Science and Technology: Unit-wise Subjective Question Bank

1. A hypothesis is a tentative, testable explanation of an observation. Example: "Plants kept in the dark will grow less than plants kept in light."

2. (i) Keep the eye vertically above the mark being read, to avoid parallax error. (ii) Start from a full-centimetre mark (not the worn end) and check the zero error.

3. (i) Observation: a plant in the corner wilts. (ii) Problem: why does it wilt? (iii) Hypothesis: it is not getting enough water. (iv) Experiment: water one pot and leave an identical pot unwatered. (v) Analysis and conclusion: if the watered plant recovers and the other wilts, the hypothesis is supported. Any four steps in order, with the example, earn full marks.

1. Monera are prokaryotes with no nuclear membrane (bacteria); Protista are unicellular eukaryotes with a true nucleus (Amoeba). Monera lack membrane-bound organelles; Protista have them.

2. Fungi cannot make their own food (heterotrophic, saprophytic) whereas plants are autotrophs. The fungal cell wall is made of chitin whereas the plant cell wall is cellulose.

3. Whittaker (1969) divided life into five kingdoms. Monera: prokaryotic, unicellular (bacteria). Protista: unicellular eukaryotes (Amoeba). Fungi: heterotrophic, chitin wall (mushroom). Plantae: multicellular autotrophs (mango). Animalia: multicellular heterotrophs without cell wall (cow). Four creditable points: kingdoms with their basis and an example each.

1. Queen: lays eggs. Worker: collects nectar and pollen, builds comb, feeds larvae. Drone: mates with the queen.

2. Honey bees give honey, wax and royal jelly. They also pollinate crops, which raises fruit and seed yield.

3. A honey bee passes through four stages (complete metamorphosis): egg, larva, pupa, adult. For the worker: egg 3 days, larva about 6 days, pupa about 12 days, so adult emerges after 21 days (queen 16, drone 24). The egg is laid in a cell; the larva is fed by nurse workers; the pupa is sealed in the cell with a wax cap; the adult chews its way out. A labelled four-stage diagram earns a mark.

1. The two alleles of a gene separate during gamete formation, so each gamete carries only one allele of each gene.

2. Father X^{N}Y; mother X^{N}X^{c}. Sons get the father's Y and one of the mother's X: X^{N}Y (normal) or X^{c}Y (colour-blind), each with probability 1/2.

3. Gametes: T, t from each parent.

Genotypic ratio TT : Tt : tt = 1 : 2 : 1. Phenotypic ratio tall : dwarf = 3 : 1.

4. Human cells have 22 pairs of autosomes and one pair of sex chromosomes: XX in females, XY in males. Every egg carries X. Half the sperms carry X and half carry Y. If an X sperm fertilises the egg the baby is XX (girl); if a Y sperm does, the baby is XY (boy). So the father's sperm decides the sex, with equal chance of each.

1. A voluntary action is controlled by the cerebrum and is done by will (writing). A reflex action is rapid, involuntary and controlled by the spinal cord (withdrawing a hand from a hot pan).

2. Insulin from the pancreas; thyroxine from the thyroid gland (also adrenaline from the adrenal gland).

3. Deoxygenated blood enters the right atrium from the vena cava, passes to the right ventricle, then through the pulmonary artery to the lungs. Oxygenated blood returns by the pulmonary vein to the left atrium, goes to the left ventricle and is pumped to the body through the aorta. Valves keep the flow in one direction. A labelled sketch of the four chambers earns the diagram mark.

4. Blood enters each kidney by the renal artery. In each nephron, the glomerulus filters water, glucose, salts and urea into the Bowman's capsule. As the filtrate passes along the tubule, useful substances (all glucose, most water and salts) are reabsorbed into the blood. The remaining water, urea and excess salts form urine, which goes through the ureter to the bladder and leaves by the urethra.

1. The greenhouse effect is the trapping of the Sun's heat in the atmosphere by gases such as carbon dioxide and methane, which keeps the Earth warm; an excess of these gases causes global warming.

2. Follow the 3R principle: reduce use of single-use plastics, reuse containers and bags, and compost kitchen waste.

3. Acid rain is rain with a pH below 5.6. Cause: sulphur dioxide and oxides of nitrogen from factories, vehicles and burning coal dissolve in rain to form sulphuric and nitric acids. Effects: it damages buildings and statues, harms crops and forests, and acidifies lakes so fish die. Prevention: use low-sulphur fuel, install scrubbers in chimneys, and reduce vehicle emissions.

4. Ozone in the stratosphere absorbs harmful ultraviolet rays. CFCs from old refrigerators, air-conditioners and aerosol sprays rise to the stratosphere; ultraviolet light breaks them to release chlorine, which destroys ozone. Effects: more UV reaches Earth, causing skin cancer and eye cataracts, reducing crop yield and harming plankton. Remedy: phase out CFCs (the Montreal Protocol).

1. To every action there is an equal and opposite reaction, and they act on different bodies. Example: a rocket pushes gases down and the gases push the rocket up.

2. Earth: W=mg=50\times10=500 N. Moon: W=50\times1.67=83.5 N. (Mass stays 50 kg.)

3. a=\dfrac{v-u}{t}=\dfrac{20-0}{10}=2\ \text{m s}^{-2}. F=ma=1500\times2=3000 N.

4. Principle: conservation of linear momentum. Total momentum before firing is zero, so m_1v_1+m_2v_2=0.

The gun recoils at 1.5\ \text{m s}^{-1}, opposite to the bullet.

1. Pressure applied to a confined fluid is transmitted equally and undiminished in all directions.

2. The pointed tip has a very small area, so for the same force the pressure (P=F/A) is much greater and the nail penetrates.

3. By Pascal's law, \dfrac{F_1}{A_1}=\dfrac{F_2}{A_2}, so F_2=F_1\dfrac{A_2}{A_1}=100\times\dfrac{500}{5}=10\,000 N.

4. Upthrust =V\rho g=0.002\times1000\times10=20 N. Apparent weight =30-20=10 N.

1. Specific heat capacity is the heat needed to raise the temperature of 1 kg of a substance by 1 °C (or 1 K). Unit: J kg⁻¹ K⁻¹.

2. Water is densest at 4 °C. On cooling, water above 4 °C sinks until the whole pond reaches 4 °C; below 4 °C the cooler water becomes lighter and stays on top, so ice forms at the surface while the bottom stays near 4 °C.

3. Q=mc\Delta T=0.5\times4200\times(100-20)=0.5\times4200\times80=168\,000 J.

4. Heat lost by hot water = heat gained by cold water. With final temperature T:

1. In a transverse wave the particles vibrate perpendicular to the direction of the wave (light, waves on a string). In a longitudinal wave they vibrate parallel to it (sound).

2. (i) The angle of incidence equals the angle of reflection. (ii) The incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.

3. The pulse travels down and back, so the distance is 2d=vt:

4. Using \dfrac{1}{f}=\dfrac{1}{u}+\dfrac{1}{v} with real distances positive: \dfrac{1}{v}=\dfrac{1}{10}-\dfrac{1}{30}=\dfrac{3-1}{30}=\dfrac{1}{15}, so v=15 cm (a real image beyond the lens). Magnification m=\dfrac{v}{u}=\dfrac{15}{30}=0.5, so the image is real, inverted and half the size.

1. At constant temperature, the current through a conductor is directly proportional to the potential difference across it: V=IR.

2. A motor converts electrical energy to mechanical energy (works on Fleming's left-hand rule); a generator converts mechanical energy to electrical energy (works on electromagnetic induction).

3. \dfrac{1}{R}=\dfrac{1}{6}+\dfrac{1}{3}=\dfrac{1+2}{6}=\dfrac{1}{2}, so R=2\ \Omega. Total current I=\dfrac{12}{2}=6 A. Branch currents: I_1=\dfrac{12}{6}=2 A and I_2=\dfrac{12}{3}=4 A; check 2+4=6 A.

4. Total power =4\times60=240 W =0.24 kW. Energy per day =0.24\times5=1.2 kWh. For 30 days: 1.2\times30=36 kWh = 36 units. Bill =36\times10= Rs 360.

5. A step-down transformer has fewer turns on the secondary than on the primary. An alternating current in the primary produces a changing magnetic flux in the iron core, which induces a smaller alternating emf in the secondary (electromagnetic induction). \dfrac{V_p}{V_s}=\dfrac{N_p}{N_s}\Rightarrow\dfrac{220}{11}=\dfrac{1000}{N_s}\Rightarrow N_s=\dfrac{1000\times11}{220}=50 turns.

1. A light year is the distance travelled by light in one year in a vacuum, about 9.46\times10^{12} km.

2. Telecommunication (TV, phone and internet signals) and weather forecasting; also GPS navigation and remote sensing.

3. d=4\times9.46\times10^{12}=3.784\times10^{13} km.

4. The universe began about 13.8 billion years ago from an extremely hot, dense point that expanded rapidly; as it expanded it cooled, and matter formed atoms, stars and galaxies. Evidence: (i) galaxies are moving apart, so the universe is expanding (red shift of light from distant galaxies); (ii) cosmic microwave background radiation fills space, the cooled remnant of the early universe.

1. RAM is temporary (volatile) memory used while a program runs and is lost when power goes off. ROM is permanent (non-volatile) memory holding start-up instructions.

2. Shopping is possible at any time from any place, and prices can be compared quickly; the cost of running a shop is lower.

3. Cyber crime is a crime committed using computers or the internet, such as hacking, phishing or spreading viruses. Rules: use strong, private passwords; do not share personal details or open links from unknown senders; keep anti-virus software updated; log out of public computers.

1. The physical and chemical properties of elements are a periodic function of their atomic numbers.

2. Their outermost shells are complete (2 electrons in helium, 8 in the rest), so they neither gain, lose nor share electrons.

3. X (11): 2, 8, 1 — group 1, period 3 (sodium). Y (17): 2, 8, 7 — group 17, period 3 (chlorine). X loses one electron to become X⁺ and Y gains it to become Y⁻, giving XY (NaCl) with an ionic bond.

4. Across a period (left to right): nuclear charge increases while the shell number is the same, so atomic size decreases and metallic character decreases. Down a group: extra shells are added, so atomic size increases and metallic character increases.

1. 4\text{Al}+3\text{O}_2\rightarrow2\text{Al}_2\text{O}_3. (Aluminium 4 = 4; oxygen 6 = 6.)

2. Neutralisation is the reaction of an acid with a base to form a salt and water. Example: HCl + NaOH → NaCl + H₂O.

3. (i) Temperature: milk sours faster in a warm room. (ii) Concentration: concentrated acid reacts faster with marble than dilute acid. (iii) Surface area: powdered marble reacts faster than a lump. (iv) Catalyst: MnO₂ speeds the decomposition of hydrogen peroxide.

4. C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. Carbon 3 = 3, hydrogen 8 = 8, oxygen 10 = 6 + 4. It is a combustion (oxidation) reaction. A pH of 3 is below 7, so the solution is acidic (fairly strongly), and it would turn blue litmus red.

1. At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure: PV= constant.

2. Pass the gas through lime water: it turns milky because insoluble calcium carbonate forms. Ca(OH)₂ + CO₂ → CaCO₃ ↓ + H₂O.

3. P_1V_1=P_2V_2\Rightarrow1\times500=2\times V_2\Rightarrow V_2=250\ \text{cm}^3.

4. T_1=27+273=300 K and T_2=127+273=400 K.

5. Put marble chips (CaCO₃) in a flask with a thistle funnel and a delivery tube; add dilute hydrochloric acid through the funnel (the funnel end must dip into the acid). CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂ ↑. Collect the gas by upward delivery (downward displacement of air) because CO₂ is heavier than air; it is also soluble in water, so water collection is avoided. A neat labelled sketch (flask, funnel, delivery tube, gas jar) takes one to two marks.

1. Sodium is very reactive and reacts vigorously with oxygen and moisture of air, so it is kept under kerosene to keep air and water away.

2. Aluminium forms a thin, tough layer of aluminium oxide on its surface, which protects the metal below from further attack.

3. Rusting is the slow corrosion of iron in damp air to form reddish-brown hydrated iron(III) oxide. It needs both oxygen and water. Prevention: painting or oiling; galvanising (zinc coating); making alloys like stainless steel.

4. The ore is bauxite (Al₂O₃·2H₂O), purified to alumina (Al₂O₃). Alumina is dissolved in molten cryolite (which lowers the melting point) and electrolysed in a steel tank lined with carbon (cathode) using carbon anodes. At the cathode, Al³⁺ gains electrons to give molten aluminium that collects at the bottom; at the anode, oxygen is released and burns the carbon anodes to CO₂.

1. A homologous series is a family of organic compounds with the same functional group and similar properties, in which successive members differ by CH₂. Example: alkanes (CH₄, C₂H₆, C₃H₈).

2. Methane CH₄, ethane C₂H₆, propane C₃H₈, butane C₄H₁₀ (general formula \text{C}_n\text{H}_{2n+2}).

3.

4. Ethanol (C₂H₅OH) is oxidised by an oxidising agent such as acidified potassium dichromate to ethanoic (acetic) acid, CH₃COOH. The functional group is carboxyl, –COOH. With ethanol, in the presence of concentrated H₂SO₄, it forms an ester and water: CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O.

1. Gypsum slows down the setting of cement so that the mortar can be worked before it hardens.

2. Soap is the sodium salt of a fatty acid; detergent is a synthetic salt of sulphonic acid. Soap forms scum in hard water; detergent does not, and works in hard and soft water.

3. Oil or fat is heated with sodium hydroxide solution. The ester bonds break (saponification) to give glycerol and sodium salts of fatty acids (soap): fat + 3NaOH → glycerol + 3 soap. Common salt is added to make the soap separate as a layer (salting out); it is then moulded, perfumed and dried.

4. Nitrogen (N) promotes leaf and stem growth; phosphorus (P) helps roots and flowering; potassium (K) improves disease resistance and fruit quality. Overuse pollutes water (eutrophication), harms soil organisms and can burn crops.