Month: September 2024

JAC Board Class 9th Science Solutions Chapter 12 Sound

JAC Class 9th Science Sound InText Questions and Answers

Poge 162

Question 1.
How does the sound produced by a vibrating object in a medium reach your ear?
Answer:
When an object vibrates, it sets the particles of the medium around it in vibration. The particles in the medium in contact with the vibrating object are displaced from their equilibrium position. It then exerts a force on the adjacent particles. After displacing the adjacent particle, the first particle of the medium comes back to its original position. This process continues in the medium till the sound reaches our ear.

Page 163

Question 1.
Explain how sound is produced by your school bell.
Answer:
When the bell continues to vibrate forward and backward, it creates a series of compressions and rarefactions resulting in the production of sound.

Question 2.
Why are sound waves called mechanical waves?
Answer:
Sound waves need material medium to propagate, therefore, they are called mechanical waves. Sound waves can propagate through a medium only because of the interaction of the particles present in that medium.

Question 3.
Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer:
No, because a sound wave needs a medium through which it can propagate. Since there is no atmosphere on the moon, no material medium is available and we cannot hear any sound on the moon.

Page 166

Question 1.
Which wave property determines:
(a) loudness
(b) pitch?
Answer:
(a) Amplitude
(b) Frequency

Question 2.
Guess which sound has a higher pitch: guitar or car horn?
Answer:
Guitar has a higher pitch than car horn, because sound produced by the strings of guitar has a higher frequency than that of a car horn. The higher the frequency, the higher is the pitch.

Page 166

Question 1.
What are wavelength, frequency, time period and amplitude of a sound wave?
Answer:

1. Wavelength: The distance between two consecutive compressions or two consecutive rarefactions is known as wavelength. Its SI unit is metre (m).
2. Frequency: The number of complete oscillations per second is known as the frequency of a sound wave. It is measured in hertz (Hz).
3. Time period: The time taken by two consecutive compressions or rarefactions to cross a fixed point is called the time period of the wave.
4. Amplitude: The maximum height reached by the crest or the maximum depth reached by the trough of a
   sound wave is called its amplitude.

Question 2.
How are the wavelength and frequency of a sound wave related to its speed?
Answer:
Speed, wavelength and frequency of a sound wave are related by the following equation:
Speed (v) = Wavelength (λ) x Frequency (v)
V = λ × v

Question 3.
Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Answer:
Frequency of the sound wave, v = 220 Hz
Speed of the sound wave, v = 440 ms^-1
For a sound wave,
Speed = Wavelength × Frequency
v = λ × v
∴ λ = \(\frac{v}{v}\) = \(\frac{440}{220}\) = 2
Hence, the wavelength of the sound wave is 2 m.

Question 4.
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:
The time interval between two successive compressions is equal to the time period of the wave. This time period is reciprocal of the frequency of the wave and is given by the relation:
T = \( \frac{1}{\text { Frequency }}\) = \(\frac{1}{500}\) = 0.002 s

Page 166

Question 1.
Distinguish between loudness and intensity of sound.
Answer:
Intensity of a sound wave is defined as the amount of sound energy passing through a unit area per second. Loudness is a measure of the response of the ear to the sound. The loudness of a sound is defined by its amplitude.

Page 167

Question 1.
In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?
Answer:
The speed of sound depends on the nature of the medium. Sound travels the fastest in solids. Its speed decreases in liquids and it is the slowest in gases. Therefore, for a given temperature, sound travels fastest in iron.

Page 168

Question 1.
An echo is heard in 3s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 ms^-1?
Answer:
Speed of sound, v = 342 ms^-1
Echo returns in time, t = 3s
Distance travelled by sound
= v × t = 342 × 3 = 1026 m
In the given time interval, sound has to travel a distance that is twice the distance between the reflecting surface and the source.
Hence, the distance of the reflecting surface from the source
= \(\frac{1026}{2}\) m = 513 m.

Page 169

Question 1.
Why are the ceilings of concert halls curved?
Answer:
The ceilings of concert halls are curved so that the sound, after reflection (from the walls), spreads uniformly in all directions.

Page 170

Question 1.
What is the audible range of the average human ear?
Answer:
The audible range of an average human ear is 20 Hz to 20,000 Hz.

Question 2.
What is the range of frequencies associated with
(a) Infrasound?
(b) Ultrasound?
Answer:
(a) Infrasound has frequencies less than 20 Hz.
(b) Ultrasound has frequencies more than 20,000 Hz.

Page 172

Question 1.
A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff?
Answer:
Time taken by the sonar pulse to return, t = 1.02s
Speed of sound in salt water, v = 1531 ms^-1
Distance travelled by the sonar pulse
= Speed of sound × Time taken
= 1.02 × 1531 = 1561.62 m
Distance travelled by the sonar pulse during its transmission and reception in water
= 2 × actual distance = 2d
Actual distance of the cliff from the submarine, d
Distance travelled by the sonar pulse
= \(\frac{Distance travelled by the sonar pulse2}{2}\) = \( \frac{1561.62}{2}\) = 780.81 m

JAC Class 9th Science Sound Textbook Questions and Answers

Question 1.
What is sound and how is it produced?
Answer:
Sound is a form of energy which gives the sensation of hearing. It is produced by the vibrations caused in the medium by vibrating objects.

Question 2.
Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.
Answer:
When a vibrating body moves forward, it creates a region of high pressure in its vicinity. This region of high pressure is known as compression. When it moves backward, it creates a region of low pres – sure in its vicinity. This region is known as rarefaction. As the body continues to move forward and backward, it produces a series of compressions and rarefactions. This is shown in the figure below.

Question 3.
Cite an experiment to show’ that sound needs a material medium for its propagation.
Answer:
Take an electric bell and an air tight glass bell jar connected to a vacuum pump. Suspend the bell inside the jar, and press the switch of the bell. You will be able to hear the bell ring. Now pump out the air from the glass jar. The sound of the bell will become progressively fainter and after some time, the sound will not be heard. This is so because almost all air has been pumped out. This shows that sound needs a material medium to travel.

Question 4.
Why is sound wave called a longitudinal wave?
Answer:
Sound wave is called a longitudinal wave because it is produced by compressions and rarefactions in the air. The air particles vibrate parallel to the direction of propagation of sound.

Question 5.
Which characteristics of the sound help you to identify your friend by his voice while sitting with others in a dark room?
Answer:
The quality or timber of sound enables us to identify our friend by his voice.

Question 6.
Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
Answer:
The speed of sound (344 m/s) is less than the speed of light (3 × 108 m/s). Sound of thunder takes more time to reach the earth as compared to light. Hence, a flash is seen before we hear a thunder.

Question 7.
A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 ms^-1.
Answer:
For a sound wave,
Speed = Wavelength × Frequency = λ × v
Speed of sound in air = 344 m/s (Given)
(a) For, v = 20 Hz
λ₁ = \(\frac{v}{v}\) = \(\frac{344}{20}\)
= 17.2 m

(b) For, v = 20000 Hz
λ₂ = \(\frac{v}{v}\) = \(\frac{344}{20,000}\)
= 0.0172 m
Hence, for humans, the wavelength range for hearing is 0.0172 m to 17.2 m.

Question 8.
Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.
Answer:
Velocity of sound in air = 346 m/s
Velocity of sound wave in aluminium = 6420 m/s
Let the length of the rod be l
Time taken for sound wave in air,
t₁ =\(\frac{l}{Velocity in air}\)
Velocity in air Time taken for sound wave in aluminium,
t₂ = \(\frac{l}{Velocity in aluminium}\)
Therefore, = \(\frac{\mathrm{t}_{1}}{\mathrm{t}_{2}}\)
= \(\frac{Velocity in aluminium}{Velocity in air}\) = \(\frac{6420}{ 346}\)
= 18.55

Question 9.
The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
Answer:
Frequency = 100 Hz (given)
This means that the source of sound vibrates 100 times in one second. Therefore, number of vibrations in 1 minute, i.e., in 60 seconds = 100 × 60 = 6000 times.

Question 10.
Does sound follow the same laws of reflection as light does? Explain.
Answer:
Sound follows the same laws of reflection as light does. The incident sound wave and the reflected sound wave make equal angles with the normal to the surface at the point of incidence. Also, the incident sound wave, the reflected sound wave and the normal to the point of incidence, all lie in the same plane.

Question 11.
When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?
Answer:
An echo is heard when the time for the reflected sound is heard after 0.1s.
Time taken = \(\frac{Total distance}{Velocity}\)
On a hotter day, the velocity of sound is more. If the time taken by echo is less than 0.1s, it will not be heard.

Question 12.
Give two practical applications of reflection of sound waves.
Answer:
Two practical applications of reflection of sound waves are:

1. Reflection of sound is used to measure the distance and speed of underwater objects. This technique is known as SONAR.
2. Working of a stethoscope is also based on reflection of sound. In a stethoscope, the sound of the patient’s heartbeat reaches the doctor’s ear by multiple reflections.

Question 13.
A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g =10 ms^-2 and speed of sound = 340 ms^-1.
Answer:
Height of the tower, s = 500m
Velocity of sound, v = 340 ms^-1.
Acceleration due to gravity, g = 10 ms^-2
Initial velocity of the stone, u = 0 (since the stone is initially at rest)
Let the time taken by the stone to fall to the base of the tower be t₁
According to the second equation of motion:
s= ut₁ + \(\frac{1}{2} \mathrm{gt}_{1}^{2}\)
500 = (0 × t₁) + \( \left(\frac{1}{2} \times 10 \times t_{1}^{2}\right)\)
\( \mathrm{t}_{1}^{2}\) = 100
t₁ = 10s
Now, time taken by the sound to reach the top from the base of the tower, t₂ = \(\frac{500}{340}\) = 1.47s
Therefore, the splash is heard at the top after time, t.
Where, t = t₁ + t₂ = 10 + 1.47 = 11.47s.

Question 14.
A sound wave travels at a speed of 339 ms^-1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
Answer:
Speed of sound, v = 339 ms^-1
Wavelength of sound,
λ = 1.5 cm = 0.015 m
Speed of sound = Wavelength × Frequency
v = λ × v
∴ v = \(\frac{v}{λ}\) = \(\frac{ 339 }{0.015}\) = 22600 Hz
The frequency range of audible sound for humans is between 20 Hz to 20,000 Hz. Since the frequency of the given sound is more than 20,000 Hz, it is not audible.

Question 15.
What is reverberation? How can it be reduced?
Answer:
The repeated or multiple reflections of sound in a large enclosed space is known as reverberation. The reverberation can be reduced by covering the ceiling and walls of the enclosed space with sound absorbing materials, such as fibre board, loose woollens, etc.

Question 16.
What is loudness of sound? What factors does it depend on?
Answer:
Loudness is a measure of sound energy reaching the ear per second. Loudness depends on the amplitude of vibrations. In fact, loudness is proportional to the square of the amplitude of vibrations.

Question 17.
Explain how bats use ultrasound to catch a prey.
Answer:
Bats produce high – pitched ultrasonic squeaks. These high – pitched squeaks are reflected by objects and their preys and returned to the bats’ ears. This allows the bat to know the distance and direction of their prey.

Question 18.
How is ultrasound used for cleaning?
Answer:
Objects to be cleaned are put in a cleaning solution and ultrasonic sound waves are passed through that solution. The high frequency of these ultrasonic waves detaches the dirt from the objects.

Question 19.
Explain the working and application of a sonar.
Answer:
SONAR is an acronym for sound Navigation And Ranging. It is an acoustic device used to measure the depth, direction and speed of underwater objects, such as submarines and ship wrecks, with the help of ultrasounds. It is also used to measure the depth of seas and oceans.

A beam of ultrasonic sound is produced and transmitted by the transducer (a device that produces ultrasonic sound) of the SONAR, which travels through sea water.
The echo produced by the reflection of this ultrasonic sound is detected and recorded by the detector, which is converted into electrical signals. The distance (d) of the underwater object is calculated from the time (t) taken by the echo to return with speed (v) which is given by 2d = v × t.
This method of measuring distance is also known as ‘echo – ranging’.

Question 20.
A sonar device on a submarine sends out a signal and receives an echo 5s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625m.
Time taken to hear the echo, t = 5s
Distance of the object from the submarine, d = 3625m
Total distance travelled by the sonar waves during the transmission and reception in water = 2d
Velocity of sound in water,
v = \(\frac{2 \mathrm{~d}}{t}\) = \(\frac{2 \times 3625}{5}\) = 1450ms^-1

Question 21.
Explain how7 defects in a metal block can be detected using ultrasound.
Answer:
Defects in metal blocks do not allow ultrasound waves to pass through them and they are reflected back. This fact is used to detect defects in metal blocks. Ultrasound is passed through one end of a metal block and detectors are placed on the other end. The defective part of the metal block does not allow ultrasound to pass through it. As a result, it will not be detected by the detector. Hence, defects in metal blocks can be detected using ultrasound.

Question 22.
Explain how the human ear works.
Answer:
The human ear consists of three parts – outer ear, middle ear and inner ear.

1. Outer ear: This is also called ‘pinna’. It collects the sound from the surroundings and directs it towards auditory canal.
2. Middle ear: The sound reaches the end of the auditory canal where there is a thin membrane called eardrum or tympanic membrane. The sound waves set this membrane in vibration. These vibrations are amplified by three small bones. Malleus, Incus and Stapes in the middle ear.
3. Inner ear: These vibrations reach the cochlea in the inner ear and are converted into electrical signals which are sent to the brain by the auditory nerve, and the brain interprets them as sound.
   

JAC Class 9 Science Solutions

JAC Board Class 9th Science Solutions Chapter Chapter 15 Improvement in Food Resources

JAC Class 9th Science Improvement in Food Resources InText Questions and Answers

Page 204

Question 1.
What do we get from cereals, pulses, fruits and vegetables?
Answer:
Cereals provide us carbohydrates which give energy. Pulses provide us proteins which build our body. Vegetables and fruits provide vitamins and minerals.

Page 205

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

1. Factors responsible for loss of grains, during storage and production are:
   • Biotic factors like rodents, pests, insects, etc.
   • Abiotic factors like temperature, humidity, moisture, etc.
2. Combination of both biotic and abiotic factors causes:
   • infestation of insects
   • weight loss
   • poor germination ability
   • degradation in quality
   • discolouration
   • poor market price

Question 2.
What are the desirable agronomic characteristics for crop improvements?
Answer:
Desirable agronomic characteristics for crop improvements are as follows:

1. Tallness and profuse branching are desirable characters for fodder crops.
2. Dwarfness is desired in cereals so that less nutrients are consumed by these crops.

Page 206

Question 1.
What are macronutrients and why are they called macronutrients?
Answer:
Macronutrients are the essential elements which are utilised by plants in large quantities. Many macronutrients are required by the plants for the following functions:

1. As the constituent of protoplasm
2. N, P, S are present in proteins
3. Ca is present in cell wall
4. Mg is an important constituent of chlorophyll

Question 2.
How do plants get nutrients?
Answer:
Plants get nutrients from air, water and soil. There are sixteen nutrients essential for the growth of plants. Carbon and oxygen are supplied by air. Hydrogen is supplied by water. The remaining thirteen nutrients are supplied by soil.

Page 207

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

1. Effects of using manures on soil quality:
   • The manures enrich the soil with nutrients.
   • They provide a lot of organic matter (humus) to the soil and thus restore water retention capacity of sandy soils and drainage in clayey soils.
   • The addition of manures reduces soil erosion.
   • They provide food for soil organisms, like soil friendly bacteria.
2. Effects of using fertilisers on soil quality:
   • By the continuous use of fertilisers, the soil becomes powdery, dry and the rate of soil erosion increases.
   • By the use of fertilisers, the organic matter decreases which further decrease the porosity of soil and the plant roots do not get oxygen properly.
   • The nature of soil changes to acidic or basic.

Page 208

Question 1.
Which of the following conditions will give the most benefits? Why?
(a) Farmers use high-quality seeds, do not adopt irrigation or use fertilisers.
(b) Farmers use ordinary seeds, adopt irrigation, use fertilisers.
(c) Farmers use quality seeds, adopt irrigation, use fertilisers and use crop protection measures.
Answer:
Use of any quality seeds is not sufficient until they are properly irrigated, enriched with fertilisers and protected from biotic factors. Hence, option (c) will give the most benefits.

Page 209

Question 1.
Why should preventive measures and biological control methods be preferred for protecting crops?
Answer:
Diseases in plants are caused by pathogens. To get rid of pathogens, some preventive measures and biological control methods are used as they are simple, economical and minimise pollution without affecting the soil quality.

Question 2.
What factors may be responsible for losses of grains during storage?
Answer:
The factors responsible for the losses of grains during storage are:

1. Abiotic factors like moisture (present in food grains), humidity (of air) and temperature.
2. Biotic factors like insects, rodents, birds, mites, bacteria and fungi.

Page 210

Question 1.
Which method is commonly used for improving cattle breeds and why?
Answer:
Cross breeding is a process in which indigenous varieties of cattle are crossed by exotic breeds to get a breed which is high yielding. During cross – breeding, the desired characters are taken into consideration. The offspring should be high yielding, should have early maturity and should be resistant to climatic conditions.

Page 211

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 foodstuff (which is unfit for human consumption) into highly nutritious animal protein food”.
Answer:
The basic aim of poultry farming is to raise domestic fowl for egg production and chicken for meat. These poultry birds are not only the efficient converters of agricultural by – products, particularly cheaper fibrous wastes (which are unfit for human consumption but can be formulated into cheaper diets for poultry birds) into high – quality meat but also help in providing eggs, feathers and nutrient – rich manure. For this reason, it is said that, “poultry is India’s most efficient converter of low fibre foodstuff into highly nutritious animal protein food”.

Page 211

Question 1.
What management practices are common in dairy and poultry farming?
Answer:
Management practices are common in dairy and poultry farming:

1. Shelter: Dairy animals and poultry birds require proper shelter, i.e., well – designed, dairy and hygienic shelter.
2. Feeding: To get good yield of food production, proper feed is provided to dairy animals and poultry birds.
3. Caring for animal health: Animals and birds must be protected from diseases caused by viruses, bacteria or fungi.

Question 2.
What are the differences between broilers and layers and in their management?
Answer:
The poultry bird groomed for obtaining meat is called broiler. The egg laying poultry bird is called layer. The housing, nutritional and environmental requirements of broilers are somewhat different from those of egg layers. The ration (daily food requirement) for broilers is protein- rich with adequate fat. The level of vitamins A and K is kept high in the poultry feeds. Layers require enough space and proper lightning. They are vaccinated against various diseases. Broilers are taken care of to avoid mortality and to maintain feathering and carcass quality.

Page 213

Question 1.
How are fish obtained?
Answer:
There are two ways of obtaining fish. One is from natural resources, which is called capture fishing. The other way is by fish farming, which is called culture fishery.

Question 2.
What are the advantages of composite fish culture?
Answer:
In composite fish culture, a combination of five or six fish species is cultured in a single fish pond. These species are selected so that they do not compete for food among themselves and have different types of food habits. As a result, the food available in all the parts of the pond is used. For example, Catlas are surface feeders, Rohus feed in the middle – zone of the pond, Mrigals and common carps are bottom feeders and grass carps feed on the weeds. Together, these species can use all the food in the pond without competing with each other. This increases the fish yield from the pond.

Page 213

Question 1.
What are the desirable characters of bee varieties suitable for honey production?
Answer:
The desirable characters of bee varieties suitable for honey production:

1. The variety of bee should be able to collect a large amount of honey.
2. The bees should stay in a given beehive for a longer period.
3. The bees should have capacity of breeding well.
4. The variety of bee should be disease resistant.

Question 2.
What is pasturage and how is it related to honey production?
Answer:
Pasturage means the flowers available to the bees for nectar and pollen collection. In addition to adequate quantities of pasturage, the kind of flowers available will determine the taste of the honey.

JAC Class 9th Science Improvement in Food Resources Textbook Questions and Answers

Question 1.
Explain any one method of crop production which ensures high yield.
Answer:
One method used for crop production which ensures high yield is plant breeding. It is the science involved in improving the varieties of crops by breeding plants. The plants from different areas/places are picked up with desired traits and then hybridisation or cross-breeding of these varieties is done to obtain a plant/crop of desired characteristics. The high – yielding crop variety shows the following characteristics. High yield, early maturation, less water for irrigation, better quality seeds are produced, less fertiliser required, adapts itself to the environmental conditions.

Question 2.
Why are manure and fertilisers used in fields?
Answer:
Manures and fertilisers are used in fields to enrich the soil with the required nutrients, to improve fertility of the soil, crop yield and quality. Manure helps in enriching the soil with organic matter and nutrients. This improves the fertility and structure of the soil. On the other hand, fertilisers ensure a healthy growth and development in plants. They are a good source of nitrogen, phosphorus and potassium. A balanced combination of manures and fertilisers in the soil should be used to get an optimum yield.

Question 3.
What are the advantages of intercropping and crop rotation?
Answer:
Both Intercropping and crop rotation are used to get maximum benefit on limited land:

1. Intercropping ensures maximum utilisation of the nutrients supplied by the soil. It helps in preventing pests and diseases to spread throughout the field. It also increases soil fertility.
2. Crop rotation prevents soil depletion, increases soil fertility, and reduces soil erosion. Both these methods reduce the need for fertilisers. These also help in controlling weeds and control the growth of pathogens and pests in the crops.

Question 4.
What is genetic manipulation? How is it useful in agricultural practices?
Answer:
Genetic manipulation is a process of incorporating desirable (genes) characters into crop varieties by hybridisation. Hybridisation involves crossing between genetically dissimilar plants. This is done for production of varieties with desirable characteristics like profuse branching in fodder crops, high – yielding varieties in maize, wheat, etc.
Genetic manipulation is useful in developing varieties which show:

1. increased yield
2. better quality
3. shorter and early maturity period
4. better adaptability to adverse environmental conditions
5. desirable characteristics

Question 5.
How do storage grain losses occur?
Answer:
The storage grain losses can occur due to the following reasons:

1. Biotic factors: Like insects, rodents, fungi, mites and bacteria These organisms infect the grains and degrade the quantity and quality of the grains.
2. Abiotic factors: Various factors, like inappropriate moisture and temperature, can lead to the loss of grains and their discolouration, loss in weight, etc.

Question 6.
How do good animal husbandry practices benefit farmers?
Answer:
Good animal husbandry practices produce draught animals that can be used for the agricultural purposes like tilling, irrigation and carting. The draught animals perform these works and make the work easy for the farmer.

Question 7.
What are the benefits of cattle farming?
Answer:
Cattle farming is beneficial in the following ways:

1. Milk production is increased by high – yielding animals.
2. Good quality of meat, fibre and skin can be obtained.
3. Good breed of draught animals can be obtained.

Question 8.
For increasing production, what is common in poultry, fisheries, and bee-keeping?
Answer:
Proper management technique is a common factor in increasing production in poultry, fisheries, and beekeeping. Management techniques like regular cleaning of farms are of utmost importance. Maintenance of temperature, prevention, and cure of diseases of the farmed organisms are also required to increase the number of animals and the yield.

Question 9.
How do you differentiate among capture fishing, mariculture and aquaculture?
Answer:

1. Capture fishing is the method of obtaining fishes from natural resources.
2. Mariculture is the culture of marine fishes for commercial use. It is the farming of marine fishes of high economic value in seawater. For example, the farming of finned fishes like mullets, bhetki, pearl spots, etc.
3. Aquaculture involves the production of aquatic animals that are of high economic value such as prawns, lobsters, fishes, crabs, etc.

JAC Class 9 Science Solutions

JAC Board Class 9th Science Solutions Chapter 14 Natural Resources

JAC Class 9th Science Natural Resources InText Questions and Answers

Page 193

Question 1.
How is our atmosphere different from the atmospheres on Venus and Mars?
Answer:
Our atmosphere contains gases like nitrogen, oxygen, carbon dioxide, water vapour and other gases in very small amounts. Atmospheres of Venus and Mars have about 95% of carbon dioxide. So, life is not possible there.

Question 2.
How does the atmosphere act as a blanket?
Answer:
The atmosphere acts as a blanket by performing the following functions:

1. It keeps the average temperature of the earth fairly constant during day time and even during the course of whole year. .
2. It prevents a sudden increase in the temperature during day time.
3. It slows down the escape of heat from the surface of the earth into outer space during night time.

Question 3.
What causes winds?
Answer:
An uneven heating of the earth’s surface causes winds. On being heated, air becomes lighter and rises up. As a result, a region of low pressure is created. Then, air from a high pressure region moves to the low pressure region, causing wind.

Question 4.
How are clouds formed?
Answer:
During daytime, on being heated, a large amount of water evaporates from various water bodies and goes into the air. A part of this water vapour also reaches the atmosphere through biological activities. This causes the air in the atmosphere to heat up. When this heated air rises, it expands and cools, which results in the condensation of water vapour forming water droplets. The presence of dust and other suspended particles in air also facilitates the process of condensation. The formation of water droplets leads to the formation of clouds.

Question 5.
List any three human activities that you think would lead to air pollution.
Answer:
Three human activities which lead to air pollution are:
(a) Burning of fuels like coal, petroleum, kerosene.
(b) Smoke released from industries.
(c) Emissions from vehicles.

Page 194

Question 1.
Why do organisms need water?
Answer:
Organisms need water for the following activities:
(a) All cellular processes occur inside water.
(b) Transportation of substances in our body takes place by dissolving in water.
(c) Terrestrial animals require water for getting rid of wastes from their body.
(d) Plants require water for photosynthesis.

Question 2.
What is the major source of fresh water in the city/town/village where you live?
Answer:
The major sources of water are:
(a) Water in the form of snow, ice – covered mountains
(b) Underground water in well
(c) Surface water like in lakes, rivers, ponds
(d) Rainfall
(e) Stored rainwater in tanks, dams

Question 3.
Do you know of any activity which may be polluting this water source?
Answer:
Yes, the water is polluted by sewage, dumping waste in river, factory waste, etc.

Page 196

Question 1.
How is soil formed?
Answer:
Soil is formed by breaking down of rocks at or near the surface of the earth through various physical, chemical and biological processes by various factors such as the sun, water, wind and living organisms.
1. Sun: During day time, the rocks get heated up. This causes the rocks to expand. During night time, these rocks cool down and contract. However, all parts of the rocks do not undergo expansion and contraction at the same rate. This causes the formation of cracks and breaking up of huge rocks into smaller pieces.

2. Water: Water catalyses the process of formation of soil in two ways:

• Water goes into the cracks and crevices formed in the rocks. When this water freezes, its volume increases. As a result, the size of the cracks also increases. This helps in the weathering of rocks.
• Running water wears away hard rocks over long periods of time. Water moving in fast speed carries big and small particles of rocks downstream. These rocks rub against each other, resulting in breaking down of rocks. These smaller particles are carried away by running water and deposited down its path.

3. Wind: Strong winds carry away rocks, which causes rubbing of rocks. This results in the breaking down of rocks into smaller and smaller particles.

4. Living organisms: Some living organisms like lichens help in the formation of soil. Lichens also grow on rocks. During their growth, lichens release certain substances, which cause the rock surface to powder down forming a thin layer of soil. On this thin layer of soil, some small plants like moss also grow. They further cause the breaking down of the rock particles with the growth of their roots.

Question 2.
What is soil erosion?
Answer:
The removal of fertile topsoil by air, wind or water is called soil erosion.

Question 3.
What are the methods of preventing or reducing soil erosion?
Answer:
The following are some methods which can prevent or reduce soil erosion:

1. Soil should have some vegetation, like grass, growing on it, so that it does not get carried away by rainwater or wind.
2. Afforestation or planting of trees, so that roots hold the soil and prevent soil erosion.
3. Overgrazing should be avoided.

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

1. Water in liquid state: present in various sources like lakes, rivers, underground water, etc.
2. Water vapour (gaseous state): Water evaporates from water bodies and due to transpiration by plants.
3. Clouds: Condensed water vapour is present in clouds.
4. Water as rain is in liquid state while that as snowfall is in solid state.

Question 2.
Name two biologically important compounds that contain both oxygen and nitrogen?
Answer:
Two biologically important compounds that contain both oxygen and nitrogen are:

• Amino acids
• Deoxyribonucleic acid (DNA)

Question 3.
List any three human activities which would lead to an increase in the carbon dioxide content of air.
Answer:
The following activities of human beings may increase carbon dioxide content of air:
(a) Burning of fuels in various processes like heating, cooking, transportation and industries.
(b) Human induced forest fires.
(c) The process of deforestation, i.e., the cutting down of trees. This decreases the uptake of carbon dioxide for photosynthesis. Eventually, the content of carbon dioxide increases.

Question 4.
What is the greenhouse effect?
Answer:
Some gases like carbon dioxide, methane and 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 greenhouse effect.

Question 5.
What are the two forms of oxygen found in the atmosphere?
Answer:
Oxygen is present in free form like O₂ (oxygen molecule), ozone (O₃) and combined form like oxides of metals and non-metals, e.g., CO₂, NO₂, SO₂, H₂O, etc.

JAC Class 9th Science Natural Resources Textbook Questions and Answers

Question 1.
Why is the atmosphere essential for life?
Answer:
Atmosphere is very important for sustaining life:

1. It contains various gases like O₂, CO₂, N₂ which are required for various life processes by plants and animals.
2. CO₂ gas is used by plants to prepare food by the process called photosynthesis
3. Oxygen is required for burning, combustion and for respiration.
4. Ozone layer is acting as a protective layer, which prevents the harmful U.V. rays to enter the earth’s atmosphere.
5. C₂ dissolved in water forms carbonates which are required by the animals to form shells.

Question 2.
Why is water essential for life?
Answer:
Water is essential for life because of the following reasons:

1. All life processes that take place in the cells require water medium.
2. Water is needed for transportation of various substances from one part of the body to the other in dissolved form.
3. All reactions taking place within our body and within the cells occur between substances that are dissolved in water.
4. Terrestrial life – forms require fresh water for the transportation of substances and also to get rid of high amounts of wastes.

Question 3.
How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Answer:
All living organisms are directly or indirectly dependent on soil. dissolved in water forms carbonates which are required by the animals to form shells.

Question 2.
Why is water essential for life?
Answer:
Water is essential for life because of the following reasons:

1. All life processes that take place in the cells require water medium.
2. Water is needed for transportation of various substances from one part of the body to the other in dissolved form.
3. All reactions taking place within our body and within the cells occur between substances that are dissolved in water.
4. Terrestrial life-forms require fresh water for the transportation of substances and also to get rid of high amounts of wastes.

Question 3.
How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Answer:
All living organisms are directly or indirectly dependent on soil. Plants obtain water and minerals from the soil and prepare food for themselves and animals. Other organisms that live in water are not totally independent on soil because the microbes growing on the soil in water are the primary producers in the soil which start the food chain and even other microbes that live in soil help in the decomposition of dead plants and animals in water to return the nutrients and elements back to the water.

Question 4.
You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Answer:
Prediction of weather can be done by studying wind patterns which decide rainfall patterns. It also shows areas of low pressure and high pressure. In large parts of India, rains are mostly. brought by the South – West or North – East monsoons.

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?
Answer:
If the human activities which lead to increasing levels of air, water and soil pollution are spread in wider area, the pollutants will spread more, but if these are limited and confined to a place, the soil and water pollution can be controlled to some extent and air pollution can also be minimised.

Question 6.
Write a note on how forests influence the quality of air, soil and water resources.
Answer:
Forests influence the quality of air, soil and water resources in various ways. Some of them are as follows:
1. Forests balance the percentage of carbon dioxide and oxygen in the atmosphere. The increasing amount of carbon dioxide caused by human activities is balanced by a larger
intake of carbon dioxide by plants during the process of photosynthesis. Simultaneously, a large amount of oxygen is released.

2. Forests prevent soil erosion. Roots of plants bind the soil tightly in a way that the surface of the soil cannot be eroded away by wind, water, etc.

3. Forests help in the replenishment of water resources. During the process of transpiration, a huge amount of water vapour goes into the air and condenses to form clouds. These clouds cause rainfall that recharges water bodies. Also, roots of plants facilitate the seepage of rainwater into the ground and help to recharge the water table.

JAC Class 9 Science Solutions