NCERT Solutions Class 9. 203 Pages. Free Flip-Book by Study Innovations

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Chapter 10 Gravitation

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Question 1 State the Universal law gravitation?

Answer : According to Universal Law of Gravitation every object in
universe attracts every other object with a force known as Gravitational
force.
It states that
Force be the force of attraction between two objects and of
masses and is given by

Here G is the constant known as Universal Gravitational constant and its
value is

Question 2. Write the formula to find the magnitude of the
gravitational force between the earth and an object on the surface of
the earth.

Answer:

Let be the be the force of attraction between earth and an object on
its surface. Again assume that be the mass of earth and be the
mass of object on the surface of earth. Formula for the magnitude of the
gravitational force between the earth and an object on the surface of
the earth is given by using Universal Law of Gravitation. So required
formula is

Page 136

Question 1: What do you mean by free fall?

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Answer : Gravity of earth attracts every object towards its center. When
an object is dropped from a certain height , it begins to fall towards
Earth’s surface under the influence of gravitational force. Such a motion
of object is called free fall.

Question 2 : What do you mean by acceleration due to gravity?

Answer : When an object falls freely towards the surface of earth from a
certain height, then its velocity changes. This change in velocity
produces acceleration in the object which is known as acceleration due
to gravity denoted bu letter . The value of acceleration due to gravity is

.

Page 138

Question 1 what are the differences between mass of an object and its
weight?

Answer.

Mass:-
1. Mass is the quantity of matter contained in the body
2. It is the measure of inertia of the body
3. It is a constant quantity for any object.
4. It is a scalar quantity and only only has magnitude
5. SI unit of mass is Kg

Weight:-
1. Weigh is the gravitational force acting on the body
2. It is the measure of gravity
3. Weight of an object is not a constant quantity it is different at
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different laces.
4. It is a vector quantity as it has both magnitude and direction.
5. Its SI unit is N (newton) same as the SI unit of force.

Question 2 . Why is the weight of an object on the moon (1/6)th its
weight on the earth?

Answer : Gravity is directly related to mass. The more mass an object
has, the more gravitational pull it has.
Now, the moon is significantly smaller than the earth (in fact, it is about
the size of the earth’s core). Gravity is dependent on the size of the
object. Your weight on the moon is 1/6 of that on earth because the
moon has 1/6 the mass of the earth.

Page 141

Question 1. Why is it difficult to hold a school bag having a strap made
of a thin and strong string?

Answer: It is difficult to hold a school bag having a thin strap because the
pressure on the shoulders is quite large. This is because the pressure is
inversely proportional to the surface area on which the force acts. The
smaller is the surface area the larger wold be the pressure on the
surface. In the case of a thin strap, the contact surface area is very small.
Hence pressure exerted on the shoulder is very large.

Question 2 .What do you mean by buoyancy?

Answer :The upward force exerted by a liquid on an object that is
immersed in it is known as buoyancy.

Question 3. Why does an object float or sink when placed on the surface

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of water?

Answer : If the density of an object is more then the density of the liquid
then the object would sink this happens because in this case buoyant
force that is acting on the object due to liquid is less than the force of
gravity acting on the object. If the density of object is less than the
density of the liquid , then it floats on the surface of the liquid , this
happens because the buoyant force acting on the object is greater than
the force of gravity.

Page 142

Question 1. You find your mass to be 42 Kg on a weighting machine. Is
your more or less than 42 K?

Answer : On a weighing machine mass is measured by comparing the
weights. So when you weigh your body an upward force (buoyant force)
acts on it which causes machine to show your weight less than the
actual weight.

Question 2. You have a bag of cotton and an iron bar, each indicating a
mass of 100 Kg when measured on a weighing machine. In reality one is
heavier than other. Can you say which one is heavier and why?

Answer :Actual weight of any object is equal to the sum of its measured
weight and the buoyant force. The bag of cotton is heavier since it is
larger than iron bar, so the buoyant force is larger in case of cotton
henceactual weight of cotton bag is more and it is heavier.

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Chapter 11 – Work and Energy

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Question 1: A force of 7 N acts on an object. The displacement is, say 8
m, in the direction of the force (Fig. 11.3). Let us take it that the force
acts on the object through the displacement. What is the work done in
this case?

Answer: When a force F acts on an object to displace it through a
distance S in its direction, then the work done W on the body by the
force is given by:
Work done = Force × Displacement
W=F×S
Where,
F=7N
S=8m
Therefore, work done, W = 7 × 8
= 56 Nm
= 56 J

Question 1: When do we say that work is done?

Answer: Work is done whenever the given conditions are satisfied:
(i) A force acts on the body.
(ii) There is a displacement of the body caused by the applied force
along the direction of the applied force.

Question 2:Write an expression for the work done when a force is acting
on an object in the direction of its displacement.

Answer:When a force F displaces a body through a distance S in the
direction of the applied force, then the work done W on the body is
given by the expression:
Work done = Force × Displacement
W=F×s
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Question 3:Define 1 J of work.
Answer:1 J is the amount of work done by a force of 1 N on an object
that displaces it through a distance of 1 m in the direction of the applied
force.
Question 4:A pair of bullocks exerts a force of 140 N on a plough. The
field being ploughed is 15 m long. How much work is done in ploughing
the length of the field?
Answer:Work done by the bullocks is given by the expression:
Work done = Force × Displacement
W=F×d
Where,
Applied force, F = 140 N
Displacement, d = 15 m

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Chapter 12 : Sound
Page 163
Question: 1 - Explain how sound is produced by your school bell.

Answer:- School bell starts vibrating when heated which creates
compression and rarefaction in air and sound is produced.

Question: 2 - Why are sound waves called mechanical waves?
Answer: Since sound waves do some mechanical work while making
disturbance in medium, hence sound waves are called mechanical wave.

Question: 3 -Suppose you and your friend are on the moon. Will
you be able to hear any sound produced by your friend?
Answer: Since sound waves require medium to propagate and there is
no medium present on the moon. So, I will not able to hear the sound of
my friend on the moon.
Page 165

Question: 1 - Question: 1 - Which wave property determines (a)
loudness, (b) pitch?

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Answer: (a) Amplitude of sound waves determines loudness. Louder
sound has greater amplitude and vice versa.
(b) Frequency of the sound waves determined pitch of the sound.
Question: 2 - Guess which sound has a higher pitch: guitar or car horn?
Answer: Sound of the car horn has higher pitch.
Question: 3 - What are wavelength, frequency, time period and
amplitude of a sound wave?

Answer: Wavelength: Wavelength is the distance between two
consecutive compressions or rarefaction of wave.
Frequency: The number of sound wave produced in one second is called
frequency.
Time period: Time period is the time taken to produce one wave of
sound.

Amplitude: Amplitude is the maximum displacement along the mean
position of the particles of medium.

Question: 4 - How are the wavelength and frequency of a sound wave
related to its speed?

Answer: The relation between frequency and wavelength of sound wave
is given as follows:
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Velocity (v)=Wavelength(λ)X Frequency (ν), v = λX ν

This means the speed is equal to the product of wavelength and
frequency of the sound wave.

This equation is also called the ‘wave equation’ and applicable to all
types of wave.

Question: 5 - Calculate the wavelength of a sound wave whose
frequency is 220 Hz and speed is 440 m/s in a given medium.

Answer:
Given,
Frequency (ν) = 220 Hz
Velocity (v) = 440m/s
Wavelength (λ) =?
We know;

Thus, wavelenght = 2m
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Question: 6 - A person is listening to a tone of 500 Hz sitting at a
distance of 450 m from the source of the sound. What is the time
interval between successive compressions from the source?

Answer: Since, the time interval between successive compressions is
called time period or time interval.
Here given,
Frequency (ν) = 500Hz
T (Time period) =?

We know that;

Thus, time interval between two consecutive compression of the given
wave = 0.2 s

Question: 7 - Distinguish between loudness and intensity of sound.

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Answer: Loudness of sound is determined of amplitude and intensity of
the sound wave is determined by frequency of sound waves.

Page 167
Question: 1 - In which of the three media; air, water or iron does the
sound travel the fastest at a particular temperature?

Answer:At particular temperature sound travels fastest in iron.
Page 168
Question: 1 - An echo returned in 3 s. What is the distance of the
reflecting surface from the source, given that the speed of sound is 342
m /s?

Answer:To return an echo sound has to cover distance of two way.

Here, given,
Speed of sound = 342 m/s
Time = 3s

Thus,

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Distance = speed X time

⇒ Distance = 342m/s×3 s=1026 m
Thus,the distance between the source and reflecting
surface=1026÷2=513m
Page 169
Question: 1 -Why are the ceilings of concert halls curved?
Answer: Since, concert halls are big, so audience at the back rows of the
hall may not hear clear sound of speaker. To overcome this problem, the
ceiling of the concert halls is made concave. Concave ceiling helps the
sound wave to reflect and send to farther distance which makes the
concert hall enable to send clear sound to the audience even sitting in
back rows of hall.

Page 170
Question: 1 - What is the audible range of the average human ear?
Answer: 20 Hz to 20000 Hz

Question: 2 - What is the range of frequencies associated with

(a) Infrasound
(b) Ultrasound

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Answer:

(a) Infrasound: Less than 20 Hz

(b) Ultrasound: More than 20000 Hz
Page 172

Question: 1 - A submarine emits a SONAR pulse, which returns from an
underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s,
how far away is the cliff ?

Answer:To return the SONAR pulse back, its wave has to travel two way.
Here, given,
Velocity (v) of sound wave = 1531m/s
Time (T) = 1.02 s

Thus, Distance = speed X time
Distance=1531 ms^(-1)×1.02 s=1561.62 m

So,the distance between the source and reflecting
surface=1561.62÷2=780.81m

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Chapter 13
Why Do We Fall Ill
Intext Questions
On Page 178

Question 1:State any two conditions essential for good health.

Solution:Good health of a person depends on
a) Social environment.
b) Public cleanliness.
c) Good economic conditions and earnings.
d) Social equality and harmony.

Question 2:State any two conditions essential for being free of disease.

Solution:The conditions essential for being free of diseases are:
a) Having good food (balanced diet)
b) Personal and public hygiene maintenance

Question 3:Are the answers to the above questions necessarily the same
or different? Why?

Solution:The answers are not same all the time, because the meaning of
health varies from person to person.

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For example, good health for a dancer may be being able to stretch his
body into difficult but graceful positions. On the other hand, good health
for a musician may mean having enough breathing capacity in his/her
lungs to control his/her voice. There is one similarity in both the cases. If
the conditions essential for good health are maintained, then the chance
of getting any disease is zero.

On Page 180

Question 1:List any three reasons why you would think that you are sick
and ought to see a doctor. If only one of these symptoms were present,
would you still go to the doctor? Why or why not?

Solution:When there is a disease, its symptoms and signs appear. These
symptoms may be headache, cough, loose-motions, wound with pus,
etc. These symptoms indicate disease but do not tell what the disease is.
So, it is advisable to go to the doctor to diagnose any signs of a disease
on the basis of these symptoms. The doctor will get laboratory tests
done, if required, for the confirmation of a particular disease.

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Question 2:In which of the following case do you think the long-term
effects on your health are
likely to be most unpleasant?
•If you get jaundice,
•If you get lice,
•If you get acne.
Why?

Solution:Our body will not be effected by lice and acne very much. But in
case of Jaundice, there will be severe long lasting effects. For example:
a) High temperature, headache and joint pains.
b) Feeling of nausea and vomiting.
c) Initiating rashes.

The patient will suffer from poor health and will recover by taking the
suitable treatment and complete bed rest.

On Page 187

Question 1:Why are we normally advised to take bland and nourishing
food when we are sick?

Solution:All the normal functions of the body get disturbed in case
illness. So, a nourishing food is required, which is easily digestible and
contains all the nutrients. This is the main reason that bland and
nourishing food is advised to take during sickness.

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Question 2:What are the different means by which infectious diseases
are spread?

Solution:Infectious diseases spread by different means. These are:

a) Through air: An infected person when sneezes or coughs releases
droplets containing germs which infect another healthy person through
air and microbes enter a new body.
Examples: common cold, pneumonia and tuberculosis.

b) Through water: contaminated water will infect many people and
make them ill.
Example: cholera, amoebiasis, hepatitis spread through water.

c) Through sexual contactSome diseases like AIDS and syphilis, etc., are
transmitted by exual contact. Other than this, AIDS virus also spread
through blood, infected syringes, infected mother to her baby during
pregnancy and through breast feeding.

d) Through vectorsThere are some animals which act as intermediaries
or vectors for a particular diseases. The vectors carry diseases from
infected person to the healthy person.
For example, mosquito spread malaria causing organism in humans,
while sucking their blood.

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Question 3:What precautions can you take in your school to reduce the
incidence of infectious diseases?

Solution:To prevent the incidence of infectious diseases in school
following precautions can be taken:

a) Avoid contact of students suffering from air borne diseases like
common cold, cough, eye, flu, etc.
b) By checking the availability of clean drinking water in school.
c) Clean surroundings in school will not allow the growth and
multiplication of vectors.
d) Starting childhood immunisation programmers in schools.

Question 4:What is immunisation?

Solution:Immunisation is a process of administration (injecting) of
vaccine into a healthy person in order to develop immunity against a
disease. Immunity means the ability of a body to recognize, destroy and
eliminate external disease causing agents.

Question 5:What are the immunisation programmes available at the
nearest health centre in your locality? Which of these diseases are the
major health problems in your area?

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Solution:The following immunisation programme is available at the
nearest health centre in our locality
a) Immunisation for infants-OPT, BCG, polio, measles and MMR.
b) For children-Typhoid, TT. DT, small pox and TAB.
c) For pregnant woman- TT and hepatitis-B.

The diseases like typhoid, polio, measles, tetanus are the major health
problems in our locality. To prevent these diseases, our government
have initiated expanded immunisation programme all over the country.

Exercises

Question 1:How many times did you fall ill in the last one years? What
were the illnesses?
(a) Think of one change you could make in your habits in order to avoid
any of/most of the above illnesses.
(b) Think of one change you would wish for in your surroundings in order
to avoid any of/most of the above illnesses.

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Solution:I fell ill twice in the last one year. The disease, I first suffered
from was diarrhoea and secondary the dengue fever.
(a) The changes I brought in my habits after suffering from these disease
to protect myself in near future are
(i) I will always drink clean, pure water and wash hands before eating
anything.
(ii) I will live in clean surroundings where disease spreading vectors
could not mulitply.
For example, mosquitoes.
(b) Pure drinking water should be available always. The intake of impure
water is the main cause of many infectious diseases.

Question 2:A doctor/nurse/health-worker is exposed to more sick
people than others in the community. Find out how she/he avoids
getting sick herself/himself.

Solution:A doctor/nurse/health-worker take following precautions to
avoid become sick themselves
(i) Get immunisation done against all the infectious diseases.
(ii) Take balanced diet (rich in proteins especially) to strengthen their
immune system.
(iii) Dispose off blood samples, urine or stool, sputum, etc., carefully.
(iv) Wear masks while diagnosing mouth or chest infections.
(v) Clean their hands and wear gloves even while doing minor surgeries.

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Question 3:Conduct a survey in your neighbourhood to find out what
the three most common diseases are. Suggest three steps that could be
taken by your local authorities to bring down the incidence of these
diseases.

Solution:(i) I conducted a survey in my neighbourhood and found
following three most common diseases.
(ii) I will live in clean surroundings where disease spreading vectors
could not mulitply.
For example, mosquitoes.

(b) Pure drinking water should be available always. The intake of impure
water is the main cause of many infectious diseases.

Question 4:A doctor/nurse/health-worker is exposed to more sick
people than others in the community. Find out how she/he avoids
getting sick herself/himself.

Solution:A doctor/nurse/health-worker take following precautions to
avoid become sick themselves

(i) Wear masks while diagnosing mouth or chest infections.

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(ii) Clean their hands and wear gloves even while doing minor surgeries.
(iii) Get immunisation done against all the infectious diseases.
(iv) Take balanced diet (rich in proteins especially) to strengthen their
immune system.
(v) Dispose off blood samples, urine or stool, sputum, etc., carefully.
Question 5:Conduct a survey in your neighbourhood to find out what
the three most common diseases are. Suggest three steps that could be
taken by your local authorities to bring down the
incidence of these diseases.
Solution:I conducted a survey in my neighbourhood and found following
three most common diseases.

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Typhoid
Symptoms: Headache and fever which remains high in the second week
and then declines
Steps could be taken :
• Proper hygiene in surrounding areas of living.
• Safe disposal of excreta and other wastes.
• Providing TAB and typhoid oral vaccine.

Cholera
Symptoms: Painless watery diarrhoea, effortless vomiting

Steps could be taken :
• Good sanitary condition in community.
• Provision of clean,purified drinking water.
• Providing standard cholera vaccination in the locality.
Dengue fever
Symptoms: High fever with headache, weakness and joint pains

Steps could be taken :
• Maintenance of hygienic conditions in community.
• Preventing the mosquito breeding sites.
• Public awarness programme against musquito borne diseases.

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Question 6:A baby is not-able to tell her/ his caretakers that she/ he is
sick. What would help us to find out
(a) That the baby is sicks?
(b) What is the sickness?
Solution:(a) Symptoms to help in finding out that the baby is sick are:
Redness of eyes
Drooping of eyes
Continuous crying
High temperature of body.

(b) Signs which help to indicate the sickness in baby
High fever. Headache. Muscular pain. Feeling of shivering and cold
indicate malaria.
Loose motions. Stomach pain indicate diarrhea.
Redness and persistent rubbing of eyes indicate eye flu.
Pale skin. Yellow urine. Yellowing of eyes indicate jaundice.
Doctors suggest for laboratory tests. if there is fever with no other
symptoms to find out the kind of sickness.

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Question 7:Under which of the following conditions is a person most
likely to fall sick?
(a) When she is recovering from malaria.
(b) When she has recovered from malaria and is taking care of someone
suffering from chicken pox.
(c) When she is on a four-day fast after recovering from malaria and is
taking care of someone suffering from chicken pox. Why?

Solution:In condition (c), a person is most likely to fall sick. The reason's
are:
(a) in case of malaria, body becomes weak and loss of body fluids occur.
In this condition, it she takes four days fast, her recovery from malaria
related weakness will not occur and she will become weaker.

(b) Her immune system is already weak due to malaria and if she takes
care of someone suffering from chicken pox, there is high probability
that she may also suffer this diseases.

Question 8:Under which of the following conditions are you most likely
to fall sick?
(a) When you are taking examinations.
(b) When you have travelled by bus and train for two days.
(c) When your friend is suffering from measles. Why?

Solution:In condition (c), Chance of falling sick are maximum.

Measles is an infectious viral disease of young children which spreads
through nasal or throat discharge. In. contact of a friend suffering from
measles can cause you sick.

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Chapter 14
Natural Resources
Intext Questions

On Page 193

Question 1:How is our atmosphere different from the atmosphere on
Venus and Mars?

Solution:The main difference is the composition of both the atmosphere
.The atmosphere of Earth contains a mixture of many gases like nitrogen
(78.08%), oxygen (20.95%), carbon dioxide (0.03%) and water vapour (in
varying proportion). On the other hand, the atmosphere on Venus and
Mars mainly contains carbon dioxide. i.e., about 95-97%. It may be the
reason that there are no life in the existence in both Venus and Mars.

Question 2:How does the atmosphere act as a blanket?

Solution:The atmosphere acts as a blanket by performing the following
functions:
(a) It keeps the average temperature of the Earth fairly constant during
day time and even during the course of whole year.
(b) It prevents a sudden increase in the temperature during day time.
(c) It slows down the escape of heat from the surface of the Earth into
outer space during night time.

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Question 3:What causes winds?

Solution:Unequal heating of atmospheric air generates the winds.. The
heat causes rising up of air along with water vapour. As the air rises, it
expands and cools. This cooling causes the water vapour in the air to
condense. The condensation of water occurs if some particles (like dust
particles) act as the ‘nucleus’ for these drops to stick around. These tiny
droplets grow bigger by more and more condensation of other water
droplets and finally form the clouds.

Question 4:How are clouds formed?

Solution:During the day time, water evaporates from water bodies and
goes into the atmosphere.
Air also becomes hot due to sunlight and starts rising up taking along
with water vapour.
As the air rises up, it expands and cools.

This cooling of air causes water vapour in the air to condense. The
process of condensation of water occurs. Small droplets grow and
become big by more and more condensation of other droplets of water.
These steps form the clouds.

Question 5:List any three human activities that you think would lead to
air pollution.

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Solution:The following activities lead to air pollution:
Excessive burning of fossil fuels, i.e., coal and petroleum produces high
amount of oxides of nitrogen and sulphur.
Many industries release high amount of poisonous gases into the
atmosphere causing air pollution.
Industrialization

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On Page 194

Question 1:Why do organisms need water?

Solution:Organisms need water because:

Substances dissolve in water for reactions to take place
Cellular processes need water for their functioning.
Transportation of substances within the body needs water.
Water helps in digestion of food and its absorption in the blood.
It helps to maintain body temperature.

Question 2:What is the major source of freshwater in the
city/town/village where you live?

Solution:Underground water is the major source of water in
city/town/village,. It is drawn with the help of hand pumps and tube-
wells. The other nearby sources are rivers, lakes and ponds.

Question 3:Do you know of any activity which may be polluting this
water source?

Solution:The activities which may be polluting the water bodies are:
Disposal of garbage or sewage from cities/towns and from factories.
Release of hot water from the industries which may disturb the
temperature of water body by disturbing the BOD.

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On Page 196

Question 1:How is soil formed?

Solution:The formation of soil takes place in the following ways:

Rocks near the surface of Earth are broken down by various physical,
chemical and some biological processes. This process takes millions of
years.

This weathering leads to the formation of fine particles called soil.

There are some other factors responsible to the formation of soil.
These are:

Cracking and breaking down of rocks by sun heat that causes them into
small particles.

Water dissolves rocks by freezing and fast flowing.

Wind causes erosion of rocks by fast blowing.
Lichens and mosses grow on rock surfaces and break them into powder
down and form a thin layer of soil.

Question 2:What is soil erosion?

Solution:Removal of top layer soil is known as soil erosion. It is rich in
humus and nutrients. The agents of soil erosion are mainly flowing water
or wind. Land becomes infertile if this process occurs for long time and
the reason for the same is the loss of its valuable nutrients.
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Question 3:What are the methods of preventing or reducing soil
erosion?

Solution:Preventive methods of soil erosion are as follows:

Afforestation
Contour Ploughing
Step (terrace) Farming
Soil Cover
Overgrazing

On Page 201

Question 1:What are the different states in which water is found during
the water cycle?

Solution:During the water cycle, water is found in solid state (snow, ice.
etc.), liquid state (ground water, river water, etc.) and gaseous state
(water vapours).

Question 2:Name two biologically important compounds that contain
both oxygen and nitrogen.

Solution:The biologically important compounds that contain both
oxygen and nitrogen are nitrates (NO2) and nitrates (NO3).

Question 3:List any three human activities which would lead to an
increase in the carbon dioxide content of air.

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Solution:The human activities which would lead to an increase in
CO2content of air are;
Deforestation increases the level of CO2 in the environment.
Respiration is the natural way to release of CO2 by plants. It is balanced
by the release of oxygen by plants. So, it is not harmful for the
environment.
Combustion of Fuels leads to increase in CO2 level in the atmosphere.
Fuels are burnt to carryout activities like cooking, transportation and in
industrial processes.
Question 4:What is the greenhouse effect?

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Solution:Some gases like carbon dioxide, methane, nitrous oxide prevent
the escape of heat from the Earth's surface by trapping it. This increases
the average temperature of the Earth.
This is called the green house effect. An increase in the content of such
gases would lead to a situation of global warming.

Question 5:what are the two forms of oxygen found in the atmosphere?

Solution:The two forms of oxygen found in the atmosphere are;
Elemental oxygen is normally found in the form of diatomic molecule
(O2) in the lower part of atmosphere. It is about 21% in the air and non-
poisonous.
Ozone is found in the stratosphere part of atmosphere. It contains three
atoms of oxygen (O3).

Exercises

Question 1:Why is the atmosphere essential for life?

Solution:Atmosphere is essential for life due to following reasons:

It maintains the appropriate climate for the sustain of life

It keeps the average temperature of the Earth steady during the day and
even throughout the year.

It prevents the sudden increases in temperature during the daylight
hours.

The gases it contains are required for sustaining life on Earth. These
gases are:

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o Oxygen , Carbon dioxide and Nitrogen

A thick layer of ozone (in stratosphere) of atmosphere filters the harmful
UV radiations reaching the Earth. The UV rays produce harmful effects
on all living organisms.

Question 2:Why is water essential for life?

Solution:Water is essential for life because of these reasons:

It provides medium to carry out all the cellular processes.

All the reactions that occur in our body and within cells occur between
substances that are dissolved in water.

It is required for the transportation of materials from one part of the
body to the other.

lt helps to maintain body temperature.

Water makes up about 7o % of body weight of all the living organisms.

Question 3:How are living organisms dependent on soil? Are organisms
that live in water totally independent of soil as a resource?

Solution:Living organisms depend on soil in the following ways:

Soil helps to bind the roots of plants to provide them anchorage. The
nutrients in soil are absorbed by the plants for their growth and
development.

It provides natural habitat for various living organisms, e.g., bacteria,
fungi, algae, earthworms, etc. These help to maintain the fertility of soil.

Many animals like rats, rabbits, etc., make their home in the soil.

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Earthworm performs all its activities in the soil. It maintains the fertility
of soil by releasing nitrogen rich excreta.
Organisms that live in water are not totally independent of soil as a
resource. These organisms depend on aquatic plants for food and other
substances These aquatic plants in turn require minerals for their
sustenance These minerals are carried to water bodies from soil by
rivers, rain water, etc. without the supply of minerals from the soil to the
water bodies, it is impossible to imagine aquatic life.

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Question 4:You have seen weather reports on television and in
newspapers. How, do you think we are able to predict the weather?

Solution:Meteorologists collect information regarding the pattern of
temperature, speed of wind, air presser and all other features which
influence weather. All these information are collected by remote sensing
and weather forecast satellites. This information is then compiled in
meterological departments which prepare a weather report that is
displayed on the maps. This information is further transmitted through
radio, television and newspaper.

Question 5:We know that many human activities lead to increasing
levels of pollution of the air, water-bodies and soil. Do you think that
isolating these activities to specific and Limited areas would help in
reducing pollution?

Solution:Yes. Isolating human activities to specific areas would help in
reducing levels of pollution. For example, setting up of industries in
isolated regions will control pollution to some extent. The pollution
caused by these industries will not contaminate water
resources, agriculture land, fertile land, etc.

Question 6:Write a note on how forests influence the quality of our air,
soil and water resources.

Solution:Forests influence the quality of air, soil and water resources in
the ways as below:

A. Influence of forests on air :

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Forests help to maintain oxygen and carbon dioxide balance in the air,
They reduce the level of CO2in the air and to prevent greenhouse effect.
These maintain temperature of the environment,
Forests increase the rate of photosynthesis in surrounding region.
B.Influence of forests in quality of soil:
Trees spread their roots deep inside the Earth and bind the soil particles
firmly. This reduces soil erosion.
Forests help to maintain nutrient cycles (biogeochemical cycles) in the
atmosphere.
C. Influence of forests in quality of water:
Water cycle will be maintained by the help of trees
Forests conserve water and make them available on the surface of Earth
as water sources.

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Chapter 15
Improvement in Food Resources
Intext Questions

On Page 204

Question 1:What do we get from cereals, pulses, fruits and vegetables?

Solution:The things we get from cereals, pulses, fruits and vegetables
are as follows:
Cereals(wheat, rice, maize, etc.): are the sources of carbohydrates
which provide energy.
Pulses(pea, gram and soybean, etc.): are source of proteins.
Vegetables and fruits: provide us vitamins, minerals, carbohydrates,
proteins and fats.

On Page 205

Question 1:How do biotic and abiotic factors affect crop production?

Solution:Factors which affect crop production are:
Biotic factors which cause loss of grains are rodents, pests, insects, etc.
and abiotic factors, such as temperature, humidity, moisture, etc.
Affects of both biotic and abiotic factors on crop production are in the
following ways:
Weight loss
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Infestation of insects
Poor germination ability
Discoloration
Question 2:What are the desirable agronomic characteristics for crop
improvement?

Solution:Desirable agronomic characteristics are:
Desirable characters for fodder crops are tallness and profuse branching
And
Dwarfness is desired in cereals, so that fewer nutrients are consumed by
these crops.
On Page 206

Question 1:What are the macronutrients and why are they called
macronutrients?

Solution:Macronutrients are essential elements which are required by
plants in major quantities.
Some of the main macronutrients are:
(i) N, P, S which are found in proteins.
(ii) Ca is found in cell wall.
(iii) Mg is a part of chlorophyll.

Question 2:How do plants get nutrients?

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Solution:Soil is the main source of nutrients for plants. Plants absorb the
dissolved nutrients by the roots from the soil. This water absorbed by
the roots is transported by the xylem tissue throughout the plant body.

On Page 207

Question 1:Compare the use of manure and fertilisers in maintaining soil
fertility.

Solution:Use of manure in maintaining soil quality:
(i) Manures are the very rich source of organic matter (humus) for the
soil. Humus helps to restore water retention capacity of sandy soil and
drainage in clayey soil.
(ii) Manures are the sources of soil organisms like soil friendly bacteria.

Use of fertilisers on soil quality

(i) Excess use of fertilisers cause to dryness of soil and hence the rate of
soil erosion increases.
(ii) Continuous use of fertilisers decreases the organic matter which
reduce the porosity of the soil and the plant roots do not get sufficient
oxygen.

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On Page 208
Question 1:Which of the following conditions will give the most
benefits? Why?
(i) Farmers use high-quality seeds, do not adopt irrigation or use
fertilisers.
(ii) Farmers use ordinary seeds, adopt irrigation, use fertilisers and use
crop protection measures.
(iii) Farmers use quality seeds, adopt irrigation use fertilizer and use crop
protection measures.

Solution:The (iii) third option is the best option which provides the best
conditions to get most benefits. For this, farmers use quality seeds,
adopt irrigation, use fertilizers and use crop protection measures. This is
because the use of only quality seeds is not sufficient until they are
properly irrigated, enriched with fertilizers and protected from biotic
factors.

On Page 209

Question 1:Why should preventing measures and biological control
methods be preferred for protecting crops?

Solution:In plants, diseases are caused by Pathogens.To remove
pathogens, some preventive measure and biological control methods
are used which are :

Minimise pollution without affecting the soil quality

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Simple
Economic
Question 2:What factors may be responsible for the losses of grains
during storage?

Solution:Following are the factors responsible for loss of grains during
storage:
(i) Abiotic factors like humidity and temperature.
(ii) Biotic factors like insects, rodents, birds, mites and bacteria.

On Page 210

Question 1:Which method is commonly used for improving cattle breeds
and why? How is cross breeding useful in animals?

Solution:To improve the cattle breed breeds, we generally use the cross
breeding method. It is a process in which a cross is made between
indigenous varieties of cattle by exotic breeds to get a
cross breed which is high-yielding. During cross breeding, the desired
characters taken into considerations are the offsprings should be high
Yielding, should have early maturity and should
be resistant to diseases and climatic conditions.

On Page 211

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Question 1:Discuss the implications of the following statement It is
interesting to note that poultry is India's most efficient converter of low
fibre food stuff (which is unfit for human consumption) into highly
nutritious animal protein food.

Solution:The poultry birds are efficient converters of agricultural by
products, particularly cheaper fibrous wastes into high quality meat and
in providing egg, feathers and nutrient rich manure. So, the given
statement is correctly said for the poultry birds.

Question 2:What management practices are common in dairy and
poultry farming?

Solution:Well designed and hygenic shelter.
Proper food is required to get good yield of egg and meat.
Complete protection from diseases causing agents like virus, bacteria or
fungi.
Question 3:What are the differences between broilers and layers and in
their management?

Solution:

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The poultry bird giving meat are called broilers and the egg laying birds
are called layers.
The ration required for broilers should be rich in protein with sufficient
fat. The food should also have high vitamin-A and K. Layers require
enough space and lighting.

On Page 213

Question 1:How are fish obtained?

Solution:Fish are obtained by two ways:
(i) Capture fisheries from natural resources
(ii) Fish farming by culture for commercial purposes.

Question 2:What is the advantage of composite fish culture?

Solution:Combination of five or six fish species in a single fish pond is
known as composite fish culture. Basis of selection of species is food
habits so that they do not compete for food among themselves. As a
result, the food available in all parts of the pond is utilized without
competing with each other. This increases the fish yield from the pond.

Question 3:What are the desirable characters of the varieties suitable
for honey production?

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Solution:Desirable characters in varieties for honey production are:
(a) Capacity to collect a large amount of honey.
(b)Should stay in beehive for a longer time.
(c) Should have good breeding capacity.

Question 4:What is pasturage and how is it related to honey producton?

Solution:Flowers available for nectar and pollen collection is known as
pasturage . The quality and taste of honey depends on adequate
quantity of pasturage and flowers available.

Exercises

Question1:Explain anyone method of crop production which ensures
high yield.

Solution:Inter cropping is a method used for a high yielding crop
production. In this method, two or more crops are grown
simultaneously on the same field in definite pattern. A few rows of one
crop alternate with a few rows of second crop.
Example: soybean, maize or finger millet (bajara) and caw pea (labia).
The selected crops should have different nutrient requirements. This
ensures maximum utilisatian of the nutrients supplied. It also prevents
pests and diseases from spreading to all the plants belonging to one
crop in a field. This method gives a better crop yield.

Question 2:Why are manure and fertilizers used in fields?

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Solution:The essential nutrients of the soil are full filled by manures and
fertilizers supply. Therefore, they help in good vegetative growth, giving
rise to healthy plants that rise in high crap production.
Question 3:What are the advantages of inter-cropping and crop
rotation?

Solution:Advantages of inter-cropping
Maintain soil fertility.
Save time and labour.
Increases productivity per unit area.
Both crops can be easily harvested and threshed separately.
Advantages of crop rotation
Improves soil fertilitiy.
Reduces pest infestation and diseases. Helps in weed control.
Avoids depletion of a particular nutrient from soil.
Question 4:What is genetic manipulation? How is it useful In agricultural
practices?

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