RRB ALP – Science Revision Module
1) Motion (Kinematics, Speed, and Velocity) Motion Motion is the change in position of an object with respect to time and a reference point. Distance and Displacement Distance: Total path covered (scalar quantity). Displacement: Shortest straight-line distance between initial and final position (vector quantity). Speed Speed = Distance / Time SI Unit: m/s Scalar quantity Average Speed = Total distance / Total time Velocity Velocity = Displacement / Time Vector quantity (has magnitude and direction) Average Velocity = Total displacement / Total time Acceleration Acceleration = Change in velocity / Time SI Unit: m/s² Positive acceleration → Increase in speed Negative acceleration → Retardation Equations of Motion (Uniform Acceleration) v = u + at s = ut + ½at² v² = u² + 2as Where: u = initial velocity v = final velocity a = acceleration t = time s = displacement 2) Laws of Motion and Friction Newton’s Laws of Motion Given by Isaac Newton First Law (Law of Inertia) A body continues in its state of rest or uniform motion unless acted upon by an external force. Second Law Force = Mass × Acceleration F = ma Third Law Every action has an equal and opposite reaction. Momentum Momentum = Mass × Velocity SI Unit: kg·m/s Friction Force opposing relative motion between surfaces in contact. Types: Static friction Sliding friction Rolling friction Friction depends on: Nature of surfaces Normal reaction 3) Work, Power, and Energy Work Work = Force × Displacement (in direction of force) W = F × s SI Unit: Joule (J) 1 Joule = Work done by 1 N force moving object by 1 m. Power Power = Work / Time SI Unit: Watt (W) 1 Horsepower = 746 W Energy Capacity to do work. SI Unit: Joule Types: Kinetic Energy (KE) = ½mv² Potential Energy (PE) = mgh Law of Conservation of Energy Energy can neither be created nor destroyed; it only changes form. 4) Gravitation Universal Law of Gravitation Proposed by Isaac Newton F = Gm₁m₂ / r² G = 6.67 × 10⁻¹¹ N·m²/kg² Acceleration Due to Gravity g ≈ 9.8 m/s² g decreases: At higher altitudes At equator Escape Velocity Escape velocity of Earth = 11.2 km/s 5) Mass, Weight, and Density Mass Quantity of matter SI Unit: kg Same everywhere Weight Weight = mg Depends on gravity SI Unit: Newton Density Density = Mass / Volume SI Unit: kg/m³ Density of water = 1000 kg/m³ Relative Density = Density of substance / Density of water 6) Pressure and Buoyancy Pressure Pressure = Force / Area SI Unit: Pascal (Pa) 1 Pa = 1 N/m² Atmospheric Pressure Due to weight of air column; measured using a barometer. Buoyancy Upward force exerted by fluid on immersed object. Archimedes’ Principle Given by Archimedes A body immersed in a fluid experiences an upward force equal to the weight of the displaced fluid. Applications: Floating of ships Hydrometer Submarines 7) Sound and Wave Motion Wave Transfer of energy without transfer of matter. Types: Mechanical waves Electromagnetic waves Wave Terms Wavelength (λ) Frequency (f) Time Period (T) Amplitude Wave equation: v = fλ Sound Produced by vibrations Cannot travel in vacuum Speed in air ≈ 340 m/s Factors affecting speed: Temperature Medium 8) Heat and Temperature Heat Energy transferred due to temperature difference. Units: Joule (SI) Calorie 1 calorie = 4.186 J Temperature Scales Celsius (°C) Kelvin (K) Fahrenheit (°F) Conversion: K = °C + 273 Modes of Heat Transfer Conduction (solids) Convection (fluids) Radiation (no medium required) 9) Light (Reflection, Refraction, Lenses, Mirrors) Reflection Laws: Angle of incidence = Angle of reflection Incident ray, reflected ray, and normal lie in same plane Mirrors Plane mirror → Virtual, erect image Concave mirror → Real & inverted (generally) Convex mirror → Virtual & diminished Mirror Formula: 1/f = 1/v + 1/u Refraction Bending of light when passing from one medium to another. Snell’s Law: n₁ sin i = n₂ sin r Refractive index: n = Speed in vacuum / Speed in medium Lenses Lens Formula: 1/f = 1/v − 1/u Power of lens: P = 1/f (in meter) Unit: Diopter 10) Electricity and Magnetism Electric Current I = Q / t Unit: Ampere Potential Difference Unit: Volt Ohm’s Law V = IR Electric Power P = VI Unit: Watt Magnetism Like poles repel; unlike poles attract Magnetic field lines go from North to South Electromagnets work due to electric current Right-hand thumb rule gives direction of magnetic field around conductor. 11) Units and Measurements SI Base Units Length → meter (m) Mass → kilogram (kg) Time → second (s) Current → ampere (A) Temperature → kelvin (K) Luminous intensity → candela (cd) Amount of substance → mole (mol) Derived Units Force → Newton Energy → Joule Power → Watt Pressure → Pascal Important Conversions 1 km = 1000 m 1 hour = 3600 s 1 N = 1 kg·m/s² 1) Matter and Its States Definition of Matter Matter is anything that has mass and occupies space. Characteristics of Particles of Matter Very small in size Have spaces between them Continuously moving (possess kinetic energy) Attract one another (intermolecular force) Physical Properties of Matter Mass Volume Density (Density = Mass / Volume) State States of Matter 1. Solid Definite shape and volume Strong intermolecular force Very small spaces between particles Least compressible 2. Liquid Definite volume but no fixed shape Moderate intermolecular force Slightly compressible Can flow 3. Gas No definite shape or volume Very weak intermolecular force Highly compressible High kinetic energy Change of State Change of state occurs due to temperature or pressure change. Melting: Solid → Liquid Freezing: Liquid → Solid Boiling/Vaporization: Liquid → Gas Condensation: Gas → Liquid Sublimation: Solid → Gas directly Latent Heat Heat absorbed or released during change of state without change in temperature. Latent heat of fusion Latent heat of vaporization 2) Atomic Structure and Molecules Structure of Atom The nuclear model was proposed by Ernest Rutherford. An atom consists of: Protons (positive charge) Neutrons (no charge) Electrons (negative charge) Protons and neutrons are present in the nucleus; electrons revolve in fixed shells or energy levels. Important Terms Atomic Number (Z) Number of protons in an atom. Mass Number (A) Number of protons + neutrons. A = p + n Isotopes Atoms of the same element having same atomic number but different mass numbers. Electronic Configuration Maximum electrons in a shell = 2n² (where n = shell number) K shell = 2 L shell = 8 M shell = 18 Valency Combining capacity of an atom. Determined by electrons in the outermost shell (valence electrons). Molecules Smallest particle of a substance that can exist independently. Types: Homoatomic (O₂, N₂) Heteroatomic (H₂O, CO₂) 3) Chemical Reactions and Equations Chemical Reaction A process in which new substances are formed with new chemical properties. Indicators of reaction: Change in colour Change in temperature Gas evolution Formation of precipitate Chemical Equation Symbolic representation of a chemical reaction. Example: 2H₂ + O₂ → 2H₂O It must be balanced according to the Law of Conservation of Mass. Types of Chemical Reactions Combination Reaction A + B → AB Decomposition Reaction AB → A + B Displacement Reaction A + BC → AC + B Double Displacement Reaction AB + CD → AD + CB Redox Reaction Oxidation and reduction occur simultaneously. Oxidation Addition of oxygen Removal of hydrogen Loss of electrons Reduction Removal of oxygen Addition of hydrogen Gain of electrons 4) Acids, Bases, and Salts Acids Substances that produce H⁺ ions in aqueous solution. Examples: HCl, H₂SO₄, HNO₃ Properties: Sour taste Turn blue litmus red pH < 7 Bases Substances that produce OH⁻ ions in aqueous solution. Examples: NaOH, KOH Properties: Bitter taste Turn red litmus blue pH > 7 Salts Formed by neutralization reaction. Acid + Base → Salt + Water Example: HCl + NaOH → NaCl + H₂O pH Scale Range: 0 to 14 7 → Neutral < 7 → Acidic 7 → Basic 5) Metals and Non-Metals Physical Properties of Metals Lustrous Malleable Ductile Good conductors of heat and electricity Sonorous Chemical Properties of Metals React with oxygen → Metal oxides React with water → Hydrogen gas React with acids → Salt + Hydrogen Non-Metals Brittle Poor conductors Not sonorous Form acidic oxides Reactivity Series K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au More reactive metals displace less reactive metals from their compounds. Corrosion Slow destruction of metals due to reaction with environment (e.g., rusting of iron). 6) Carbon and Its Compounds Properties of Carbon Tetravalent Forms covalent bonds Shows catenation (self-linking ability) Allotropes of Carbon Diamond Graphite Fullerene Hydrocarbons Compounds containing only carbon and hydrogen. Alkanes → Single bonds Alkenes → Double bonds Alkynes → Triple bonds Functional Groups –OH → Alcohol –COOH → Carboxylic acid –CHO → Aldehyde –CO– → Ketone 7) Periodic Classification of Elements The periodic table was first systematically arranged by Dmitri Mendeleev. Modern Periodic Law Properties of elements are periodic functions of their atomic numbers. Structure of Modern Periodic Table 7 Periods (rows) 18 Groups (columns) Important Periodic Trends Across a Period: Atomic size decreases Metallic character decreases Electronegativity increases Down a Group: Atomic size increases Metallic character increases 8) Common Chemical Formulae and Their Uses Water → H₂O → Universal solvent Common salt → NaCl → Food seasoning Baking soda → NaHCO₃ → Baking, antacid Washing soda → Na₂CO₃·10H₂O → Cleaning agent Bleaching powder → CaOCl₂ → Disinfectant Ammonia → NH₃ → Fertilizer production Sulphuric acid → H₂SO₄ → Car batteries Hydrochloric acid → HCl → Laboratory reagent Nitric acid → HNO₃ → Fertilizers 1) Cell: The Fundamental Unit of Life Discovery of Cell The cell was first observed by Robert Hooke in 1665 while examining cork under a microscope. Cell Theory Proposed by Matthias Schleiden and Theodor Schwann. Cell theory states: All living organisms are made up of cells. Cell is the basic structural and functional unit of life. New cells arise from pre-existing cells. Types of Cells Prokaryotic Cells No true nucleus No membrane-bound organelles Example: Bacteria Eukaryotic Cells True nucleus present Membrane-bound organelles present Example: Plant and animal cells Structure of Cell 1. Cell Membrane Selectively permeable Controls movement of substances 2. Cell Wall (Plant cells only) Provides rigidity and protection 3. Cytoplasm Jelly-like substance Site of metabolic activities 4. Nucleus Control center Contains genetic material (DNA) 5. Mitochondria “Powerhouse of the cell” Site of respiration 6. Ribosomes Protein synthesis 7. Endoplasmic Reticulum (ER) Rough ER → Protein synthesis Smooth ER → Lipid synthesis 8. Golgi Apparatus Packaging and secretion 9. Lysosomes “Suicide bags” Intracellular digestion 10. Chloroplast (Plant cells) Site of photosynthesis 2) Plant and Animal Tissues Tissue Group of similar cells performing a specific function. Plant Tissues A) Meristematic Tissue Actively dividing cells Types: Apical, Intercalary, Lateral B) Permanent Tissue Simple (Parenchyma, Collenchyma, Sclerenchyma) Complex (Xylem and Phloem) Xylem → Transports water Phloem → Transports food Animal Tissues Epithelial Tissue → Protective covering Connective Tissue → Support (Blood, Bone, Cartilage) Muscular Tissue → Movement Nervous Tissue → Control and coordination 3) Diversity in Living Organisms Classification Organisms are classified based on similarities and differences. Five Kingdom Classification proposed by Robert H. Whittaker: Monera Protista Fungi Plantae Animalia Basis of Classification Cell structure Mode of nutrition Body organization Reproduction 4) Life Processes 1. Nutrition Autotrophic Nutrition Plants prepare food by photosynthesis. Photosynthesis equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ Heterotrophic Nutrition Organisms depend on others for food. Types: Holozoic Saprophytic Parasitic 2. Respiration Process of breaking down food to release energy. Aerobic respiration: Glucose + Oxygen → CO₂ + H₂O + Energy Anaerobic respiration occurs without oxygen. 3. Transportation In Plants Xylem → Water Phloem → Food In Humans Circulatory system Heart pumps blood Blood carries oxygen and nutrients 4. Excretion Removal of metabolic wastes. In Humans: Kidneys → Urine formation Lungs → CO₂ removal Skin → Sweat 5) Control and Coordination Nervous System Components: Brain Spinal cord Nerves Brain parts: Cerebrum → Thinking Cerebellum → Balance Medulla → Involuntary actions Reflex action is rapid, automatic response. Endocrine System Hormones are chemical messengers. Important glands: Pituitary (Master gland) Thyroid Adrenal Pancreas Hormones regulate growth, metabolism, reproduction. 6) Reproduction in Plants and Animals Asexual Reproduction Single parent involved. Types: Binary fission Budding Spore formation Vegetative propagation Sexual Reproduction Two parents involved. Involves fusion of male and female gametes. In humans: Fertilization Zygote formation Embryo development 7) Heredity and Evolution Heredity Transmission of traits from parents to offspring. Laws of inheritance given by Gregor Mendel: Law of Dominance Law of Segregation Law of Independent Assortment Genes Units of heredity present on chromosomes. Evolution Gradual change in organisms over generations. Theory of Natural Selection proposed by Charles Darwin. Key idea: Survival of the fittest. 8) Human Diseases, Causes, and Prevention Types of Diseases Communicable Diseases Spread by pathogens. Examples: Tuberculosis, Malaria Non-Communicable Diseases Not infectious. Examples: Diabetes, Cancer Causes Bacteria Viruses Fungi Protozoa Nutritional deficiency Prevention Vaccination Hygiene Balanced diet Safe drinking water Exercise 9) Our Environment and Ecosystems Environment Surroundings in which organisms live. Ecosystem Interaction between living (biotic) and non-living (abiotic) components. Components of Ecosystem Producers → Green plants Consumers → Herbivores, carnivores Decomposers → Bacteria and fungi Food Chain Producers → Primary consumers → Secondary consumers Food Web Interconnected food chains. Ozone Layer Protects Earth from harmful UV radiation. Environmental Issues Pollution Global warming Deforestation 100 Model Questions Q.1) What is the SI unit of force? Answer: Newton Explanation: Force is measured in Newton (N). One Newton is the force required to produce an acceleration of 1 m/s² in a body of mass 1 kg. Q.2) Define velocity. Answer: Displacement per unit time Explanation: Velocity is a vector quantity defined as displacement divided by time. It includes both magnitude and direction. Q.3) What is acceleration due to gravity on Earth? Answer: 9.8 m/s² Explanation: The acceleration due to gravity near Earth’s surface is approximately 9.8 m/s². Q.4) State Newton’s First Law of Motion. Answer: A body remains at rest or in uniform motion unless acted upon by an external force. Explanation: This law is also called the law of inertia and explains resistance to change in motion. Q.5) What is momentum? Answer: Product of mass and velocity Explanation: Momentum = mass × velocity and is measured in kg·m/s. Q.6) What is the SI unit of energy? Answer: Joule Explanation: Energy is measured in Joules (J) in the SI system. Q.7) Write the formula for kinetic energy. Answer: ½mv² Explanation: Kinetic energy depends on mass and square of velocity. Q.8) What is potential energy? Answer: Energy possessed due to position Explanation: Example: mgh represents gravitational potential energy. Q.9) State Ohm’s Law. Answer: V = IR Explanation: Voltage across a conductor is directly proportional to current when temperature remains constant. Q.10) What is the SI unit of electric current? Answer: Ampere Explanation: Current is measured in amperes (A). Q.11) What type of lens is used to correct myopia? Answer: Concave lens Explanation: Myopia (short-sightedness) is corrected using a diverging (concave) lens. Q.12) Define density. Answer: Mass per unit volume Explanation: Density = Mass / Volume, SI unit is kg/m³. Q.13) What is Archimedes’ Principle? Answer: A body immersed in a fluid experiences an upward force equal to the weight of displaced fluid. Explanation: This explains floating of ships and submarines. Q.14) What is the speed of sound in air? Answer: Approximately 340 m/s Explanation: Sound travels at about 340 m/s in air at room temperature. Q.15) What is reflection of light? Answer: Bouncing back of light from a surface Explanation: The angle of incidence equals the angle of reflection. Q.16) What is refraction? Answer: Bending of light when it passes from one medium to another Explanation: Caused by change in speed of light. Q.17) What is the SI unit of pressure? Answer: Pascal Explanation: 1 Pascal = 1 N/m². Q.18) Define power. Answer: Work done per unit time Explanation: SI unit is Watt. Q.19) What is latent heat? Answer: Heat absorbed or released without temperature change Explanation: Occurs during change of state. Q.20) What is universal law of gravitation? Answer: Every two masses attract each other with a force proportional to product of their masses and inversely proportional to square of distance between them. Explanation: Given by Newton. Q.21) What is matter? Answer: Anything that has mass and occupies space Explanation: All physical substances are matter. Q.22) Name the three states of matter. Answer: Solid, Liquid, Gas Explanation: Based on particle arrangement and intermolecular force. Q.23) What is atomic number? Answer: Number of protons in an atom Explanation: It determines identity of an element. Q.24) What is mass number? Answer: Sum of protons and neutrons Explanation: A = p + n. Q.25) Define valency. Answer: Combining capacity of an element Explanation: Depends on electrons in outermost shell. Q.26) What is an isotope? Answer: Atoms of same element with different mass numbers Explanation: They have same atomic number. Q.27) What is a molecule? Answer: Smallest particle of a substance that can exist independently Explanation: Example: H₂O. Q.28) What is a chemical reaction? Answer: Process in which new substances are formed Explanation: Involves breaking and making of bonds. Q.29) What is oxidation? Answer: Addition of oxygen or loss of electrons Explanation: Opposite of reduction. Q.30) Define reduction. Answer: Removal of oxygen or gain of electrons Explanation: Occurs along with oxidation. Q.31) What is pH value of a neutral solution? Answer: 7 Explanation: Pure water has pH 7. Q.32) What is an acid? Answer: Substance that produces H⁺ ions in solution Explanation: Example: HCl. Q.33) What is a base? Answer: Substance that produces OH⁻ ions in solution Explanation: Example: NaOH. Q.34) What is neutralization? Answer: Reaction between acid and base forming salt and water Explanation: Example: HCl + NaOH. Q.35) What is corrosion? Answer: Slow destruction of metals by chemical reaction Explanation: Rusting is example. Q.36) Name the gas evolved when metal reacts with acid. Answer: Hydrogen Explanation: Metal + Acid → Salt + Hydrogen. Q.37) What is the reactivity series? Answer: Arrangement of metals in decreasing order of reactivity Explanation: Used to predict displacement reactions. Q.38) What is catenation? Answer: Ability of carbon to form long chains Explanation: Due to strong C–C bonds. Q.39) Name the functional group –OH. Answer: Alcohol Explanation: Presence of –OH indicates alcohol. Q.40) Who proposed modern periodic law? Answer: Henry Moseley Explanation: Based on atomic number. Q.41) Who discovered the cell? Answer: Robert Hooke Explanation: Observed cork cells in 1665. Q.42) What is the basic unit of life? Answer: Cell Explanation: All organisms are made of cells. Q.43) What is the powerhouse of the cell? Answer: Mitochondria Explanation: Site of respiration and ATP production. Q.44) What contains genetic material in a cell? Answer: Nucleus Explanation: Contains DNA. Q.45) What is tissue? Answer: Group of similar cells performing a specific function Explanation: Example: Muscular tissue. Q.46) What transports water in plants? Answer: Xylem Explanation: Conducts water from roots to leaves. Q.47) What transports food in plants? Answer: Phloem Explanation: Carries food from leaves to other parts. Q.48) What is photosynthesis? Answer: Process by which plants make food using sunlight Explanation: Produces glucose and oxygen. Q.49) What is respiration? Answer: Breakdown of food to release energy Explanation: Occurs in mitochondria. Q.50) What is excretion? Answer: Removal of metabolic wastes Explanation: Kidneys help in excretion. (Continuing…) Q.51) What is heredity? Answer: Transmission of traits from parents to offspring Explanation: Governed by genes. Q.52) Who is known as the Father of Genetics? Answer: Gregor Mendel Explanation: Proposed laws of inheritance. Q.53) What is evolution? Answer: Gradual change in organisms over generations Explanation: Explained by natural selection. Q.54) Name the organ that pumps blood. Answer: Heart Explanation: Pumps blood throughout body. Q.55) What are communicable diseases? Answer: Diseases that spread from person to person Explanation: Example: Tuberculosis. Q.56) What causes malaria? Answer: Plasmodium Explanation: Transmitted by female Anopheles mosquito. Q.57) What is ecosystem? Answer: Interaction between living and non-living components Explanation: Includes biotic and abiotic factors. Q.58) What are producers in ecosystem? Answer: Green plants Explanation: They prepare their own food. Q.59) What is food chain? Answer: Sequence of organisms where each is eaten by the next Explanation: Shows energy flow. Q.60) What protects Earth from UV rays? Answer: Ozone layer Explanation: Absorbs harmful ultraviolet radiation. Q.61) What is the SI unit of work? Answer: Joule Explanation: Work is said to be done when a force causes displacement. Its SI unit is Joule (J), equal to 1 Newton × 1 meter. Q.62) Define displacement. Answer: Shortest distance between initial and final position Explanation: Displacement is a vector quantity and includes direction. Q.63) What is friction? Answer: Force opposing relative motion between surfaces in contact Explanation: Friction always acts opposite to the direction of motion. Q.64) What is the formula for pressure? Answer: Force divided by area Explanation: Pressure = Force / Area and is measured in Pascal. Q.65) What is the unit of frequency? Answer: Hertz Explanation: Frequency is the number of vibrations per second. Q.66) What is the unit of electric power? Answer: Watt Explanation: Electric power = Voltage × Current. Q.67) What is the mirror formula? Answer: 1/f = 1/v + 1/u Explanation: It relates focal length, image distance, and object distance. Q.68) Which mirror is used as rear-view mirror in vehicles? Answer: Convex mirror Explanation: It provides a wider field of view and forms diminished images. Q.69) What is boiling point of water at standard atmospheric pressure? Answer: 100°C Explanation: Water boils at 100°C under normal atmospheric pressure. Q.70) What is the SI unit of temperature? Answer: Kelvin Explanation: Kelvin is the SI unit used in scientific measurements. Q.71) What is sublimation? Answer: Direct change of solid into gas Explanation: Example: Camphor and dry ice. Q.72) What is the maximum number of electrons in K shell? Answer: 2 Explanation: According to 2n² rule, K shell (n=1) holds 2 electrons. Q.73) What is a balanced chemical equation? Answer: Equation with equal number of atoms on both sides Explanation: It obeys law of conservation of mass. Q.74) What is the chemical formula of washing soda? Answer: Na₂CO₃·10H₂O Explanation: It is sodium carbonate decahydrate. Q.75) What is the chemical formula of baking soda? Answer: NaHCO₃ Explanation: It is sodium hydrogen carbonate. Q.76) What is the pH value of an acidic solution? Answer: Less than 7 Explanation: Acids have pH below 7. Q.77) What type of oxide is formed by non-metals? Answer: Acidic oxide Explanation: Example: CO₂ forms carbonic acid in water. Q.78) What is galvanization? Answer: Coating iron with zinc Explanation: Prevents rusting. Q.79) What is the valency of carbon? Answer: 4 Explanation: Carbon is tetravalent. Q.80) What determines the position of an element in periodic table? Answer: Atomic number Explanation: Modern periodic law is based on atomic number. Q.81) What is the function of ribosomes? Answer: Protein synthesis Explanation: Ribosomes are sites of protein formation. Q.82) What is the control center of the cell? Answer: Nucleus Explanation: It regulates all cell activities. Q.83) What is meristematic tissue? Answer: Actively dividing plant tissue Explanation: Responsible for plant growth. Q.84) What type of tissue is blood? Answer: Connective tissue Explanation: Blood connects different parts of the body. Q.85) What is autotrophic nutrition? Answer: Mode of nutrition in which organisms make their own food Explanation: Example: Green plants. Q.86) What is anaerobic respiration? Answer: Respiration without oxygen Explanation: Produces less energy and may produce alcohol or lactic acid. Q.87) What is the main excretory organ in humans? Answer: Kidney Explanation: Kidneys filter blood and form urine. Q.88) What is reflex action? Answer: Rapid automatic response to stimulus Explanation: Controlled by spinal cord. Q.89) Which hormone regulates blood sugar level? Answer: Insulin Explanation: Secreted by pancreas. Q.90) What is vegetative propagation? Answer: Asexual reproduction in plants through vegetative parts Explanation: Example: Potato through tuber. Q.91) What is fertilization? Answer: Fusion of male and female gametes Explanation: Forms zygote. Q.92) What is gene? Answer: Unit of heredity Explanation: Located on chromosomes. Q.93) What is natural selection? Answer: Survival of the fittest Explanation: Individuals with favorable traits survive and reproduce. Q.94) What is a pathogen? Answer: Disease-causing microorganism Explanation: Includes bacteria, viruses, fungi. Q.95) What deficiency causes scurvy? Answer: Vitamin C deficiency Explanation: Leads to bleeding gums and weakness. Q.96) What is vaccination? Answer: Administration of weakened pathogen to develop immunity Explanation: Prevents infectious diseases. Q.97) What are decomposers? Answer: Organisms that break down dead matter Explanation: Example: Bacteria and fungi. Q.98) What is a food web? Answer: Network of interconnected food chains Explanation: Shows complex feeding relationships. Q.99) What is global warming? Answer: Rise in Earth’s average temperature due to greenhouse gases Explanation: Caused mainly by CO₂ increase. Q.100) What is biodiversity? Answer: Variety of living organisms in a region Explanation: High biodiversity ensures ecological stability.