RBSE Class 9 Science Chapter 13: Environment Important Textbook Questions and Solutions

Environment has been defined as the group of all the conditions, which affects the existence, growth and progress of an organism or a group of organisms. Thus, it includes all the components and conditions of the surrounding that affects the existence, growth and progress of organisms. It can also be said that environment is a “Life Support System” because the existence and perpetuation of all the constituent organisms of the biosphere depends on it.

RBSE Class 9 Science Chapter 13 solutions will help students in understanding how a question should be answered. These solutions has been designed to help the students solve the textbook questions with ease. The RBSE Solutions for Science Chapter 13: Environment provided here comes with well-prepared exercises, along with detailed explanations, structured by our expert teachers that further makes learning and understanding of concepts an easy task.

Students can also get all subjects Class 9 solutions for Rajasthan Board here.

RBSE Class 9 Science Chapter 13: Objective Textbook Questions and Solutions

Q1. Which of the following is not an air pollutant?

(A) Marsh gases

(B) SO2

(C) CO

(D) DDT2

Answer: D

Q2. Who coined the term ecosystem?

(A) Odum

(B) Tansley

(C) Haeckel

(D) Haber

Answer: B

Q3. The main gas responsible for the GreenHouse effect is:

(A) CO2

(B) SO2

(C) NO2

(D) CO

Answer: A

Q4. Which of the following is an artificial ecosystem?

(A) Forest

(B) Grassland

(C) Desert

(D) Cropland

Answer: D

Q5. Adsorption, absorption, condensation etc. are useful for the control of which type of pollution:

(A) Air

(B) Water

(C) Thermal

(D) Soil

Answer: A

RBSE Class 9 Science Chapter 13: Very Short Answer Type Questions and Solutions

Q6. Define the term ‘ecology’.

Answer: Ecology is a branch of science including human science, population, community, ecosystem and biosphere. Ecology is the study of organisms, environment and how the organisms interact with each other and their environment. It is studied at various levels such as organism, population, community, biosphere and ecosystem.

Q7. Write the names of two main air pollutants.

Answer: The names of two main air pollutants are: Carbon Monoxide and Sulfur Dioxide

Q8. What are decomposers?

Answer: Decomposers : They mainly include the bacteria and the fungi. In an ecosystem, bacteria usually degrade the dead animal matter while the fungi are responsible for the degradation of plant material.

Q9. Define noise pollution.

Answer: The word noise is derived from a Latin word ‘Nausea’ which means sickness in which one feels to vomit. Noise is an unpleasant and undesirable sound, which leads to discomfort to human beings. The intensity of sound is measured in decibels (dB). The faintest sound which can be heard by Human ear is 1 Db. Due to increasing noise around the civilizations; noise pollution has become a matter of concern. Some of its major causes are vehicles, aircraft, industrial machines, loudspeakers, crackers, etc. Some other appliances also contribute to noise pollution like television, transistor, radio, etc. when used at high volume.

Q10. Write the chemical conditions produced by thermal pollution.

Answer: The chemical conditions produced by thermal pollution are:

  • Increase in chemical oxygen demand (COD)
  • Increase in biological oxygen demand (BOD)
  • Increase in toxicity

RBSE Class 9 Science Chapter 13: Short Answer Type Questions and Solutions

Q11. Write the names and examples of the abiotic components of the ecosystem.

Answer: The names and examples of the abiotic components of the ecosystem are inorganic, organic and climatic factors like – air, water, soil, sunlight, etc.

  • Inorganic substances : It includes nutritive elements and components like – carbon, nitrogen, sulphur, phosphorus, carbon-di-oxide, water, etc. They are cycled in the ecosystem.
  • Organic compounds : It includes proteins, fats, carbohydrates, humic substances etc. They are basically related to the living body and connect the abiotic and biotic components.
  • Climatic factors : They are of two types-

Environmental factors like sunlight, temperature, humidity, precipitation etc.

Edaphic factors like topography, soil texture etc.

Q12. What are biotic components and how are they categorized?

Answer: The living components of the environment are known as the biotic components. They can be further categorized as producers, consumers and decomposers.

  • Producers : These are the chlorophyll containing plants, which include algae, grass, trees etc. They convert solar energy into chemical energy during photosynthesis. They are the source of food for majority of animals. They are also termed as autotrophs as they synthesize their own food.
  • Consumers : These are the organisms which cannot synthesize their own food and depend on other organisms for their nourishment. They are known as the consumers and are heterotrophs. Mostly they are animals. Animals which directly depend upon plants for their food are known as herbivorous. For example – grasshopper, goat, sheep, rabbit etc. The animals which depend upon herbivorous animals for their food requirement are known as carnivorous. For example snake, lion, frog etc. They may be predators or parasites. The animals which can derive their food from both plants and animals are known as omnivorous. For example – cockroach, human beings, etc.
  • Decomposers : This category mainly includes bacteria and fungi. In an ecosystem bacteria generally work upon the animal tissue while fungi on plant tissue. They digest dead organic matter with the help of enzymes and in this way the basic elements of the cell components are released into the atmosphere, which are then reused by producers.

Q13. Explain types of ecosystem?

Answer: Ecosystem are of two types :

  • Natural ecosystem : They are naturally under their own control and are self sustained with the human interference of the least order.

(a) Terrestrial ecosystem : Example- Forest, grassland, desert etc.

(b) Aquatic ecosystem : They are of two types (i) Fresh water and (ii) Marine water. The freshwater ecosystem again may be of two types: lotic (example – river, streams etc.) and lentic (example – pond, lake etc.).

  • Artificial ecosystem : These ecosystems are man-made and are under their control. Example cropland which includes fields of wheat, bajra, rice etc. Here man tries to control the biotic community and physicochemical factors. Apart from the above systems, even the space eco-system has been recognized.

Q14. What is Global Warming?

Answer: Global warming is the phenomenon of gradual increase in temperature near the Earth’s surface. This phenomenon has been observed over the past one or two centuries. This change has disturbed the climatic pattern of the earth. However, the concept of global warming is quite controversial. But, the scientists have provided relevant data in support of the fact that the temperature of the Earth is rising constantly.

There are several causes of global warming which have a negative effect on human, plant and animal lives. These causes may be natural or might be the outcome of human activities.

Q15. What is artificial ecosystem ? Give example.

Answer: These ecosystems are man-made and are under their control. Example: cropland which includes fields of wheat, bajra, rice etc. Here man tries to control the biotic community and physicochemical factors. Apart from the above systems, even the space eco-system has been recognized.

Q16. What is water cycle?

Answer: The entire process by which water forms water vapour, forms clouds and then comes back to the earth surface in the form of rains and then flows into the oceans is known as the water cycle.

Q17. What is Pollution?

Answer: Pollution is the unwanted change in the air, water, soil, biological creatures etc. which degrades the basic composition of these resources. It can have adverse impact on the biotic components, specially man, by bringing about direct or indirect changes in one or more abiotic components of the environment. Some pollutants like bad-odour, noise etc. can have psychological consequences.

Q18. Explain the natural causes of Air pollution?

Answer: Air pollution may be caused naturally or it can be man made. Following are the natural causes of air pollution:

  • Volcanic eruption : In this gaseous pollutants such as Sulphur-di-oxide (SO2 ), Hydrogen sulphide (H2 S), Carbon-mono-oxide (CO) etc. are evolved.
  • Forest fires.
  • Marsh gases (like methane – CH4 )
  • Products of natural decomposition of various organic and inorganic substances.
  • Suspended particulate matter.
  • Extra-terrestrial substances.
  • Cosmic-dust.
  • Allergens and irritants like pollens, spores etc.

Q20. What are the effects of Air Pollution?

Answer: The effects of Air Pollution are:

  • Sulphur-di-oxide : Chest congestion, headache, vomiting etc. Disorders caused by it may become fatal.
  • Oxides of nitrogen : They cease the activity of cilia. This is the reason why carbon and dust particles may reach the lungs causing various respiratory disorders.
  • Hydrogen sulphide : Causes irritation in throat and eyes and nausea.
  • Carbon-mono-oxide : It reduces the oxygen carrying capacity of blood and causes fatigue.
  • Hydrogen cyanide : It affects the nerve cells and results in dry throat, vague vision, headache etc.
  • Ammonia : It causes swelling in upper respiratory tract.

Q21. Explain the causes of Soil Pollution?

Answer: The causes of Soil Pollution are:

  • Industrial wastes/effluent : The solid and liquid effluent from industries are spread on the soil without any type of pre-treatment. The fly-ash which spreads for miles harm the soil to a great extent. The minerals, chemicals, toxins etc. of the effluents pollute the soil and make it barren.
  • Urban effluents : Paper, glass, metallic boxes, plastic, fibres, food-waste, rubber, dyes, paint etc. are the solid urban wastes, which pollute the soil to a large extent. The liquid urban wastes include the organic and inorganic chemicals, oil, grease, toxic substance etc. which spread on the soil and pollute it. These effluents have pathogens which cause various diseases.
  • Agricultural activities : In-judicious, unforeseen use of chemical fertilizers in excess and excessive irrigation makes the soil waterlogged and devoids the soil of the essential nutrients. This makes the soil barren.

Q22. How can we control Air Pollution?

Answer: Few strategies of controlling Air Pollution are:

  • Adsorption : It is a physical process that depends upon the surface properties of some substances. In it the flow of liquid and gas is coupled with a solid, so that the solid holds a thin film of the liquid or gas on the outside surface – thus entrapping it. Activated charcoal, silica gel. Resin etc. are used as adsorbents. In this process the adsorbents may be reused, hence it is an economic (thrift) process.
  • Absorption : This also is a physical process. In it the gases are allowed to dissolve in fluids. Water is the best solvent or medium for absorption.
  • Condensation : The gaseous vapours are controlled by condensation. It is the best method for removing the hydrocarbons having very low vapour pressure at ambient temperature, (i.e. air temperature of the surroundings). Air pollution can be satisfactorily controlled by using water or air cooled condensers.
  • By chemical reactions : Pollutants can be removed from the air by various chemical reactions.

Q23. Give the examples of pollutants of anthropogenic origin (manmade).

Answer: The examples of pollutants of anthropogenic origin are:

  • Industrial effluents (discharge)
  • Vehicular effluents
  • Domestic effluents
  • Substances produced by burning of fossils
  • Explosives and other chemicals used in wars etc.
  • Various substances used in agriculture and agricultural practices.

Q24. Name the fourteen big rivers which became victims of intense water pollution.

Answer: All the fourteen big rivers of Bharat, including Ganga, Yamuna, Godavari, Gomti, Kosi, Kauvery, Ravi, Son, Chinaab, Jhelum, Narmada, Mahi, Tapti and Krishna are the victims of intense water pollution.

Q25. What measures should be taken for ensuring water availability?

Answer: Following measures may be taken for ensuring water availability :

  • Take proper measures to control pollution of puddles, rivers, rivulets, lakes etc.
  • Conservation of natural vegetation.
  • Improvement in the catchment area of rivers, rivulets, lakes, ponds etc.
  • Proper sewage treatment before immersing it in water bodies.
  • Construction of water reservoirs.
  • Development of underground water reservoirs on large scale.
  • Rain water harvesting.
  • Recharging the groundwater and aquifers.

Q26. How can we control water pollution?

Answer: Integrated water and waste management programs are required to get rid of the menace of water pollution. This approach comprises

  • Water treatment
  • Wastewater treatment
  • Waste water recycling
  • Product recovery.

Q27. What are the techniques of waste water treatment to control water pollution?

Answer: The following techniques of waste water treatment can be made use of:

  • Oxidation and stabilization ponds – The effluent water is stabilized in these ponds which gets oxidised in sufficient sun-light and hot-climate.
  • Treatment of sewage effluent water and reuse it for agricultural purpose.
  • Remove the pollutants :

(a) separation of salts by reverse osmosis

(b) removal of metals by electrolysis, ion dispersion resins etc.

(c) Controlled culture of water hyacinth (though it is very harmful for the existence of water bodies)

(d) Root zone treatment technique.

Q28. What are the various substances which pollute water by dissolving in it?

Answer: The various substances which pollute water by dissolving in it include:

  • Acids
  • Base
  • Coal
  • Dyes
  • Fats, Soap and waxes
  • Gaseous adjunct (dissolved gases)
  • Fertilizers
  • Insecticides
  • Weedicides
  • Farm products
  • Poisonous metals like mercury and its compounds
  • Synthetic detergents
  • Oil
  • Proteins and carbohydrates
  • Dissolved solids
  • Other organic pollutants
  • Radioactive substances
  • Thermal pollutants, which include heated industrial waste water or water from the cooling towers of the nuclear power plants
  • Colours
  • Biological pollutants – Virus, Algae, Fungi etc.
  • Odour and Turbidity etc.

Q29. Write the biological effects produced by thermal pollution.

Answer: The biological effects produced by thermal pollution are:

  • Changes in physiological activities
  • Change in Metabolic rates
  • Change in biochemical parameters
  • Interference in reproduction
  • Variation in the rate of reproduction
  • Increase in direct mortality of aquatic organisms.

Q30. Explain the structure of the ecosystem.

Answer: Ecosystem is made up of two main components: biotic and abiotic.

Abiotic components : It includes inorganic, organic and climatic factors like – air, water, soil, sunlight etc.

(i) Inorganic substances: It includes nutritive elements and components like – carbon, nitrogen, sulphur, phosphorus, carbon-di-oxide, water etc. They are cycled in the ecosystem.

(ii) Organic compounds : It includes proteins, fats, carbohydrates, humic substances etc. They are basically related to the living body and connect the abiotic and biotic components.

(iii) Climatic factors: They are of two types –

(a) Environmental factors like sunlight, temperature, humidity, precipitation etc.

(b) Edaphic factors like topography, soil texture etc.

Biotic components: The living components of the environment are known as the biotic components. They can be further categorized as producers, consumers and decomposers.

Producers: These are the chlorophyll containing plants which include algae, grass, trees etc. They convert solar energy into chemical energy during photosynthesis. They are the source of food for majority of animals. They are also termed as autotrophs as they synthesize their own food.

Consumers: These are the organisms which cannot synthesize their own food and depend on other organisms for their nourishment. They are known as the consumers and are heterotrophs. Mostly they are animals. Animals which directly depend upon plants for their food are known as herbivorous. For example – grasshopper, goat, sheep, rabbit etc. The animals which depend upon herbivorous animals for their food requirement are known as carnivorous. For example snake, lion, frog etc. They may be predators or parasites. The animals which can derive their food from both plants and animals are known as omnivorous. For: example – cockroach, man etc.

Decomposers: This category mainly includes bacteria and fungi. In an ecosystem bacteria generally work upon the animal tissue while fungi on plant tissue. They digest dead organic matter with the help of enzymes and in this way the basic elements of the cell components are released into the atmosphere, which are then reused by producers.

RBSE Class 9 Science Chapter 13: Essay Type Questions and Solutions

Q31. Explain the causes and effects of air pollution.

Answer: The effects of Air Pollution are:

  • Sulphur-di-oxide : Chest congestion, headache, vomiting etc. Disorders caused by it may become fatal.
  • Oxides of nitrogen : They cease the activity of cilia. This is the reason why carbon and dust particles may reach the lungs causing various respiratory disorders.
  • Hydrogen sulphide : Causes irritation in throat and eyes and nausea.
  • Carbon-mono-oxide : It reduces the oxygen carrying capacity of blood and causes fatigue.
  • Hydrogen cyanide : It affects the nerve cells and results in dry throat, vague vision, headache etc.
  • Ammonia : It causes swelling in upper respiratory tract.

The causes of Air Pollution are:

  • Volcanic eruption : In this gaseous pollutants such as Sulphur-di-oxide (SO2 ), Hydrogen sulphide (H2 S), Carbon-mono-oxide (CO) etc. are evolved.
  • Forest fires.
  • Marsh gases (like methane – CH4 )
  • Products of natural decomposition of various organic and inorganic substances.
  • Suspended particulate matter.
  • Extra-terrestrial substances.
  • Cosmic-dust.
  • Allergens and irritants like pollens, spores etc.

Q32. Give a schematic description of the nitrogen cycle.

Answer: Nearly 78% of our atmosphere is made up of nitrogen gas. This gas is the component of many molecules essential for life. Nitrogen fixing bacteria are found either as free living forms or in symbiotic association with some types of dicots. Generally, these nitrogen fixing bacteria are present in special root nodules of pod bearing plants. Apart from these bacteria, the nitrogen atoms also form nitrates and nitrites by various physical reactions. The high temperature and pressure generated in the atmosphere at the time of lightning, converts nitrogen to oxides of nitrogen. These oxides dissolve in rain water and form acid which fall on earth surface; then after it is used by various life forms.

The plants, generally, absorb nitrates and nitrites and convert them into amino-acids which are used in protein synthesis. There are some other biochemical options which are used for synthesis of other nitrogen containing complex molecules. These proteins and other complex compounds are then used by the animals. When the plant or animal dies, various bacteria present in the soil convert the nitrogenous compounds into nitrates and nitrites and other types of bacteria break down these nitrate and nitrite molecule into nitrogen elements.

Thus, in nature there operates a nitrogen cycle in which nitrogen, passing from its basic form in the atmosphere converts into simple molecules in the soil and water and then in living beings it forms very complex compounds. Later on, they break down, releasing the nitrogen atoms back into nature.

Q33. What is Greenhouse Effect?

Answer: In a glass house, the internal temperature is very high as compared to the external temperature because the glass does not allow the heat waves to transmit back in the atmosphere. This concept is made use of in maintaining warm tropical plants in the cold climate. This type of cover is known as a greenhouse.

Similar, phenomenon occurs in the atmosphere too. Some gases prevent the escape of heat into the outer atmosphere. Increase in the amount of such gases in the atmosphere may rise the average temperature of the earth’s atmosphere. This type of effect is known as the greenhouse effect. Carbon-di-oxide is a greenhouse gas. Increase in the amount of carbon-di-oxide in the atmosphere will increase the heat content of the atmosphere. These activities lead to global warming.

Q34. Define Ozone Layer. How Ozone Layer is degrading day by day.

Answer: The elemental oxygen is generally present in the form of bi-atomic molecule. However, in the upper layer of atmosphere tri-atomic molecules are also present. Its formula is O3 and is known as ozone. In contrast to the biatomic oxygen molecules, the ozone is toxic. It absorbs the harmful radiations of the sun. Thus it prevents those radiations from reaching the earth surface which may harm various life forms.

Recently, it has been detected that the ozone layer present in upper atmosphere is degrading.

Different types of compounds, made by man, for example the chloro-fluoro-carbons (CFCs) are present in the atmosphere in a stable state. CFCs are chlorine and fluorine containing organic molecules. They are very stable and do not degrade even by biological processes. Once they reach near the ozone molecules, they react with them. This results in decrease in the amount of ozone and this leads to thinning of the ozone layer. Recently, ozone hole has been observed above Antarctica.

Q35: State the difference between lithosphere, hydrosphere and atmosphere?

Answer: The differences between lithosphere, hydrosphere and atmosphere are as follows:

Atmosphere: The atmosphere is a protective layer that safeguards the earth from the harsh conditions of the solar system. The air is a poor conductor of heat. During the day, it prevents a sudden increase in the temperature of the earth and prevents the heat to escape to the outer space during the night. It keeps the average temperature of the earth steady.

Lithosphere – A lithosphere is the rigid, outermost shell on Earth. It is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of a rocky planet, the crust, is defined on the basis of its chemistry and mineralogy. This includes the crust and the uppermost mantle, which constitute the hard and rigid outer layer of the Earth. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the soil forming process is called the pedosphere.

Hydrosphere – The hydrosphere is the combined mass of water found on, under, and above the surface of the earth. It has been estimated that there are 1386 million cubic kilometres of water on earth. This includes water in liquid and frozen forms in groundwater, oceans, lakes and streams approximately 75% of Earth’s surface, an area of some 361 million square kilometers is covered by ocean.

Q36. Describe briefly about Oxygen Cycle?

Answer: Oxygen is one of the most abundant element on earth. Its quantity is nearly 21% of the atmospheric gases. It is also present on a large scale, on the earth surface, in the form of water and other compounds and in air in the form of carbon-di-oxide also. It is present in the form of metal and silicon oxides in the earth’s crust. It is also present in the form of carbonate, sulphate, nitrate and oxides of minerals. It is an essential component of biomolecules like – carbohydrates, proteins, nucleic acid and fats or lipids.

Oxygen from atmosphere is used in three processes – Respiration, combustion and formation of oxides of nitrogen. Oxygen returns to the atmosphere by only one process i.e. photosynthesis. This forms the outline of oxygen cycle in nature. Although we consider oxygen to be of importance in the respiratory process but for some organisms, mainly bacteria elemental oxygen is toxic. Actually nitrogen fixation does not take place in the presence of oxygen.

Q37. Define Biosphere?

Answer: Biosphere or the living world is the narrow zone of earth where land, water and air interact with each other to support life. The plant and animal kingdom together form the biosphere. Biosphere is subdivided into three parts:

Lithosphere – Includes all solid components of the earth

Hydrosphere – Includes all liquid components of the earth.

Atmosphere – Includes the gaseous part of earth.

Q38. What are the sources of Thermal Pollutions?

Answer: The sources of thermal pollution include:

Coolants of nuclear power plants: The temperature of the effluent coolants of these power plants is on an average 10ºC higher than the water entering the system. This affects aquatic life adversely.

Effluents of the thermal power plants: These power plants use coal for generating electricity. For the purpose, water from nearest water body is made use of and then the effluent having a temperature of at least 15ºC more is again sent to the water body. This warm effluent reduces the amount of dissolved oxygen, which results in the death of fishes and other aquatic living beings.

Effluents from the hydro electric power plants : This is perhaps the only process of power generation in which there is negative thermal loading of a water system.

Industrial effluents : The cloth, paper, sugar etc. industries produce heated effluents which have a temperature that is approximately 8 to 10ºC high. The effect caused by the temperature of these effluents depends on the original temperature and size of the water body.

Domestic sewage: The domestic sewage is immersed in water bodies without pre-treatment. Normally, the temperature of the domestic waste is higher and hence, may increase the water temperature. This leads to reduction of the number of aquatic organisms. This may also lead to anaerobic conditions because of which fishes may die.

Q39. Explain the effect on Biological Communities due to thermal pollution.

Answer: The effect on Biological Communities due to thermal pollution are as follows:

  • The distribution patterns of living organisms change.
  • Unwanted changes in algal population.
  • Formation of water blooms by cyanobacteria.
  • Attack of destructive organisms.

Q40. In modern-agricultural practices, what are the chemicals used to protect plants?

Answer: In modern-agricultural practices various chemicals like- pesticides (like DDT), fungicides bactericides and herbicides are used on large scale to protect plants from pathogens, diseases, weeds, etc. These chemicals do not decompose, in general and remain in the soil. Plants, at times, absorb them and they reach the higher trophic levels by means of the food chain. In this process, there is biomagnification of these substances and they become toxic for human consumption.

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