Curiosity

Chapter 1 of NCERT Class 7 Curiosity (Science) — 'The Ever-Evolving World of Science' — introduces students to science as an ongoing process of questioning, experimenting, and exploring rather than a fixed collection of facts. It previews the major topics covered across the textbook and encourages students to think like scientists.

• 1Science is described as a process — a way of thinking that welcomes curiosity, asks questions, and is open to the unknown — not merely a collection of facts.
• 2Grade 7 science asks deeper questions: How do things work? Why do events happen the way they do? What patterns do we see in nature?
• 3Topics covered include properties of materials (e.g., why some fruits are sour, what happens to a haldi stain), electric circuits with batteries and lamps, and classification of materials into metals and non-metals.
• 4Changes around us are a key theme: some changes are reversible and others cannot be reversed; batteries running out, ice melting, fruits ripening, and rocks breaking into pebbles are examples.
• 5Heat flow is explored through everyday examples such as an ice cube melting in a glass and the melting of a glacier.

Class 7 Science Chapter 2 — Exploring Substances: Acidic, Basic, and Neutral — teaches students how to identify whether substances are acidic, basic, or neutral using natural and synthetic acid-base indicators such as litmus, red rose extract, turmeric, and onion.

• 1Substances are classified as acidic, basic, or neutral based on how they affect indicators like litmus paper.
• 2Litmus, obtained from lichens, is an acid-base indicator available in two forms — blue and red paper strips. Acids turn blue litmus red; bases turn red litmus blue.
• 3Substances that do not change the colour of either blue or red litmus paper are neutral (e.g., tap water, sugar solution, salt solution).
• 4Acidic substances (e.g., lemon juice, vinegar, tamarind water) generally taste sour; basic substances (e.g., baking soda solution) feel soapy or slippery and generally taste bitter.
• 5Red rose extract is a natural acid-base indicator: it turns red in acidic solutions and green in basic solutions.

Chapter 3 of Class 7 Science (Curiosity) covers electricity — how circuits are built from cells, batteries, lamps (incandescent and LED), and switches, and how materials are classified as conductors or insulators.

• 1An electric cell is a portable source of electrical energy with two terminals — positive (+ve, metal cap) and negative (–ve, metal disc).
• 2A battery is a combination of two or more cells connected so that the positive terminal of one cell connects to the negative terminal of the next.
• 3In an incandescent lamp, a thin wire called the filament gets hot and glows when current passes through it; a broken filament causes the lamp to 'fuse'.
• 4An LED (Light Emitting Diode) has no filament and has polarity — current can pass through it in one direction only; the longer wire is the positive terminal.
• 5A complete electrical circuit provides a continuous path for current; the direction of current is taken from the positive to the negative terminal of the cell.

Chapter 4 of Class 7 Science (Curiosity) — 'The World of Metals and Non-metals' — teaches students to distinguish metals from non-metals by exploring five key properties: malleability, ductility, sonority, and conduction of heat and electricity, plus how metals react with air and water to form rust and corrosion.

• 1Metals (copper, aluminium, iron) are lustrous, hard, malleable, and ductile; non-metals (coal, sulfur) are non-lustrous and brittle.
• 2Malleability is the property by which materials can be beaten into thin sheets — gold and silver are the most malleable metals; aluminium foil and silver foil on sweets are everyday examples.
• 3Ductility is the property by which materials can be drawn into wires — gold is so ductile that one gram can be drawn into a 2 kilometre-long wire.
• 4Sonority is the property of metals that allows them to produce a ringing sound when struck; non-metals like coal and wood produce only dull sounds.
• 5Metals are good conductors of heat and electricity; non-metals are generally poor conductors — this is why cooking vessel handles are made of wood and electricians wear rubber gloves.

Chapter 5 of Class 7 Curiosity (Science) covers physical and chemical changes — how to tell them apart, what combustion and rusting involve, how reversibility classifies changes, and how natural processes like weathering and erosion reshape rocks over time.

• 1A physical change alters only physical properties (shape, size, state) of a substance; no new substance is formed. Examples: folding paper, inflating a balloon, melting ice.
• 2A chemical change produces one or more new substances through a chemical reaction. Examples: blowing air into lime water turns it milky (calcium carbonate forms), mixing vinegar with baking soda releases carbon dioxide.
• 3The lime water test is used to detect carbon dioxide — lime water turns milky in the presence of CO₂.
• 4Combustion is a chemical reaction in which a substance reacts with oxygen and produces heat and/or light. Wood, paper, cotton, and kerosene are examples of combustible substances.
• 5Three conditions are required for combustion (the fire triangle): a combustible substance (fuel), oxygen, and heat sufficient to reach the substance's ignition temperature.

Chapter 6 of Class 7 Curiosity (Science) covers adolescence — the period of rapid physical, emotional, and behavioural change that typically occurs between the ages of 10 and 19. It explains puberty, secondary sexual characteristics, menstruation, nutrition, hygiene, and how to handle adolescence responsibly.

• 1Adolescence generally begins around 10 years of age and lasts until 19 years; it is the stage of development between childhood and adulthood.
• 2Physical changes during adolescence include increased height and weight, broader shoulders in boys, breast development in girls, voice changes (hoarseness in boys due to voice box growth), growth of facial and body hair, and acne caused by increased oily skin secretions.
• 3Secondary sexual characteristics — such as voice change, facial hair in boys, and breast development in girls — help distinguish males from females but are not directly involved in reproduction; they mark the onset of puberty.
• 4Puberty is the stage in which the body undergoes external and internal changes to develop into an adult capable of reproduction.
• 5The menstrual cycle in girls recurs generally every 28–30 days (healthy range: 21–35 days); the discharge phase (menstruation) lasts three to seven days. Menstruation begins at puberty and naturally stops at age 45–55.

Chapter 7 of Class 7 Science (Curiosity) explains heat transfer in nature — covering the three processes of conduction, convection, and radiation — and connects them to real-world phenomena such as land and sea breezes, the water cycle, groundwater infiltration, and aquifers.

• 1Conduction is the transfer of heat from the hotter part of an object to the colder part through particles in contact; the particles pass heat to their neighbours but do not move from their positions.
• 2Materials that allow heat to pass through easily are good conductors (e.g., metals such as aluminium and iron); materials that resist heat flow are poor conductors or insulators (e.g., glass, wood, clay, porcelain, and air).
• 3Woollen clothes trap air in their pores; because air is a poor conductor of heat, this reduces heat loss from the body and keeps us warm.
• 4Convection is heat transfer by the actual movement of particles; it occurs in liquids and gases. When heated, air or water expands, becomes lighter, and rises, while cooler fluid moves in to take its place.
• 5Land heats up and cools down faster than water. During the day, warm air rises over the hotter land, and cooler air moves from the sea to the land (sea breeze). At night the process reverses, producing a land breeze.

Chapter 8 of Class 7 Science (Curiosity) covers the measurement of time and motion — tracing ancient timekeeping devices (sundials, water clocks, hourglasses) through the pendulum clock to modern atomic clocks, and introducing speed, average speed, and uniform vs non-uniform linear motion.

• 1Ancient timekeeping devices included sundials (shadow position), water clocks (flow of water in or out), hourglasses (sand flow between bulbs), and candle clocks (markings burned through).
• 2India's Ghatika-yantra (sinking bowl water clock), first mentioned by Aryabhata, took 24 minutes to fill and sink, giving the time unit 'ghati'; a day was divided into 60 equal ghatis.
• 3The world's largest stone sundial, the Samrat Yantra at Jantar Mantar in Jaipur, stands 27 metres tall; its shadow moves at about 1 millimetre per second and can measure time intervals as short as 2 seconds.
• 4A simple pendulum consists of a metallic bob on a thread; its time period (time for one complete oscillation) depends on the length of the pendulum but not on the bob's mass.
• 5The pendulum clock was invented in 1656 and patented in 1657 by Christiaan Huygens, inspired by Galileo Galilei's earlier pendulum experiments.

Chapter 9 of Class 7 Curiosity Science — 'Life Processes in Animals' — covers how animals obtain and digest food (nutrition) and how they breathe and release energy from food (respiration), with detailed study of the human digestive and respiratory systems and comparisons across different animal groups.

• 1Digestion is the process of breaking complex food components (carbohydrates, proteins, fats) into simpler forms; it occurs along the alimentary canal from mouth to anus.
• 2Saliva in the mouth contains a digestive juice that breaks starch into sugar — shown when starchy food like chapati tastes sweet after prolonged chewing (iodine test: chewed rice shows less/no blue-black colour).
• 3The stomach secretes digestive juice, acid, and mucus: the juice breaks down proteins, the acid kills harmful bacteria, and the mucus protects the stomach lining.
• 4The small intestine (about 6 metres long — the longest part of the alimentary canal) receives secretions from the liver (bile, which neutralises acid and breaks down fats) and the pancreas (pancreatic juice, which breaks down carbohydrates, proteins, and fats); finger-like projections on its inner lining increase surface area for nutrient absorption.
• 5The large intestine (about 1.5 metres, wider than the small intestine) absorbs water and some salts from undigested food, forming semi-solid stool stored in the rectum before egestion through the anus.

Chapter 10 of Class 7 Curiosity (Science) covers Life Processes in Plants — how plants grow, make food through photosynthesis, transport water and nutrients via xylem and phloem, and release energy through respiration.

• 1Plants require both sunlight and water for growth — the plant in sunlight with water grows best, the one without water may die, and the one in the dark shows the least growth.
• 2Leaves are the 'food factories' of plants; they are broad, flat, and green due to the pigment chlorophyll, which captures sunlight efficiently.
• 3Photosynthesis is the process by which plants use carbon dioxide, water, sunlight, and chlorophyll to produce glucose (a simple carbohydrate) and oxygen: Carbon dioxide + Water → Glucose + Oxygen.
• 4Starch is detected in a leaf using an iodine test — a blue-black colour indicates the presence of starch; the leaf must first be decolourised in alcohol so the colour change is visible.
• 5Only the green (chlorophyll-containing) parts of a leaf in sunlight produce starch; leaves kept in the dark do not produce starch even if they have chlorophyll.

Chapter 11 of Class 7 Science Curiosity covers light — how it travels in a straight line, how shadows are formed, and how reflection works in plane mirrors and simple optical devices like the pinhole camera, periscope, and kaleidoscope.

• 1Luminous objects emit their own light (e.g., Sun, stars, lightning, fireflies); non-luminous objects like the Moon only reflect light.
• 2Light travels in a straight line, demonstrated by the matchbox-hole activity and the bent-pipe activity.
• 3Transparent materials allow light to pass almost completely; translucent materials allow it to pass partially; opaque materials block light entirely.
• 4A shadow is formed when an opaque object blocks light from reaching a screen. Three things needed: a light source, an opaque object, and a screen.
• 5Opaque objects form darker shadows; translucent objects make lighter shadows; even some transparent objects can create faint shadows. Changing the colour of an opaque object does not change the colour of its shadow.

Chapter 12 of NCERT Class 7 Science (Curiosity) explains Earth's rotation and revolution, how they cause day-night cycles and seasons, and how solar and lunar eclipses occur when the Sun, Earth, and Moon align.

• 1The Earth rotates on its own axis — an imaginary line through the North and South Poles — completing one rotation in about 24 hours.
• 2When viewed from above the North Pole, Earth rotates in the anti-clockwise direction, that is, from West to East.
• 3Earth's West-to-East rotation causes the Sun to appear to rise in the East, move across the sky, and set in the West; the same rotation makes the Moon and stars also appear to rise in the East and set in the West.
• 4The Earth's axis of rotation points very close to the Pole Star, so the Pole Star appears nearly stationary while all other stars appear to revolve around it.
• 5Earth also revolves around the Sun in a nearly circular orbit (when viewed from above), completing one revolution in about 365 days and 6 hours.