wheat.

(a) Name the nutrient found insufficient.
Answer:
Nitrogen

(b) How do you think growing peas will help in replenishing the soil?
Answer:
Pea plants give shelter to Rhizobium bacteria. These bacteria carry out nitrogen fixation in soil. Thus, pea plants help in replenishing nitrogen in soil.

Question 5.
Why does it take less time to prepare curd in summers as compared to preparing it in winters?
Answer:
Microorganisms reproduce at a faster rate between 20 to 40°C. They reproduce at a much slower rate when temperature is below this range. Milk is converted into curd by multiplication of lactobacillus. This is why it takes less time to prepare curd in summers as compared to preparing it in winters.

Question 6.
How are the following diseases transmitted?
(a) Malaria
Answer:
By female Anopheles mosquito

(b) Common cold
Answer:
Through cough droplets in air

(c) Tetanus
Answer:
Through cut by a rusted iron article

(d) Typhoid
Answer:
Through contaminated food and water

Question 7.
What are antibiotics? How are they produced? Give two examples of these.
Answer:
A substance which prevents the multiplication of bacteria or kills the bacteria is called antibiotic. Antibiotics are prepared from microorganisms. Examples: Penicillin, Streptomycin.

E. Answer the following questions:

Question 1.
‘Microorganisms are very useful in manufacturing different food items.’ Explain the above statement.
Answer:
Fermentation is useful in the food and beverages industries in various ways. Some examples are as follows:

• Fermentation in batter helps in making tasty dosa.
• Fermentation in dough helps in raising the dough while making bread and cake.
• Fermentation of fruit juice helps in making wine.

These examples show that microorganisms are very useful in manufacturing different food items.

Question 2.
Give reasons for the following:

(a) Yeast is added to the batter used to make ‘dosas’.
Answer:
Yeast is added to the batter so that fermentation can take place. Fermented batter is good for making tasty dosa.

(b) It is important to brush one’s teeth before going to bed.
Answer:
Food particles remain stuck between teeth. Bacteria in out mouth eat these food particles. In the process, bacteria damage our teeth. Brushing of teeth helps in reducing the chances of bacteria damaging out teeth. Hence, it is important to brush one’s teeth before going to bed.

(c) Reducing the quantity of salt in pickle can cause it to go bad soon.
Answer:
Salt helps in removing water from pickle. This helps in preservation of pickle over a longer duration. Less salt would mean some water would be left in the pickle.
This may result in pickle getting bad sooner.

(d) Food, from puffed or enlarged cans, should not be consumed.
Answer:
Puffed or enlarged cans mean that air has leaked inside the can. Presence of air inside the can may help microbes to proliferate. This would spoil the food items. Hence, food from puffed or enlarged cans should not be consumed.

(e) When using frozen food items one should take out only the required quantities; thawed food should never be frozen.
Answer:
We know that microorganisms do no multiply below zero degrees Celsius. Once the food is thawed, its temperature becomes same as room temperature. This gives the microbes a chance to multiply which can spoil the food. Hence, while using frozen food items one should take out only the required quantity. Thawed food should not be consumed.

Question 3.
How do communicable diseases spread? Suggest ways to prevent the following diseases:
(a) Tuberculosis
(b) Athlete’s foot
(c) Cholera
Answer:
Communicable diseases spread through various means like air, vectors, person to person contact, and contaminated food and water.
(a) Tuberculosis can be prevented by living in well ventilated and well lit places.
(b) Cleaning your feet, shoes and socks; at a regular basis helps in preventing athlete’s foot.
(c) Avoid eating or drinking contaminated food and water helps in preventing cholera.

Question 4.
What are pathogens? Name two pathogens each that cause diseases in (i) plants and (u) animals.
Answer:
Microorganisms which can cause diseases are called pathogens, (i) Bacteria and (ii) Fungi are the examples of pathogens which cause diseases in plants and animals.

Question 5.
Mohan bought samosas from a roadside vendor and ate it. After some time, he felt nausea and started vomiting. He had severe pain in the abdominal region and suffered from diarrhoea. What could be the reason for his condition? What is it called? How could it be prevented?
Answer:
This could have happened due to food poisoning. Food poisoning can be prevented by avoiding eating food from roadside vendors.

Question 6.
Which diseases the following children are most likely to suffer from?
(a) Ramu drinks water from a nearby lake. This water is neither boiled nor disinfected.
Answer:
Cholera

(b) Ashu does not take bath every day. He maintains poor personal hygiene.
Answer:
Ringworm

(c) Pulkit has been bitten by an infected street dog.
Answer:
Rabies

(d) Sohan is living in an area where the population is very high. He does not use a mosquito net (while sleeping), or insect-repellant creams (while playing in the open).
Answer:
Malaria

(e) Mohan was with two of his friends who were coughing and sneezing (they were suffering from common cold). One of these friends did not keep a handkerchief in front of his mouth while coughing and sneezing.
Answer:
Common cold

Value Based Questions

Soham and his wife were overjoyed after the birth of their daughter. They share their1 joy with their relatives and friends. Soham’s wife decides to take their daughter for her first round of vaccinations. However, Soham’s mother does not like the idea of putting the child through the discomfort of ‘injections’. Soham explains to his mother in a polite and patient way, that this slight discomfort and pain is necessary as it shall ensure that the child lives a long and healthy life.

Question 1.
Was Soham right in supporting his wife’s decision? List any two values that are demonstrated by his behaviour.
Answer:
Soham is right in supporting his wife’s decision. Mohan cares for his family and have respect for women.

Question 2.
How does vaccination help in providing immunity?
Answer:
Vaccination introduces weak or dead pathogen in the body. The body prepares antibody against these pathogens. Thus, the body learns to fight that disease even in future. That is how vaccination helps in providing immunity.

Question 3.
Find out the names of any five diseases that can be prevented by timely vaccination of children.
Answer:
Tuberculosis, Diptheria, Mumps, Pertussis, Tetanus

Something To Do

Question 1.
Visit a nearby health centre, or contact a doctor. Find out the names of diseases for which vaccinations are available and the age at which they have to be given to the child.
Answer:
Do it yourself

Question 2.
Genetic engineering is a branch of science in which microorganisms are being extensively used. Try to find out the role of microorganisms in genetic engineering.
Answer:
Useful genes from bacteria can be transferred to a crop or a useful animal. For example; BT cotton has a beneficial gene from a bacteria.

Question 3.
Visit an animal health centre or a veterinarian (a physician for animals). Collect information about various vaccinations that are available for domestic animals (like cows) and pets (like dogs).
Answer:
Do it yourself

Question 4.
Write how the following methods of preservation work. Also, add two examples of foods that can be preserved by each of these methods.

Method	How it works	Examples (of food preserved)
Pickling	Removes moisture from food.	Raw mango, lemon pickles
Ozone treatment	Kills microbes	Fruits, vegetables
Drying	Removes moisture	Rice, wheat, maize
Adding preservatives	Inhibit the growth of microbes	Jams, jelly
Canning	Kills microbes	Tomato, beans, mushroom
Vacuum packing	Removes air from packet	Fried food
Freezing	Prevents proliferation microbes of microbes	Fruits, vegetables
Radiation	Kill microbes	Fruits, vegetables
Salting	Removes moisture	Fish, pickles

Question 5.
Find out about the temperature at which the following occur/exist/work:

(a) Decomposition
Answer
20 to 40°C

(b) Pasteurization
Answer:
80 to 100°C

(c) Steamer
Answer:
100 to 120°C

(d) Refrigerator
Answer:
0 to 20°C

(e) Deep freezer
-20°C

(f) Human body
Answer:
20 to 40°C
Based on the information provided in the picture, predict the chances of growth and survival of microbes in each of the above.
Answer:
Microbes will survive and grow in case of a and f.

DAV Class 8 Science Chapter 2 Solutions – Microorganisms: Friends or Foes Important Questions and Answers

I. Fill in the blanks:

1. Malaria is spread by ________ .
Answer:
Mosquito

2. Flu is spread through ________ .
Answer:
Air

3. Diarrhoea is spread by contaminated ________ .
Answer:
Water

4. Adding salt in food helps in removal of ________ from food item.
Answer:
Water

5. Sodium benzoate is a ________ .
Answer:
Food preservative

II. Tick the correct answer:

Question 1.
Malaria is caused by which of these?
(a) Bacteria
(b) Virus
(c) Fungi
(d) Protozoa
Answer:
(d) Protozoa

Question 2.
Ringworm is caused by which of these?
(a) Bacteria
(b) Virus
(c) Fungi
(d) Protozoa
Answer:
(c) Fungi

Question 3.
Which of these diseases can be spread by a dog’s bite?
(a) Tetanus
(b) Rabies
(c) Dengue
(d) Chikungunya
Answer:
(b) Rabies

Question 4.
Pasteurization is used for which of these food items?
(a) Milk
(b) Vegetables
(c) Fruits
(d) Pickles
Answer:
(a) Milk

Question 5.
Smut is a disease of which plant?
(a) Lemon
(b) Rice
(c) Tobacco
(d) Potato
Answer:
(b) Rice

Question 6.
Ranikhet is a disease of which of these animals?
(a) Cattle
(b) Poultry
(c) Dog
(d) Cat
Answer:
(b) Poultry

III. Answer the following questions:

Question 1.
Define microorganisms.
Answer:
Organisms which are invisible to the naked eye but visible under the microscope are called microorganisms. Examples: bacteria, yeast, protozoans and algae.

Question 2.
Explain the beneficial role of microorganisms in agriculture.
Answer:
Some bacteria and blue-green algae (cyanobacteria) help in nitrogen fixation. This is important as this is the only way through which a plant can get nitrogenous nutrients. Rhizobium bacteria live in the root nodules of leguminous plants. They help in nitrogen fixation in soil.

Question 3.
How do bacteria cause tooth decay?
Answer:
Many bacteria live in our mouth. They eat the food particles which remain stuck between the teeth. During eating the food particles, bacteria produce acids which corrode the tooth enamel and results in tooth cavities in the long run.

Question 4.
What do you understand by food poisoning?
Answer:
Food poisoning happens because of consumption of contaminated food. Vomiting, nausea, severe pain in abdomen, diarrhoea and dehydration are the symptoms of food poisoning. Clostridium and Staphylococci are the bacteria which cause food poisoning and Aspergillus is a fungus which causes food poisoning.

Question 5.
What are the main goals of food preservation?
Answer:
Prevention of growth of microorganism and retarding the oxidaton of fats are the main goals of food preservation.

IV. Projects:

Question 1.
Make a list of food items which can be preserved by drying in the sun.
Answer:
Do it yourself.

Question 2.
Make a list of food items which are preserved by using salt or sugar.
Answer:
Do it yourself.

Question 3.
How does your family ensure that you get clean and safe drinking water? What are its benefits?
Answer:
Do it yourself.

The DAV Class 8 Science Book Solutions Pdf and DAV Class 8 Science Chapter 1 Question Answer – The Cell Its Structure and Functions are essential study tools for DAV public school students in Class 8.

DAV Class 8 Science Ch 1 Question Answer – The Cell Its Structure and Functions

DAV Class 8 Science Ch 1 Solutions – The Cell Its Structure and Functions

Something To Know

A. Fill in the blanks.

Question 1.
All living organisms are made up of ________ .
Answer:
cells

Question 2.
The ________ provides rigidity and protection to the plant cell.
Answer:
cell wall

Question 3.
All cellular activities are controlled by the ________ .
Answer:
nucleus

Question 4.
The ________ is known as the powerhouse of the cell.
Answer:
mitochondria

Question 5.
________ is a group of cell performing a specific function.
Answer:
tissue

Question 6.
It was ________ who observed cells for the first time.
Answer:
Robert Hooke

B. Match the following:

Column I	Column II
(1) Golgi Complex	(a) Genes
(2) Ribosomes	(b) Cork
(3) Chromosomes	(c) Chloroplasts
(4) Dead cells	(d) Packaging centre
(5) Photosynthesis	(e) Protein synthesis

Answer:

Column I	Column II
(1) Golgi Complex	(d) Packaging centre
(2) Ribosomes	(e) Protein synthesis
(3) Chromosomes	(a) Genes
(4) Dead cells	(b) Cork
(5) Photosynthesis	(c) Chloroplasts

C. Tick (✓) the correct option:

Question 1.
The cell organelle, which acts as a storage bag for a cell, is known as the-
(a) Chloroplast
(b) Mitochondria
(c) Chromoplast
(d) Vacuole
Answer:
(d) Vacuole

Question 2.
Hen’s egg is-
(a) A cell organelle
(b) A tissue
(c) A single cell
(d) An organ
Answer:
(c) A single cell

Question 3.
The nucleus is separated from the cytoplasm by the
(a) Cytoplasm
(b) Nuclear membrane
(c) Cell membrane
(d) Protoplasm
Answer:
(b) Nuclear membrane

Question 4.
Which of the following will not be found in an egg cell, human liver cell and an amoeba?
(a) Ribosomes
(b) Mitochondria
(c) Cell membrane
(d) Cell wall
Answer:
(d) Cell wall

Question 5.
Which of the following represents the correct sequence?
(a) Tissue cell → organ → organ system
(b) Organ → tissue → organ system → cell
(c) Cell → organ → tissue → organ system
(d) Cell → tissue organ → organ system
Answer:
(a) Tissue cell → organ → organ system

Question 6.
Which, amongst the following pairs, can be found only in a plant cell but not in an animal cell?
(a) Cell wall and plastids
(b) Plastids and cilia
(c) Cell wall and cell membrane
(d) Plastids and mitochondria
Answer:
(a) Cell wall and plastids

D. Answer the following questions in brief:

Question 1.
List the main factors that determine the shape of a cell.
Answer:
Location and function of a cell determines its shape.

Question 2.
Distinguish between unicellular and multicellular organisms. Give two examples of each.
Answer:

Unicellular Organisms	Multicellular Organisms
Composed of a single cell.	Composed of more than one cell.
Examples: amoeba, bacteria	Examples: cockroach and monkey

Question 3.
Give reasons for the following:
(a) The cell is called the structural and fundamental unit of life.
Answer:
All organisms are made up of cells. A cell is capable of independent existence. Due to this, cell is called the structural and fundamental unit of life.

(b) Plant cells are more rigid than animal cells.
Answer:
Cell wall is present in plant cell. Due to this, plant cells are more rigid than animal cells.

Question 4.
Which cell organelle is known as the “Powerhouse of the cell”? Why is it so called?
Answer:
Mitochondria are the site of cellular respiration. Energy is produced during this process. Due to this, mitochondria are called the Powerhouse of the cell.

Question 5.
Name the cell organelles responsible for imparting colour to the leaves and fruits of a plant.
Answer:
Chloroplast is responsible for imparting colour to the leaves. Chromoplast is responsible for imparting colour to fruits.

Question 6.
What are cilia and flagella? Write one similarity and one dissimilarity between the two of them.
Answer:
These are small extensions on some cells. These structures help in locomotion in a cell. Cilia are much smaller than flagella.

Question 7.
If onion peel cells and cheek cells are observed through a microscope, state the two major differences that the observer is likely to see.
Answer:

Onion peel cells	Cheek cells
Cells are arranged in rows.	Cells randomly arranged.
Cell wall is present.	Cell wall is absent.

Question 8.
Classify the following into cells, tissue and organ: skin, fat cell, RBC, blood, ear, muscle.
Answer:

Cell	Tissue	Organ
Fat cell, RBCs	Blood, muscle	Skin, ear

E. Answer the following questions:

Question 1.
“All cells in an organism do not have the same shape.” Justify the above statement by drawing at least three different types found in human beings.
Answer:

These figures show that liver cell is irregular in shape, fat cell is spherical and muscle cell is spindle-shaped. This shows that all cells in an organism do not have the same shape.

Question 2.
Where, and how, are chromosomes formed? State their significance.
Answer:
Chromosomes are formed in the nucleus during cell division. When the cell is ready to divide, the chromatin (in nucleus) condenses to form thicker, thread-like chromosomes. Chromosomes are responsible for inheritance of characters from one generation to the next generation.

Question 3.
With the help of well labelled diagrams, highlight three differences between plant cell and animal cell.
Answer:

Plant cell	Animal cell
Cell wall is present.	Cell wall is absent.
Chloroplast is present.	Chloroplast is absent.
Vacuole is very large.	Vacuoles are small.

Question 4.
Write the functions performed by the following cell organelles,
(a) Endoplasmic Reticulum
(b) Golgi Complex
(d) Nucleus
(d) Chromoplasts
(e) Vacuoles
(f) Mitochondria
Answer:
(a) Transport of substance
(b) Packaging of substances
(c) Controlling the functions of a cell
(d) Imparting colour to flowers and fruits
(e) Storage
(f) Respiration

Question 5.
The cell membrane is a veiy important component of a cell. How is damage to the cell membrane likely to impact the functions of the cell?
Answer:
When the cell membrane gets damaged, it exposes the cell’s contents to external environment. This results in stoppage of all functions of the cell, and eventually to cell death.

Question 6.
Define the lerm ‘cell’ , for plants/animals. Name the different organelles that make a cell. Explain why none of these is called the structural and functional unit of life?
Answer:
Cell is the fundamental and structural unit of life. Different cell organelles in a plant cell are; nucleus, Golgi complex, mitochondria, chloroplast, endoplasmic reticulum, lysosome, vacuole, and ribosome. None of the cell organelles is capable of independent existence. So, they are not called the structural and functional unit of life.

Value Based Questions

The biology teacher started her lesson on the structure and functions of the animal/ plant cells by talking about a cricket team. She told her students that a team wins its matches only when all its members Vork as a team’ and do their assigned roles in an efficient, sincere and responsible way. She then went on to say that the animal/plant cells also work properly as their different parts work as a ‘team’ and do their specific functions. She advised her students to imbibe the ‘team spirit’ and do their specific functions as responsible members of any ‘team’ they may be a part of.

Question 1.
Name two of the values that the teacher spoke of in her class.
Answer:
Team spirit, and sticking to your role.

Question 2.
Have a group discussion in which students suggest how, ‘working as a team’ can improve the ‘overall working; of a home or a school.
Answer:
Do it yourself.

Question 3.
Have a ‘play’ in the class in which a group of students give themselves names corresponding to the different cell organelles of a plant/animal cell. Each ‘name’ has to then explain her/his role in the working of the cell.
Answer:
Do it yourself.

Something To Do

Question 1.
Hydrilla is an aquatic plant that can be seen in lakes and ponds. It has small, thin leaves. Take a Hydrilla leaf and place it on a glass slide. Observe it under a microscope.
Note your observations.

Question 2.
Divide the class into four groups of students.
Each group will prepare a short report on the topics/questions given below. Two students from each group may then present the report to the whole class.
(a) When were cells discovered? Were they discovered before or after the invention of the compound microscope?
Answer:
Cells were discovered in 1665; much before the invention of the compound microscope.

(b) Does the size and number of cells depend upon the size of the organism?
Answer:
Size of cells does not depend on the size of the organism. But number of cells depends on the size of an organism. Number of cells in an elephant would be much higher than that in a mouse.

(c) List the functions of cell organelles and also mention the organ/organ system, that the organelle is similar to, in the human body.
Answer:

Cell organelle	Function	Similar organ
Nucleus	Controls the functions of a cell.	Brain
Endoplasmic reticulum	Transport of substances.	Circulatory system
Lysosome	Digestion	Digestive system
Golgi complex	Packaging	Liver
Cell membrane	Protection, boundary	Skin

(d) List the advantages of having a cell wall as the outermost boundary in cells.
Answer:
Cell wall gives following advantages to cell:

• Gives extra protection to cell.
• Makes the cell more rigid.
• Prevents excess expansion of cell in case of osmosis of too much water into the cell.

Question 3.
Complete the crossword puzzle given below.

Across →	Down ↓
3. Storage structures of a cell.	1. Help Paramecium in locomotion.
5. Regulates the entry and exit of materials in and out of the cell.	2. Structure that helps in protein synthesis.
7. Impart colour to flowers and fruits.	4. Help plant cells in converting solar energy into usable form.
8. Provides shape and rigidity to a plant cell.	6. Control centre of the cell.
10. Powerhouse of the cell.	9. Responsible for transferring traits from one generation to next.

Answer:

Across →	Down ↓
3: Vacuoles	1: Cilia
5: Cell Membrane	2: Ribosome
7: Chromoplast	4: Chloroplasts
8: Cell wall,	6: Nucleus
10: Mitochondria	9: Gene

DAV Class 8 Science Chapter 1 Solutions – The Cell Its Structure and Functions Important Questions and Answers

I. Fill in the blanks:

1. ________ was the first scientist to observe cells.
Answer:
Robert Hooke

2. Cell wall is ________ in amoeba.
Answer:
Absent

3. Cell membrane is ________ in a plant cell.
Answer:
Present

4. Chloroplast imparts ________ colour to a plant part.
Answer:
Green

5. Materials are stored in ________ in a cell.
Answer:
Golgi complex

II. Tick (✓) the correct answer:

Question 1.
Which of these is the smallest cell?
(a) RBC
(b) Neuron
(c) Mycoplasma
(d) Egg
Answer:
(c) Mycoplasma (✓)

Question 2.
What is the name of the protoplasm which is present in the nucleus?
(a) Cytoplasm
(b) Nucleoplasm
(c) Life fluid
(d) Nuclear fluid
Answer:
(b) Nucleoplasm (✓)

Question 3.
Which of these cell organelles is also known as powerhouse of the cell?
(a) Golgi complex
(b) Endoplasmic reticulum
(c) Mitochondria
(d) Chloroplast
Answer:
(c) Mitochondria (✓)

Question 4.
Which of these is the site for photosynthesis?
(a) Golgi complex
(b) Endoplasmic reticulum
(c) Mitochondria
(d) Chloroplast
Answer:
(d) Chloroplast (✓)

Question 5.
What is the function of ribosome?
(a) Cellular respiration
(b) Protein synthesis
(c) Lipid synthesis
(d) Cell division
Answer:
(b) Protein synthesis (✓)

III. Answer the following questions:

Question 1.
Define cell.
Answer:
The basic structural and functional unit of living organisms is called cell.

Question 2.
What is a unicellular organism?
Answer:
Some organisms are composed of a single cell. These are called unicellular organisms.

Question 3.
What is a multicellular organism?
Answer:
Some organisms are composed of more than one cell. These are called multicellular organisms.

Question 4.
Write a brief note on cell membrane.
Answer:
All living cells are bound by a thin membrane called plasma membrane or cell membrane. The cell membrane provides protection to the contents of the cell and controls the entry and exit of various substances as per a cell’s requirement.

Question 5.
Mitochondria are also known as powerhouse of the cell. Why?
Answer:
Cellular respiration takes place in mitochondria and energy is generated. Due to this, mitochondria are also called the powerhouse of the cell.

Question 6.
What do you understand by cellular level of organization?
Answer:
This level of organization is found in unicellular and in some simple multicellular organisms. In such organisms, a single cell is responsible for all life functions.

IV. Projects:

Question 1.
Ask your teacher to show slides of animal cell and plant cell. Make a note of various cell organelles which can be seen through a compound microscope.
Answer:
Do it yourself.

Question 2.
Take wool of different colours, some beads and a chart paper. Make a model of animal cell with these materials.
Answer:
Do it yourself.