# Class 9 science notes, answers: SEBA, NBSE, TBSE, NCERT

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Get class 9 Science notes, questions, answers, solutions, textual answers, pdf, extras of SEBA (Board of Secondary Education, Assam), NBSE (Nagaland Board of School Education), TBSE (Tripura Board of School Education) or any other board following NCERT books. The solutions made available here should be seen as references and nothing more.

We have provided a short introduction to each chapter so that you get some ideas about what you are going to read in that chapter. Click on the links mentioned under each chapter to get the solutions for that chapter. The in-text questions refer to the questions that are in the middle of each chapter, while the exercise questions refer to the questions asked at the end of each chapter.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 1: Matter in our Surroundings

Summary: Everything in our universe from the air we breathe, the stars, the stones and even the food we eat is made up of matter. Although ancient Indian and Egyptian civilizations classified matter in their own way, scientists today have classified matter based on its physical and chemical properties. In this chapter, Matter in our Surroundings, we will study the physical properties of nature. The matter is made up of particles and the three physical states that it can exist in are solid, liquid and gas. Depending on which state it is in, the arrangement of the particles, their characteristics, and their behaviour can vastly differ. For example, the way that a solid matter reacts to heat and pressure can be very different from the way that a liquid and gaseous matter reacts to heat and pressure. In fact, we also learn that the states of matter are inter-convertible based on the temperature and pressure applied. A most common example of this is water which can exist as solid ice, as liquid water and as steam in a gaseous form. We will also learn about different phenomenons like what happens to the different states of matter when heat energy is applied.

#### SEBA, NBSE, TBSE,NCERT solutions for class 9 science Chapter 2: Is Matter Around Us Pure?

Summary: Based on recent scientific research matter is now divided into Solid, Liquid, Gas, Plasma and Bose-Einstein Condensate. All matter around us exists in a pure state as a substance or an impure state as mixtures. Pure substances have the same elements and they cannot be separated into another matter. But mixtures may have different elements or substances that can be separated. In this chapter, Is Matter Around Us Pure? we will understand ways of separating different kinds of mixtures by using methods like evaporation, centrifugation, distillation, etc. These methods are selected based on the physical and chemical properties of the mixtures and the different substances in them. We will also understand how simple mixtures show the properties of the elements or the substances in them and do not combine into something else, e.g., a mixture of iron and sulphur. However, when the substances in a mixture react with one another to form a completely new substance, it is called a compound, e.g. iron and sulphur react to form iron sulphide. Lastly, we will learn that just like each element behaves in a particular way and has a unique set of chemical properties, compounds also behave in a particular way because different elements combine in a fixed ration to form them.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 3: Atoms and Molecules

Summary: In this chapter, Atoms and Molecules, we will learn about ‘Laws of Chemical Combinations’ which are rules that substances follow when reacting chemically to form different products. There are 5 such laws and we will study the first two which are ‘Law of Conservation of Mass’ and ‘Law of Constant Proportion’. The first law explains that no matter how reactants react to form a product, their total mass remains the same as the total mass of the end products because mass cannot be created or destroyed. The second law states that elements always combine together in the same proportion of their mass to form a particular compound. John Dalton was the first scientist to explain both these laws with his theory, ‘Dalton’s Atomic Theory’. His theory stated that all matter is made up of tiny particles called atoms which cannot be created, divided or destroyed and that they combine in a particular way to form compounds. The IUPAC lists the symbols of the atoms of different elements. We will also learn about the atomic masses of all these elements. Except the atoms of Noble Gases, atoms of all other elements react and exist as a combination of elements known as molecules which have their characteristics like atomicity and molecular mass.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 4: Structure of Atom

Summary: John Dalton’s concept that atoms are indivisible had to be discarded at the end of the 19th century when scientists found that atoms are further made up of ‘subatomic particles. The subatomic particles were charged (electrons and protons) and neutral (neutrons). The three scientists who discovered electrons, protons and neutrons with the help of different experiments were, respectively, J.J. Thomson, E. Goldstein, and J. Chadwick. After this discovery, several scientists like J.J. Thomson, Rutherford, and Neil Bohr tried to prove the model of the atom and how the subatomic particles resided inside the atom. Out of these, Rutherford’s model could explain most of the questions and that most of the atom’s mass is concentrated in the nucleus which is made up of protons and neutrons which are positively charged while the electrons revolve around the nucleus in well-defined orbits. But Bohr’s model further clarified that the electrons revolved around the nucleus in special orbits called discrete orbits and only radiated energy while moving from one orbit to another. Finally, in this chapter, Structure of Atom, we will learn about atomic numbers and mass numbers as well as the distribution of electrons and their valence. Finally, we will learn about how atomic numbers and mass numbers change to create isotopes and isobars.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 5: Fundamental Unit of Life: Cell

Summary: In this chapter, Fundamental Unit of Life: Cell, we will learn about the Cell Theory given by Schleiden and Schwann which states that all plants and animals are composed of cells and that a cell is the basic unit of all life forms. Depending on the number of cells, living beings can be divided into i. Unicellular organisms have singles cells that perform simple functions and have short life spans ii. Multicellular organisms have a large number of cells that perform complex functions and have long life spans. Based on their organization, cells are i. Prokaryotic cells are small in size, with a single chromosome and no nucleolus or ii. Eukaryotic cells which are large-sized, have multiple chromosomes and a nucleolus. We will also learn how cell shapes differ based on their type and function and the different kinds of cells in the human body. There are different components in a cell-like the plasma membrane, nucleus and cytoplasm and their characteristics and functions differ in plant and animal bodies. Finally, we will learn about other components found inside a cell-like Endoplasmic Reticulum, Golgi Apparatus, Mitochondria, Ribosomes, Plastids, Vacuoles, Lysosomes, etc., their various functions and their presence or absence in plants and animal bodies.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 6: Tissue

Summary: Similar cells are grouped together to carry out a specific life function and are called tissues. There are different ways of classifying tissues based on their structure, function and whether they are found in plants or animals. Plant tissues are widely grouped as Meristematic and Permanent Tissues. Meristematic Tissues are living tissues that can divide and form new cells and contribute to the growth of plants. Permanent tissues may be living or dead that have lost their capacity to divide and have a permanent shape, size or function. Based on their structure and composition, both these types of tissues can be further classified based on their origin and locations in a plant body to form specialized tissues that help the plant survive. We will also learn about how animal tissues are divided mainly into Epithelial, Connective, Muscular and Nervous Tissues. Each kind of tissue is further subdivided into various other types of tissues based on their cellular structures, complexity, functions, and location. For example, Connective tissues can be further divided into Areolar, Adipose, Skeletal, and Fluid Tissues the Fluid Tissues ultimately form the blood and lymph of the animal. Thus, all these tissues have their specific functions which ultimately help the animal survive.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 7: Diversity in Living Organism

Summary: The Biodiversity of a place helps us understand the variety of living organisms in it and a systematic way of identifying, naming and classifying all organisms is important and this branch of biology is called Taxonomy. Based on their various characteristics, there have been different classification systems for organisms like 1. Two Kingdom classification 2. Five Kingdom Classification. A way of grouping organisms from simple to complex categories was proposed by Carolus Linnaeus, the father of Taxonomy. He also proposed a scientific naming system that can remain the same in all languages. The five kingdoms of classification are Monera, Protista, Fungi, Plantae, and Animalia. Based on characteristics like differentiated body parts, presence of vascular tissue, reproduction, and seed types, the Plant Kingdom is divided into Thallophyta, Bryophyte, Pteridophyta, Gymnosperms and Angiosperms. Similarly based on characteristics like symmetry, germ layers, presence of coelom and notochord, the Animal Kingdom is divided into Porifera or Sponges, Coelenterata,  Platyhelminthes, Mollusca, Annelida, Arthropoda, Echinodermata, Hemichordata and Chordata. Chordata is subdivided into Prochordata and Vertebrata and finally, Vertebrata is subdivided into Pisces, Amphibia, Reptilia, Aves, and Mammalia. Mammalia or mammals are the most advanced in the animal kingdom and include humans, cats, dogs, whales, etc.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 8: Motion

Summary: In this chapter, we will understand a body at rest and a body in Motion, the different types of motion and how to quantify them. A body is at rest when its position does not change with reference to a point and is said to be in motion when it changes position continuously with reference to a point. Motion can be circular, linear or oscillatory. We will also understand the difference between Distance which is the length of the actual path travelled and Displacement which is the shortest length between the initial point and far point. Also, the first is a scalar quantity with an only magnitude but no direction and the second is a vector quantity with both magnitude and direction. Motion can be Uniform, where a body travels an equal distance in an equal interval of time or it can be Non-uniform, where a body travels the unequal distance in equal intervals of time. Non-uniform motion can further be Accelerated or De-accelerated. We will also understand Speed which is the distance travelled by a body per unit time and Velocity, which is the speed of a body in a given direction. Finally, we will learn how to quantify and measure the speed, velocity, acceleration, and de-acceleration of a body.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 9: Force and Laws of Motion

Summary: To do any work, we either push or pull an object and this is called Force. There are many effects of force, e.g. it can set a stationary object in motion (e.g. kicking a football ) or stop a moving body (e.g. stop running with brakes). In this chapter, Force, and Laws of Motion, we will also learn about Balanced and Unbalanced Forces and the Laws of Motion. Galileo Galilei first said that objects move with a constant speed when no force acts on them. But Sir Isaac Newton modified and developed this into Newton’s Laws of Motion. His first law also called the Law of Inertia states that an object retains its state of rest of motion until an external force is applied to change that state. This helps us understand about Inertia and Momentum of an object. The Second Law states that the rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force. The Third Law states that to every action there is an equal and opposite reaction. We will also learn about the effects of these laws in our daily life and how to measure the mass, momentum, the velocity of objects.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 10: Gravitation

Summary: The force which pulls objects towards the centre of the earth is called the gravitational force of the earth. In 1687, Sir Isaac Newton proposed that every object in the universe attracts every other object with a force based on its mass and distance. In order to measure this force, Newton proposed G as the universal gravitational constant and assigned a value to it. Both Newton’s Third law of motion and his law of gravitation help us understand the relationship between the Force, Mass, and Acceleration between objects (F= m x a). While every object exerts equal and opposite force on each other, their mass also attracts each other. For example, in the case of the stone falling freely to the earth, both the stone and the earth attract each other with a force. But since in this case, the mass of the earth is much greater than the mass of the stone, the force exerted by the earth is much greater than the force exerted by the stone. In this chapter, Gravitation, we also learn about acceleration due to gravity and the difference between mass and weight, thrust and pressure. Finally, we learn about Buoyant Force and Archimedes’ Principle and how to calculate the Relative Density of an object.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 11: Work and Energy

Summary: In this chapter, Work and Energy, we learn about the relationship between work, energy and power and the various forms of energy. In scientific terms, work is said to be done when force is applied to a body and the body moves under the influence of force. The amount of work done can be calculated by the formula Work= Force x Displacement. Work done can be positive, negative or zero based on whether the force is applied in the same direction, opposite direction or at right angles to the direction of motion of the body. The capacity for doing work is energy. Energy can be found in different forms like Kinetic, Potential, Chemical energy, etc. We will learn about these various forms of energy, how to quantify them and where they can be seen in everyday life. When we measure the various forms of energy, we realize that the total energy in a system always remains the same, that energy cannot be created or destroyed but only transformed from one form to another. This is the Law of Conservation of Energy. Finally, Power is defined as the rate of energy conservation and we will learn how to measure the power of a gadget or system.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 12: Sound

Summary: In this chapter, Sound, we will learn about sound and its different characteristics. Sound is produced when objects vibrate and the substance through which sound travels is called a medium and can be solid, liquid or gas. Sound travels in the form of waves and sound waves can be longitudinal which means they form an area of high density or pressure called compression followed by an area of low density or pressure called rarefaction. They are mechanical and cannot travel in a vacuum without a medium. We will also learn about the Wavelength of a sound which is the combined length of compression and rarefaction and the Frequency of a sound which is the number of complete waves or vibrations created per second. Other things to learn about sound are time period, amplitude (which further has a pitch, loudness, and timbre) and velocity. The speed of sound differs according to the medium and can cause effects like the sonic boom. We will also learn about the reflection of sounds like echo and reverberation and how they are used in practical applications. Based on the frequency, sound can be infrasonic and ultrasonic with different uses. Finally, we will learn SONAR and the detailed structure of the human ear.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 13: Why Do We Fall Ill?

Summary: In this chapter, Why Do We Fall Ill? we will learn about health and its absence which is a state of disease, as well as the different kinds of diseases and their prevention and treatment. According to the World Health Organization (WHO), health is a ‘state of physical, mental and social well-being of a person. Any disturbance in the structure or function of any organ or body part is called disease and it is caused by pathogens (virus, bacteria) or by lack of balanced nutrition or public health services. Both personal well-being and community well-being is important to maintain a good state of health. Based on the symptoms and signs of a disease we can determine whether it is acute (short term) or chronic (long term). Diseases can be infectious which spread due to infection by microorganisms like bacteria, viruses, fungi, etc. or non-infectious which do not spread through infection but can be caused due to poor lifestyle, pollution or genetics. Infectious diseases spread through air, water, vectors or through sexual contact. Various infectious agents like various bacteria and viruses cause different diseases with specific symptoms and prevention. We will also learn about Antibiotics that are effective in treating certain diseases caused by some harmful bacteria.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 14: Natural Resources

Summary: Natural resources are living and non-living resources found on i) the earth’s crust called the lithosphere ii) the water found on the earth’s surface and underground called hydrosphere and iii) the air covering the earth like a blanket called the atmosphere, which together makes up the Biosphere. Natural resources help maintain the balance of life and their pollution causes many problems. For example, the air is a mixture of gases including oxygen which is essential for life and the earth’s atmosphere made up of air protects us from extreme temperatures and prevents damage. Air pollution leads to an increase in the number of harmful gases in the air and leads to respiratory and other health problems in humans and stunted growth in plants. Other environmental hazards include acid rain, the greenhouse effect, depletion of the ozone layer, smog, etc. Similarly, water and soil are crucial to life on earth and their pollution affects all animals and plants. The cycling of chemical elements like carbon, oxygen, nitrogen, phosphorus, sulphur, and water is called biogeochemical cycles and they are important for maintaining the availability of natural resources. The different cycles we will learn about are the water cycle, the oxygen cycle, the carbon cycle, and the nitrogen cycle.

#### SEBA, NBSE, TBSE, NCERT solutions for class 9 science Chapter 15: Improvement in Food Resources

Summary: In this chapter, Improvement in Food Resources, we will look at the food resources available to us and the different ways of improving their quality and production and protecting them from harm. Food is important for all life forms and food provides us with nutrients like carbohydrates, proteins, fats, vitamins, and minerals. To feed the billion-plus population of India it is necessary to increase the efficiency of production for both crops and livestock. The Green revolution was a successful program in many countries to increase food production by use of technology, irrigation, improved seeds, etc. Such improvements are brought about by improvements in i. Crop variety by improving the quality of seeds including hybridization ii.Crop production with the help of nutrient management, irrigation and cropping patterns and iii.Crop protection improvement by pest control and storage of grains. We will also more about the importance of organic farming. Similar to improving crop yields, animal husbandry is the scientific management of domestic animals to obtain more food and bi-products. It extends to cattle farming, poultry farming, fish production, and beekeeping. We will further learn about the different kinds of cattle and poultry, fish production and apiary and how to care for them and prevent diseases in them.

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1. Please put the online notes pdf formats for all the chapters of respective subjects in a single Pdf instead of individual chapters. It is very inconvenient to download the notes of revert chapter one by one.

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