NCERT Solutions for Class 9 Science

NCERT Solutions for Class 9 Science - Free PDF Download

Class 9 Science Textbook builds the foundation of Class 9 students. NCERT Solutions for Class 9 Science is the best way to check your understanding the topics given in the chapter. Students face problem in finding the correct Class 9 Science NCERT Solutions that is why Studyrankers have prepared detailed NCERT Solutions that will every students in completing their homework and understanding the concepts. These solution will come at rescue whenever you get stuck in any question. The textbook is divided into three disciplines physics, chemistry and biology not in the textbook but in the question papers. You need to understand the basic concepts of physics and chemistry before trying to solve NCERT questions. Biology portion comes with environment part included so you must understand what is given inside a topic that will help you in solving question effectively. Class 9 NCERT Solutions provided are chapterwise so you only need to click on the desired chapter name to get solutions of that chapter.

You can also check NCERT Solutions for Class 9 Maths in order to improve application of formulas and problem solving skills.

Chapterwise NCERT Solutions for Class 9 Science

We have provided the short introduction of each chapter which you can read before starting finding the NCERT Solutions for Class 9 Science.

Why to Use NCERT Solutions for Class 9 Science from StudyRankers?

The solutions provided here accurate and prepared by Studyrankers experts that are well qualified and experienced. These will provide you a better learning experience and improving your marks in the examination. You can understand the concepts of various numerical questions in physics. It will be boost confidence of students and they can score good marks in class test or any examinations. Before solving NCERT Solutions which is given at the end of the every chapter, you need to finish all the topics and subtopics provided in that chapter. You can use our study resources in a better way and after doing this, you're ready for solving Class 9 Science NCERT Solutions. If you try to solve exercise questions then it will clear your doubts and also introduce you to various new things. Other than this, Science textbook also contains various questions in between the text of the chapter which are logic related questions, you also also need to solve as sometime these can also come in examinations and also it will improve your logical skills.

Matter in Our Surroundings

NCERT Solutions Class 9 Science Chapter 1 is about Matter. Everything in this universe is made up of material which scientists have named “matter”. The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand everything is matter. Early Indian philosophers classified matter in the form of five basic elements – the “Panch Tatva”– air, earth, fire, sky and water.

Modern day scientists have evolved two types of classification of matter based on their physical properties and chemical nature, both of them are discussed in this chapter. First physical properties are discussed. Matter is made up of particles. Size of particles are very small. There are spaces between particles. It can be observed through experiments. When solute particels are dissolved in solution. Relative experiments has been discussed. Particles of matter attract each other. All these physical properties are studied with relevant experiments. Different states of matter solid, liquid and gas is discussed with their relative physical properties like intermolecular forces of attraction, shape, size and composition of particles in them. Matter can change their state from solid to liquid, liquid to gas, gas to liquid. For example, water on heating changes to its gaseous state, steam. On cooling water changes into ice which is the solid state of water. Change in pressure can also change physical state. For example, Increase in pressure, will make particles come together, so, gas can be converted into liquid. Process of evaporation is discussed with concept of latent heat. Latent heat is the heat energy required for change in physical state.

In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation. Factors on which evaporation and its rate depend are discussed. Heat, wind, humidity are factors. Evaporation increases with increase in temperature, wind speed and decrease with humidity. Evaporation takes place of surface water by taking heat from below. Since, heat is lost, cooling effect can be observed.

Is Matter Around us pure?

So, is there any way to find out whether substances of daily use, like ghee, milk, even water is pure or not? Such ways are discussed in this chapter. In fact, milk itself is not a pure substance. It is a mixture. Mixtures are constituted by more than one kind of pure form of matter. Pure substances can be elements or compounds Different types of mixtures are discussed in this chapter-Solution, suspension and colloidal.

A solution is a homogeneous mixture of two or more substances. The major component of a solution is called the solvent, and the minor, the solute. The concentration of a solution is the amount of solute present per unit volume or per unit mass of the solution. Materials that are insoluble in a solvent and have particles that are visible to naked eyes, form a suspension. A suspension is a heterogeneous mixture. Colloids are heterogeneous mixtures in which the particle size is too small to be seen with the naked eye, but is big enough to scatter light. Colloids are useful in industry and daily life. The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium. Properties of solution, colloid and suspension are discussed in detail.

Different methods to separate components of mixture are discussed. Some of them are chromatography, distillation, Crystallisation. Physical and chemical changes are discussed. . An element is a form of matter that cannot be broken down by chemical reactions into simpler substances. A compound is a substance composed of two or more different types of elements, chemically combined in a fixed proportion. Properties of a compound are different from its constituent elements, whereas a mixture shows the properties of its constituting elements or compounds.

Atoms and Molecules

Chapter 3 NCERT Solutions of Class 9 Science is about Atoms. An Indian philosopher Maharishi Kanad, postulated that if we go on dividing matter (padarth), we shall get smaller and smaller particles. Ultimately, a stage will come when we shall come across the smallest particles beyond which further division will not be possible. He named these particles Parmanu. In same era, ancient Greek philosophers – Democritus and Leucippus suggested that if we go on dividing matter, a stage will come when particles obtained cannot be divided further. Democritus called these indivisible particles atoms which means indivisible. These were philosophies. They were not based on experiments. The chapter starts with laws of chemical compositions - Law of constant proportion, Law of conservation of mass.

During a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is known as the Law of Conservation of Mass. In a pure chemical compound, elements are always present in a definite proportion by mass. This is known as the Law of Definite Proportions. Concept of atom is discussed. An atom is the smallest particle of the element that cannot usually exist independently and retain all its chemical properties. A molecule is the smallest particle of an element or a compound capable of independent existence under ordinary conditions. It shows all the properties of the substance. A chemical formula of a compound shows its constituent elements and the number of atoms of each combining element. Clusters of atoms that act as an ion are called polyatomic ions. They carry a fixed charge on them. The chemical formula of a molecular compound is determined by the valency of each element.

In ionic compounds, the charge on each ion is used to determine the chemical formula of the compound. Scientists use the relative atomic mass scale to compare the masses of different atoms of elements. Mole concept has been dealt. Atoms of carbon-12 isotopes are assigned a relative atomic mass of 12 and the relative masses of all other atoms are obtained by comparison with the mass of a carbon-12 atom. The Avogadro constant 6.022 × 1023 is defined as the number of atoms in exactly 12 g of carbon-12. The mole is the amount of substance that contains the same number of particles (atoms/ ions/ molecules/ formula units etc.) as there are atoms in exactly 12 g of carbon-12. Mass of 1 mole of a substance is called its molar mass.

Structure of Atom

Atoms and molecules are the fundamental building blocks of matter. The existence of different kinds of matter is due to different atoms constituting them. In the chapter we are going to discuss the constituents of atoms and how this constitutes are arranged in the atom. Defining atom was the major challenge before the scientists. It was known by 1900 that the atom was indivisible particle but contained at least one sub-atomic particle – the electron identified by J.J. Thomson. Credit for the discovery of electron and proton goes to J.J. Thomson and E.Goldstein, respectively. The first model of atom was plum pudding model of Thomson. After that, Ruther fold’s idea came into existence. His atomic model was based on alpha-particle scattering experiment done by him. We have to study his experiment and its observation.

Rutherford’s model of the atom proposed that a very tiny nucleus is present inside the atom and electrons revolve around this nucleus. The stability of the atom could not be explained by this model. So, more suitable model was to be found. Neils Bohr’s model of the atom was more successful. He proposed that electrons are distributed in different shells with discrete energy around the nucleus. If the atomic shells are complete, then the atom will be stable and less reactive. J. Chadwick discovered presence of neutrons in the nucleus of an atom. So, the three sub-atomic particles of an atom are: (i) electrons, (ii) protons and (iii) neutrons. Electrons are negatively charged, protons are positively charged and neutrons have no charges. The mass of an electron is about 1/2000 times the mass of hydrogen atom. The mass of a proton and a neutron is taken as one unit each. Shells of an atom are designated as K,L,M,N,… Valency is the combining capacity of an atom.

The atomic number of an element is the same as the number of protons in the nucleus of its atom. The mass number of an atom is equal to the number of nucleons in its nucleus. Isotopes are atoms of the same element, which have different mass numbers. Isobars are atoms having the same mass number but different atomic numbers. Elements are defined by the number of protons they possess.

Fundamental Unit of Life

This was in the year 1665 when Robert Hooke made an important observation through a self-designed microscope. He saw that the cork resembled the structure of a honeycomb consisting of many little compartments. Cork is a substance which comes from the bark of a tree. Cell is a Latin word for ‘a little room’. This was an important incident took place history of science. This was the very first time that someone had observed that living things appear to consist of separate units. Cell is the basic building block of all living beings. The shape and size of cells are related to the specific function they perform. Some cells like Amoeba have changing shapes. Each living cell has the capacity to perform certain basic functions that are characteristic of all living forms. These are activities like digestion of food, respiration, transportation etc.

Structure of Cell is discussed in this chapter. Cells are enclosed by a plasma membrane composed of lipids and proteins. The cell membrane is an active part of the cell. It regulates the movement of materials between the ordered interior of the cell and the outer environment. In plant cells, a cell wall composed mainly of cellulose is located outside the cell membrane. The presence of the cell wall enables the cells of plants, fungi and bacteria to exist in hypotonic media without bursting. . The nucleus in eukaryotes is separated from the cytoplasm by double-layered membrane and it directs the life processes of the cell. Cell organelles are discussed one by one The ER functions both as a passage way for intracellular transport and as a manufacturing surface. The Golgi apparatus consists of stacks of membrane-bound vesicles that function in the storage, modification and packaging of substances manufactured in the cell. Most plant cells have large membranous organelles called plastids, which are of two types – chromoplasts and leucoplasts. Mitochondria are known as the powerhouses of the cell. Energy is generated in this.

Chromoplasts that contain chlorophyll are called chloroplasts and they perform photosynthesis. The primary function of leucoplasts is storage. Most mature plant cells have a large central vacuole that helps to maintain the turgidity of the cell and stores important substances including wastes. Prokaryotic cells have no membrane-bound organelles, their chromosomes are composed of only nucleic acid, and they have only very small ribosomes as organelles. Cell division is discussed as process of reproduction is explained in brief. Cells in organisms divide for growth of body, for replacing dead cells, and for forming gametes for reproduction.

Tissues

In unicellular organisms, a single cell performs all basic functions. For example, in Amoeba, a single cell carries out movement, intake of food and gaseous exchange and excretion. But in multi- cellular organisms there are millions of cells. Most of these cells are specialised to carry out specific functions. Each specialised function is taken up by a different group of cells. We can say that, multi-cellular organisms show division of labour. Cells specialising in one function are often grouped together in the body.

A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue. There is difference in animal tissues and plant tissues.

Plant tissues are of two main types – meristematic and permanent. Meristematic tissue is the dividing tissue present in the growing regions of the plant. Permanent tissues are derived from meristematic tissue once they lose the ability to divide. They are classified as simple and complex tissues. Parenchyma, collenchyma and sclerenchyma are three types of simple tissues. Xylem and phloem are types of complex tissues.

Animal tissues can be epithelial, connective, muscular and nervous tissue. Depending on shape and function, epithelial tissue is classified as squamous, cuboidal, columnar, ciliated and glandular.

The different types of connective tissues in our body include areolar tissue, adipose tissue, bone, tendon, ligament, cartilage and blood. Striated, unstriated and cardiac are three types of muscle tissues. Nervous tissue is made of neurons that receive and conduct impulses. Striated, unstriated and cardiac are three types of muscle tissues. Nervous tissue is made of neurons that receive and conduct impulses.

All these different types of tissues are discussed with their well labelled diagram.

Diversity in Living Organisms

Each organism is different from the other to a lesser or greater extent. We all can consider people around us. They all are having different types nose, different colours of eyes. These differences are among human beings. These differences become more if we move from human beings to monkeys, and increases more if we mover from human beings to fish. The living world is diverse in many ways.

This different variety of life around us has evolved on the earth over millions of years. However, we do not have more than a tiny fraction of this time to try and understand all these living organisms, so we cannot look at them one by one. Instead, we look for similarities among the organisms, which will allow us to put them into different classes and then study different classes or groups as a whole. Different diverse groups can be created based on certain characteristics.

Attempts at classifying living things into groups have been made since time immemorial. The characteristics of body design used for classification of plants will be very different from those important for classifying animals. This is because the basic designs are different, based on the need to make their own food (plants), or acquire it (animals). Therefore, these design features (having a skeleton, for example) are to be used to make sub-groups, rather than making broad groups.

Classification of life forms will be closely related to their evolution. All living organisms are divided on the above bases into five kingdoms, namely Monera, Protista, Fungi, Plantae and Animalia.

Plantae and Animalia are further divided into subdivisions on the basis of increasing complexity of body organisation. Plants are divided into five groups: Thallophytes, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms. Animals are divided into ten groups: Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca, Echinodermata, Protochordata and Vertebrata.

The binomial nomenclature makes for a uniform way of identification of the vast diversity of life around us. The binomial nomenclature is made up of two words – a generic name and a specific name.

Motion

Motion is defined for movement. If any object is continuously changing its position with time, it is said to be in motion. Examples are, a moving car, a boy running. If any object is not changing its position with time it is said to be in rest. A body may be in rest for one object and in motion for another. Two people sitting in train are in rest with respect to each other. But, they are in motion with some person the train. So, rest or motion is defined for some particular reference point. Here, we are basically concerned about straight line motion. Distance is total path covered by a person in motion. Speed defined as distance travelled by time taken. Displacement is defined as shortest distance between initial and final distance. Velocity is defined as displacement by time. After that, concept of uniform and Non-uniform motion is discussed. Uniform motion is defined as when same distance is travelled at same time. The acceleration of an object is the change in velocity per unit time. Uniform and non-uniform motions of objects can be shown through graphs. Distance time and velocity time graph has been discussed. The motion of an object moving at uniform acceleration can be described with the help of equation of motion.
v=u+at

S=ut +1/2 at²

v²-u²=2as

Here, v is final velocity, u is initial velocity, a is acceleration, s is displacement, t is time. If an object moves in a circular path with uniform speed, its motion is called uniform circular motion.

Force and Law of Motion

Motion was discussed in previous chapter. What causes motion? A ball on the ground, when given a small hit, does not move forever. Such observations suggest that rest is the “natural state” of an object. This remained the belief until Galileo Galilee and Isaac Newton developed an entirely different approach to understand motion. In force, both magnitude and direction is considered. Concept of balanced and unbalanced force is discussed. In balanced force, net force is zero, as equal magnitude of force is applied from opposite sides. Net force is zero. In unbalanced force, net force is not equal to zero. For change of state from rest to motion, or motion to rest, or to change velocity of an object, unbalanced force is required. So, this much is the concept of force. Newton’s laws of motion are discussed after that.

First law of motion: An object continues to be in a state of rest or of uniform motion along a straight line unless acted upon by an unbalanced force. The natural tendency of objects to resist a change in their state of rest or of uniform motion is called inertia. The first law is also known as law of inertia. The law has been explained with several examples. The mass of an object is a measure of its inertia. Its SI unit is kilogram (kg). Force of friction always opposes motion of objects.

Second law of motion says, The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force. From this, it can be derived force = mass multiplied by acceleration. The SI unit of force is kg m s –2 . This is also known as newton and represented by the symbol N. A force of one newton produces an acceleration of 1 ms –2 on an object of mass 1 kg. The momentum of an object is the product of its mass and velocity and has the same direction as that of the velocity. Its SI unit is kg ms –1 ,also known as Newton.

Third law of motion says, To every action, there is an equal and opposite reaction and they act on two different bodies. In an isolated system (where there is no external force), the total momentum remains conserved.

Gravitation

In previous chapter it is discussed force is required for motion. We have learnt that a force is needed to change the speed or the direction of motion of an object. We always observe that an object dropped from a height falls towards the earth. We know that all the planets go around the Sun. The moon goes around the earth. In all these cases, there must be some force acting on the objects, the planets and on the moon. Sir Isaac Newton figured out that force responsible for all these things is Gradational force. The gravitational force is force acting between two bodies due to their masses. The chapter starts with the concept of gravitation. After that Universal Law of Gravitation was discussed. The gravitational force acting between two bodies is directly proportional to the product of their masses and inversely proportional to the square of distance between them.

The gravitational force is responsible for motion of planets, free fall of any object, tides in oceans. Whenever objects fall towards the earth under this force alone, we say that the objects are in free fall. g is signified as acceleration due to gravity. it decrease with increase in altitude. If two bodies are thrown from same height, irrespective of their masses both of them will fall together with same acceleration due to gravity g. Equations of motions can be written accordingly. The concept of mass and weight is discussed. Mass of an object is the measure of its inertia. Weight is gravitational force acting on the body. For body of mass m, weight is mg, where g is acceleration due to gravity. g is depends upon mass of earth and radius of earth. So, value of g will vary with that. Moon is having lesser mass and radius than earth. Value of g is 1/6 th of earth at moon. So, weight of any object on moon will be 1/6 th of his weight at earth, though the mass will remain the same. It is important to understand the difference between mass and weight.

Thrust and Pressure are discussed after that. Thrust is vertical force acting on any object. it can be due to weight. Pressure is defined as thrust/area. The concept has been explained in chapter with suitable examples. Thrust is also created by liquids kept on the base and walls of the container in which they are enclosed. Pressure exerted in any confined mass of fluid is transmitted undiminished in all directions.

When an object is placed in the liquid, upward force is experienced on it. The force is Buoyant force. The magnitude of this buoyant force depends on the density of the fluid. "When a body is immersed fully or partially in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it." This is principle. Relative density is the ratio of density of that object with respect of density of water. If it is more than 1, the object will sink in water, otherwise it will float.

Work and Energy

In previous chapter, we have discussed about force, motion and gravitation. Another concept that helps us understand and interpret many natural phenomena is ‘work. We need energy for other activities like playing, singing, reading, writing, thinking, jumping, cycling and running. Activities that are strenuous require more energy. Work and energy are related. Both are explained one by one.

First, the concept of work is to be understood. Definition of work done is different from day to day life. Work is defined for a force. Work is defined as force multiplied by displacement. If there is no displacement, we say there is no work. The concept is dealt here. SI unit of work done is joule. 1 Joule of work done is defined as if 1 Newton of force make a displacement of 1m in direction of applied force. It is important, in displacement direction is considered. If the force and displacement are in same direction the work done is positive. If force and work done are perpendicular to each other, work done is zero. If displacement is made in opposite direction of force applied, the work done is in opposite direction.

Energy is defined as capacity to do the work. The Sun is the biggest natural source of energy to us. How does an object with energy do work? An object that possesses energy can exert a force on another object. When this happens, energy is transferred from the former to the latter. The second object may move as it receives energy and therefore do some work. The unit of energy is, therefore, the same as that of work, that is, joule (J). 1 J is the energy required to do 1 joule of work.

Forms of Energy are discussed after that. Kinetic energy is energy possessed by a body in motion. Kinetic energy of a body moving with a certain velocity is equal to the work done on it to make it acquire that velocity. It is given as 1/2 mv2. m is mass of body in motion and v is velocity of body. Potential energy is defined as energy stored in an object. For example, when an spring is contracted or expanded, some energy is stored in it. The spring comes back to its original position when left using energy stored in it. Similarly, if some object is kept at some height, gravitational potential energy is stored in it. We can say, the potential energy possessed by the object is the energy present in it by virtue of its position or configuration.

Energy is conserved. If an object is kept at height it gains potential energy, when dropped its potential energy started converting into kinetic energy. At any point of time during free fall, the net energy is same. That is some of potential energy and kinetic energy will remain always same. This is law of conservation of energy.

Rate of doing work is known as Power. Power = work/time. The SI unit of power is watt. 1 W = 1 J/s. The energy used in one hour at the rate of 1kW is called 1 kW h. It is also known as commercial unit of energy.

Sound

Sound is a form of energy which produces a sensation of hearing in our ears. Different types of sound we hear in our day to day to life. These are the sounds of bird, horn of cars, children crying around and many more. There are also other forms of energy like mechanical energy, light energy etc. We know that energy is conserved and can change its form. When we clap, the mechanical energy is converted into sound energy.

Sound is produced due to vibration of different objects. Sound travels as a longitudinal wave through a material medium. Sound travels as successive compressions and rarefactions in the medium. In sound propagation, it is the energy of the sound that travels and not the particles of the medium. Sound cannot travel in vacuum. The change in density from one maximum value to the minimum value and again to the maximum value makes one complete oscillation.

The distance between two consecutive compressions or two consecutive rarefaction is called the wavelength, λ. The time taken by the wave for one complete oscillation of the density or pressure of the medium is called the time period, T. The number of complete oscillations per unit time is called the frequency. It is 1/(Time Period).

The speed v, frequency ν, and wavelength λ, of sound are related by the equation, v = λν. The speed of sound depends primarily on the nature and the temperature of the transmitting medium. The law of reflection of sound states that the directions in which the sound is incident and reflected make equal angles with the normal to the reflecting surface at the point of incidence and the three lie in the same plane.

For hearing a distinct sound, the time interval between the original sound and the reflected one must be at least 0.1 s. The persistence of sound in an auditorium is the result of repeated reflections of sound and is called reverberation. Sound properties such as pitch, loudness and quality are determined by the corresponding wave properties. Loudness is a physiological response of the ear to the intensity of sound. The amount of sound energy passing each second through unit area is called the intensity of sound.

The audible range of hearing for average human beings is in the frequency range of 20 Hz – 20 kHz.
Sound waves with frequencies below the audible range are termed “infrasonic” and those above the audible range are termed “ultrasonic”. Ultrasound has many medical and industrial applications. The SONAR technique is used to determine the depth of the sea and to locate under water hills, valleys, submarines, icebergs, sunken ships etc.

Why do we Fall Ill?

Health and disease in human communities are very complex issues. In our organs or tissues, there are various specialised activities going on – the heart is beating, the lungs are breathing, the kidney is filtering urine, the brain is thinking. All these activities are interconnected. For healthy well-being, it is very important every organ of human beings should work properly. In this chapter the term health is defined and explained.

Health is a state of physical, mental and social well-being. The health of an individual is dependent on his/her physical surroundings and his/her economic status.

Diseases are conditions in which there is lack of physical, mental and social well-being. Different types of diseases are explained. Diseases are classified as acute or chronic, depending on their duration. Disease may be due to infectious or non-infectious causes. Infectious agents belong to different categories of organisms. These organisms may be unicellular and microscopic or multicellular. The category to which a disease-causing organism belongs decides the type of treatment. Infectious agents are spread through air, water, physical contact or vectors. It is important to note down. Prevention of disease is more desirable than its successful treatment.

Infectious diseases can be prevented by public health hygiene measures that reduce exposure to infectious agents. Infectious diseases can also be prevented by using immunisation. Effective prevention of infectious diseases in the community requires that everyone should have access to public hygiene and immunisation.

Natural Resources

Chapter 14 Class 9 Science NCERT Solutions is about Natural Resources. The resources available on the Earth and the energy from the Sun are necessary to meet the basic requirements of all life-forms on the Earth. These are the land, the water and the air. All these resources are discussed one by one.

Air is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour. Role of atmosphere as climate controller is discussed. After that, wind formation is discussed. Movement of air form land to sea and sea to land is discussed.

Uneven heating of air over land and water-bodies causes winds. Evaporation of water from water-bodies and subsequent condensation give us rain.

The fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur. When these fuels are burnt, nitrogen and sulphur too are burnt and this produces different oxides of nitrogen and sulphur.

Rainfall patterns depend on the prevailing wind patterns in an area. Various nutrients are used again and again in a cyclic fashion. This leads to a certain balance between the various components of the biosphere.

Water is another important Natural resource. The availability of water is not the only factor that decides the sustainability of life in a region. Other factors like the temperature and nature of soil also matter. But water is one of the major resources which determine life on land. Addition of undesirable substances to water-bodies, removal of desirable substances from water-bodies, change in temperature can cause water pollution.

Soil is an important resource that decides the diversity of life in an area. Earth is called the crust and the minerals found in this layer supply a variety of nutrients to life-forms. Process of soil formation has been explained in this chapter.

Biogeochemical Cycles has been explained- The water cycle, the Nitrogen cycle, Carbon Cycle, Greenhouse effect and Oxygen cycle has been explained.

Formation, importance and reasons of depletion of Ozone layer has been explained in brief.

We need to conserve our natural resources and use them in a sustainable manner. That is the motto of this chapter.

Improvement in Food Resources

All living organisms need food. Food supplies proteins, carbohydrates, fats, vitamins and minerals, all of which we require for body development, growth and health. Both plants and animals are major sources of food for us. We obtain most of this food from agriculture and animal husbandry. The improvement in food resources includes both enhancing the quantity and quality of food resources.

Efforts have been made to fulfil the required nutrition of the growing population. This has been done in the form of green revolution, white revolution and green revolution. But, these have caused loss of natural resources. Manure and fertilizers are the main sources of nutrient supply to crops. Organic farming is a farming system with minimal or no use of chemicals as fertilizers, herbicides, pesticides etc. and with a maximum input of organic manures, recycled farm wastes, and bio-agents, with healthy cropping systems. Mixed farming is a system of farming on a particular farm which includes crop production, rising of livestock etc. Mixed cropping is growing of two or more crops simultaneously on the same piece of land. Growing two or more crops in definite row patterns is known as inter-cropping.

The growing of different crops on a piece of land in pre-planned succession is called crop rotation. Varietal improvement is required for higher yield, good quality, biotic and abiotic resistance, shortening the maturity duration, wider adaptability and desirable agronomic characteristics.

Farm animals require proper care and management such as shelter, feeding, breeding and disease control. This is called animal husbandry. Poultry farming is done to raise domestic fowls. Poultry production includes egg production and broiler production for poultry meat.

To enhance poultry production, cross breeding is done between Indian and exotic breeds for variety improvement.

Fish may be obtained from marine resources as well as inland resources. To increase production of fish, they can be cultured in marine and inland ecosystems. Marine fish capture is done by fishing nets guided by echo- sounders and satellites. Composite fish culture system is commonly used for fish farming. Bee-keeping is done to get honey and wax. All such things are discussed in chapter with different conditions responsible for getting improvised food from them.

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How many chapters are there in Science Class 9 textbook?

There are total 15 chapters in the Science Class 9 textbook through which you will learn about various new things and concepts which will enhance your knowledge.

How many units does the NCERT textbook of Class 9 Science consist of?

There are total 5 units which are divided into 15 chapters. Each will provide you with an interesting details of various branches such as physics, chemistry, biology and environment and ecology.

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