Science

Plants make their own food using water, carbon dioxide, and minerals through photosynthesis — a process that requires chlorophyll and sunlight, and produces carbohydrates and releases oxygen.

• 1Plants are autotrophs — they make food from water, carbon dioxide, and minerals; animals and most other organisms are heterotrophs that depend on plants directly or indirectly.
• 2Photosynthesis requires four essentials: chlorophyll, sunlight, carbon dioxide, and water; it produces carbohydrates (including starch) and releases oxygen.
• 3Leaves are the food factories of plants; carbon dioxide enters through stomata (pores surrounded by guard cells); water and minerals travel from roots to leaves through vessels.
• 4Chlorophyll is the green pigment in leaves that captures sunlight energy; leaves of other colours (red, brown) also contain chlorophyll masked by other pigments and also carry out photosynthesis.
• 5Plants get nitrogen from soil bacteria — Rhizobium lives in roots of leguminous plants (gram, peas, moong, beans) converting atmospheric nitrogen into a usable form; this is a symbiotic relationship.

Animals cannot prepare their own food and must obtain it from plants or other animals. Animal nutrition is a five-step process: ingestion, digestion, absorption, assimilation, and egestion.

• 1Animal nutrition involves five steps: ingestion, digestion, absorption, assimilation, and egestion.
• 2The human digestive system consists of the alimentary canal (buccal cavity, oesophagus, stomach, small intestine, large intestine, rectum, anus) and associated glands: salivary glands, liver, and pancreas.
• 3Saliva breaks down starch into sugars; the stomach secretes hydrochloric acid (kills bacteria, creates acidic medium) and digestive juices that break down proteins.
• 4The small intestine is about 7.5 metres long; thousands of finger-like villi on its inner walls increase surface area for absorption of digested food into blood vessels.
• 5The liver — the largest gland in the body — secretes bile stored in the gall bladder; bile plays an important role in the digestion of fats. The pancreatic juice acts on carbohydrates, fats, and proteins.

Temperature — measured by a thermometer — is the reliable indicator of how hot or cold an object is, and heat always flows from a hotter body to a colder one through three processes: conduction (solids), convection (liquids and gases), and radiation (requires no medium).

• 1Our sense of touch is unreliable for judging temperature — the same water can feel hot to one hand and cold to the other simultaneously.
• 2Temperature is the reliable measure of hotness; it is measured by a thermometer.
• 3Clinical thermometer range: 35°C to 42°C; normal human body temperature is 37°C.
• 4Laboratory thermometer range: generally –10°C to 110°C; used for substances other than the human body.
• 5Heat flows from a hotter object to a colder object; the three modes are conduction, convection, and radiation.

Acids taste sour and turn blue litmus red; bases taste bitter, feel soapy, and turn red litmus blue. When an acid reacts with a base, they neutralise each other to form a salt and water, releasing heat.

• 1Acids are sour in taste; the word acid comes from the Latin word acere, meaning sour.
• 2Bases are bitter in taste and feel soapy on touching; examples include sodium hydroxide (soap) and magnesium hydroxide (milk of magnesia).
• 3Litmus, extracted from lichens, is the most common natural indicator — mauve (purple) in distilled water, red in acidic solutions, blue in basic solutions.
• 4China rose (Gudhal) indicator turns acidic solutions dark pink (magenta) and basic solutions green.
• 5Turmeric is a natural indicator that turns red/dark in basic (alkaline) solutions.

Physical changes alter shape, size, colour, or state without forming any new substance and are generally reversible; chemical changes produce one or more new substances and are called chemical reactions.

• 1Physical changes affect physical properties (shape, size, colour, state); no new substance forms and the change is generally reversible.
• 2Chemical changes produce one or more new substances and are also called chemical reactions.
• 3Rusting requires both oxygen and water: Fe + O₂ + H₂O → iron oxide (Fe₂O₃); it is faster in humid and coastal areas due to moisture and salt water.
• 4Rusting is prevented by coating iron with paint, grease, chromium, or zinc; coating iron with zinc is called galvanisation.
• 5Burning magnesium ribbon produces magnesium oxide (MgO), which dissolves in water to form magnesium hydroxide [Mg(OH)₂], a base.

Respiration is the process by which all living organisms break down food (glucose) to release energy; it includes cellular respiration inside cells and breathing, which takes in oxygen-rich air and expels air rich in carbon dioxide.

• 1Cellular respiration is the breakdown of food (glucose) in the cell with release of energy; it occurs in the cells of all living organisms.
• 2Aerobic respiration uses oxygen to break down glucose into carbon dioxide and water; anaerobic respiration occurs without oxygen.
• 3Yeast respires anaerobically and produces alcohol and carbon dioxide — this is why yeast is used in wine and beer production.
• 4During heavy exercise, muscle cells respire anaerobically and produce lactic acid; accumulation of lactic acid causes muscle cramps.
• 5An average adult breathes 15–18 times per minute at rest; during heavy exercise breathing rate can rise to 25 times per minute.

Class 7 Science Chapter 7 explains how blood is pumped through the body by the four-chambered heart via arteries, veins, and capillaries, how kidneys remove waste as urine, and how plants transport water and minerals through xylem and food through phloem. It also covers transpiration, excretion in different animals, and the role of haemoglobin, platelets, and root hair.

• 1Blood is made of plasma, RBCs (carry oxygen via haemoglobin), WBCs (fight germs), and platelets (help clot wounds); haemoglobin gives blood its red colour.
• 2Arteries carry oxygen-rich blood from the heart to body parts and have thick elastic walls; veins carry carbon dioxide-rich blood back to the heart and have valves; capillaries are extremely thin tubes connecting them.
• 3The human heart has four chambers — two atria (upper) and two ventricles (lower); a partition keeps oxygen-rich and carbon dioxide-rich blood from mixing.
• 4A resting person's pulse rate is 72–80 beats per minute; each heartbeat generates one pulse in the arteries; pulse can be felt at the inner wrist.
• 5The human excretory system consists of two kidneys, two ureters, a urinary bladder, and urethra; adult urine is about 1–1.8 L per day and contains 95% water, 2.5% urea, and 2.5% other wastes.

Plants reproduce through two modes — asexual (vegetative propagation, budding, fragmentation, and spore formation) and sexual (pollination followed by fertilisation) — producing new individuals from roots, stems, leaves, buds, or seeds.

• 1Plants reproduce by two modes: asexual (without seeds) and sexual (from seeds via fertilisation).
• 2Asexual methods include vegetative propagation, budding (yeast), fragmentation (algae such as Spirogyra), and spore formation (fungi, moss, ferns).
• 3Vegetative propagation produces new plants from roots, stems, leaves, or buds; examples include rose stem cuttings, potato eyes, Bryophyllum leaf buds, sweet potato and dahlia roots.
• 4Plants produced by vegetative propagation take less time to grow and bear flowers and fruits, and are exact copies of the parent plant.
• 5The stamen is the male reproductive part (anther contains pollen grains with male gametes); the pistil is the female part (ovary contains ovules with the egg/female gamete).

Speed is the distance covered by an object in a unit time, calculated as total distance divided by total time taken. Its basic unit is metre per second (m/s).

• 1Speed = Total distance covered ÷ Total time taken; basic unit is m/s.
• 2Uniform motion: constant speed along a straight line. Non-uniform motion: speed keeps changing.
• 3A simple pendulum's bob makes one oscillation when it travels from its mean position to one extreme, to the other extreme, and back; the time for this is the time period.
• 4The time period of a given pendulum is constant — a slight change in initial displacement does not affect it (established by Galileo Galilei, 1564–1642).
• 5Distance covered = Speed × Time; Time taken = Distance ÷ Speed.

Class 7 Science Chapter 10 covers electric circuit symbols, the heating effect of electric current (used in heaters, irons, and fuses), and the magnetic effect of electric current (used to make electromagnets and electric bells).

• 1Electric components such as cells, batteries, switches, bulbs, and wires are represented by standard symbols; a circuit drawn using these symbols is called a circuit diagram.
• 2In the symbol for an electric cell, the longer line represents the positive terminal and the shorter, thicker line represents the negative terminal.
• 3A battery is a combination of two or more cells connected so that the positive terminal of one cell is joined to the negative terminal of the next cell.
• 4When the switch is in the ON position the circuit is closed and current flows throughout; when OFF the circuit is open and no current flows in any part of it.
• 5The heating effect of electric current: a wire gets heated when current passes through it; the heat produced depends on the material, length, and thickness of the wire.

Light travels along straight lines and changes direction when it hits a shiny surface (reflection). Sunlight is white light made up of seven colours — red, orange, yellow, green, blue, indigo and violet.

• 1Light travels along straight lines — a candle seen through a straight pipe cannot be seen through a bent pipe.
• 2A plane mirror forms an image that is erect, virtual, the same size as the object, and at the same distance behind the mirror as the object is in front of it.
• 3In a plane mirror image, left and right sides are interchanged (only sides swap — the image is not upside down); this is why AMBULANCE is written in reverse on the vehicle.
• 4A concave mirror can form a real and inverted image; when the object is placed very close, the image is virtual, erect and magnified. Concave mirrors are used by dentists and in torch and headlight reflectors.
• 5A convex mirror always forms an erect, virtual, smaller image and is used as a rear-view or side mirror in automobiles because it shows objects spread over a large area.

A forest is a dynamic living system of trees, shrubs, herbs, micro-organisms, animals, soil, and water that are all interdependent — providing oxygen, regulating the water cycle, preventing soil erosion, and serving as a habitat for countless species.

• 1Forests have three vegetation layers: trees at the top (forming the canopy), shrubs in the understorey, and herbs at the lowest layer.
• 2Decomposers — micro-organisms such as mushrooms, beetles, millipedes, and ants — convert dead plants and animal tissues into humus, a dark-coloured substance that returns nutrients to the soil.
• 3Forests are called 'green lungs' because plants release oxygen through photosynthesis and absorb carbon dioxide, maintaining the balance of these gases in the atmosphere.
• 4The forest canopy intercepts and slows falling raindrops; root systems help water seep into the ground, acting as a natural absorber that prevents floods and maintains the water table year-round.
• 5All food chains in a forest are interlinked — for example, grass → insects → frog → snake → eagle. Disturbing any one chain affects all others.

Chapter 13 of Class 7 Science (NCERT) explains what wastewater and sewage are, how they are treated in a Wastewater Treatment Plant through physical, chemical, and biological processes, and why proper sanitation is essential for public health.

• 1Sewage is a complex liquid waste containing organic impurities (faeces, oil, urea, pesticides), inorganic impurities (nitrates, phosphates, metals), nutrients, and disease-causing bacteria and microbes.
• 2Sewerage is the network of pipes (sewers) that transports sewage from its source to a treatment plant; manholes are located every 50–60 m along the line.
• 3WWTP treatment sequence: bar screens (remove rags, cans, plastic) → grit and sand removal tank → settling tank (sludge + skimming of oil/grease) → aeration tank (aerobic bacteria consume organic waste).
• 4Sludge is decomposed by anaerobic bacteria in a separate tank, producing biogas used as fuel or to generate electricity; dried sludge is used as manure.
• 5Treated water is discharged into rivers, seas, or the ground; chlorine or ozone may be used for final disinfection.