Science and Technology विज्ञान आणि तंत्रज्ञान

Quick summary

This chapter explains how objects move and why their motion changes. It covers distance and displacement, speed and velocity, acceleration, the three equations of motion, Newton's three laws of motion and the law of conservation of momentum.

Key points

• Motion is relative. An object is in motion if its position changes with respect to its surroundings; otherwise it is at rest.
• Distance is the length of the actual path travelled. Displacement is the shortest distance between the start and end points, in a given direction. Displacement can be zero even when distance is not (for example, a round trip).
• Distance and speed are scalars (only size). Displacement, velocity, acceleration, force and momentum are vectors (size + direction).
• Velocity changes if speed changes, or direction changes, or both.
• Acceleration is the rate of change of velocity. If velocity decreases, acceleration is negative (deceleration). If velocity is constant, acceleration is zero.
• In uniform circular motion speed stays constant but direction changes at every point, so velocity changes and the motion is accelerated.
• Newton's first law (law of inertia): an object stays at rest or in uniform straight-line motion unless an unbalanced force acts on it.
• Newton's second law: the rate of change of momentum is proportional to the applied force and is in the direction of the force (F = ma).
• Newton's third law: every action force has an equal and opposite reaction force. They act on two different objects, so they do not cancel each other.
• Law of conservation of momentum: if no external force acts, the total momentum of two objects before collision equals the total momentum after collision. A gun recoils and a rocket moves forward because of this.

Important terms

• Speed – distance travelled in unit time.
• Velocity – displacement in unit time.
• Acceleration (त्वरण) – change in velocity divided by time taken.
• Inertia (जडत्व) – the tendency of an object to resist a change in its state of rest or motion; it depends on mass.
• Momentum (संवेग) – product of mass and velocity, P = mv.
• 1 newton – the force that produces an acceleration of 1 m/s² in a mass of 1 kg.

Formulas

1 N = 1 kg × 1 m/s² = 10⁵ dyne.

5 important questions

Q1. Distinguish between distance and displacement.

Distance is the actual path length travelled; it is a scalar and is never negative. Displacement is the shortest distance between start and end points in a fixed direction; it is a vector and can be zero.

Q2. A force gives a 16 kg object an acceleration of 3 m/s². Find the force. What acceleration will the same force give a 24 kg object?

F = ma = 16 × 3 = 48 N. For 24 kg: a = F/m = 48/24 = 2 m/s².

Q3. A gun of mass 4 kg fires a bullet of mass 20 g with a velocity of 300 m/s. Find the recoil velocity of the gun.

Before firing, total momentum = 0. After firing, m₁v₁ + m₂v₂ = 0.
0.02 × 300 + 4 × v₂ = 0, so 4v₂ = −6 and v₂ = −1.5 m/s.
The gun moves back at 1.5 m/s (the minus sign shows the opposite direction).

Q4. Give reason: Action and reaction forces are equal and opposite, yet they do not cancel.

Because they act on two different objects. Forces cancel only when they act on the same object.

Q5. Why is uniform circular motion called accelerated motion?

In circular motion the direction of motion changes at every point. So velocity keeps changing even though speed is constant, which means there is acceleration.

Exam tip

Always change units to SI (g → kg, km/h → m/s by multiplying by 5/18) before using the equations of motion.

Quick summary

This chapter explains when work is said to be done, the two main forms of mechanical energy (kinetic and potential), the law of conservation of energy, free fall, and power – the rate of doing work.

Key points

• Work is done only when a force acts on an object and the object is displaced. No displacement means no work (pushing a wall does no work).
• If force and displacement are at an angle θ, only the part of the force along the displacement does work: W = F s cos θ.
• Positive work: force and displacement in the same direction (θ = 0°). Negative work: force opposite to displacement (θ = 180°), e.g. friction, or gravity when you lift a bag. Zero work: force perpendicular to displacement (θ = 90°), e.g. in uniform circular motion.
• Energy is the capacity to do work. Its units are the same as work: joule (SI) and erg (CGS).
• Kinetic energy is energy due to motion. Potential energy is energy stored due to position or state (a raised stone, a stretched rubber band, a wound spring).
• Potential energy at a height depends on the reference level chosen (usually the ground).
• Law of conservation of energy: energy can neither be created nor destroyed; it only changes from one form to another. The total energy stays constant.
• In free fall, potential energy changes into kinetic energy. At every point, PE + KE is the same (mgh at the top). Just before hitting the ground all of it is kinetic energy.
• Power is the rate of doing work. A machine that does the same work in less time is more powerful.
• An object with zero momentum (v = 0) has zero kinetic energy.

Important terms

• Work (कार्य) – product of force and displacement in the direction of force.
• 1 joule – work done when a force of 1 N displaces an object by 1 m in its own direction.
• Kinetic energy (गतिज ऊर्जा) – energy an object has because of its motion.
• Potential energy (स्थितिज ऊर्जा) – energy stored because of position or state.
• Free fall – motion of an object under gravity alone.
• Power (शक्ती) – work done per unit time.

Formulas

• 1 J = 10⁷ erg
• 1 kW = 1000 W; 1 horse power (hp) = 746 W
• 1 kWh (commercial unit of energy, "1 unit" of electricity) = 3.6 × 10⁶ J

5 important questions

Q1. Derive the formula for kinetic energy.

Let force F act on a body of mass m at rest (u = 0) and displace it by s. Work W = Fs = ma × s. From v² = u² + 2as, s = v²/2a. So W = ma × v²/2a = ½ mv². This work is stored as kinetic energy, so KE = ½ mv².

Q2. Find the work done when a force of 10 N moves an object 5 m at an angle of 60° to the force.

W = F s cos θ = 10 × 5 × cos 60° = 50 × ½ = 25 J.

Q3. Show that the kinetic energy of a freely falling object on reaching the ground equals its initial potential energy.

At height h: PE = mgh, KE = 0. Just before reaching the ground, v² = 0 + 2gh, so KE = ½ m(2gh) = mgh and PE = 0. Total energy stays mgh, so PE has fully changed into KE.

Q4. Why is the work done on an object in uniform circular motion zero?

The force (towards the centre) is perpendicular to the displacement (along the tangent) at every point. θ = 90° and cos 90° = 0, so W = 0.

Q5. A motor lifts 50 kg of water to a height of 20 m in 10 s. Find its power. (g = 10 m/s²)

W = mgh = 50 × 10 × 20 = 10,000 J. P = W/t = 10,000/10 = 1000 W = 1 kW.

Exam tip

For "give reason" questions, state which of force or displacement is zero, or the angle between them – that decides the type of work.

Quick summary

This chapter explains electric potential, potential difference, electric current and resistance. It covers Ohm's law, resistivity, conductors and insulators, and how resistors behave when connected in series and in parallel.

Key points

• Charge flows from a point of higher potential to a point of lower potential, just as water flows from a higher level to a lower level.
• A cell keeps a potential difference between its two terminals; this pushes electrons through a circuit.
• Metals have free electrons (loosely bound outer electrons). Their flow through a conductor is electric current.
• Electrons move from the negative terminal to the positive terminal; the conventional current is taken from positive to negative.
• Ohm's law: at constant temperature, the current through a conductor is directly proportional to the potential difference across its ends (V = IR). The V–I graph is a straight line through the origin.
• Resistance depends on length (R ∝ L), area of cross-section (R ∝ 1/A), the material and temperature.
• Conductors (copper, silver, aluminium) have very low resistance; insulators (rubber, glass, plastic) have very high resistance. Nichrome has high resistivity, so it is used in heaters.
• Series connection: same current through all resistors; the voltage divides; Rs = R₁ + R₂ + R₃. Effective resistance is more than the largest one.
• Parallel connection: same potential difference across all; the current divides; 1/Rp = 1/R₁ + 1/R₂ + 1/R₃. Effective resistance is less than the smallest one.
• Household appliances are connected in parallel, so each gets the full 230 V and if one stops working the others still work.

Important terms

• Potential difference – work done to carry a unit positive charge from one point to another.
• Electric current (विद्युत धारा) – amount of charge flowing through a cross-section per unit time.
• Resistance (रोध) – opposition a conductor offers to the flow of current.
• Resistivity (रोधकता) – resistance of a conductor of unit length and unit cross-sectional area; a property of the material.
• Circuit diagram – a drawing of a circuit using standard symbols.

Formulas

5 important questions

Q1. State Ohm's law and write its formula.

At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends. V ∝ I, so V = IR, where R is the resistance.

Q2. A 1 m nichrome wire has resistance 6 Ω. What is the resistance if the length is reduced to 70 cm?

R ∝ L. New R = 6 × (0.70/1) = 4.2 Ω.

Q3. Resistors of 15 Ω and 30 Ω are connected (a) in series (b) in parallel. Find the effective resistance.

(a) Rs = 15 + 30 = 45 Ω. (b) 1/Rp = 1/15 + 1/30 = 3/30, so Rp = 10 Ω.

Q4. Why are domestic appliances connected in parallel?

Each appliance gets the same full voltage, each can be switched on or off separately, and if one fails the rest keep working. Total resistance is also lower.

Q5. Distinguish between conductors and insulators.

Conductors have very low resistance and many free electrons, so current flows easily (copper, aluminium). Insulators have very high resistance and almost no free electrons, so current does not flow (rubber, plastic).

Exam tip

In numericals, first decide series or parallel, find the effective resistance, then use V = IR for current.

Quick summary

This chapter explains the laws of chemical combination, how atomic and molecular masses are measured, the mole concept, valency and radicals, and how to write chemical formulae of compounds.

Key points

• Law of conservation of matter (Lavoisier): in a chemical reaction, the total mass of reactants equals the total mass of products. Matter is neither created nor destroyed.
• Law of constant proportion (Proust): a pure compound always contains the same elements in the same proportion by mass, whatever its source. In water, H : O = 1 : 8 by mass; in CO₂, C : O = 3 : 8.
• Atoms are extremely small, so their mass is measured relative to a reference atom. Hydrogen and later oxygen were used; today carbon-12 is the reference.
• Unified atomic mass (u), also called dalton: 1/12 of the mass of one carbon-12 atom. 1 u = 1.66053904 × 10⁻²⁷ kg.
• Molecular mass = sum of atomic masses of all atoms in a molecule. Example: H₂O = 2 × 1 + 16 = 18 u.
• Mole: the quantity of a substance whose mass in grams equals its molecular mass. One mole of any substance contains 6.022 × 10²³ particles (Avogadro's number).
• Valency is the combining capacity of an atom = number of electrons it gives, takes or shares to complete its octet. Na is monovalent (gives 1 electron), Mg is bivalent.
• Some metals show variable valency: iron (Fe²⁺ ferrous, Fe³⁺ ferric), copper (Cu⁺ cuprous, Cu²⁺ cupric).
• Radicals are ions. Positive ones are basic radicals (Na⁺, NH₄⁺, Ca²⁺, Al³⁺). Negative ones are acidic radicals (Cl⁻, OH⁻, NO₃⁻, SO₄²⁻, CO₃²⁻, PO₄³⁻). Groups of atoms with a charge (NH₄⁺, SO₄²⁻) are composite radicals.
• To write a formula: write symbols of the radicals, write their valencies below, cross-multiply, simplify. Example: Al³⁺ and SO₄²⁻ give Al₂(SO₄)₃.

Important terms

• Atomic mass – mass of an atom relative to 1/12 of a C-12 atom.
• Molecular mass (रेणुवस्तुमान) – total of atomic masses in a molecule.
• Mole (मोल) – gram molecular mass of a substance; contains 6.022 × 10²³ particles.
• Avogadro's number (Nₐ) – 6.022 × 10²³.
• Valency (संयुजा) – combining capacity of an element.

Formulas

• Number of moles (n) = mass in grams ÷ molecular mass
• Number of molecules = n × 6.022 × 10²³
• Mass = n × molecular mass
• Atomic masses used often: H = 1, C = 12, N = 14, O = 16, Na = 23, Mg = 24, Cl = 35.5, Ca = 40.

5 important questions

Q1. State the law of constant proportion with an example.

A pure chemical compound always contains the same elements combined in the same proportion by mass. Example: water from any source has hydrogen and oxygen in the ratio 1 : 8 by mass.

Q2. Find the molecular mass of Na₂SO₄.

Na₂SO₄ = 2(23) + 32 + 4(16) = 46 + 32 + 64 = 142 u.

Q3. How many molecules are present in 90 g of water?

Molecular mass of H₂O = 18. Moles = 90/18 = 5 mol. Molecules = 5 × 6.022 × 10²³ = 3.011 × 10²⁴.

Q4. Two samples of slaked lime: m (7 g with 5 g Ca, 2 g O) and n (1.4 g with 1.0 g Ca, 0.4 g O). Which law is proved?

Ratio Ca : O in m = 5 : 2; in n = 1.0 : 0.4 = 5 : 2. Same ratio from different sources, so the law of constant proportion is proved.

Q5. Write the formula of calcium oxide and aluminium hydroxide.

Ca²⁺ and O²⁻ → valencies 2 and 2 → CaO. Al³⁺ and OH⁻ → valencies 3 and 1 → Al(OH)₃.

Exam tip

For mole problems, always write the three steps: molecular mass, number of moles, then mass or number of particles.

Quick summary

This chapter describes ionic compounds, the Arrhenius theory of acids and bases, the strength and concentration of solutions, the pH scale, neutralization, the reactions of acids and bases, water of crystallisation and electrolysis.

Key points

• Ionic compounds are made of oppositely charged ions held by an ionic bond. Na gives one electron to Cl to form Na⁺ and Cl⁻ in NaCl.
• Arrhenius theory: an acid gives H⁺ ions in water; a base gives OH⁻ ions in water. A salt is formed from a basic radical (other than H⁺) and an acidic radical (other than OH⁻).
• Strong acids (HCl, H₂SO₄, HNO₃) dissociate almost fully; weak acids (acetic acid, carbonic acid) dissociate only a little. Similarly NaOH, KOH are strong bases; NH₄OH is a weak base.
• Alkalis are bases highly soluble in water (NaOH, KOH, Ca(OH)₂).
• Basicity of an acid = number of H⁺ ions one molecule gives (HCl 1, H₂SO₄ 2, H₃PO₄ 3). Acidity of a base = number of OH⁻ ions one molecule gives.
• pH scale runs from 0 to 14. pH 7 is neutral (pure water), below 7 acidic, above 7 basic.
• Neutralization: acid + base → salt + water. The salt formed need not always be neutral.
• Metal oxides are basic, non-metal oxides are acidic, and oxides like ZnO and Al₂O₃ are amphoteric (react with both acids and bases).
• Acid + metal → salt + hydrogen gas. Acid + carbonate → salt + water + CO₂ (lime water turns milky).
• Water of crystallisation: a fixed number of water molecules in a crystal. Blue vitriol is CuSO₄·5H₂O; on heating it turns white and becomes blue again when water is added.
• Electrolysis of water (with a little dilute H₂SO₄) gives hydrogen at the cathode and oxygen at the anode in the ratio 2 : 1 by volume.

Important terms

• Concentration – amount of solute in a fixed amount of solution.
• Molarity (M) – number of moles of solute in 1 litre of solution.
• Indicator – a substance that shows acid or base by colour change (litmus, phenolphthalein, methyl orange, universal indicator).
• Cation / anion – positive ion / negative ion.
• Electrolyte – a compound which conducts electricity in molten or dissolved state.

Formulas

• Concentration (g/L) = mass of solute (g) ÷ volume of solution (L)
• Molarity (mol/L) = moles of solute ÷ volume of solution (L); written as [NaCl] = 1
• HCl + NaOH → NaCl + H₂O
• Zn + 2HCl → ZnCl₂ + H₂↑
• CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑
• CuSO₄·5H₂O (blue) → CuSO₄ (white) + 5H₂O on heating

5 important questions

Q1. Define acid and base according to Arrhenius theory.

An acid is a substance which gives H⁺ ions when dissolved in water (HCl → H⁺ + Cl⁻). A base gives OH⁻ ions in water (NaOH → Na⁺ + OH⁻).

Q2. Classify the oxides: CaO, CO₂, ZnO, SO₃, Na₂O, Al₂O₃.

Basic: CaO, Na₂O. Acidic: CO₂, SO₃. Amphoteric: ZnO, Al₂O₃.

Q3. 4 g of NaOH is dissolved to make 1 L of solution. Find its molarity.

Molecular mass of NaOH = 23 + 16 + 1 = 40. Moles = 4/40 = 0.1. Molarity = 0.1 mol/L, so [NaOH] = 0.1 M.

Q4. What happens when crystals of blue vitriol are heated and then water is added after cooling?

On heating, the crystals lose their water of crystallisation and turn into a white powder. When water is added after cooling, the blue colour returns.

Q5. Explain the formation of sodium chloride.

Sodium (2, 8, 1) gives its one outer electron to chlorine (2, 8, 7). Both get a complete octet and form Na⁺ and Cl⁻ ions, which are held together by an ionic bond.

Exam tip

Learn the colour of each indicator in acid and base; "odd one out" and "what will you observe" questions are common.

Quick summary

Plants are classified into groups based on their body structure, the presence of tissues for conduction, and whether they produce seeds. This chapter explains the main divisions of the plant kingdom from simple algae to flowering plants.

Key points

• Plants are autotrophs: they make their own food by photosynthesis.
• Criteria for classification, in order: (1) whether the body is divided into root, stem and leaves; (2) presence of conducting tissues (xylem and phloem); (3) whether seeds are formed; (4) whether seeds are enclosed in a fruit; (5) number of cotyledons.
• Plants are first divided into Cryptogams (no flowers or seeds; reproduce by spores) and Phanerogams (have special reproductive organs and form seeds).
• Thallophyta (algae): body is a thallus, not divided into root, stem, leaves. Mostly grow in water. Can be unicellular or multicellular. Examples: Spirogyra, Ulothrix, Chlamydomonas. (Fungi are no longer kept with plants because they lack chlorophyll.)
• Bryophyta: simple plants with root-like, stem-like and leaf-like parts; no conducting tissues. They grow in moist places and need water for reproduction, so they are called the amphibians of the plant kingdom. Examples: Marchantia (liverwort), Funaria (moss), Riccia.
• Pteridophyta: body has true roots, stem and leaves, and conducting tissues. No flowers or seeds. Asexual reproduction by spores, sexual reproduction by zygote formation. Examples: ferns like Nephrolepis, Adiantum, Selaginella, Equisetum.
• Gymnosperms: seed-bearing plants with naked seeds (no fruit covering). Mostly evergreen, tall, woody trees. Male and female flowers are borne on different sporophylls of the same plant. Examples: Cycas, Pinus, Thuja.
• Angiosperms: flowering plants; seeds are enclosed in a fruit. Two groups: monocots (one cotyledon) and dicots (two cotyledons).
• Monocots: fibrous roots, parallel venation, flower parts in multiples of 3 (maize, wheat, banana, onion). Dicots: tap root, reticulate venation, flower parts in multiples of 4 or 5 (tamarind, mango, beans, sunflower).

Important terms

• Thallus – plant body not divided into root, stem and leaves.
• Cryptogams (बीजरहित वनस्पती) – plants with hidden reproductive organs; no seeds.
• Phanerogams – seed-producing plants.
• Cotyledon (बीजपत्र) – the part of the seed which stores food for the embryo.
• Sporophyll – a leaf-like structure that bears spores.

Key facts

5 important questions

Q1. Why are bryophytes called the amphibians of the plant kingdom?

They grow on moist soil (land), but they need water for fertilization and reproduction, just as amphibians live on land but need water to breed.

Q2. Write the characteristics of Pteridophyta.

Body divided into true root, stem and leaves; conducting tissues present; no flowers and seeds; reproduce asexually by spores and sexually by zygote formation. Example: fern.

Q3. Distinguish between gymnosperms and angiosperms.

Gymnosperms have naked seeds not covered by fruit and do not have true flowers (e.g. Cycas). Angiosperms bear flowers and their seeds are enclosed in fruits (e.g. mango).

Q4. Distinguish between monocot and dicot plants.

Monocots: one cotyledon, fibrous roots, parallel venation, flower parts in threes (maize). Dicots: two cotyledons, tap root, reticulate venation, flower parts in fours or fives (bean).

Q5. Which criteria are used for classifying plants?

Differentiation of the body into root, stem and leaves; presence of conducting tissues; formation of seeds; seeds covered by fruit or not; and number of cotyledons.

Exam tip

Diagrams of Spirogyra, Marchantia, Funaria and fern are often asked – practise drawing and labelling them.

Quick summary

This chapter explains how energy and nutrients move through an ecosystem. It covers food chains, food webs, trophic levels, the pyramid of energy and the three main bio-geo-chemical cycles: carbon, oxygen and nitrogen.

Key points

• The sun is the main source of energy for every ecosystem. Green plants (producers) capture it by photosynthesis.
• A food chain shows who eats whom in a straight line: grass → grasshopper → frog → snake → eagle.
• Many food chains are joined together into a food web. Food webs make an ecosystem stable.
• Each step of a food chain is a trophic level: producers (1st), herbivores or primary consumers (2nd), carnivores or secondary consumers (3rd), tertiary consumers / apex consumers (top).
• At each trophic level, a large part of the energy is used for life processes and lost as heat. Only about 10% passes to the next level. So the amount of energy keeps decreasing from producers to apex consumers.
• The pyramid of energy is always upright, with producers at the broad base.
• Energy flow is one way: from sun → producers → consumers; it does not return to the sun or plants.
• Flow of nutrients is cyclic: decomposers (bacteria, fungi) break down dead bodies and return nutrients to soil and air, from where plants take them again.
• Carbon cycle: CO₂ is taken in by plants in photosynthesis and returned by respiration, decomposition, burning of fuels, forest fires and volcanoes.
• Oxygen cycle: oxygen is released by photosynthesis and used in respiration, combustion and formation of oxides.
• Nitrogen cycle: nitrogen-fixing bacteria (Rhizobium in root nodules) and lightning convert atmospheric N₂ into nitrates; plants use them for proteins; decomposers form ammonia; denitrifying bacteria return N₂ to the air.

Important terms

• Producers (उत्पादक) – green plants that make food.
• Consumers – organisms that depend on others for food.
• Decomposers (विघटक) – microbes that break down dead matter.
• Trophic level – the step at which an organism obtains its food in a food chain.
• Bio-geo-chemical cycle – cyclic movement of elements between living (biotic) and non-living (abiotic) parts of the environment.
• Aerobes / anaerobes – microbes that need / do not need oxygen.

Key facts

5 important questions

Q1. Give reason: Energy flow through an ecosystem is one way.

Energy from the sun is taken by plants and passed to herbivores and carnivores. At each level some energy is lost as heat. It never flows back to the previous level or to the sun, so the flow is one way.

Q2. Correct the statement: Carnivores occupy the second trophic level.

Wrong. Herbivores (primary consumers) occupy the second trophic level. Carnivores occupy the third or higher trophic levels.

Q3. Explain the relation between a food chain and a food web.

A food chain is one linear path of food. In nature an organism eats many types of food and is eaten by many. So many food chains cross each other and form a network called a food web.

Q4. Why is the flow of nutrients cyclic?

Decomposers break down dead plants and animals and release nutrients back into soil, water and air. Plants absorb these nutrients again, so nutrients move in a cycle.

Q5. Why is balance in bio-geo-chemical cycles necessary?

These cycles keep the amount of carbon, oxygen and nitrogen constant in nature. If one is disturbed (for example extra CO₂ from burning fuels), it causes problems like global warming.

Exam tip

Draw a neat labelled diagram for any cycle asked; marks are given for arrows and labels.

Quick summary

Microbes are tiny living things that can be seen only with a microscope. This chapter explains useful microbes like Lactobacilli, Rhizobium and yeast, the use of microbes in industry and medicine (antibiotics, vaccines), and harmful microbes like fungi and Clostridium.

Key points

• Lactobacilli are rod-shaped bacteria that change lactose (milk sugar) into lactic acid. This turns milk into curd. They are used to make yoghurt, buttermilk, cheese, and also in pickles and silage. They help digestion (probiotics).
• Rhizobium lives in root nodules of leguminous plants (beans, groundnut, fenugreek). It fixes atmospheric nitrogen into nitrogen compounds. This is symbiosis – both plant and bacteria benefit. Such crops are rich in protein and improve soil fertility.
• Yeast is a unicellular fungus that reproduces by budding. It ferments sugars and releases CO₂ and alcohol. CO₂ makes bread and idli dough spongy.
• Molasses from sugarcane is fermented by yeast (Saccharomyces) to produce ethanol, used as alcohol and as a biofuel. Grape juice is fermented to make wine (wineries near Nashik).
• Antibiotics are chemicals produced by microbes that kill or stop the growth of harmful microbes. Penicillin was discovered by Alexander Fleming from the fungus Penicillium.
• Broad-spectrum antibiotics act against many types of bacteria. Antibiotics must be taken only on a doctor's prescription and the full course must be completed.
• Vaccines are made from weakened or killed pathogens; they make the body produce antibodies.
• Harmful fungi grow on leather, gunny bags, wood and food (pickles, jam) in moist conditions. They release poisonous mycotoxins, so such food should not be eaten.
• Clostridium bacteria are rod-shaped, anaerobic and form bottle-shaped endospores. They spoil cooked food and cause food poisoning (C. botulinum), tetanus and gas gangrene.
• Other diseases are caused by viruses (AIDS, hepatitis, influenza), bacteria (cholera, typhoid, tuberculosis) and protozoa (malaria).

Important terms

• Fermentation (किण्वन) – breakdown of sugars by microbes, without oxygen, producing alcohol or acids and gases.
• Symbiosis (सहजीवन) – a relationship in which two organisms help each other.
• Antibiotic (प्रतिजैविक) – a substance made by microbes that destroys harmful microbes.
• Mycotoxins – poisonous chemicals produced by fungi.
• Pathogen – a microbe that causes disease.

Key facts

5 important questions

Q1. What is the importance of Rhizobium for farmers?

Rhizobium in root nodules of leguminous plants fixes atmospheric nitrogen into compounds plants can use. It increases soil fertility and protein content of crops, so farmers need less chemical fertilizer.

Q2. Why does bread become soft and spongy?

Yeast in the dough ferments sugar and releases CO₂ gas. The gas forms bubbles in the dough, which makes the bread swell and become soft and spongy.

Q3. Define antibiotic. What are broad-spectrum antibiotics?

An antibiotic is a chemical produced by microbes that kills or stops the growth of other harmful microbes. Broad-spectrum antibiotics act against a wide variety of bacteria (e.g. tetracycline).

Q4. Why should food on which fungus has grown not be eaten?

Fungi release poisonous substances called mycotoxins into the food, which can cause illness.

Q5. Name the microbes found in curd, bread, root nodules and spoiled cooked food.

Curd – Lactobacilli; bread – yeast; root nodules – Rhizobium; spoiled cooked food – Clostridium.

Exam tip

"Match the pairs" and "name the microbe" questions are very common – learn the table above well.

Quick summary

This chapter explains weather and climate, how weather is forecast in India, and why climate matters for living things. It also covers solid waste – its types and scientific management – and basic first aid for disaster victims.

Key points

• Weather is the state of the atmosphere at a place for a short time (hours or days). Climate is the average weather of a region over a long period (many years).
• Of all abiotic factors that affect biodiversity, climate is the most important. It decides crops, food habits, clothing, houses and the animals and plants of a region.
• Meteorology is the science that studies the atmosphere, weather and climate. Centres that record climatic factors are called observatories.
• The India Meteorological Department (IMD) was founded by the British in 1875 at Shimla; its head office is now in New Delhi. Weather maps are prepared twice every 24 hours with the help of satellites.
• Monsoon forecasting in India is over 100 years old. In the 1990s, a monsoon model based on 16 worldwide climatic parameters was developed under Dr Vasant Gowarikar (used 1990–2002). Today mathematical (dynamic) and holistic models are used.
• Solid waste is classified by source (urban, industrial, agricultural, biomedical, domestic) and by nature: biodegradable (wet) waste like food and peels, and non-biodegradable (dry) waste like plastic, glass and metal.
• Harmful waste includes radioactive and toxic chemicals; biomedical waste includes bandages, cotton, needles and syringes; e-waste contains toxic metals like lead and mercury.
• Scientific, eco-friendly management: vermicomposting, composting, biogas and bio-electricity from wet waste, recycling, and pyrolysis (burning at high temperature to produce energy). Wet and dry waste should be separated at home.
• 7 principles of solid waste management: Reuse, Refuse, Recycle, Rethink, Reduce, Research, Regulation and public awareness.
• First aid aims to prevent death, stop the condition from getting worse and start recovery. For a fracture, keep the part still using a splint; for burns, hold the part under clean cold running water for at least 10 minutes; for sprains use RICE – Rest, Ice, Compression, Elevation.
• An injured person with a back or spine injury must be moved on a firm stretcher without bending the body.

Important terms

• Weather (हवामान) – short-term atmospheric condition of a place.
• Climate (हवामान / वातावरण) – long-term average weather of a region.
• Solid waste (घनकचरा) – useless solid material thrown away after use.
• Vermicompost – manure made from organic waste with the help of earthworms.
• Disaster management – planning to reduce the loss and harm caused by disasters.

Key facts

5 important questions

Q1. Distinguish between weather and climate.

Weather is the condition of the atmosphere at a place for a short period and changes quickly. Climate is the average of weather conditions of a large region over a long period (about 30 years or more) and changes very slowly.

Q2. Distinguish between biodegradable and non-biodegradable waste.

Biodegradable waste (food, peels, dung) is broken down by microbes in a short time and can become compost. Non-biodegradable waste (plastic, metal, glass) does not break down easily and stays in the environment for a very long time.

Q3. Why is e-waste harmful?

Old electronic goods contain toxic substances like lead, mercury and cadmium. If dumped or burnt, these pollute soil, water and air and harm human health.

Q4. What first aid will you give to a person with a sprain?

Use RICE: let the person rest, apply an ice pack, then compress the part with a bandage, and keep the injured part raised (elevation).

Q5. How can you take part in solid waste management?

Separate wet and dry waste at home, make compost from wet waste, follow the 3 Rs (reduce, reuse, recycle), avoid plastic bags and use-and-throw articles, and spread awareness.

Exam tip

"Write notes" on meteorology, industrial waste, plastic waste and first aid principles are frequently asked.

Quick summary

Information Communication Technology (ICT) means using devices like computers, mobile phones, the internet, radio and television to collect, store, process and share information. This chapter explains how a computer works, its parts, its generations and how software helps in studying science.

Key points

• ICT has changed how we study, work and communicate. It is used in science research, banking, medicine, weather forecasting, space research and education.
• A computer has three main units: input unit (keyboard, mouse) to enter data; processing unit (CPU) with memory unit, control unit and ALU (Arithmetic Logic Unit); and output unit (monitor, printer) to show results.
• Memory stores data and results. Internal memory is of two types: RAM (works only while electricity is supplied, used while working) and ROM (read-only; its stored information cannot be changed).
• External memory includes hard disks, CDs, DVDs and pen drives.
• Hardware = all the electronic and mechanical parts of a computer. Software = the commands (programs), input and output information.
• An operating system is a program that allows communication between the user and the computer. A computer cannot work without it (earlier called DOS – Disk Operating System).
• Data is information in raw (unprocessed) form.
• Generations of computers: the first generation (1946–1959) used large valves (vacuum tubes), e.g. ENIAC. They consumed a lot of electricity, produced heat and often shut down. Later generations used transistors, integrated circuits and microprocessors, and became smaller, faster and cheaper.
• Useful application software: word processing (MS Word) for documents, spreadsheets (MS Excel) for tables, calculations and graphs, and presentation software (PowerPoint) for slides with pictures and videos.
• In a spreadsheet formula, the "=" sign is typed first and no space is left.
• C-DAC, Pune (Centre for Development of Advanced Computing) made India's first supercomputer Param under the guidance of Dr Vijay Bhatkar. It could do one billion calculations per second.

Important terms

• ICT – technology used to handle and communicate information.
• CPU – Central Processing Unit, the "brain" of the computer.
• RAM / ROM – Random Access Memory / Read Only Memory.
• Hardware / Software – physical parts / programs and data.
• Spreadsheet – software arranged in rows and columns for calculations and graphs.

Key facts

5 important questions

Q1. How does a computer work?

Data is entered through the input unit. The processing unit (CPU) stores it in memory, the control unit directs the work and the ALU does calculations. The result is shown through the output unit such as a monitor or printer.

Q2. Why did first generation computers shut down often?

They used large valves which consumed a lot of electricity and produced a lot of heat. The heat made them shut down many times.

Q3. Distinguish between RAM and ROM.

RAM is temporary working memory; its contents remain only while power is on and can be changed. ROM is permanent; its information can only be read and cannot be changed.

Q4. Which software is used to draw graphs from experiment data?

A spreadsheet program (such as MS Excel). Data is entered in rows and columns and a graph is made from it.

Q5. What precautions should be taken while using a computer?

Use licensed and safe software, keep an antivirus updated, take backups of data, do not open unknown links, keep passwords secret and sit with correct posture, taking breaks.

Exam tip

Learn the fill-in-the-blank facts: RAM, multimedia/presentation, spreadsheet, valves (heat) and electricity supply.

Quick summary

This chapter studies how light is reflected by plane and spherical mirrors. It explains the images formed by plane, concave and convex mirrors, the terms used for spherical mirrors, the sign convention, the mirror formula, magnification and uses of mirrors.

Key points

• Laws of reflection: (1) the angle of incidence equals the angle of reflection; (2) the incident ray, reflected ray and normal at the point of incidence lie in the same plane.
• Plane mirror image: virtual, erect, same size as the object, as far behind the mirror as the object is in front, and laterally inverted (left appears right).
• To see your full image in a plane mirror, the mirror must be at least half your height.
• Two plane mirrors at an angle A form n = (360/A) − 1 images.
• A concave mirror has its inner surface reflecting; it converges light. A convex mirror has its outer surface reflecting; it diverges light.
• For a spherical mirror: R = 2f (radius of curvature is twice the focal length).
• Concave mirror images: object at infinity → image at F, point-sized, real; beyond C → between F and C, real, inverted, small; at C → at C, same size; between C and F → beyond C, enlarged, real; at F → at infinity; between F and P → behind the mirror, virtual, erect, enlarged.
• Convex mirror always forms a virtual, erect, diminished image between P and F, behind the mirror.
• Cartesian sign convention: distances are measured from the pole; distances in the direction of incident light (usually to the right) are positive, against it are negative; heights above the principal axis are positive, below negative. Focal length of concave mirror is negative and of convex mirror positive.
• Uses: concave – torch, headlights, projector lamp, floodlight (bulb at F), shaving mirror, dentist's mirror, solar cookers and furnaces. Convex – rear-view mirrors of vehicles (wide field of view), mirrors at sharp turns, in shops for security.

Important terms

• Pole (P) – centre of the mirror surface.
• Centre of curvature (C) – centre of the sphere of which the mirror is a part.
• Radius of curvature (R) – radius of that sphere.
• Principal axis – line through the pole and centre of curvature.
• Principal focus (F) – point where rays parallel to the principal axis meet (or appear to meet) after reflection.
• Focal length (f) – distance between pole and principal focus.
• Real image – can be taken on a screen; virtual image – cannot.

Formulas

If M is negative the image is real and inverted; if positive, virtual and erect. |M| > 1 means enlarged.

5 important questions

Q1. An object 4 cm high is kept 30 cm from a concave mirror of focal length 15 cm. Find the position, size and nature of the image.

u = −30 cm, f = −15 cm. 1/v = 1/f − 1/u = −1/15 + 1/30 = −1/30, so v = −30 cm. M = −v/u = −(−30)/(−30) = −1, so h₂ = −4 cm. The image is at 30 cm in front of the mirror (at C), real, inverted and of the same size.

Q2. A convex mirror has focal length 18 cm. The image is half the size of the object. Find the object distance.

M = +½ = −v/u, so v = −u/2. Using 1/v + 1/u = 1/f: −2/u + 1/u = 1/18, so −1/u = 1/18 and u = −18 cm. The object is 18 cm in front of the mirror.

Q3. Why are convex mirrors fitted on the outside of cars?

A convex mirror always gives an erect, diminished image and covers a much wider field of view, so the driver can see more traffic behind.

Q4. Why does sunlight focused by a concave mirror burn paper?

A concave mirror converges the parallel rays of the sun at its focus. All the heat energy is concentrated at one point, which raises the temperature of the paper enough to burn it.

Q5. If a spherical mirror breaks, what type of mirrors are its pieces?

Each piece is still a part of the same sphere, so each piece is a spherical mirror of the same type and the same focal length.

Exam tip

Always write the sign of u, v and f before using the mirror formula; most mistakes happen in signs.

Quick summary

Sound is a form of energy that travels as a wave through a medium. This chapter explains longitudinal waves, the characteristics of a sound wave, the speed of sound in different media, the range of hearing, echo, reverberation, SONAR and the structure of the human ear.

Key points

• Sound is produced by vibrating objects and needs a medium (solid, liquid or gas). It cannot travel through vacuum.
• In air, sound travels as a longitudinal wave: particles vibrate back and forth in the direction of the wave, forming compressions (high density) and rarefactions (low density). In transverse waves (like on a string), particles move perpendicular to the wave.
• Characteristics of a wave: wavelength (λ), frequency (ν), time period (T) and amplitude. Pitch depends on frequency; loudness depends on amplitude.
• The velocity of sound is highest in solids and least in gases (steel about 5960 m/s, pure water about 1498 m/s, air about 344 m/s at 22 °C). It increases with temperature.
• Humans hear 20 Hz to 20,000 Hz (20 kHz) – the audible range. Below 20 Hz is infrasound (earthquakes, whales); above 20 kHz is ultrasound (bats, dolphins, dogs can hear it).
• Ultrasound is used in sonography, cleaning, detecting cracks in metal, and in SONAR. Bats use echoes of ultrasound to find their way.
• Echo is the repetition of a sound after reflection from a distant surface. Our brain keeps a sound for 0.1 s, so for a distinct echo the reflecting surface must be at least 17.2 m away (at 22 °C).
• Reverberation is the persistence of sound due to repeated reflections. It is more in a closed, empty hall. It is reduced with curtains, carpets, soft boards and furniture that absorb sound.
• SONAR (Sound Navigation and Ranging) uses ultrasonic waves to find the depth of the sea and locate sunken ships, submarines and fish.
• The human ear has the outer ear, eardrum, three small bones (hammer, anvil, stirrup) and the snail-shaped cochlea, which changes vibrations into nerve signals. Never put sharp objects into the ear or listen to very loud music on earphones.

Important terms

• Frequency – number of vibrations per second; unit hertz (Hz).
• Wavelength – distance between two successive compressions or rarefactions.
• Amplitude – maximum displacement or maximum change in pressure/density.
• Echo (प्रतिध्वनी) – sound heard again after reflection.
• Reverberation (निनाद) – lingering of sound due to multiple reflections.

Formulas

5 important questions

Q1. A sound wave has frequency 1.5 kHz and wavelength 25 cm. How long will it take to travel 1.5 km?

v = νλ = 1500 × 0.25 = 375 m/s. Time = 1500/375 = 4 s.

Q2. Nita heard thunder 4 s after seeing lightning. How far was the lightning? (v = 340 m/s)

Distance = v × t = 340 × 4 = 1360 m.

Q3. A SONAR signal returns from the sea bed after 4 s. If sound travels at 1550 m/s in sea water, find the depth.

Sound goes down and comes back, so one way takes 2 s. Depth = 1550 × 2 = 3100 m.

Q4. Why can't we hear an echo in a classroom?

For a distinct echo the reflecting wall must be at least 17.2 m away. In a classroom the walls are closer, so the reflected sound returns in less than 0.1 s and mixes with the original sound.

Q5. Why are the ceilings of cinema halls and conference halls curved?

A curved ceiling reflects sound evenly towards all parts of the hall, so the sound reaches every listener clearly.

Exam tip

In echo and SONAR sums, remember the sound travels twice the distance – divide by 2.

Quick summary

Carbon is found in all living things and in fuels, plastics, medicines and many daily-use materials. This chapter explains the occurrence and properties of carbon, its allotropes, coal and its types, hydrocarbons, and two important compounds – carbon dioxide and methane.

Key points

• Carbon (atomic number 6, electronic configuration 2, 4) has 4 valence electrons, so it is tetravalent. It forms covalent bonds by sharing electrons.
• Compounds from plants and animals are organic compounds; all contain carbon. Compounds from minerals are inorganic.
• Carbon occurs free (diamond, graphite, coal) and in compounds (CO₂ in air, carbonates like limestone and marble, fuels, food).
• Allotropy: an element existing in different physical forms with the same chemical properties. Carbon, sulphur and phosphorus show allotropy.
• Crystalline forms of carbon: diamond (hardest natural substance, each C bonded to 4 others in a 3-D structure, bad conductor of electricity, used in jewellery, cutting glass and rock drilling); graphite (soft, slippery, layers of carbon atoms that slide over each other, good conductor, used in pencils, lubricants, electrodes, arc lamps; one layer is called graphene); fullerene (C₆₀, football-like shape, found in soot and interstellar space, named after architect Buckminster Fuller; Nobel prize 1996 to Kroto, Curl and Smalley).
• Non-crystalline (amorphous) forms: coal, charcoal, coke.
• Coal forms from plants buried for millions of years. Its four types in order of carbon content: peat (first stage, high water), lignite (brown coal), bituminous (household coal), anthracite (purest, hardest). Coke is obtained when volatile matter is removed from coal.
• Hydrocarbons contain only carbon and hydrogen. Saturated hydrocarbons have only single bonds (methane, ethane). Unsaturated have at least one double or triple bond (ethene, ethyne).
• CO₂: colourless gas, molecular mass 44, turns lime water milky, used in fire extinguishers, soft drinks (soda water), dry ice for cooling, decaffeinating coffee, and by plants in photosynthesis.
• Methane (CH₄): about 87% of natural gas; main part of biogas (55–60%); formed when organic matter decays without air; found in marshy places, so called marsh gas. It burns with a blue flame and is a good fuel.

Important terms

• Covalent bond (सहसंयुज बंध) – bond formed by sharing electron pairs.
• Allotropes (अपरूपे) – different forms of the same element.
• Hydrocarbon – compound of carbon and hydrogen only.
• Fossil fuel – fuel formed from remains of living things buried long ago (coal, petrol, natural gas).

Formulas

• C + O₂ → CO₂ + heat
• CH₄ + 2O₂ → CO₂ + 2H₂O + heat (combustion of methane)
• CH₄ + Cl₂ → CH₃Cl + HCl (chlorination, in sunlight)
• 2NaOH + CO₂ → Na₂CO₃ + H₂O
• Ca(OH)₂ + CO₂ → CaCO₃ (milky) + H₂O
• NaHCO₃ + acid → salt + H₂O + CO₂ (fire extinguisher)

5 important questions

Q1. Why are carbon and its compounds used as fuels?

They burn in air (oxygen) and give out a large amount of heat and light. They are easily available and their burning is easy to control.

Q2. Diamond and graphite are both carbon. Why is diamond hard and graphite soft?

In diamond each carbon atom is bonded to four others in a strong 3-D network, which makes it very hard. In graphite carbon atoms form flat layers that are weakly held and slide over each other, making it soft and slippery.

Q3. Why is methane called marsh gas?

Methane is formed when plant matter decomposes in the absence of air in marshy places, and it bubbles up from the surface of marshes.

Q4. How does a soda-acid fire extinguisher work?

It contains sodium bicarbonate solution and a capsule of dilute sulphuric acid. When the capsule breaks, the acid reacts with sodium bicarbonate and produces CO₂ under pressure, which pushes out a stream that covers the fire and cuts off oxygen.

Q5. Write the types of coal.

Peat, lignite, bituminous coal and anthracite. Anthracite has the highest carbon content and is the best quality coal.

Exam tip

Learn the uses and two physical properties of each allotrope; these are frequent 2-mark questions.

Quick summary

This chapter is about salts and other substances we use every day: common salt, baking soda, bleaching powder, washing soda, soap, radioactive substances and their uses, chemicals in the kitchen, artificial food colours, dyes, deodorants and Teflon.

Key points

• Salts are formed from an acid and a base. Salts like Na₂SO₄ and K₃PO₄ are simple salts. Salts can be neutral, acidic or basic, which is checked with universal indicator or pH paper.
• Common salt (NaCl): obtained from sea water by evaporation and also as rock salt (halite). A 25% solution is saturated brine. On electrolysis of fused (molten) salt, chlorine is released at the anode and liquid sodium at the cathode.
• Baking soda (sodium bicarbonate, NaHCO₃): a white, weakly basic powder. On heating or with acid it gives CO₂, so it makes cakes, dhokla and bhaji soft and crisp. Baking powder = baking soda + a mild acid like tartaric acid. Also used in fire extinguishers and as an antacid.
• Bleaching powder (calcium oxychloride, CaOCl₂): releases chlorine; used to bleach cloth and to disinfect drinking water and swimming pools (the smell of tap water in the rainy season is due to chlorine).
• Washing soda (Na₂CO₃·10H₂O): has 10 molecules of water of crystallisation. Removes permanent hardness of water, so soap lathers easily. Used in washing, glass, soap and paper industries.
• Soap is a sodium or potassium salt of fatty acids. In hard water, calcium and magnesium salts form scum and soap does not lather.
• Radioactivity: the spontaneous emission of radiation by unstable nuclei (discovered by Henri Becquerel; studied by Marie and Pierre Curie). Three types of rays: alpha (He²⁺, charge +2, bend towards the negative plate), beta (electrons, charge −1, bend towards the positive plate) and gamma (electromagnetic, no charge, no mass, travel at the speed of light).
• Uses of radioactive isotopes: cobalt-60 for cancer treatment and food preservation; iodine isotopes for thyroid disorders; radiography for detecting flaws in metal; improving seeds in agriculture; carbon-14 for dating fossils.
• Radiation is harmful: it damages the nervous system, causes genetic defects and cancer, so strict safety is needed.
• Teflon (polytetrafluoroethene, (C₂F₄)ₙ, discovered by Roy Plunkett in 1938) is a non-stick coating for utensils.
• Artificial food colours and some deodorants (with aluminium chlorohydrate) can cause allergies and other health problems.

Important terms

• Water of crystallisation – fixed number of water molecules present in a salt's crystal.
• Hard water – water containing calcium and magnesium salts.
• Radioactivity (किरणोत्सारिता) – spontaneous emission of radiation from an unstable nucleus.
• Isotope – atoms of the same element with different mass numbers.
• Anodising – coating aluminium with a thin oxide layer by electrolysis (aluminium is the anode).

Formulas

• 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ (on heating)

5 important questions

Q1. What is radioactivity? Name the three radiations.

The spontaneous emission of invisible radiation by the unstable nucleus of an element is called radioactivity. The three radiations are alpha, beta and gamma rays.

Q2. Why does baking soda make food soft and spongy?

On heating, baking soda decomposes and releases CO₂ gas. The gas bubbles make the dough rise, so the food becomes soft and spongy.

Q3. How does washing soda make hard water soft?

Washing soda reacts with the calcium and magnesium salts in hard water and changes them into insoluble carbonates, which settle down. The water becomes soft and soap lathers easily.

Q4. Write two uses of bleaching powder.

It is used to bleach cotton and linen, and to disinfect drinking water and swimming pool water.

Q5. Write any three uses of radioactive substances.

Cobalt-60 is used in cancer treatment; radioactive iodine is used to treat thyroid problems; radiography is used to find flaws in metal parts; carbon-14 is used to find the age of fossils.

Exam tip

Fill-in-the-blank questions often ask chemical names – learn the formula table well.

Quick summary

This chapter explains three life processes: transportation of water, minerals and food in plants; excretion in plants and humans; and control and co-ordination in plants and humans through movements, the nervous system and hormones.

Key points

• Transport in plants: roots absorb water and minerals from soil. Water moves up through xylem; food made in leaves moves to other parts through phloem.
• Root pressure: root cells take in water and become turgid, pushing water upward into xylem. Transpiration (loss of water vapour through stomata) creates a pull that draws water up in tall plants.
• Translocation: movement of food (sugars, amino acids) through phloem from leaves to roots, fruits and seeds; it needs energy (ATP).
• Excretion in plants: plants store wastes in leaves, bark and fruits that later fall off; some wastes are stored as gums, resins, latex or crystals of calcium oxalate (raphides).
• Human excretory system: a pair of kidneys, ureters, urinary bladder and urethra. The functional unit of the kidney is the nephron. Its cup-like Bowman's capsule holds a network of capillaries called the glomerulus, where blood is filtered. Useful substances are reabsorbed; urine is formed.
• When kidneys fail, blood is cleaned with an artificial kidney – dialysis.
• Control in plants: plants respond by movements. Growth-related (tropic) movements: towards light (phototropic – shoot), towards gravity (gravitropic/geotropic – root), towards water (hydrotropic), towards chemicals (chemotropic – pollen tube towards ovule). Growth-irrelevant movements: touch-me-not (Mimosa) leaves closing, insectivorous plants.
• Plant hormones: auxins (cell growth), gibberellins (stem elongation), cytokinins (cell division), abscisic acid (inhibits growth, causes wilting and falling of leaves), ethylene (ripening of fruits).
• Nervous system in humans: made of neurons (nerve cells). A neuron has a cell body (cyton), dendrites and a long axon. Information travels as electrical impulses; the gap between two neurons is a synapse.
• The central nervous system = brain and spinal cord, protected by the skull, vertebral column and three membranes (meninges). The brain has the cerebrum (thinking, memory, intelligence, voluntary actions), cerebellum (balance and co-ordination of voluntary muscles) and medulla oblongata (involuntary actions like heartbeat, breathing, coughing, sneezing).
• Reflex action: a quick automatic response controlled by the spinal cord (e.g. pulling the hand away from a hot vessel).
• Chemical co-ordination: endocrine glands release hormones directly into blood – e.g. thyroxine (thyroid), insulin (pancreas), adrenaline (adrenal), growth hormone (pituitary).

Important terms

• Transpiration (बाष्पोत्सर्जन) – loss of water as vapour from leaves.
• Translocation – movement of food through phloem.
• Nephron – functional unit of the kidney.
• Dialysis – cleaning of blood with a machine when kidneys fail.
• Neuron (चेतापेशी) – structural and functional unit of the nervous system.
• Hormone (संप्रेरक) – chemical messenger secreted by endocrine glands.

Key facts

5 important questions

Q1. How is water transported in tall trees?

Roots absorb water by root pressure into xylem. As water evaporates from leaves through stomata (transpiration), a pulling force is created which draws the column of water up through xylem to the top.

Q2. Explain the structure of a nephron.

A nephron has a cup-like Bowman's capsule containing a bunch of capillaries called the glomerulus, followed by a coiled tubule and a collecting duct. Blood is filtered in the glomerulus, useful substances are reabsorbed in the tubule and the remaining fluid becomes urine.

Q3. Match: growth of pollen tube towards ovule, shoot, root, growth towards water.

Pollen tube – chemotropic; shoot – phototropic; root – gravitropic; towards water – hydrotropic.

Q4. What is a reflex action? Give an example.

A sudden, automatic response to a stimulus, controlled by the spinal cord without thinking by the brain. Example: pulling your hand back on touching a hot vessel.

Q5. Distinguish between excretion in plants and in humans.

Plants have no special excretory organs; they store waste in leaves, bark, gums and resins or remove it through stomata. Humans have a well-developed excretory system of kidneys, ureters, bladder and urethra that removes urea as urine.

Exam tip

Practise diagrams of the neuron, nephron and human brain; they carry easy marks.

Quick summary

This chapter explains how characters pass from parents to offspring (heredity) and why offspring differ (variation). It covers chromosomes, DNA and RNA, genes, Mendel's experiments with pea plants and some genetic disorders.

Key points

• Heredity is the transfer of characters from parents to offspring. Differences among individuals of the same species are variations. The study of heredity and variation is genetics.
• Sexual reproduction produces more variation than asexual reproduction.
• Chromosomes in the nucleus carry hereditary characters. They are made mainly of DNA and proteins. Each chromosome has two arms joined at the centromere (primary constriction).
• Human body cells have 46 chromosomes (23 pairs): 22 pairs of autosomes and 1 pair of sex chromosomes (allosomes) – XX in females and XY in males.
• DNA has a double helix structure (Watson and Crick, 1953). Each strand is a chain of nucleotides. Bases: adenine and guanine (purines), cytosine and thymine (pyrimidines). A pairs with T, G pairs with C.
• A gene is a segment of DNA that carries the information to make a particular protein. Genes are the structural and functional units of heredity.
• RNA has uracil instead of thymine and is single-stranded. Three types: mRNA (carries the message from DNA to ribosomes), tRNA (brings amino acids), rRNA (part of ribosomes).
• Gregor Mendel (father of genetics) studied 7 pairs of contrasting characters in pea plants (e.g. tall–dwarf, round–wrinkled seed, yellow–green seed).
• Monohybrid cross (one pair, tall TT × dwarf tt): F1 all tall (Tt). F2 phenotypic ratio 3 tall : 1 dwarf; genotypic ratio 1 TT : 2 Tt : 1 tt.
• Dihybrid cross (two pairs, e.g. round-yellow × wrinkled-green): F2 phenotypic ratio 9 : 3 : 3 : 1.
• Genetic disorders: chromosomal – Down syndrome (one extra chromosome 21, total 47), Turner syndrome (44 + X, female, sterile), Klinefelter syndrome (44 + XXY, male, sterile); monogenic – albinism, sickle cell anaemia, haemophilia; polygenic – diabetes, hypertension; mitochondrial – Leber's hereditary optic neuropathy.

Important terms

• Dominant / recessive – a character that appears in F1 / one that stays hidden in F1.
• Phenotype – external visible character (tall); genotype – the gene pair (TT, Tt).
• Homozygous / heterozygous – same alleles (TT, tt) / different alleles (Tt).
• Allele – the alternative forms of a gene.
• Sickle cell anaemia – red blood cells become sickle-shaped and carry less oxygen.

Key facts

5 important questions

Q1. Explain Mendel's monohybrid cross with a chart.

Tall (TT) × dwarf (tt) gives F1 all tall (Tt). Selfing F1 (Tt × Tt) gives TT, Tt, Tt, tt in F2. Phenotypic ratio 3 tall : 1 dwarf; genotypic ratio 1 : 2 : 1. Draw a checker board to show it.

Q2. What is a gene? Why is it called a unit of heredity?

A gene is a part of DNA that carries the code for making a particular protein. Since characters are passed from parents to offspring through genes, genes are the structural and functional units of heredity.

Q3. Describe the structure of DNA.

DNA is a double helix of two strands of nucleotides coiled around each other. Each nucleotide has a sugar (deoxyribose), a phosphate and a nitrogen base. Bases pair as A–T and G–C.

Q4. Write a note on Down syndrome.

It is caused by an extra 21st chromosome (trisomy 21), giving 47 chromosomes. The child shows slow mental and physical growth and a flat face. It cannot be cured, but care and training help.

Q5. Distinguish between autosomes and sex chromosomes.

Autosomes (22 pairs) control body characters and are the same in males and females. Sex chromosomes (1 pair) decide sex – XX in females and XY in males.

Exam tip

Always draw the checker board (Punnett square) for crosses – it earns marks even if the ratio is asked only.

Quick summary

This chapter introduces tissues in animals and plants, tissue culture, and biotechnology – using living cells to make useful products. It also covers how biotechnology helps agriculture and introduces agro-complementary businesses like dairy, poultry, sericulture and fisheries.

Key points

• A tissue is a group of cells having the same origin, structure and function.
• Animal tissues: epithelial (protective covering), connective (joins parts), muscular and nervous.
• Epithelial tissue: simple squamous (lining of air sacs/alveoli, blood vessels), cuboidal (kidney tubules, glands), columnar (lining of intestine), ciliated (respiratory tract), glandular (glands).
• Connective tissue: blood, bone, cartilage, tendons (join muscle to bone), ligaments (join bone to bone), adipose (fat).
• Muscles: striated (voluntary, attached to bones), smooth (involuntary, in stomach, intestine), cardiac (involuntary, in heart, contract rhythmically).
• Nervous tissue is made of neurons with long axons.
• Plant tissues: meristematic (dividing, at tips of root and shoot; active cells with dense cytoplasm and a big nucleus) and permanent (non-dividing). Permanent tissues are simple (parenchyma, chlorenchyma – contains chloroplasts, aerenchyma – air spaces that help aquatic plants float, collenchyma, sclerenchyma) and complex (xylem – carries water, phloem – carries food).
• Tissue culture: growing cells or tissues outside the body (ex vivo) in an aseptic, nutrient-rich medium. Used to produce many identical plantlets quickly, disease-free plants, and plants that are hard to grow from seed.
• Biotechnology uses two main techniques: genetic engineering (changing genes to get desired characters) and tissue culture.
• Benefits in agriculture: high-yield and disease-resistant crops (e.g. Bt cotton), crops tolerant to drought or salt, more nutritious crops, bio-fertilizers and bio-pesticides.
• Agro-complementary businesses: dairy, poultry farming (rearing chickens for eggs and meat), sericulture (rearing silkworms for silk), apiculture (bee-keeping for honey), fisheries, goat and sheep rearing (livestock), mushroom farming and agritourism.

Important terms

• Tissue (ऊती) – group of similar cells doing one job.
• Meristem – plant tissue capable of cell division.
• Tissue culture (ऊतीसंवर्धन) – growing tissue in a sterile nutrient medium.
• Genetic engineering – changing an organism's genes to get desired traits.
• Sericulture (रेशीम उद्योग) – rearing silkworms for silk.

Key facts

5 important questions

Q1. Correct the statements: (a) Simple squamous epithelium is present in respiratory tract. (b) Chlorenchyma helps the plant float.

(a) Ciliated epithelium is present in the respiratory tract. (b) Aerenchyma helps the plant float in water.

Q2. Write a note on meristematic tissue.

It is found at growing tips of root and shoot. Its cells are small, active, have dense cytoplasm and a large nucleus, and keep dividing. It helps the plant grow; its cells later differentiate into permanent tissues.

Q3. What is tissue culture? Give its uses.

Growing cells or tissues of an organism outside the body in a sterile, nutrient-rich medium. It gives many identical, disease-free plants in a short time, and plants of species that rarely produce seeds.

Q4. Explain the impact of biotechnology on agriculture.

It gives high-yield, pest-resistant and drought-tolerant crops (like Bt cotton), more nutritious food, bio-fertilizers and bio-pesticides, so farmers get better production with less chemical use.

Q5. Write a note on sericulture.

Sericulture is rearing silkworms on mulberry leaves to obtain silk. The silkworm spins a cocoon of silk thread, which is boiled and reeled to make silk. It is a good side business for farmers.

Exam tip

"Odd one out" and "correct the statement" questions come from the tissue tables – revise them carefully.

Quick summary

Telescopes help us see distant objects in space. This chapter explains the different kinds of light (electromagnetic radiation), optical telescopes (refracting and reflecting), radio telescopes like GMRT, telescopes in space, and the role of ISRO.

Key points

• Light is an electromagnetic wave. Our eyes see only visible light with wavelengths from 400 nm to 800 nm. Others include radio waves, microwaves, infrared, ultraviolet, X-rays and gamma rays.
• Heavenly bodies give out all these radiations, so different telescopes are needed for each.
• Hans Lippershey made the first telescope (1608). Galileo made one in 1609 and was the first to use a telescope to observe space.
• Refracting telescope: uses two convex lenses – a large objective lens and an eyepiece. Big lenses are heavy and suffer from chromatic aberration (colour errors).
• Reflecting telescope: uses a large concave mirror. Two types: Newtonian (a small plane mirror sends rays to an eyepiece on the side) and Cassegrain (a small convex mirror sends rays back through a hole in the concave mirror).
• India's biggest optical telescope (3.6 m mirror) is at the Aryabhatta Research Institute of Observational Sciences, Devasthal near Nainital – the largest in Asia.
• Ground-based optical telescopes face problems: city lights, clouds, and the atmosphere disturbing light. So they are built on mountains far from cities, or placed in space.
• Radio telescope: a large metal dish collects radio waves and focuses them on a receiver; a computer makes an image.
• GMRT (Giant Metrewave Radio Telescope) at Narayangaon near Pune has 30 dishes of 45 m diameter each, spread over 25 km, so it works like one dish of 25 km diameter. It uses radio waves of about a metre wavelength.
• Space telescopes: NASA's Hubble (optical, 94-inch mirror, about 589 km above the Earth); NASA's Chandra X-ray telescope (1999), named after Indian-born scientist Subrahmanyan Chandrasekhar.
• ISRO (Indian Space Research Organisation, Bengaluru, set up in 1969) launches satellites using PSLV and GSLV. In 2015 it launched Astrosat, with ultraviolet and X-ray telescopes on one satellite.

Important terms

• Electromagnetic spectrum – the full range of electromagnetic radiations by wavelength.
• Objective / eyepiece – the lens facing the object / the lens near the eye.
• Chromatic aberration – coloured fringes in an image formed by lenses.
• Radio telescope – telescope that receives radio waves from space.

Key facts

5 important questions

Q1. What are the difficulties in using ground-based optical telescopes? How are they overcome?

City lights at night, clouds and the atmosphere absorb and disturb light coming from stars. To avoid this, telescopes are built on high mountains far from towns, and some are sent into space (like Hubble).

Q2. Explain the construction of a radio telescope.

It has a large curved metal dish (one or more) that reflects radio waves from space to a receiver at its focus. The signals are sent to a computer that analyses them and forms an image of the source.

Q3. Why are X-ray telescopes placed in space?

The Earth's atmosphere absorbs X-rays coming from space, so they do not reach the ground. Hence X-ray telescopes like Chandra must work above the atmosphere.

Q4. Explain the Cassegrain telescope.

Light from space falls on a large concave mirror and is reflected towards a small convex mirror. The convex mirror reflects it back through a hole in the centre of the concave mirror to the eyepiece, which gives a magnified image.

Q5. Fill in: GMRT is used for ___ waves; the first scientist to use a telescope for space was ___.

GMRT is used for radio waves; Galileo was the first to use a telescope for observing space.

Exam tip

Learn the pairs: X-rays – Chandra, optical – Hubble, Indian radio – GMRT, satellites – ISRO.