Atmospheric Pressure [2 marks]

Atmospheric pressure is the force exerted per unit area by the weight of the air column of the atmosphere on the earth's surface. At sea level it is about 101,325 Pa (76 cm of mercury).

Experiment to demonstrate atmospheric pressure [4 marks]

Materials required: a glass tumbler filled to the brim with water, a stiff postcard or plastic sheet, a bucket (for safety).

Procedure:

1. Fill the glass completely with water so that no air bubble remains.
2. Place the postcard over the mouth of the glass and press it gently.
3. Holding the card in place, invert the glass quickly over the bucket.
4. Now remove the hand supporting the card.

Observation: The card does not fall and the water does not spill out.

Conclusion: The atmospheric pressure acting upward on the card is greater than the weight of the water column in the glass, so the card is held in place. This proves the existence of atmospheric pressure.

Ensuring students' engagement

• Ask students to predict what will happen before inverting the glass, then compare with the result.
• Let students perform the activity in small groups and repeat it with a half-filled glass to see the difference.
• Relate the concept to daily life: drinking with a straw, syringe, rubber sucker, and the working of a barometer.
• Use questioning, group discussion, and a quick oral quiz at the end to check understanding.

1. Explaining why a bulb glows (2 marks)

A bulb glows because electric current heats its filament until it becomes white-hot (incandescence).

• The battery acts as a source of electrical energy; its terminals maintain a potential difference across the circuit.
• This potential difference drives electric current through the connecting wires and the bulb's filament.
• The filament is a thin, high-resistance wire (tungsten). As current passes, electrical energy is converted into heat energy (Joule heating, (H = I^2Rt)).
• The filament becomes so hot (about 2500 °C) that it emits light — first infrared, then visible light. That is why we see the bulb glow.

So the sequence is: potential difference → current → heating of filament → light.

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2. Interactive activities on series vs parallel circuits (4 marks)

Activity 1: "Two bulbs, two ways" (hands-on, groups of 4)

Materials: 2 dry cells (1.5 V each), 2 bulbs with holders, connecting wires, switch, screwdriver.

• Task A: Connect the two bulbs one after another in a single loop (series). Observe brightness. Then unscrew one bulb and note what happens to the other.
• Task B: Connect the two bulbs side by side across the same battery (parallel). Observe brightness. Again unscrew one bulb and note the result.
• Students record observations in a table:

Activity 2: "Body circuit" (kinesthetic)

• Students stand in a line holding hands = series; teacher "breaks" the line by tapping one student's shoulder — the whole "circuit" stops.
• Students then form two rows branching from the same two "terminal" students = parallel; breaking one row does not stop the other.
• This makes the idea of one path vs many paths concrete.

Activity 3: "Predict–Test–Explain" with a PhET simulation

• On the "Circuit Construction Kit" simulation, students build both circuits, measure current with an ammeter and voltage with a voltmeter, and verify:
  • Series: (I) same everywhere, (V = V_1 + V_2), (R = R_1 + R_2)
  • Parallel: (V) same across branches, (I = I_1 + I_2), (\dfrac{1}{R} = \dfrac{1}{R_1} + \dfrac{1}{R_2})
• They first predict, then test, then explain the difference in brightness using resistance.

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3. Assessment (part of the 4 marks)

a) Formative (during activity):

• Observation checklist: correct connection, safety, teamwork.
• Oral questioning: "Why did the second bulb go out in series?" "Why are house lights connected in parallel?"
• Lab notebook/lab report: circuit diagram, table, conclusion.

b) Summative:

• Short written test — draw and label series and parallel circuits; state two differences; solve a simple numerical on equivalent resistance.
• Application question: "Why is a parallel connection used in domestic wiring?" (full marks for: each appliance gets full voltage, works independently, separate switch).

Rubric (for the activity report, 4 marks):

This way I assess knowledge, skill (connection and measurement), and application together.

1. Difference between Weather and Climate [3 marks]

Key idea: Weather is the day-to-day state of the atmosphere; climate is the average pattern of weather of a place over a long period. Climate is the sum total of weather conditions of a place.

2. Three Lesson Objectives on 'Soil' for Grade 6 [2 marks]

After teaching the topic 'Soil', students will be able to:

1. State the meaning of soil and name the main layers of soil (topsoil, subsoil, parent rock) correctly.
2. Identify and describe the different types of soil — sandy, clayey, loamy and sandy-loam — on the basis of their colour, texture and water-holding capacity.
3. Explain the importance of soil in plant growth and human life, and suggest at least two ways of conserving soil in their locality (e.g., terracing, planting trees).

3. Pedagogical Strategies for Self-Learning [2 marks]

Self-learning means learning done by the student independently, with the teacher acting as a facilitator. The following strategies can be applied:

1. Project work and assignment: Give topic-based projects (e.g., collecting and labelling different soil samples) so students explore, observe and record on their own.
2. Guided reading and reference work: Provide textbooks, library books and worksheets with guiding questions so students read, find answers and prepare notes themselves.
3. Problem-solving and discovery method: Present a problem or question and let students find the solution through observation, experiment and reasoning rather than direct telling.
4. Use of ICT and audio-visual materials: Assign educational videos, mobile apps and online resources for self-study, with follow-up discussion in class.
5. Self-assessment tools: Use checklists, rubrics, portfolios and reflective diaries so students judge their own progress and correct themselves.
6. Group discussion and peer learning: Let students share findings in small groups, which builds confidence and independent thinking.
7. Learning by doing: Field visits, kitchen-garden work and simple experiments (e.g., testing water-holding capacity of different soils) promote self-learning through direct experience.

Differences between Monocotyledonous and Dicotyledonous Plants

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Lesson Plan: Grassland Ecosystem through Field Visit Method

Subject: Science (Biology)
Class: 9
Topic: Grassland Ecosystem
Teaching Method: Field Visit (Observation) Method
Time: 45 minutes
Marks: 3

1. Specific Objectives

After completing the lesson, students will be able to:

• define a grassland ecosystem;
• identify the biotic (producers, consumers, decomposers) and abiotic components of a grassland;
• explain the food chain and energy flow in a grassland ecosystem.

2. Teaching Materials

Notebook, pencil, magnifying glass, measuring tape, chart of food chain, camera (if available).

3. Pre-visit Preparation (5 min)

• Divide students into groups of five.
• Assign each group a task: Group A — abiotic components; Group B — producers; Group C — consumers; Group D — decomposers.
• Give clear instructions on observation, safety and record-keeping.

4. Field Visit and Observation (20 min)

• Take students to a nearby grassland (school ground, pasture or open field).
• Students observe and record:
  • Abiotic: soil, sunlight, air, water, temperature.
  • Producers: grasses, herbs, small shrubs.
  • Consumers: grasshoppers, butterflies, frogs, birds, cattle, goats.
  • Decomposers: earthworms, fungi, bacteria in soil.
• Teacher guides students to trace a food chain, e.g. grass → grasshopper → frog → snake.

5. Discussion and Conclusion (15 min)

• Groups present their findings.
• Teacher explains the interrelationship among components and the flow of energy.
• Students draw a food web of the grassland on a chart.

6. Evaluation (5 min)

• Name any two producers and two consumers of a grassland.
• Write one food chain observed during the visit.
• Why are decomposers important in a grassland ecosystem?

7. Homework

Draw a labelled diagram of a grassland ecosystem showing its components and food chain.

(a) Arguments supporting the statement:

Science as a product:

• The curriculum prescribes specific knowledge, facts, concepts, laws, theories (e.g., matter, energy, living beings) that students must master — these are the "products" of scientific inquiry.
• Grade-wise learning outcomes and competencies define what students should know at each level.
• Textbooks and prescribed content represent accumulated scientific knowledge.
• Examinations assess mastery of this body of knowledge.

Science as a process:

• Emphasis on scientific method: observation, hypothesis, experimentation, data collection, interpretation, conclusion.
• Activity-based, practical, project work, laboratory and field-based learning.
• Development of scientific skills (measuring, classifying, inferring) and scientific attitude (curiosity, objectivity, skepticism).
• Constructivist approach where learners actively construct knowledge.

ICT as content:

• Specific ICT topics are included as subject matter: computer fundamentals, hardware/software, word processing, spreadsheet, internet, email, cyber safety, digital citizenship.
• These have prescribed learning outcomes and are assessed.

ICT as medium:

• ICT tools (multimedia, simulations, videos, online resources, smart boards) used to teach science and other subjects.
• Makes abstract concepts concrete, supports self-learning, blended/distance learning.
• Teachers expected to integrate ICT into pedagogy.

(b) Major deficiencies of letter grading system in Nepal:

1. Loss of finer discrimination — broad bands hide differences (89% and 75% both "A").
2. No rank/percentile information — difficult to compare across students/schools/years.
3. Grade inflation — pressure on schools leads to inflated internal marks.
4. Weak internal assessment — no uniform standard, moderation, or trained manpower.
5. Poor diagnostic feedback — doesn't identify specific weak areas.
6. Selection difficulty — colleges/scholarships/employers can't differentiate.
7. Misinterpretation — all same grades treated as equal.
8. Neglect of non-cognitive domains — affective/psychomotor skills poorly graded.
9. Concentration at top grades — devalues certificates, causes stress.
10. Limited use for teaching improvement — no item/competency-wise analysis.
11. Equivalence/migration problems — conversion to marks/GPA abroad is difficult.
12. No uniform national grade boundaries — inconsistent interpretation.

a) Basic assumptions of the electronic theory of valency [5]

1. Electrons are arranged in shells (orbits) around the nucleus, and each shell can hold a fixed maximum number of electrons (2n², where n is the shell number).
2. The outermost shell is the valence shell. The electrons present in it are called valence electrons, and these alone take part in chemical combination.
3. Atoms tend to attain the nearest noble gas configuration (a stable duplet of 2 or an octet of 8 electrons) in the valence shell. This tendency is the driving force of chemical bonding.
4. Atoms gain, lose or share electrons to complete their octet/duplet:
   • Loss of electrons → cation (electropositive element, e.g. Na → Na⁺).
   • Gain of electrons → anion (electronegative element, e.g. Cl → Cl⁻).
   • Sharing of electrons → covalent bond (e.g. H₂, CH₄).
5. The number of electrons lost, gained or shared equals the valency of the element, and the number of bonds formed is decided by the number of unpaired (or available) valence electrons.

b) Difference between ionization energy and electron affinity [5]

Note: Both quantities are expressed in kJ/mol (or eV/atom) and both depend on atomic size and nuclear charge.

a) Second law of thermodynamics

Statement (Kelvin–Planck): It is impossible to construct a heat engine working in a cyclic process that converts all the heat absorbed from a single reservoir completely into work; some heat must always be rejected to a sink.

Statement (Clausius): It is impossible for a self-acting machine, unaided by an external agency, to transfer heat from a colder body to a hotter body.

Explanation: The first law only demands conservation of energy; it does not forbid a ship sailing by cooling the sea, or an engine running on a single reservoir. The second law supplies this missing restriction. It fixes the direction of natural processes (heat flows spontaneously hot → cold, never the reverse), makes a cyclic heat engine need two reservoirs, and limits the maximum efficiency to the Carnot value

$\eta = 1 - \frac{T_2}{T_1}$

where $T_1$ is the source and $T_2$ the sink temperature in kelvin. Since $T_2$ can never be 0 K, $\eta$ is always less than 100%. It also explains why heat cannot be converted fully into work and why entropy of an isolated system never decreases.

Differences between petrol engine and diesel engine

b) Why a refrigerator uses more power in summer

A refrigerator is a heat pump working between the cold interior at temperature $T_2$ and the outside room air at temperature $T_1$. Its coefficient of performance is

$\text{COP} = \frac{T_2}{T_1 - T_2}$

In summer the room air is hotter, so $T_1$ rises while $T_2$ is kept fixed (say about 4 °C). The temperature difference $T_1 - T_2$ becomes large, so the COP falls. To extract the same quantity of heat $Q_2$ from the food, the work needed is

$W = \frac{Q_2}{\text{COP}}$

Since COP is smaller in summer, $W$ is larger. Moreover, the compressor has to run for a longer time and against a higher condensing pressure, and heat leaks into the cabinet faster from the hotter surroundings. Hence more electrical power is consumed in summer than in winter for cooling the same quantity of food by the same device.

(a) Laboratory preparation of hydrogen gas [2]

Diagram:

   Thistle funnel
        |
        |        delivery tube
   _____|_____    ______________
  |     |     |  /              \        gas jar
  |  dil.H2SO4|_/                \     ___|___
  |    +      |                   \   |  H2   |
  |  Zn granules                   \  |       |
  |___________|                     \_|       |
   Woulfe bottle                  ~~~~~~~~~~~~~~  water trough

Labels: thistle funnel, Woulfe bottle (reaction vessel) containing zinc granules and dilute sulphuric acid, delivery tube, water trough, gas jar (collecting vessel), hydrogen gas.

Reaction: Dilute H₂SO₄ is poured through the thistle funnel onto zinc granules. Hydrogen is evolved and collected by downward displacement of water, since it is almost insoluble in water.

$\text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2\uparrow$

Uses of hydrogen gas: [4]

1. Manufacture of ammonia by Haber's process, for fertilisers.
2. Hydrogenation of vegetable oils to make vanaspati ghee.
3. Filling balloons (lightest gas).
4. Fuel in rockets and fuel cells.
5. Oxy-hydrogen flame for welding and cutting metals.
6. Manufacture of hydrochloric acid and methanol.

(b) Metallurgy [1]

The process of extraction of metals from their ores and their purification is called metallurgy.

Physical properties of iron: [3]

1. Greyish-white, lustrous metal.
2. Malleable and ductile.
3. Good conductor of heat and electricity.
4. Melting point about 1535 °C; boiling point about 2750 °C; density about 7.8 g/cm³.
5. Strongly magnetic and hard.

Difference between bacteria and virus [2]

Structure of DNA [3]

DNA (deoxyribonucleic acid) has the Watson and Crick double helix structure (1953).

 5' P-S-P-S-P-S-P-S 3'      S = deoxyribose sugar
      |   |   |   |         P = phosphate
      A = T   G ≡ C ...     A=T (2 H-bonds)
      |   |   |   |         G≡C (3 H-bonds)
 3' P-S-P-S-P-S-P-S 5'

• It consists of two polynucleotide strands wound around each other in a right-handed helix.
• Each nucleotide has a phosphate group, deoxyribose sugar and a nitrogen base (adenine, guanine, cytosine, thymine).
• The sugar-phosphate backbone lies outside; the bases point inwards.
• Bases pair by hydrogen bonds: adenine with thymine (2 bonds), guanine with cytosine (3 bonds). So A = T and G = C (Chargaff's rule).
• The two strands are antiparallel (one runs 5'→3', the other 3'→5').
• One full turn is 3.4 nm long and has 10 base pairs; the helix diameter is 2 nm.

Process of DNA replication [3]

DNA replication is semi-conservative: each new DNA molecule has one old and one new strand.

1. Unwinding: The enzyme helicase breaks the hydrogen bonds between base pairs and unzips the double helix at the replication fork.
2. Template: Each separated strand acts as a template.
3. Complementary pairing: Free nucleotides pair with the exposed bases (A with T, G with C).
4. Joining: DNA polymerase joins the nucleotides, building the new strand in the 5'→3' direction. The leading strand is made continuously, the lagging strand in Okazaki fragments, which DNA ligase joins.
5. Result: Two identical daughter DNA molecules, each with one parental and one new strand.

Climate Change

Climate change refers to the significant and long-term change in the average weather patterns (temperature, rainfall, wind, etc.) of the earth, either at global or regional level. It is mainly caused by the increase in greenhouse gases in the atmosphere due to human activities. In the present context, climate change has become a serious global environmental problem.

Causes of Climate Change

1. Burning of fossil fuels: Coal, petroleum and natural gas used in industries, vehicles and homes release carbon dioxide (CO₂), the main greenhouse gas.
2. Deforestation: Cutting down forests reduces the absorption of CO₂ and increases its amount in the atmosphere.
3. Industrialization and urbanization: Factories and growing cities emit greenhouse gases and heat.
4. Agriculture and livestock: Use of chemical fertilizers, paddy fields and livestock release methane (CH₄) and nitrous oxide (N₂O).
5. Waste and garbage: Decomposing waste in landfills produces methane.
6. Use of aerosols and refrigerants: CFCs and other gases damage the ozone layer and trap heat.
7. Natural factors: Volcanic eruption, solar variation and forest fire also contribute to climate change to some extent.

Effects of Climate Change

1. Rise in temperature: Global average temperature is increasing, causing hot days and heat waves.
2. Melting of glaciers and snow: Himalayan glaciers of Nepal are melting fast, which may cause glacier lake outburst floods (GLOF).
3. Change in rainfall pattern: Irregular, untimely and heavy rainfall causes floods, landslides and droughts.
4. Effect on agriculture: Crops fail, production decreases, and food security is threatened.
5. Rise in sea level: Melting ice raises sea level, sinking coastal areas and islands.
6. Loss of biodiversity: Many plants and animals are becoming extinct due to changed habitat.
7. Effect on health: Spread of diseases like malaria, dengue, diarrhea and shortage of clean water.
8. Displacement of people: Floods, landslides and drought force people to leave their homes (climate refugees).

Measures Adopted by the Government of Nepal

1. Formulation of policies and plans: Nepal has prepared the Climate Change Policy (2011), National Adaptation Programme of Action (NAPA), Local Adaptation Plan of Action (LAPA) and National Determined Contribution (NDC).
2. Establishment of institutions: Climate Change Management Division under the Ministry of Forests and Environment and Climate Change Council headed by the Prime Minister have been formed.
3. Afforestation and forest conservation: Community forestry programmes and plantation drives are conducted to increase forest cover.
4. Promotion of renewable energy: Use of biogas, solar energy, micro-hydro and improved cooking stoves is encouraged to reduce dependence on fuelwood.
5. Adaptation programmes: Early warning systems for floods and landslides, drought-resistant crops and climate-friendly farming are promoted.
6. Participation in international efforts: Nepal is a party to the UNFCCC, Kyoto Protocol and Paris Agreement, and takes part in international climate conferences.
7. Awareness programmes: Public awareness, education and training on climate change are conducted through schools, media and local bodies.
8. Disaster risk reduction: Embankments, bio-engineering and rescue and relief programmes are carried out to reduce climate-induced disasters.

Conclusion

Climate change is a global problem but its effects are more severe in developing countries like Nepal. Therefore, both the government and the public should work together to reduce its causes and adapt to its effects.

Comparison and Contrast of Science Curriculum and Textbook of Grade 8

1. Comparison (Similarities) — 5 marks

The Grade 8 Science curriculum and its textbook are closely related and share the following similarities:

1. Same subject scope: Both cover the same major content areas — Scientific Learning, Living Beings (classification, adaptation, life process), Force and Motion, Work Energy and Power, Heat, Light, Sound, Electricity and Magnetism, Matter (mixture, acid-base-salt, metal and non-metal), Earth and Space (structure of the earth, atmosphere, solar system), and Environment and Sustainable Development.

2. Same level and sequence: Both are prepared for the same grade level (Class 8) and follow the same order of units as arranged in the curriculum grid.

3. Competency-based approach: Both aim to develop scientific knowledge, skills (observation, experiment, measurement, classification), scientific attitude, and application of science in daily life.

4. Activity-oriented: Both give place to experiments, demonstrations, project work, field visits and practical activities.

5. Local relevance: Both try to link scientific concepts with the local environment, technology and everyday experiences of the learners.

6. Same terminal goals: Both prepare students for the Secondary Education Examination (SEE) and for further study of science at the secondary level.

7. Nepali context and values: Both incorporate national needs such as health, sanitation, environment protection, disaster management and use of local technology.

2. Contrast (Differences) — 5 marks

Conclusion

In short, the curriculum is the blueprint and the textbook is the constructed building based on that blueprint. The curriculum provides direction, scope and standards, while the textbook translates those standards into concrete learning material. Both are complementary — neither can fully serve the purpose of science teaching at Grade 8 without the other.