Science Paper 2 Paper 2 Science Marathon - CTET Science

Class 8 Science Complete Revision (NCERT Focus)

Chapter List and Structure

Class 8 Science consists of 13 chapters, each covering essential concepts for foundational understanding and exam preparation. The chapters are:

• Crop Production and Management
• Microorganisms: Friend and Foe
• Coal and Petroleum
• Combustion and Flame
• Conservation of Plants and Animals
• Reproduction in Animals
• Reaching the Age of Adolescence
• Force and Pressure
• Friction
• Sound
• Chemical Effects of Electric Current
• Some Natural Phenomena
• Light

Crop Production and Management

Crop production involves systematic steps to ensure healthy…

Class 8 Science Complete Revision (NCERT Focus)

Chapter List and Structure

Class 8 Science consists of 13 chapters, each covering essential concepts for foundational understanding and exam preparation. The chapters are:

• Crop Production and Management
• Microorganisms: Friend and Foe
• Coal and Petroleum
• Combustion and Flame
• Conservation of Plants and Animals
• Reproduction in Animals
• Reaching the Age of Adolescence
• Force and Pressure
• Friction
• Sound
• Chemical Effects of Electric Current
• Some Natural Phenomena
• Light

Crop Production and Management

Crop production involves systematic steps to ensure healthy yield and food security. The main steps are soil preparation, sowing, adding manure and fertilizers, irrigation, protection from weeds, harvesting, and storage.

• Kharif Crops: Sown in rainy season (June–September). Examples: Paddy, maize, soybean, groundnut, cotton.
• Rabi Crops: Sown in winter (October–March). Examples: Wheat, gram, pea, mustard, linseed.
• Agricultural Practices Sequence: Soil preparation → Sowing → Adding manure/fertilizers → Irrigation → Protection from weeds (weedicide like 2,4-D) → Harvesting → Storage (large scale: silos).
• Manure vs Fertilizer:
  • Manure: Natural, made from decomposed plant/animal waste, increases humus, prepared in fields.
  • Fertilizer: Man-made inorganic salts (e.g., urea, ammonium sulphate, superphosphate, NPK), prepared in factories, does not add humus.
• Irrigation Methods: Traditional (moat, chain pump, dhekli, rahat), modern (pump using biogas/diesel/solar).
• Crop Rotation: Growing different crops alternately to maintain soil fertility.
• Threshing: Separating grains from chaff after harvesting.
• Drip System: Water delivered drop by drop near roots.

Microorganisms: Friend and Foe

Microorganisms are classified into four main groups: bacteria, fungi, protozoa, and some algae. Viruses are not included in this classification as they multiply only inside host cells.

• Bacterial Diseases (Trick: "Pandit ka Tik New Hai"): Plague, diphtheria, tuberculosis, whooping cough, tetanus, leprosy, pneumonia, cholera.
• Viral Diseases (Trick: "Ae Chacha Inhe Daato Khare Gaal Pe Chhapora"): AIDS, smallpox, influenza, dengue, trachoma, measles, rabies, mumps, jaundice, chickenpox, polio.
• Protozoan Diseases (Trick: "Papa Kaam Pe Sote"): Pyorrhea, kala-azar, malaria, dysentery, sleeping sickness.
• Fungal Diseases (Trick: "Ganja Damad Fruit Khaye"): Baldness, asthma, ringworm, athlete’s foot, scabies.
• Antibiotics: Produced from bacteria and fungi (e.g., streptomycin, tetracycline, erythromycin).
• Preservation: Salt, oil, sodium benzoate, sodium metabisulphite, pasteurization (milk heated at 70°C for 15–30 sec, then cooled).
• Nitrogen Fixation: Rhizobium in legume roots and blue-green algae convert atmospheric nitrogen into usable compounds for plants.

Coal and Petroleum

Coal and petroleum are fossil fuels with various products and uses.

• Coal Products: Coke (almost pure carbon, used in steel/metals extraction), coal tar (black, thick liquid for dyes, drugs, explosives, plastics, paints, naphthalene balls), coal gas (byproduct during coke production, used for heating).
• Petroleum Products: LPG, petrol, kerosene, diesel, lubricating oil, paraffin wax, bitumen.
• Bitumen: Used for road surfacing (replacing coal tar).
• Petrochemicals: Derived from petroleum/natural gas, used in detergents, fibers (polyester, nylon, acrylic), plastics.
• Natural Gas: Hydrogen from natural gas used in fertilizer (urea) production.
• Petroleum is called "Black Gold".

Combustion and Flame

Combustion is a chemical process producing heat and light.

• Ignition Temperature: Minimum temperature at which a substance catches fire.
• Inflammable Substances: Low ignition temperature, catch fire easily (petrol, diesel, LPG).
• Phosphorus: Spontaneously ignites at room temperature, stored in water.
• Good Fuel Characteristics: Easily available, cheap, burns at moderate rate, produces high heat, leaves no residue.
• Calorific Value: Amount of heat produced by complete combustion of 1 kg of fuel (unit: kJ/kg).
  • Highest: Hydrogen (1,50,000 kJ/kg), lowest: Cow dung cakes (6,000–8,000 kJ/kg).
• Incomplete Combustion: Produces carbon monoxide (toxic, "silent killer").
• Ideal Fuel: No residue, high calorific value, easily available, cheap, moderate ignition temperature.

Conservation of Plants and Animals

Biodiversity refers to the variety of living organisms in a specific area, including plants, animals, and microorganisms.

• Biosphere Reserve: Large protected area for conservation of biodiversity.
• Wildlife Sanctuary/National Park: Protects wild animals and plants.
• Endemic Species: Found only in a particular area.
• Endangered Species: At risk of extinction, listed in Red Data Book.
• Migration: Seasonal movement of species for breeding.
• Conservation Practices: Save paper, recycle, afforestation (replanting trees).

Reproduction in Animals

Animals reproduce by sexual or asexual methods.

• Sexual Reproduction: Involves fusion of male (sperm) and female (ovum) gametes.
  • Female organs: Ovary, oviduct, uterus.
  • Male organs: Testis, sperm duct, penis.
  • Fertilization: Fusion of ovum and sperm forms zygote.
  • Internal fertilization: Inside female body (e.g., hen, cow, dog).
  • External fertilization: Outside female body (e.g., frog, fish, starfish).
  • Zygote divides to form embryo, which develops into foetus.
  • Viviparous: Give birth to young ones (human, cow, dog).
  • Oviparous: Lay eggs (hen, frog, lizard, butterfly).
  • Metamorphosis: Transformation of larva into adult.
• Asexual Reproduction: Single parent, no gamete fusion.
  • Budding (hydra, yeast), binary fission (amoeba).

Reaching the Age of Adolescence

Adolescence is the period of transition from childhood to adulthood, marked by physical, mental, and hormonal changes.

• Age Range: 11–19 years.
• Physical Changes: Increase in height, muscle development, development of reproductive organs, appearance of hair, voice changes.
• Mental Changes: Emotional development, independence, sense of responsibility.
• Hormonal Changes: Controlled by endocrine glands.
  • Pituitary gland: Master gland, controls growth and other glands.
  • Thyroid: Secretes thyroxine.
  • Adrenal: Secretes adrenaline.
  • Pancreas: Secretes insulin.
  • Testes: Secrete testosterone (male).
  • Ovaries: Secrete estrogen (female).
• Puberty: Onset of sexual maturity (girls: 10–12 years, boys: 12–14 years).
• Chromosomes: XX (female), XY (male) determine sex of child.
• Menstruation: Shedding of uterine lining if fertilization does not occur.

Force and Pressure

Force is a push or pull that changes the state of motion or shape of an object.

• Definition: Force can be a push or pull, has both magnitude and direction.
• Unit: Newton (N), also dyne ($1\,N = 10^5$ dyne).
• Formula: $F = m \times a$
• Contact Forces: Require physical contact (frictional, muscular, spring force).
• Non-contact Forces: Act at a distance (magnetic, gravitational, electrostatic).
• Pressure: Force per unit area ($P = F/A$), unit: Pascal (Pa).
• Liquids and gases exert pressure on container walls.
• Atmospheric Pressure: Pressure exerted by air around us.
• Increasing area decreases pressure (wide straps reduce pressure on shoulders).

Friction

Friction opposes relative motion between two surfaces in contact.

• Depends on: Nature and smoothness of surfaces, how hard surfaces are pressed together.
• Types: Static (at rest), sliding (in motion), rolling (rolling objects).
  • Static > Sliding > Rolling friction.
• Drag: Frictional force by fluids (liquids/gases).
• Increasing Friction: Making surfaces rough (shoe soles, tire treads).
• Decreasing Friction: Using lubricants, ball bearings, powder (carrom).
• Useful and Harmful Effects: Needed for walking, writing; unwanted in machines (wear and tear).

Sound

Sound is produced by vibrations and requires a medium to travel.

• Vibration: To and fro motion of an object.
• Frequency: Number of vibrations per second, measured in Hertz (Hz).
• Pitch: Directly proportional to frequency; higher frequency, higher pitch.
• Loudness: Proportional to square of amplitude; measured in decibels (dB).
• Human Audible Range: 20 Hz to 20,000 Hz.
• Speed: Maximum in solids, less in liquids, least in gases; does not travel in vacuum.
• Ear Structure: Outer ear (funnel-shaped), ear canal, eardrum (vibrates with sound), inner ear (sends signals to brain).
• Formulas:
  • $v = f \lambda$
  • $T = 1/f$
• Examples: Drum (high loudness, low pitch), whistle (high pitch, low loudness).

Chemical Effects of Electric Current

Electric current causes chemical changes when passed through liquids.

• Conductors: Allow easy flow of current (metals, graphite).
• Electrolytes: Liquids conducting electricity (acid, base, salt solutions).
• Electrolysis: Decomposition of a substance by electric current (e.g., water into hydrogen and oxygen).
• Electroplating: Deposition of a metal layer on another object using electric current.
• Extraction of Metals: Used in obtaining metals from ores (e.g., aluminium from bauxite).
• Heating Effect: Electric current heats up wire (heaters use nichrome wire).
• Fuse: Alloy of lead and tin, melts at low temperature to protect circuits.
• MCB: Miniature Circuit Breaker, safety device.

Some Natural Phenomena

Natural phenomena include static electricity, lightning, and earthquakes.

• Static Electricity: Produced by rubbing objects, two types of charges (positive, negative).
• Like charges repel, unlike charges attract.
• Electroscope: Device to detect charge.
• Earthing: Transferring charge to the earth.
• Lightning: Electric discharge between clouds and earth, can cause damage; lightning conductor protects buildings.
• Earthquake: Sudden shaking of earth, measured on Richter scale; focus (origin), epicenter (surface point above focus).
• Precautions: Do not use wired phones during lightning, avoid shelter under trees, use lightning conductors in buildings.

Key Tables

• Fat-soluble vitamins: A, D, E, K (stored in liver, not needed daily)
• Water-soluble vitamins: B, C (needed daily)

All content above is strictly based on the transcript and covers the most exam-relevant points for Class 8 Science revision.