Science and Technology: Unit-wise Subjective Question Bank

Groups B and C carry 40 of the 50 written marks, and they are won by writing, not by recognising. A two-mark question wants two scoring points; a four-mark question wants four. This chapter gives, unit by unit, the short and long questions the pattern keeps producing, each followed by answer notes — the scoring points in order, the way an examiner reads them. Write your own answer on paper first; then compare, and mark what you missed.

What the answer notes are, and are not

They are not model essays to memorise. They are the points that earn the marks: the definition, the reason, the example, the labelled part, the formula, the substitution, the unit. If your answer contains those points in a sensible order and in your own words, it scores full marks.

3.1 Scientific Learning

1. Write any two differences between a hypothesis and a conclusion. [2]

A hypothesis is a testable guess made before the experiment; a conclusion is a judgement made after analysing the data. A hypothesis may turn out false; a conclusion is supported by the evidence collected.

2. Why is a control used in an experiment? [2]

The control is the set-up in which the factor being tested is absent or unchanged. Comparing the test with the control shows that any difference is caused by that factor and not by something else.

3. A student measured the mass of a stone as 150 g and found that it raised the water in a measuring cylinder from 50 ml to 110 ml. Find its density. [2]

Volume = 110 - 50 = 60 cm³; density = \frac{150}{60} = 2.5 g/cm³.

4. Describe the steps of the scientific method with an example. [4]

(i) Observation — the plants near the window grow taller. (ii) Problem — does light affect plant growth? (iii) Hypothesis — plants grow taller with more light. (iv) Experiment — two identical pots, one in light and one in the dark, same soil and water. (v) Analysis — measure and compare the heights after two weeks. (vi) Conclusion — accept or reject the hypothesis on the evidence. Note that only light is changed; soil, water and seed are controlled.

3.2 Information and Communication Technology

1. Differentiate between hardware and software with one example each. [2]

Hardware is the physical part of a computer that can be touched (keyboard); software is the set of instructions that tells the hardware what to do (a word processor). Hardware wears out; software does not, though it can be replaced or updated.

2. Write any two differences between RAM and ROM. [2]

RAM is volatile — its contents vanish when the power goes — while ROM keeps its contents. RAM is read and written during work; ROM is normally only read, and holds the start-up instructions.

3. Mention any four rules of safe and respectful use of the internet. [4]

(i) Keep a long, mixed password and never share it. (ii) Do not post personal details — address, school, phone number — or another person's photograph without permission. (iii) Do not open links or attachments from strangers; they may carry malware. (iv) Report bullying or threatening messages to a parent or teacher instead of replying; verify information before forwarding it.

4. Explain the four functional units of a computer with a block diagram in words. [4]

Input unit takes data in (keyboard, mouse, scanner). Memory unit stores data and instructions (RAM and storage). Central processing unit processes: the arithmetic and logic unit calculates and compares, the control unit directs the other units. Output unit presents the result (monitor, printer). Data flows input → memory → CPU → memory → output, with the control unit supervising every step.

3.3 Living Beings and Their Structure

1. Write any two differences between a plant cell and an animal cell. [2]

A plant cell has a rigid cellulose cell wall; an animal cell has only the cell membrane. A plant cell has chloroplasts and one large vacuole; an animal cell has no chloroplasts and small vacuoles if any.

2. Why is the mitochondrion called the powerhouse of the cell? [2]

Cellular respiration takes place in it: food is oxidised there and the energy released is stored in a usable form for all the cell's activities. A cell with more energy demand, such as a muscle cell, has more mitochondria.

3. Write the functions of any four cell organelles. [4]

Nucleus — controls all activities and carries the hereditary material. Mitochondrion — releases energy by respiration. Ribosome — makes protein. Chloroplast — carries out photosynthesis in plant cells. (Vacuole — stores water, food and waste and keeps the plant cell turgid.)

4. What is classification? Write the five kingdoms with one example of each. [4]

Classification is the arrangement of living beings into groups according to their similarities and differences, so that they can be studied, named and compared systematically. Whittaker's five kingdoms (1969): Monera — bacteria; Protista — Amoeba; Fungi — mushroom; Plantae — fern; Animalia — frog.

3.4 Biodiversity and Environment

1. Define ecosystem and name its two components. [2]

An ecosystem is a unit in which living beings interact with one another and with their non-living surroundings. Its components are biotic (producers, consumers, decomposers) and abiotic (sunlight, air, water, soil, temperature).

2. Why is Nepal said to be rich in biodiversity in spite of its small area? [2]

Within about 200 km from south to north the land rises from about 60 m to 8,849 m, so tropical, subtropical, temperate, subalpine and alpine climates all occur. Each belt supports its own plants and animals, so a small country holds many kinds of habitat.

3. Draw a food chain of four links from a Nepali farmland and explain the flow of energy. [4]

Chain: paddy → grasshopper → frog → snake. The paddy plant is the producer, trapping sunlight. The grasshopper is the primary consumer, the frog the secondary consumer, the snake the tertiary consumer. Energy flows in one direction only, and roughly 10 % passes from one level to the next; the rest is lost mainly as heat. That is why a chain rarely has more than four or five links.

4. Write any four causes of loss of biodiversity and one measure against each. [4]

(i) Habitat destruction by clearing forest for settlement — declare and manage protected areas, plan settlement. (ii) Poaching and illegal trade — enforce the law, support anti-poaching patrols, raise awareness. (iii) Pollution of rivers and soil — treat waste, reduce chemical fertiliser and pesticide. (iv) Invasive species such as lahare banmara — remove them early and plant native species. (Climate change — reduce emissions and conserve forests.)

3.5 Life Process

1. Write the word equation of photosynthesis and name two conditions needed for it. [2]

Carbon dioxide + water, in the presence of chlorophyll and sunlight, give glucose + oxygen. Conditions: sunlight and chlorophyll (carbon dioxide and water are the raw materials).

2. Write any two differences between aerobic and anaerobic respiration. [2]

Aerobic respiration takes place in the presence of oxygen and releases much more energy, giving carbon dioxide and water. Anaerobic respiration takes place without oxygen and releases less energy, giving ethanol and carbon dioxide in yeast or lactic acid in muscle.

3. Explain the path of food through the human alimentary canal. [4]

Mouth — teeth break food; saliva begins starch digestion. Oesophagus — pushes the bolus down by peristalsis. Stomach — gastric juice with hydrochloric acid and pepsin begins protein digestion. Small intestine — bile emulsifies fat, pancreatic and intestinal juices complete digestion, and the villi absorb the nutrients. Large intestine — absorbs water and salts; the remaining waste is passed out as faeces.

4. What is transpiration? Write its importance to the plant and any two factors that affect its rate. [4]

Transpiration is the loss of water as vapour from the aerial parts of a plant, mainly through the stomata. Importance: it pulls water and dissolved minerals up from the root (transpiration pull) and cools the leaf. Factors: temperature and humidity (also wind speed, light and the number of open stomata) — the rate rises in hot, dry, windy weather and falls in humid, still air.

3.6 Force and Motion

1. State Newton's second law of motion and write its mathematical form. [2]

The rate of change of momentum of a body is directly proportional to the net force applied and takes place in the direction of that force. For constant mass, F = ma, where F is the net force in newtons, m the mass in kilograms and a the acceleration in m/s².

2. Write any two differences between mass and weight. [2]

Mass is the quantity of matter in a body, measured in kilograms, and is the same everywhere. Weight is the force with which the earth attracts the body, measured in newtons, and changes with the value of g — on the moon it is about one-sixth of the value on the earth.

3. A bus starting from rest reaches 20 m/s in 10 s. Find its acceleration and the force on it if its mass is 3,000 kg. [4]

a = \frac{v-u}{t} = \frac{20-0}{10} = 2 m/s². F = ma = 3000\times2 = 6000 N, in the direction of motion.

4. Why do passengers lurch forward when a moving bus brakes suddenly? Explain with the law involved and write two safety measures based on it. [4]

By Newton's first law, a body continues in its state of motion unless a net force acts on it. When the brakes act, the force stops the bus but not the upper part of the passenger's body, which continues forward — this is inertia of motion. Measures: wear the seat belt so the force reaches the body with the vehicle; fit head rests and avoid standing in a fast-moving vehicle; and keep a safe following distance so braking can be gradual.

3.7 Energy in Daily Life

1. Write any two differences between renewable and non-renewable sources of energy. [2]

Renewable sources are replaced naturally and do not run out — solar, hydro, wind, biogas — and they pollute little. Non-renewable sources exist in a fixed store that is being used up — coal, petroleum, natural gas — and burning them pollutes the air.

2. State the law of conservation of energy with one example. [2]

Energy can neither be created nor destroyed; it only changes from one form to another, the total remaining the same. In a hydropower plant the potential energy of stored water becomes the kinetic energy of flowing water, and then electrical energy in the generator.

3. Why should Nepal develop hydropower? Give any four reasons. [4]

(i) The natural resource is already there: steep rivers and a large fall, with about 42,000 MW economically feasible. (ii) It is renewable and clean, so it replaces imported fossil fuel and cuts pollution. (iii) It saves foreign currency spent on petroleum and can earn currency by exporting electricity. (iv) Cheap electricity runs industry, irrigation, railways and electric cooking, creating employment and reducing the use of firewood.

4. Explain any four ways of saving energy in the home. [4]

(i) Replace filament lamps with LED lamps, which give the same light for about a tenth of the power. (ii) Switch off lights, fans and chargers that are not in use; many appliances draw power on standby. (iii) Cook in a pressure cooker with a lid on, and use an induction stove or improved stove instead of an open fire. (iv) Use daylight and natural ventilation, service appliances, and dry clothes in the sun rather than in a machine.

3.8 Electricity and Magnetism

1. State Ohm's law and write its limitation. [2]

At constant temperature, the current through a conductor is directly proportional to the potential difference across it: V = IR. It holds only for metallic conductors at constant temperature; it does not apply to semiconductor devices or to a filament whose temperature changes.

2. Two resistors of 4 Ω and 6 Ω are joined in series across a 20 V supply. Find the current. [2]

R = 4 + 6 = 10 Ω; I = \frac{V}{R} = \frac{20}{10} = 2 A.

3. A house uses four 60 W bulbs for 5 hours and a 1,000 W heater for 2 hours each day. Find the daily consumption in units and the monthly bill at Rs 10 per unit for 30 days. [4]

Bulbs: 4\times60 = 240 W = 0.24 kW, for 5 h = 1.2 kWh. Heater: 1 kW for 2 h = 2 kWh. Daily total = 3.2 units. Monthly = 3.2\times30 = 96 units; bill = 96\times10 = Rs 960.

4. What is an electromagnet? Write how its strength can be increased and mention two of its uses. [4]

An electromagnet is a temporary magnet made by winding an insulated coil round a soft-iron core and passing a current through it; the magnetism lasts only while the current flows. Its strength increases with a larger current, more turns in the coil, and a soft-iron core of larger cross-section. Uses: lifting scrap iron in a crane and separating iron from waste; and in electric bells, relays, loudspeakers and electric motors.

3.9 Matter

1. Write any two differences between a compound and a mixture. [2]

In a compound the elements combine chemically in a fixed ratio by mass and the product has new properties — water, for example. In a mixture the substances are merely mixed in any ratio, keep their own properties and can be separated by physical means — air, for example.

2. An atom has an atomic number of 17 and a mass number of 35. Write the number of its protons, neutrons and electrons. [2]

Protons = atomic number = 17. Electrons = 17 (neutral atom). Neutrons = 35 - 17 = 18.

3. What are acids and bases? Write two properties of each. [4]

An acid gives hydrogen ions in water: it tastes sour, turns blue litmus red, has pH below 7 and reacts with an active metal to give hydrogen. A base gives hydroxide ions in water: it tastes bitter and feels soapy, turns red litmus blue, has pH above 7 and neutralises an acid to give a salt and water.

4. Describe how you would separate (i) sand from water, (ii) salt from salt water, (iii) iron filings from sawdust, (iv) kerosene from water. [4]

(i) Filtration — sand stays on the filter paper. (ii) Evaporation — heat the solution and the water leaves as vapour, the salt remaining. (iii) Magnetic separation — a magnet attracts the iron filings only. (iv) Decantation with a separating funnel — kerosene and water do not mix and form two layers; run off the lower layer.

3.10 Materials Used in Daily Life

1. What is an alloy? Write the composition and one use of brass. [2]

An alloy is a homogeneous mixture of a metal with one or more other metals or non-metals, made to improve its properties. Brass is copper with zinc; it is used for utensils, taps, locks and musical instruments because it is hard and does not corrode easily.

2. Why does iron rust? Write any two methods of preventing rusting. [2]

Iron rusts when it is in contact with both oxygen and moisture, forming hydrated iron oxide. Prevention: coat the surface with paint, grease or oil so that air and water cannot reach it; or galvanise it with a layer of zinc (also electroplating, or using stainless steel).

3. Write any four harmful effects of plastic and any four measures to reduce them. [4]

Harm: it is non-biodegradable and stays in soil for centuries; burning it releases poisonous gases; discarded bags block drains and cause flooding; animals swallow it and die, and microplastic enters the food chain. Measures: refuse single-use bags and carry a cloth bag; reuse containers; segregate and recycle; and replace plastic with paper, jute, glass or metal where possible.

4. Explain the cleansing action of soap in simple terms. [4]

A soap molecule has two ends: a long tail that mixes with oil and grease and a head that mixes with water. When soapy water is rubbed on dirty cloth, the tails stick into the greasy dirt and the heads stay in the water, so each particle of dirt is surrounded by soap molecules. Rubbing then lifts the dirt off the fibre as a tiny droplet held in the water, and rinsing carries it away. Hard water contains calcium and magnesium salts that form a scum with soap, which is why detergent, whose molecules do not form scum, cleans better in hard water.

3.11 The Earth and Universe

1. Write any two differences between rotation and revolution of the earth. [2]

Rotation is the spinning of the earth about its own axis, completed in about 24 hours, and it causes day and night. Revolution is the movement of the earth round the sun, completed in about 365¼ days, and together with the axial tilt it causes the seasons.

2. Why does a solar eclipse occur only at new moon? [2]

A solar eclipse needs the moon to come between the sun and the earth so that its shadow falls on the earth. The moon is in that position only at new moon, when its dark side faces us.

3. Write any four effects of the earth's axial tilt. [4]

(i) The seasons change through the year as each hemisphere is tilted towards or away from the sun. (ii) The length of day and night varies with the season and the latitude. (iii) The sun's rays fall vertically only between the two tropics, which is why those regions are hottest. (iv) The polar regions have continuous day or night for part of the year, and the equinoxes give equal day and night everywhere.

4. Why is Nepal at risk of earthquakes? Write any four precautions to take during and after one. [4]

Nepal lies along the boundary where the Indian plate pushes under the Eurasian plate; the strain released along this boundary makes the whole country seismically active. Precautions: during the shaking, drop, cover under a strong table and hold on, keeping away from windows and heavy furniture; if outdoors, move to open ground away from walls and wires. Afterwards, expect aftershocks and leave by the stairs, not the lift; check for gas leaks and switch the main supply off; and keep an emergency kit with water, torch, whistle, dry food and first-aid, and a family meeting point agreed in advance.