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Unit 1: Scientific Learning

Key Idea#

Scientific learning happens through observation, testing (experiment), research, and survey. These four methods let us discover facts, theories, and rules of science.

1.1 Laboratory Safety Rules#

A science laboratory is a special room with equipment and chemicals for scientific study. Safety rules to follow:

• Don't handle materials carelessly
• Wear mask, gloves, goggles with harmful chemicals; wear an apron/lab coat
• Know the emergency exit
• Wash hands with soap after work
• No eating, drinking, playing, or teasing in the lab
• Never taste or smell chemicals directly
• Follow the prescribed method for experiments
• Take care with burners/hot objects; never place hot equipment directly on the table

1.2 Four Methods of Scientific Learning#

A) Observation#

Definition: The process of experiencing an object, event, or process carefully using the sense organs (sight, hearing, smell, touch, taste). Tools like hand lenses and microscopes assist when direct observation is hard.

• It is the first step of scientific study.
• Not limited to the lab — can be done in gardens, zoos, botanical gardens, factories, etc.
• Steps: decide what/why to observe → observe → record → write a report.
• Report format: Title → Objective → Materials required → Method → Result/Observation → Conclusion.
• Example (Activity 1.1): Observing fungus growth on bread under a microscope — shows no green pigment, root-like mycelia, stem-like hyphae, sporangia on branch tips.

B) Scientific Test (Experiment)#

Definition: A scientific procedure performed to check whether an assumption (hypothesis) is correct or not.

• Hypothesis = an inference/assumption made from observation.
• Testing checks if the hypothesis is true — a form of experimental work.
• Example (Activity 1.3): Testing lemon juice, soap water, salt water with red/blue litmus paper to classify as acid, base, or salt.
  • Acid → turns blue litmus red
  • Base → turns red litmus blue
  • Neutral (salt) → no colour change

C) Research#

Definition: An in-depth study to find the answer to a question or curiosity; begins with curiosity/a question. Phases of research:

1. Goal setting
2. Making inference/hypothesis
3. Choice of data collection method
4. Preparing required materials
5. Data collection
6. Data analysis
7. Conclusion

• Example (Activity 1.6): Researching how chemical fertilizer and acid (vinegar) affect algae growth in pond water — fertilizer boosts algae growth (can cause eutrophication → oxygen depletion in water bodies), acid reduces/kills algae.

D) Survey#

Definition: The process of directly collecting data on a topic/problem and drawing a conclusion. Tools: Questionnaire, interview, discussion, observation. Steps of a survey:

1. Selection of objective
2. Choice of data collection method
3. Collection of data
4. Analysis of data
5. Conclusion

• Report includes: title, purpose, tools/methods, data analysis, conclusions & suggestions.
• Example: Survey on solid waste management — data often presented as a bar diagram.

Quick Comparison Table#

Method	Purpose	Key feature
Observation	Experience using sense organs	First step; no hypothesis testing
Test/Experiment	Verify a hypothesis	Done under controlled procedure
Research	Deep study to answer a curiosity	Multi-step, systematic
Survey	Collect data directly from people/field	Uses questionnaires/interviews

Likely Exam Questions#

1. Define observation. Why is it the first step of scientific learning?
2. What is a hypothesis? How is it tested?
3. List the safety precautions to follow in a science laboratory.
4. Differentiate between observation and test; between research and survey.
5. List the steps involved in conducting a survey/research.
6. Why are precautions necessary during experiments? (accidents + affects result accuracy)
7. Design a simple experiment/report format for a given scenario (e.g., studying sunlight requirement of plants).

Unit 2: Information and Communication Technology (ICT)

2.1 Tools of ICT#

ICT = integrated tools of communication (radio, TV, computer, newspapers, projectors) that create, display, store, transmit, and exchange information.

Device	Key Points
ATM (Automatic Teller Machine)	Electromechanical machine for automated banking (withdraw, deposit, transfer, bill pay). Input devices: card reader, keypad. Output devices: speaker, display screen, receipt printer, cash dispenser. Keep PIN/card safe; change PIN regularly.
Photocopy machine	Uses xerography (dry, electrostatic process) to copy documents; needs light, heat, and a photoreceptor.
Scanner	Converts hard copy → digital (soft) copy. Common type: flatbed scanner.
Printer	Converts digital data → hard copy (a "hardcopy output device"). Speed measured in CPS, LPM, PPM. Types: dot, ink-jet, laser.
Router	Connects different networks (wired/wireless); works on IP address. Types: wired & wireless.
Wi-Fi	"Wireless Fidelity" — wireless LAN using radio waves; invented by NCR Corporation, Netherlands, 1991. Transmission via: base station/ethernet, access point/router, devices.
Set-top box (STB)	Receives, decodes, and displays digital TV/internet signals via cable, fibre, or telephone line.

2.2 Search Engine, Website, ISP#

Search engine: software that searches content on the internet (e.g., Google, Yahoo, Bing, Ask, AltaVista). Excessive Google use → "Googling."

Website: a collection of web pages hosted on a server; starts with www (World Wide Web). Address = URL (Uniform Resource Locator)/web address.

• Parts of a website: Web hosting, Web address (URL), Homepage, Digital content, Navigation structure.

ISP (Internet Service Provider): company providing internet access to customers (also called Internet Access Provider/Online Service Provider).

• Telenet = world's first ISP (1974).
• Mercantile Company = first ISP in Nepal (1994).
• Features: high-speed internet, provides email addresses, protects against phishing/malware, some provide web hosting.

2.3 Social Networking Sites#

Social media = collective online communication channel for community interaction, content sharing, collaboration (Facebook, Messenger, YouTube, Twitter, Instagram, TikTok, Blogs).

Blog = short for "weblog"; personal/informational online journal; a blog updates frequently (unlike a static website). Person who runs it = blogger. Popular platform: WordPress.

Advantages of social media:

• Personal expression / agenda-setting
• Brand development (business promotion)
• Customer interaction (feedback)

Disadvantages of social media:

• Health problems (blue light ↓ melatonin → poor sleep, depression, insomnia)
• Fake accounts
• Confidential information leaks
• Targeted phishing attacks (e.g., cyberbullying)

2.4 Cybercrime, Computer Code of Conduct, Cyber Law, Internet Security#

Cybercrime: crime against a person/group that harms reputation or causes physical/mental trauma through electronic means. Also called computer crime.

Common forms of cybercrime:

1. Identity theft – misusing personal info for unauthorized financial access
2. Cyber terrorism – causing serious harm/extortion via computer against people/govt.
3. Cyberbullying – using social media/electronic means to threaten, intimidate, harass
4. Hacking – shutting down/accessing a website or network unethically
5. Defamation – harming someone's reputation online

Computer Code of Conduct (Code of ethics): guidelines for ethical computer use —

• Respect intellectual property
• Maintain security
• Behave professionally
• Ensure accuracy of information
• Comply with laws
• Report violations

Cyber Law (a.k.a. Internet law/digital law/"law of the Internet"): legal framework governing internet/computer use; gives legal status to digital signatures & e-documents.

• USA: Computer Fraud and Abuse Act (CFAA), 1986
• Nepal: "Electronic Transaction and Digital Signature Act-Ordinance" (Cyber Law), 30 Bhadra 2061 BS (15 Sept 2004); later Electronic Transactions Act, 2063 (2007) and Electronic Transaction Rules, 2064
• Related Nepali laws: Act Relating to Children, 2075 (bans immoral pictures of children); Copyright Act, 2059; Privacy Act, 2075 (violation → 3 yrs jail or Rs 30,000 fine or both)
• Penalties under Electronic Transactions Act, 2063: Hacking/unauthorized access/damaging data → up to 3 years or Rs 2 lakh fine or both; publishing illegal material → 5 years or Rs 1 lakh; computer fraud → 2 years or Rs 1 lakh.

Internet Security: protecting online activities/transactions from threats.

• Risks: Malware (viruses, worms, Trojan horses, spyware), Phishing, Identity theft, Hacking, Botnet.
• Measures: strong passwords, two-factor authentication, updated software, antivirus/security software, firewall, data backup, user education.

2.5 Robotics and Virtual Reality#

Robotics: interdisciplinary branch (mechanical + electrical + computer engineering + maths) dealing with design, construction, and use of robots. Robots have software (programming) + hardware (physical body).

• Applications: Manufacturing, Healthcare, Agriculture, Logistics, Exploration (space/deep-sea), Education, Entertainment, Security.

Virtual Reality (VR): computer-generated 3D environment that simulates real physical presence, using a headset/display + motion sensors.

• Applications: Military (training, PTSD treatment via VRET – Virtual Reality Exposure Therapy), Education (virtual field trips), Sports (training & audience experience), Mental health, Medical training (surgery practice), Fashion, Architecture.

2.6 Artificial Intelligence and Cloud Computing#

Artificial Intelligence (AI): computer programs/machines performing tasks that normally need human intelligence (language understanding, recognition, decision-making).

Three categories of AI (by capacity):

1. Narrow/Weak AI – performs one specific task (e.g., speech recognition)
2. General/Strong AI – as intelligent as a human across tasks
3. Artificial Superintelligence (ASI) – theoretical; surpasses human intelligence

• Example: Sophia, first humanoid robot, visited Nepal in 2018 (UNDP conference).
• Applications of AI: Astronomy, Healthcare, Gaming, Finance, Data security, Social media, Travel & transport, Robotics, Agriculture, Education.

Cloud Computing: using remote servers on the internet to store/manage/process data instead of local computers/servers.

• Providers in Nepal: Datahub, Silver Lining, Cloud Himalaya
• Can be public (paid, open) or private (limited users)
• Advantages: Cost-effectiveness, Accessibility (from anywhere), Reliability (backup systems), Security.

Full Forms (Frequently Asked)#

• ATM – Automatic Teller Machine
• WWW – World Wide Web
• URL – Uniform Resource Locator
• ISP – Internet Service Provider
• AI – Artificial Intelligence
• VR – Virtual Reality
• STB – Set-Top Box
• RPA – Robotic Process Automation
• VRET – Virtual Reality Exposure Therapy
• CFAA – Computer Fraud and Abuse Act

Likely Exam Questions#

1. What is a search engine? Differentiate search engine and website.
2. Differentiate printer and scanner; VR and AI; computer code of conduct and cyber law.
3. What is cybercrime? List its forms.
4. What is cyber law? Mention Nepal's key cyber-related laws and penalties.
5. What are the risks of internet security and how can they be reduced?
6. What is AI? Name its categories and applications.
7. What is robotics? List applications of robots.
8. What is cloud computing? Give its advantages.
9. Write full forms: ATM, WWW, URL, Wi-Fi, ISP, AI, VR.
10. What device converts hard copy to soft copy? (Scanner)

Unit 3: Living Beings and Their Structure

3.1 Cell — Structural & Functional Unit of Life#

Cell: the basic (structural + functional) unit of life; all life processes (digestion, respiration, reproduction, transport, photosynthesis) happen inside cells.

• Cytology = branch of biology studying cells.
• Robert Hooke discovered the cell in 1665, named it "Cellulae" (Latin: tiny rooms) after observing cork slices.
• Later: Schwann, Schleiden, Virchow established the Cell Theory.

Shape & size: Animal cells — irregular (oval, spherical, rod-like, columnar); nerve cells thread-like; muscle cells spindle-shaped. Plant cells — generally hexagonal. Bacteria — spherical, rod-like, filamentous, spiral.

• Smallest cell: Mycoplasma (~0.2 microns)
• Largest cell: Ostrich egg (15–18 cm diameter)

Cell Structure — 4 main parts#

1. Cell covering (cell membrane in animals; cell wall + membrane in plants)
2. Cytoplasm
3. Cell components (organelles + inclusions)
4. Nucleus

Key Cell Organelles & Functions#

Organelle	Function
Mitochondria	"Power house of the cell" — cellular respiration, produces energy (ATP) using glucose + O₂ → CO₂ + H₂O + heat; contains DNA
Chloroplast	Green plastid with chlorophyll; performs photosynthesis; makes plants green; contains DNA
Chromoplast	Colourful plastids (not green) in flowers/fruits — attract pollinators/seed dispersers
Leucoplast	Colourless plastid — stores starch, protein, fat
Ribosome	"Protein factory" — synthesizes protein; no membrane; involved in gene expression
Endoplasmic Reticulum (ER)	"Endoskeleton of cell"; rough ER (with ribosomes) & smooth ER (without); mechanical support, metabolism, helps build Golgi body
Golgi body (discovered by Camillo Golgi, 1898)	Secretes gum, mucus, sweat, saliva, tears; makes new cell membrane/cell plate during division; sorts proteins
Lysosome	"Suicidal bag" — contains digestive enzymes; digests dead cells, self-digests when enzyme level rises high
Vacuole	Not a true organelle; stores cell-sap (water, salts, enzymes); balances water/salt; food vacuole in amoeba

Nucleus — "Brain of the cell"#

Found in eukaryotes (plants, animals, protozoa, fungi); absent in prokaryotes (bacteria — only genetic material, no covering). 4 parts:

1. Nuclear membrane — double-layered, perforated, protective
2. Nucleolus — non-membranous, disappears/reappears during division, makes spindle fibres
3. Nucleoplasm — liquid inside nucleus
4. Chromatin fibres — genetic material (DNA + histone protein); becomes visible chromosomes during cell division. Humans: 23 pairs of chromatin fibres/chromosomes.

Functions of nucleus: controls/coordinates metabolism, transfers genetic characters, active in cell division & reproduction.

3.2 Cell → Tissue → Organ → System → Body#

Cells combine to form tissues → tissues combine to form organs → organs combine to form organ systems → systems make the complete body. Example: muscular tissue in stomach/intestine wall causes rhythmic contraction (peristalsis) to push food; glandular tissue secretes digestive enzymes.

3.3 Classification of Living Beings#

Two-Kingdom System (Carl Linnaeus, 1753)#

Classifies all organisms into Plant and Animal kingdoms based on nutrition, movement, growth, reproduction.

• Features: first scientific classification system; simple.
• Drawbacks: algae & fungi wrongly grouped with plants; prokaryotic bacteria & eukaryotic algae in same kingdom; doesn't separate unicellular/multicellular organisms; can't place lichens.

Five-Kingdom System (R.H. Whittaker, 1969 — 234 years after Linnaeus)#

Based on: cell type (prokaryotic/eukaryotic), body structure (uni/multicellular), nutrition mode, ecological role, phylogeny. Five kingdoms:

1. Monera — unicellular prokaryotes (bacteria, archaea, mycoplasma)
2. Protista — unicellular eukaryotes (amoeba, paramecium)
3. Mycota/Fungi — saprophytic/parasitic, extracellular digestion (mushroom, yeast, mucor)
4. Plantae — autotrophic, multicellular green organisms
5. Animalia — multicellular eukaryotic consumers

Advantages over two-kingdom system: separates prokaryotes/eukaryotes; separates unicellular/multicellular; reflects evolutionary trend.

3.4 Microorganisms#

Microorganisms (germs/microbes): organisms too small to see with naked eye — found in air, water, soil, food, and on/in living beings. Study = microbiology.

Type	Key features	Examples
Virus	Acellular (no cell); body = nucleic acid (DNA/RNA) in protein capsid; "bridge organism" (living inside host, non-living outside); "obligatory parasite"	Coronavirus (SARS-CoV-2 causes COVID-19), Rhinovirus, Bacteriophage
Bacteria	Unicellular prokaryote (kingdom Monera); shapes: spherical/filamentous/cylindrical; covered by capsule	Cyanobacteria, Rhizobium, Salmonella
Amoeba	Unicellular eukaryote; no fixed shape; moves via pseudopodia	Entamoeba histolytica (amoebiasis), Naegleria
Fungi	Uni/multicellular eukaryote; cell wall, no chlorophyll; saprophyte; body made of mycelia	Mucor, mushroom, yeast, penicillium

Positive Effects of Microorganisms#

• Decomposers → increase soil fertility (Nitrosomonas, Clostridium)
• Rhizobium in root nodules fixes atmospheric nitrogen
• Lactobacillus → yoghurt; Streptococcus lactis → cheese
• Used to make insulin, antibiotics, vaccines
• Yeast fermentation → alcohol, acids (used for Gundruk, pickles)
• Bacteriophage controls bacterial disease
• Used in genetic engineering

Negative Effects#

• Cause communicable diseases (TB, AIDS, pneumonia, typhoid, COVID)
• Cause food poisoning (Clostridium, Salmonella, Norovirus, Giardia) → diarrhoea, vomiting, fever
• Cause wound infection/sepsis
• Spoil stored food; pollute environment with foul smell

Food Preservation Methods#

1. Dry preservation — remove moisture (20–30°C); e.g., dry meat, dry fish, dried cereals
2. Wet preservation — dip in salt solution, citric acid, vinegar, oil (airtight container); e.g., pickles
3. Cold preservation — store at low temp (−18°C to 4.4°C) to inactivate microbes; e.g., fridge, cold storage

Likely Exam Questions#

1. Why is the cell called the structural and functional unit of life?
2. Name the four parts of the nucleus and their functions.
3. Why are mitochondria called the "power house" of the cell? Why is lysosome called a "suicidal bag"?
4. Differentiate: plant cell vs animal cell; two-kingdom vs five-kingdom system; bacteria vs virus.
5. Who proposed the two-kingdom and five-kingdom systems? State their basis.
6. What is a microorganism? Give examples of each type (virus, bacteria, amoeba, fungi).
7. What are the methods of food preservation? Explain one in detail.
8. What is food poisoning? Give its causes and prevention.
9. Why is virus called a "link/bridge organism" and not a true organism?
10. Draw and label a plant cell / animal cell.

Unit 4: Biodiversity and Environment

4.1 Biodiversity#

Definition: Variation among organisms of the same or different species regarding genus, species, and habitat/ecosystem (as per Earth Summit, 1992, Rio de Janeiro, Brazil). CBD defines it as variation among aquatic and terrestrial organisms.

• Indicates "species richness" of Earth.

Types of Biodiversity#

1. Genetic diversity — variation among individuals of same/different species (e.g., variation among humans — hair, skin, eye colour)
2. Species diversity — number & type of species in an environment (e.g., 10+ species of frogs in genus Rana)
3. Ecosystem diversity — variety of ecosystems (aquatic/terrestrial) based on climate, physical components

Importance of Biodiversity#

• Guarantees nutrition & livelihood of organisms
• Balances environment, increases ecosystem productivity
• Sustainable use of biological resources
• Supports ecotourism & national economy
• Helps adaptation to climate change

Biodiversity Status of Nepal#

• Nepal = 0.1% of world's area but very rich in biodiversity (altitude 59 m – 8884 m; tropical to alpine climate).
• Nepal ranks: 27th in world, 10th in Asia, 2nd in South Asia.
• Holds 3.2% of world's plants and 1.1% of world's animals.
• 118+ ecosystems, 15+ forest types.
• Unique species: Spiny babbler (found only in Nepal), One-horned rhino, Bengal tiger, Himalayan wild yak, 32 species of rhododendron, Marsi rice of Jumla (grows at 3050m — world's highest).

Causes of Biodiversity Degradation#

• Excessive grazing, industrial pollution, mining/blasting, unplanned construction, excess fodder/firewood collection, deforestation for farmland/settlement, forest fire, floods/landslides, global warming, poaching/illegal wildlife trade, invasive species (Banmara, water hyacinth), illegal sand/gravel mining.
• Example: Snow leopard — near extinction in Nepal; Pygmy hog — already extinct.

Conservation of Biodiversity#

In-situ conservation (in natural habitat)	Ex-situ conservation (outside natural habitat)
National parks, hunting reserves, wildlife reserves, conservation areas	Botanical garden, zoo, nursery, safari park, aquarium, seed/gene/embryo/sperm banks

• Nepal has 12 national parks (Chitwan, Sagarmatha, Bardia, Rara, Khaptad, Langtang, Makalu-Barun, Shey-Phoksundo, Shivapuri, Parsa, Banke, Shuklaphanta), 1 wildlife reserve (Koshi Tappu), 1 hunting reserve (Dhorpatan), 6 conservation areas (Annapurna, Kanchanjunga, Manaslu, Krishnasaar, Gaurishankar, Api-Nampa).
• Other measures: control poaching, establish more protected areas, control overgrazing/pollution/urbanization, strong law enforcement, public awareness education.

4.2 Sustainable Development#

Definition (Brundtland Commission, 1987): "Development that meets the needs of the present generation without compromising the ability of future generations to meet their own needs."

Three Pillars (Aspects) of Sustainable Development#

1. Economic aspect — balanced economic growth, fair distribution/use of resources, no exploitation
2. Social aspect — poverty elimination, equal access to resources, empowerment of women/marginalized groups, cultural preservation, peace & justice
3. Environmental aspect — conserving land, water, air, minerals, climate, and biodiversity; sustainable use of natural resources

Principles of Sustainable Development#

1. Principle of ecosystem & biodiversity conservation — conserve resources, use renewable energy, control pollution
2. Principle of population control & human resource management — limit population to sustain resource use; promote education/skills
3. Principle of culture conservation & public participation — conserve cultural heritage, encourage community participation

Importance of Sustainable Development#

• Balances environment & controls pollution
• Conserves natural resources
• Guides mega-project infrastructure norms
• Eliminates social inequality, establishes justice
• Ensures proportional economic opportunity

Sustainable Development Goals (SDGs) & Nepal#

• Set by UNO's 70th General Assembly, 2015 (193 countries); implemented from 2016.
• 17 goals, 169 targets, 232 indicators (2016–2030).
• Agenda/Goal 15 — relates to terrestrial ecosystems & biodiversity.
• Nepal's efforts:
  • Climate Change Council (since 2009) — cabinet meetings at Kalapatthar (2009, 5550m) and Rara Lake (2018, 2990m) to highlight climate change; drainage system at Tsho-Rolpa glacial lake (Dolakha, 4580m, 2020) to prevent glacial lake outburst
  • Community Forest Program (since 1970; Act in 1993) — increased forest area/density
  • Fourteenth Three-Year Plan (2016–19) — poverty elimination, vocational education
  • Fifteenth Periodic Plan — "Neat, Clean, Green environment"
  • National Environment Policy 2076 BS
  • Environment Conservation Act 2076 BS — compensation from polluters, climate change mitigation

Likely Exam Questions#

1. What is biodiversity? Explain its types with examples.
2. Describe the present status of biodiversity in Nepal.
3. What are the causes of biodiversity degradation?
4. Differentiate: in-situ and ex-situ conservation; genetic diversity and species diversity.
5. Define sustainable development (Brundtland Commission definition).
6. Explain the three aspects/pillars of sustainable development.
7. What are the principles of sustainable development?
8. What are SDGs? Describe Nepal's efforts to achieve them.
9. Name Nepal's national parks, wildlife reserve, hunting reserve, and conservation areas.

Unit 5: Life Process (Reproduction)

Reproduction: the biological process of producing gametes, their fusion, and development into a new offspring of the same kind — ensures continuation of generations.

Importance of Reproduction#

• Prevents extinction; balances death rate; basis of new generations; balances biodiversity magnitude.

5.1 Asexual Reproduction#

Reproduction through a specific organ without fusion of gametes.

Type	Description	Examples
Fission	Splitting of parent body/cell. Binary (into 2, longitudinal/transverse) or Multiple (into many)	Binary: amoeba, paramecium, bacteria; Multiple: Plasmodium, Chlamydomonas
Budding	Small bud grows and separates	Yeast, hydra, coral, jellyfish
Fragmentation	Body breaks into pieces, each grows into new organism	Spirogyra, Marchantia, ferns, lichens
Regeneration	Lost/cut part regrows into complete organism	Hydra, tapeworm, planaria
Sporulation	Reproduction via spores	Fungi, ferns, moss
Parthenogenesis	New body from unfertilized egg	Ants, termites, drone bees; apple/pineapple fruit forms without fertilization

Vegetative Propagation (in plants)#

Asexual reproduction via vegetative parts (root, stem, leaf) — not the flower.

Natural types:

• Root — Rose, sweet potato, dahlia, asparagus
• Underground stem: Sucker (mint, banana), Rhizome (ginger, turmeric), Corm (colocasia), Bulb (onion, garlic), Tuber (potato — buds called "eyes")
• Aerial stem — Sugarcane, crab-grass (Dubo)
• Bulbils — Pineapple, agave, lily, garlic
• Leaf — Bryophyllum, begonia, kalanchoe, sansevieria

Artificial types:

Method	Description
Cutting	Sow cut piece of stem/root/leaf (2 nodes needed) — rose, sugarcane
Layering	Bend lower branch into soil, bark removed, until roots grow
Gootee (Air layering)	Bark removed on aerial branch, wrapped with soil + plastic — litchi, mango, guava
Grafting	Join stock (rooted plant) + scion (twig of good variety) — used by NARC Nepal
Tissue culture	Lab technique; small ex-plant → callus → plantlets using culture media; produces disease-free plantlets in bulk (most advanced method)

5.2 Sexual Reproduction#

Fusion of male and female gametes of the same species → zygote → new organism.

• Unisexual = separate male/female organs (humans); Bisexual/hermaphrodite = both organs in one body (mustard flower).

Characteristics: gamete formation & fusion; genetic variation in offspring; better environmental adaptation; drives organic evolution.

5.2.1 Sexual Reproduction in Plants#

Flower parts: Male = Androecium (stamen: filament + anther, produces pollen); Female = Gynoecium (pistil: stigma + style + ovary, contains ovule).

(A) Pollination — transfer of pollen grains onto stigma.

• Self-pollination: same plant. Autogamy (same flower) or Geitonogamy (different flower, same plant). Adv: preserves parent traits, assures seed set. Disadv: no new characters, reduces vigor. Common in paddy, wheat.
• Cross-pollination: between different plants of same species. Needs pollinating agents.
  • Anemophily — wind (maize, pine)
  • Hydrophily — water (aquatic plants)
  • Entomophily — insects (bees, butterflies)
  • Ornithophily — birds (hummingbird, sunbird)

(B) Fertilization — fusion of male gamete (from pollen tube) with female gamete (egg in ovule) → zygote. Plants show double fertilization: 1 male nucleus + egg → zygote; 2nd male nucleus + polar nuclei → endosperm nucleus.

• After fertilization: ovule → seed; ovary → fruit.

5.2.2 Sexual Reproduction in Animals#

• Male gamete = sperm (produced in testes); female gamete = ovum/egg (produced in ovaries). Formation = gametogenesis.
• Fertilization = fusion of sperm + egg nuclei → zygote → embryo → baby. Development time = embryonic/pregnancy period.
• Internal fertilization — inside female body (fallopian tube) — arthropods, reptiles, birds, mammals.
• External fertilization — outside body, in water — fish, amphibians.

5.3 Seed#

Formed after fertilization: fertilized ovule (zygote → embryo) becomes a seed.

Seed Dispersal Mechanisms#

Method	Feature	Examples
Wind	Light, winged/feathery seeds	Silk cotton, dandelion, cotton
Water	Light, waterproof	Lotus, coconut, mangrove
Animals	Eaten & egested, or spiky (sticks to fur)	Guava, cocklebur, jamun
Gravity	Heavy fruits/seeds fall	Mango, coconut, apple
Bursting of pods	Pod dries and bursts, ejecting seeds	Mustard, beans, peas

Structure of Seed — 3 parts#

1. Seed coat — outer (Testa) + inner (Tegmen) layer; protects seed
2. Embryo — cotyledon (leaf-like, stores food), radicle (→ root), plumule (→ shoot)
3. Endosperm — nutrient storage (mostly in monocots; dicots usually store nutrients in cotyledons instead)

• Monocot: 1 cotyledon, has endosperm. Dicot: 2 cotyledons, usually no endosperm.

Germination#

Development of root & shoot from a seed.

• Dormancy = resting state of seed without germination.
• Radicle → root first, then plumule → shoot, cotyledons → embryonic leaves.

Factors affecting germination:

1. Water — breaks dormancy, initiates metabolism
2. Air (Oxygen) — needed for energy generation (mitochondrial respiration)
3. Temperature — ideal range 16–24°C
4. Light — needed for photosynthesis after sprouting

Likely Exam Questions#

1. What is reproduction? List types of asexual reproduction with examples.
2. Differentiate: fission and budding; self-pollination and cross-pollination; internal and external fertilization; monocot and dicot seed.
3. Describe grafting — what are stock and scion?
4. What is tissue culture? Why is it considered the most advanced method?
5. Explain pollination and fertilization in flowering plants with a diagram.
6. What is double fertilization?
7. What are the parts of a seed? Describe each.
8. What factors affect seed germination?
9. Explain methods of seed dispersal with examples.
10. Draw and label: flower parts, sperm & egg, seed structure.

Unit 6: Force and Motion

6.1 Motion, Rest, Speed, Velocity#

• Rest & motion are relative — depend on the chosen reference point.
• Motion: object changes position w.r.t. reference point. Uniform motion = equal distances in equal time; Non-uniform motion = unequal distances in equal time.
• Speed (scalar): distance/time → S = d/t (unit: m/s)
• Velocity (vector): displacement/time in a particular direction → V = s/t (unit: m/s)

Relative Velocity#

Velocity of a body with respect to another body/reference point.

• Same direction: V_AB = V_A − V_B
• Opposite direction: V_AB = V_A + V_B

Average Velocity#

Average velocity = (total distance in a direction) / (total time) = s / t Also: Average velocity = (u + v) / 2 (u = initial velocity, v = final velocity)

Acceleration#

Rate of change of velocity: a = (v − u) / t (unit: m/s²)

• Retardation (negative acceleration): when final velocity is less than initial velocity (e.g., braking).

Key formulas for numericals:

• S = d/t, V = s/t, a = (v−u)/t, average velocity = (u+v)/2

6.2 Lever#

Lever: rigid bar that turns about a fixed point (fulcrum). Invented by Archimedes (240 BC) — "Give me a lever and a place to stand, I can move the world."

• Effort (E) — force applied; Load (L) — object to be lifted
• Effort distance (E.D.) and Load distance (L.D.) — measured from fulcrum

Types of Lever#

Class	Position of Fulcrum	Examples
First-class	Fulcrum between load & effort	Beam balance, scissors, dhiki, crowbar
Second-class	Load between fulcrum & effort	Nut-cracker, lemon squeezer, wheelbarrow
Third-class	Effort between fulcrum & load	Fire tongs, shovel, hammer

Lever Principle (balanced condition)#

E × E.D. = L × L.D.

Mechanical Advantage (MA)#

MA = Load (L) / Effort (E) — no unit; affected by friction.

Velocity Ratio (VR)#

VR = Effort Distance (E.D.) / Load Distance (L.D.) — NOT affected by friction.

Efficiency (η)#

Efficiency (η) = (Output work / Input work) × 100% = (MA / VR) × 100%

• MA is always less than VR (due to friction) → efficiency is always less than 100%. A theoretical 100%-efficient machine = ideal/perfect machine.
• Input work = E × E.D.; Output work = L × L.D.

6.3 Pressure#

Pressure: force acting perpendicularly per unit area. P = F / A — SI unit: N/m² = Pascal (Pa).

• 1 Pa = force of 1N acting on area of 1m².
• Pressure ↑ when Force ↑ or Area ↓.

Applications: sharp ploughshare/knife/nail (less area → more pressure); wide tractor wheels/multiple truck tyres (more area → less pressure, avoids sinking).

Liquid Pressure#

Formula: P = h × d × g (h = depth, d = density, g = acceleration due to gravity)

• Depends on depth and density, not on shape/amount of container.
• Applications: dam/tank bottom made thicker; deep-sea divers wear special suits; water tank kept at maximum height.

Air Pressure#

• Compressed air has pressure greater than atmospheric pressure; used in air brakes, drills, air rifles; measured in millibar by pressure gauge.

Atmospheric Pressure#

• Pressure exerted by the weight of air on Earth's surface.
• At sea level = 760 mmHg = 10⁵ Pa (approx.)
• Decreases with altitude.
• Measured by Barometer. Liquid/gas pressure measured by Manometer (U-shaped tube).
• Applications: fountain pen filling, syringe (injection), bicycle tube pump.

Likely Exam Questions#

1. Define speed, velocity, and relative velocity; give formulas.
2. Differentiate: distance & displacement; MA & VR; input work & output work.
3. Numerical: calculate acceleration/retardation/average velocity/relative velocity (memorize formulas).
4. Classify a given lever (scissors, nutcracker, wheelbarrow, etc.) into class 1/2/3.
5. State the lever principle. Solve for effort/load given distances.
6. Derive/state formula for liquid pressure P = hdg.
7. Why is efficiency of a machine always less than 100%?
8. What is atmospheric pressure? State its value at sea level and instrument used to measure it.
9. Numerical: Find pressure given force & area, or given depth & density (P=hdg).
10. Explain why ploughshares/knives are sharp and why tractor wheels are wide (pressure application).

Unit 7: Energy in Daily Life

Energy: capacity to do work. SI unit = Joule (J); also measured in calorie (1 calorie = 4.2 J).

• Renewable energy (inexhaustible): solar, wind, tidal
• Non-renewable energy (cannot be replaced quickly): coal, petroleum, nuclear

7.1 Heat#

Heat transmission = transfer of heat from hotter to colder body. Three methods:

(A) Conduction#

Heat transfer in solids without actual movement of molecules (only vibration).

• Good conductors: iron, copper, aluminium, gold
• Insulators: wood, plastic
• Applications: metal cooking utensils (fast heat transfer); plastic/wood handles (prevent heat reaching hand); woollen clothes (trap air, prevent heat loss); porcelain cups (insulator)

(B) Convection#

Heat transfer in liquids/gases due to actual movement of molecules (hot rises, cold sinks).

• Sea breeze (day): land heats faster than sea → warm air rises over land → cool sea air flows to land
• Land breeze (night): land cools faster → cool air flows from land to sea
• Types: Free/Natural convection (e.g., boiling water, sea/land breeze), Forced convection (e.g., fans, water heaters)
• Applications: boiling liquids, blood circulation, fans/ACs, refrigerators, rainfall/cloud formation

(C) Radiation#

Heat transfer without any medium (works through vacuum) — e.g., heat from Sun to Earth.

• Travels as electromagnetic waves at speed of light (3×10⁸ m/s); Sun's heat takes ~8 min 20 sec to reach Earth.
• Dark/black objects absorb & emit more radiation; white/light objects absorb & emit less → white clothes preferred in summer, dark in winter.

Waves — Mechanical vs Electromagnetic#

• Mechanical waves — need a medium (e.g., sound); speed varies by medium (air: 332 m/s, water: 1481 m/s, iron: 5120 m/s)
• Electromagnetic waves — no medium needed (e.g., light, heat radiation); travel at speed of light

Thermos Flask#

Double-walled glass vessel with vacuum between walls (stops conduction/convection) + silvered surfaces (stops radiation) + insulating cork stopper → keeps hot liquids hot, cold liquids cold.

Greenhouse Effect#

Glass/plastic structure trapping short-wave solar radiation (long-wave radiation can't escape) → warms interior; used for off-season crops.

• Natural greenhouse effect: Earth's atmosphere gases (CO₂, methane, water vapour, CFCs, nitrous oxide) trap heat, keeping Earth warm enough for life.
• Excess greenhouse gases (from factories, vehicles, deforestation) → global warming → rising temperatures, changed water cycle, GLOF (glacier lake outburst flood), sea level rise, desertification, biodiversity loss.

7.2 Light — Mirrors#

Reflection: light bouncing back after striking a surface. Concave mirror: middle depressed, edges raised → converging mirror (real focus in front). Convex mirror: middle raised, edges depressed → diverging mirror (virtual focus behind).

Key Terms (Spherical Mirrors)#

Term	Symbol	Meaning
Pole	P	Centre of reflecting surface
Centre of curvature	C	Centre of the sphere the mirror is part of
Radius of curvature	R	Distance from P to C
Principal axis	—	Line through P and C
Principal focus	F	Point where parallel rays converge (concave) or appear to diverge from (convex)
Focal length	f	Distance from P to F

Real vs Virtual Image#

Real Image	Virtual Image
Formed in front of mirror	Formed behind mirror
Can be obtained on screen	Cannot be obtained on screen
Formed by actual intersection of rays	Formed where rays appear to meet
Inverted	Erect

• Concave mirror: forms real, inverted image (varies with object distance — diminished to magnified); when object is between F & P → virtual, erect, magnified image.
• Convex mirror: always forms virtual, erect, diminished image (wide field of view).

Uses#

• Concave: torch/searchlight/headlights, ENT examination (ear/nose/throat), shaving/makeup mirrors, astronomical telescopes, solar cookers
• Convex: vehicle side/rearview mirrors, street lamps, security mirrors (wide field of view)

7.3 Sound#

Sound: form of energy produced by vibration; needs a material medium to travel (mechanical, longitudinal wave) — cannot travel through vacuum.

Characteristics of Sound Waves#

Term	Symbol	Definition	Unit
Frequency	f	Number of waves per unit time	Hertz (Hz)
Time period	T	Time for one complete wave; T = 1/f	second
Wavelength	λ	Distance for one complete wave (between two crests/troughs)	metre
Amplitude	A	Max displacement from mean position	metre

Speed of sound: v = f × λ (constant in a given medium)

Types of Sound (by frequency)#

Type	Frequency	Notes
Infrasonic	Less than 20 Hz	Felt not heard; earthquakes, volcanic eruptions; elephants, rhinos (less than 5 Hz)
Audible	20 Hz – 20 kHz	Human hearing range
Ultrasonic	More than 20 kHz	Bats, rats produce/hear it; used in USG (ultrasonography), SONAR (measuring sea depth), bloodless surgery, tumor detection

• Male voice: 60–180 Hz; Female voice: 160–300 Hz.

Intensity of Sound#

I = Power (P) / Area (A) — SI unit: W/m²; measured practically in decibel (dB).

• Deafness threshold ≈ 80 dB (cannot hear sound below this).
• Factors affecting intensity: amplitude (I ∝ a²), distance from source (↓ with distance), density of medium, area of vibrating body, frequency.

Sound Pollution#

Causes: traffic, construction, loud machinery, markets, loudspeakers. Effects: hearing loss, high blood pressure, eardrum rupture, difficulty concentrating. Prevention: afforestation, silencers in vehicles, avoid loud noise, awareness programs.

Likely Exam Questions#

1. Differentiate: conduction, convection, radiation (with examples).
2. Why do woollen clothes keep us warm? Why are cooking pot handles made of plastic?
3. Explain sea breeze and land breeze.
4. Describe the structure of a thermos flask.
5. What is the greenhouse effect? Differentiate natural vs enhanced greenhouse effect.
6. Differentiate concave and convex mirror; real and virtual image.
7. State uses of concave and convex mirrors.
8. Define frequency, wavelength, amplitude, time period of a wave.
9. Numerical: v = fλ (calculate speed/frequency/wavelength).
10. Differentiate infrasound, audible sound, ultrasound with examples.
11. What is intensity of sound? What factors affect it?
12. What is sound pollution? State its causes, effects and remedies.

Unit 8: Electricity and Magnetism

8.1 Magnet#

Magnet: substance that attracts magnetic materials (iron, cobalt, nickel), attracts unlike poles & repels like poles, has N-pole & S-pole.

Natural vs Artificial Magnet#

Natural Magnet	Artificial Magnet
Magnetic property occurs naturally (e.g., Loadstone — a magnetite mineral)	Magnetic property developed as needed
Strength cannot be altered	Strength can be altered; may be temporary/permanent
—	Made by passing electricity (electromagnet) or other methods

Uses of magnets: radio, TV, fan, refrigerator, electric bell, generators, computers, headphones, MRI machines, cranes (loading iron in factories/ports), magnetic compass, door/window locks.

Molecular Theory of Magnetism#

Proposed by Weber, modified by James Alfred Ewing.

• Magnets/magnetic substances are made of tiny molecular magnets, each with N and S poles.
• In non-magnetic state: molecular magnets arranged randomly (closed chains).
• In magnetized state: molecular magnets align in one direction (open chain) — called magnetic saturation.

Demagnetization#

Loss of magnetic property when molecular magnet alignment is disturbed. Causes:

1. Heating the magnet
2. Hammering the magnet
3. Passing alternating current (AC) through it
4. Keeping like poles together forcefully for long
5. Natural loss (over time)

Conservation of magnetism: avoid heat/hammering; don't keep near current-carrying wires; store in a keeper when not in use.

Geomagnetism (Terrestrial Magnetism)#

Earth itself behaves as a huge magnet — caused by convection currents of molten iron/nickel in Earth's outer core. Evidence: buried N-S iron rod becomes magnetic; freely suspended magnet always points N-S; natural magnets occur on Earth; existence of neutral points. Applications: deflects solar wind charged particles (protects Earth); used to date rocks (paleomagnetism); magnetic compass for navigation (ships, submarines, planes).

Elements of terrestrial magnetism:

• Magnetic declination: angle between geographic meridian and geomagnetic meridian (0° at magnetic equator, 90° at magnetic poles)
• Magnetic inclination/Angle of dip: angle made by a freely suspended magnetic needle with the horizontal (0° at magnetic equator, 90° at magnetic poles; 42° in Kathmandu)

8.2 Electricity#

8.2.1 Household Electrification#

Process of bringing electricity from powerhouse to homes via transmission lines; voltage stepped down to 220V at substation transformer for domestic use.

Key devices in domestic wiring:

Device	Function
Main switch	Controls overall current (15A or 30A); connected in series
Electric meter	Measures energy consumed; unit = kWh (1 unit = 1kWh)
Distribution board	Distributes current to different circuits
MCB (Miniature Circuit Breaker)	Automatic switch; trips during excess current/short circuit; reusable (unlike fuse)
Fuse	Thin tin-lead wire; melts on excess current to protect circuit; connected in series in live wire
Switch	Turns current ON/OFF; connected in live/phase wire
Plug & socket	Distribute current safely; 2-pin or 3-pin
Electric bulb	Converts electrical → light energy; tungsten filament; connected in parallel in households

Electricity bill formula: E.C. = P × N × t (P = power in kW, N = number of devices, t = time in hours) Bill = E.C. × Rate per unit

Electric Wires (3 types)#

Wire	Colour	Feature
Phase/Live wire	Red/dark red	High potential; gives shock; has switch & fuse
Neutral wire	Blue/black	Zero potential — but still don't touch
Earth wire	Green/yellow	Connected to ground; protects from leakage current, prevents electrical fires

Wiring a Plug (steps)#

1. Open plug cover
2. Strip insulation from cable, identify live/neutral/earth wires
3. Twist bare wire ends
4. Connect live wire → right pin (with fuse); neutral → left pin; earth → top pin
5. Clamp cord; replace cover

Electric Circuit of Bulbs#

Household bulbs are connected in parallel — each gets equal voltage/brightness, can be controlled by separate switches, and one bulb failing doesn't affect others.

Likely Exam Questions#

1. Differentiate natural and artificial magnet.
2. Explain the molecular theory of magnetism with a diagram.
3. What are the causes of demagnetization? Explain one.
4. What is geomagnetism? Give evidence for its existence.
5. Define magnetic declination and angle of dip.
6. What is household electrification? Explain the functions of MCB and fuse.
7. Differentiate live wire and neutral wire; plug and socket.
8. Why is earthing necessary in domestic wiring?
9. Numerical: Calculate electricity bill using E.C. = P × N × t.
10. Why are bulbs connected in parallel in household wiring?
11. Why should a magnet be kept in a keeper when not in use?

Unit 9: Matter

Matter: anything that has mass and volume (e.g., book, water, air — but NOT heat, light, shadow).

Atom — Structure#

Atom: smallest particle of an element; cannot be seen with naked eye.

3 Subatomic Particles#

Particle	Symbol	Location	Charge	Mass
Proton	p⁺	Nucleus	Positive	1 amu
Neutron	n⁰	Nucleus	Chargeless	1 amu
Electron	e⁻	Shells/orbit	Negative	1/1837 amu

• Nucleus = protons + neutrons (center); electrons revolve in shells/orbits around nucleus.
• Atom is electrically neutral (protons = electrons).

Shells & Bohr-Bury's 2n² Rule#

Shells (energy levels): K, L, M, N (n = 1,2,3,4). Max electrons in a shell = 2n² → K=2, L=8, M=18, N=32.

Valence Shell, Valence Electron, Valency#

• Valence shell = outermost shell; valence electrons = electrons in it.
• Atoms attain stability with 2 or 8 electrons in valence shell (octet rule).
• Valency = number of electrons donated/gained/shared to attain stability.
  • 1–3 valence electrons → donates (loses) electrons
  • 4 valence electrons → shares electrons
  • 5–7 valence electrons → gains electrons
  • 8 valence electrons → valency = 0 (doesn't react) — e.g., inert gases

Molecular Formula (Criss-Cross Method)#

Steps: write symbols → write valency above each → cross the valencies as subscripts → simplify.

• MgO (Mg valency 2, O valency 2 → cancel to 1 each)
• KCl, CaCl₂, NH₃, CO₂, H₂O

Atomic Weight & Molecular Weight#

Atomic weight = number of protons + number of neutrons Molecular weight = sum of atomic weights of all atoms in the molecule.

• e.g., H₂O = 2(1) + 16 = 18 amu; CaCO₃ = 40+12+3(16) = 100 amu

Modern Periodic Table#

Created by Henry Moseley (1913) — most scientific classification, still used today. Modern Periodic Law: "Physical and chemical properties of elements are a periodic function of their atomic number."

• Elements arranged by increasing atomic number.
• 18 groups (vertical columns — similar properties) and 7 periods (horizontal rows).

Position in Periodic Table#

Category	Valence electrons	Groups	Property
Metals	1–3	Groups 1–13	Donate electrons; good conductors. Group 1 = alkali metals; Group 2 = alkaline earth metals
Non-metals	5–7	Groups 15–17	Gain electrons; poor conductors. Group 17 = halogens (very reactive)
Inert/Noble gases	8 (or 2 for He)	Group 18	Neither gain nor donate electrons; stable
Hydrogen	1	Group 1	Placed here due to 1 valence electron, but not a true metal

Characteristics of Groups (top → bottom)#

1. Same group = similar physical/chemical properties
2. Same valency, but different number of shells
3. Atomic size increases
4. Metallic character increases; non-metallic character decreases

Characteristics of Periods (left → right)#

1. Properties change gradually
2. Same number of shells, but different valence electrons (valency varies)
3. Atomic size decreases (except inert gases)
4. Metallic character decreases; non-metallic character increases

Chemical Reaction & Equation#

• Physical change: no change in composition; reversible.
• Chemical change/reaction: composition changes; new substances formed (combination, dissociation, exchange of atoms); generally irreversible.
• Reactants (left side) → Products (right side)
• Word equation: uses names. Formula/skeletal equation: uses molecular formulas (before balancing). Balanced equation: atom count equal on both sides.

Examples:

• 2Na + Cl₂ → 2NaCl
• N₂ + 3H₂ → 2NH₃
• CaCO₃ → CaO + CO₂
• Zn + 2HCl → ZnCl₂ + H₂

Likely Exam Questions#

1. Name subatomic particles with symbol, charge, mass, location.
2. State Bohr-Bury's 2n² rule.
3. What is valency? How is it determined from valence electrons?
4. Write molecular formula using criss-cross method (MgO, NaCl, CaCl₂, NH₃, etc.)
5. Calculate atomic weight/molecular weight (e.g., CaCO₃, MgCl₂).
6. Who proposed the modern periodic table? State the modern periodic law.
7. Explain position of metals, non-metals, inert gases in periodic table.
8. Differentiate group and period; metals and non-metals.
9. What is a chemical reaction/equation? Balance given equations.
10. Complete a table given proton/neutron/electron numbers → find element, atomic weight.

Unit 10: Materials Used in Daily Life

Acids#

Acid: substance that gives hydrogen ions (H⁺) when dissolved in water.

• Organic acids — found naturally in plants/animals (e.g., citric, acetic, lactic, ascorbic, formic, oxalic, carbonic acid) — mostly weak acids.
• Inorganic acids — made in lab from minerals (e.g., HCl, H₂SO₄, HNO₃) — mostly strong acids.
• Strong acid = gives more H⁺ ions; Weak acid = gives fewer H⁺ ions.

Physical Properties of Acids#

• Sour taste; soluble in water
• Turns blue litmus → red (no change on red litmus)
• Turns methyl orange → red
• Phenolphthalein stays colourless

Chemical Properties of Acids#

1. Ionization: HCl → H⁺ + Cl⁻
2. With metals → salt + hydrogen gas: Mg + 2HCl → MgCl₂ + H₂
3. With metallic carbonates → salt + water + CO₂: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
4. With bases (neutralization) → salt + water: HCl + NaOH → NaCl + H₂O

Uses of Acids#

• Citric acid — food preservation; Acetic acid — pickles; Ascorbic acid — Vitamin C medicine; Tartaric acid — baking powder
• HCl — digestion (in stomach), cleaning, PVC manufacture; Nitric acid — fertilizers, explosives; Sulphuric acid — batteries, fertilizers, dyes

Bases#

Base: metallic oxide/hydroxide. Alkali = base soluble in water. Gives hydroxide ions (OH⁻) in water.

• Strong bases: NaOH, KOH. Weak base: NH₄OH (ammonium hydroxide)

Physical Properties of Bases#

• Bitter taste, slippery/soapy feel
• Turns red litmus → blue
• Turns methyl orange → yellow
• Turns phenolphthalein → pink

Chemical Properties of Bases#

1. Ionization: NaOH → Na⁺ + OH⁻
2. With ammonium salts → produces ammonia gas: (NH₄)₂SO₄ + 2NaOH → Na₂SO₄ + 2NH₃ + H₂O
3. With acids (neutralization) → salt + water

Uses of Bases#

• Calcium hydroxide — bleaching powder, whitewash, reduce soil acidity
• Magnesium/Sodium hydroxide — antacid (gastric hyperacidity)
• Ammonium hydroxide — soap, cloth, paper manufacture, petroleum processing

Salt#

Salt: neutral compound formed from acid + base reaction.

Type	Formed from	Example
Neutral salt	Strong acid + strong base (or weak+weak)	NaCl
Acidic salt	Strong acid + weak base	NH₄Cl
Basic salt	Strong base + weak acid	Na₂CO₃

Physical properties: most tasteless (some bitter); soluble in water; colourless/white or coloured; high boiling/melting points. Chemical properties: ionizes in water; reacts with acids/bases to form new salts; displacement reaction — more reactive metal displaces less reactive metal: Fe + CuSO₄ → FeSO₄ + Cu

Uses: Table salt (NaCl) — food, preservative, makes NaOH/soap; Washing soda (Na₂CO₃) — cleansing, removes permanent hardness, glass/paper industry; Baking soda (NaHCO₃) — baking powder, antacid, fire extinguishers.

10.2 Acid Rain#

Acid rain: rain made acidic by acids in the atmosphere (normal rainwater pH ~6 due to carbonic acid; harmful when strong acids present).

Causes:

• Natural: decay of organisms, volcanic eruptions, oxides of N & S reacting with water
• Artificial (human): burning fossil fuels, vehicle emissions, factory chemicals — forms H₂SO₄, HNO₃

Effects: acidifies rivers/lakes/ponds (harms aquatic life); damages plant leaves & soil quality; destroys forests; corrodes monuments/idols.

Prevention: reduce fossil fuel use; use renewable energy (hydro, solar); locate industries away from residential areas.

10.3 Hardness of Water#

• Soft water — less/no dissolved Ca/Mg salts; more lather with soap (rainwater, boiled water, surface water)
• Hard water — contains dissolved Ca/Mg salts; less lather (usually groundwater)

Types & Removal#

Type	Contains	Removal Method
Temporary hardness	Bicarbonates of Ca/Mg	Boiling; Clark's method (add Ca(OH)₂ → precipitates as insoluble carbonate)
Permanent hardness	Sulphates & chlorides of Ca/Mg	Washing soda (forms insoluble carbonate); Permutit method (sodium zeolite exchanges Na⁺ for Ca²⁺/Mg²⁺)

Alloys#

Alloy: homogeneous mixture of a metal with another metal or non-metal — improves properties (harder, less rust, different melting point/colour).

Alloy	Composition	Uses
Steel	Iron + carbon	Buildings, bridges, railings
Stainless steel	Iron + chromium + nickel	Kitchen utensils, surgical instruments (rust-resistant)
Brass	Copper + zinc	Pooja items, gagri, idols, nuts/bolts
Bronze	Copper + tin	Plates, bowls, medals, coins, statues
Duralumin	Aluminium + copper + manganese + magnesium	Aircraft bodies (light + strong)

Properties of alloys: harder & less ductile/malleable than base metals; resist rusting; different melting point & colour; overall improved properties.

Likely Exam Questions#

1. Define acid, base, salt with examples.
2. Differentiate: organic vs inorganic acid; strong vs weak acid; bases vs alkalis.
3. Give reaction of acid/base/salt with each indicator (litmus, methyl orange, phenolphthalein) — complete a table.
4. What is neutralization reaction? Give an example.
5. What is acid rain? State its causes, effects, and prevention.
6. Differentiate temporary and permanent hardness of water; Clark's method and Permutit method.
7. What is an alloy? Name metals mixed in steel, stainless steel, brass, bronze.
8. Why is steel used more than pure iron for utensils?
9. Why does well/groundwater produce less lather than rainwater?
10. Numerical/practical: identify substance (acid/base/salt) from indicator colour table.

Unit 11: The Earth and Universe

11.1 Minerals#

Mineral: a naturally occurring, solid, pure (element or compound) substance found in Earth's crust, obtained from mines, with economic importance. Study of minerals = Mineralogy.

Types of Minerals#

Type	Sub-types	Examples
Metallic	Ferrous (contain iron), Non-ferrous, Precious	Hematite/magnetite (ferrous); copper, lead, aluminium (non-ferrous); gold, silver, platinum (precious)
Non-metallic	Gems, Non-gems	Diamond, emerald, sapphire (gems); silica, mica, gypsum, talc, graphite (non-gems)
Energy minerals	—	Coal, petroleum, natural gas, radioactive elements (uranium)

Properties of Minerals#

• Various colours (iron ores: black/reddish-brown; some colourless e.g. Muscovite)
• Mostly crystalline (fixed geometric shape); few amorphous (e.g., Opal)
• Hard, bright, lustrous
• Metallic minerals conduct heat/electricity; non-metallic are insulators
• Solid, homogeneous, definite chemical composition

Uses of Minerals#

• Agriculture: fertilizers, pesticides (N, P, K minerals)
• Industry: cement, glass, paint, ceramics (silica, gypsum, limestone)
• Construction: rocks, sand, gravel, marble, slate (roofing, idols)
• Energy: coal, petroleum, graphite, lithium (fuel, batteries)

Minerals in Nepal#

• 60+ types identified: 21 metallic, 23 chemical fertilizer/insulating, 6 gems, 9 construction, 4 fuel/geothermal.
• Himalayan region holds ~83% of total minerals.
• Notable: Iron (Phulchoki, Those/Ramechhap), Copper (107+ places), Gold (river sands — Rapti, Kaligandaki), Limestone (Udaipur, Chobhar), Rock salt (Mustang, Dolpa), Radioactive Uranium (Upper Mustang), Coal (Dang, Palpa, Pyuthan).

11.2 Origin and Age of Earth#

Earth is estimated to have originated ~4.6 billion years ago.

Hypotheses on Origin of Solar System#

Hypothesis	Proposed by	Year	Key idea
Nebular	Immanuel Kant (Germany); modified by Pierre Simon Laplace	1755 / 1796	Spinning nebula's dust/gas collected at centre → Sun; flattened outer parts formed planets
Planetesimal	George Buffon (France)	1745	A giant comet collided with Sun, splashing mass that cooled into "planetesimals" → planets
Binary	T.C. Chamberlin & F.R. Moulton (USA)	1905	A companion (binary) star pulled mass from Sun via gravity → planets
Tidal	Sir James Jeans & Harold Jeffrey (England)	1919	A passing star's gravity pulled a cigar-shaped tidal mass from Sun → planets (small ones at ends, big ones in middle)

(Note: criticism of Binary hypothesis — no evidence Sun has a binary companion.)

11.3 The Universe#

Universe: the total existence — aggregate of limitless space, time, matter, and energy (includes Earth, moon, sun, stars, all celestial bodies).

• Sky = limitless expansion of visible space; Space = boundless view of the sky.
• Observable universe diameter ≈ 46 billion light years.
• 1 Light year = distance light travels in 1 year in vacuum = 9.46 × 10¹² km.
• Astronomy = branch of science studying the universe.

Big Bang Theory (Origin of Universe)#

• Universe originated ~13.8 billion years ago.
• 1924 — Edwin Hubble observed galaxies moving away from Earth at high speed (expanding universe).
• 1927 — George Lemaître proposed that reversing this expansion leads to a single point ("Primeval atom") 13.8 billion years ago.
• The primeval atom's explosion = Big Bang → formed pre-matter → subatomic particles → atoms → molecules → galaxies, stars, planets.
• Stephen Hawking further described the universe's origin (book: A Brief History of Time).

Asteroids#

Small, irregularly shaped rock masses (no fixed shape) revolving around the Sun — "baby planets."

• Asteroid belt — between Mars & Jupiter orbits
• Kuiper belt — beyond Neptune's orbit (contains dwarf planet Pluto)
• Trojans — asteroids sharing Jupiter's/Mars's orbit
• Near-Earth asteroids — cross Earth's orbit (risk of collision)
• Largest: Ceres (~940 km diameter); Composed of rocks, minerals, metals, clay.

Comets#

Small icy solar system bodies with a long bright tail when near the Sun; highly elliptical orbits.

• Nucleus (icy solid core) → Coma (evaporated cloud around nucleus) → Tail (two types: dust tail — thick/white; ion/plasma tail — thin/bluish)
• Endocomets — stay within Kuiper belt; Exocomets — come from outside solar system
• Orbital period: 2 to 250,000 years (Halley: 75.32 yrs; Encke: 3.3 yrs)
• Repeated revolutions → comet loses mass → becomes an extinct comet (turns into asteroid-like body)

Meteoroid, Meteor, Meteorite#

Term	Meaning
Meteoroid	Small rock/metal fragment roaming the solar system
Meteor ("shooting/falling star")	Streak of light when meteoroid burns up entering atmosphere (friction in mesosphere)
Meteorite	Remnant of a meteor that reaches Earth's surface
Meteor shower	Many meteors falling in one region/time

• ~200 meteoroids enter Earth's field daily (speed 20–80 km/s); most burn up before reaching ground.

Galaxy#

Massive collection of millions of stars, nebulas, planetary systems, dark matter/energy.

• Our galaxy = Milky Way (~150 million stars incl. our Sun).
• Shapes: elliptical, spiral, lens-like, ring-like, irregular.
• ~2×10¹¹ (200 billion) galaxies in observable universe (NASA, New Horizons, 2021).
• Usually has a black hole at its centre.

Constellation#

Region of sky where stars form a recognizable pattern.

• 88 constellations total; 12 lie on the ecliptic = Zodiacs (Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces).
• Others: Ursa Major, Orion, Cassiopeia, etc. Crux = smallest; Hydra = biggest.
• Used historically for navigation and telling time/season (before compass/watches).

Likely Exam Questions#

1. Define mineral. Classify minerals with examples.
2. Describe the status/potential of minerals in Nepal.
3. What are the four hypotheses on the origin of the solar system? Explain the Nebular hypothesis.
4. What is the Big Bang theory? Who contributed to it (Hubble, Lemaître, Hawking)?
5. Differentiate: asteroid and comet; meteor and meteorite; asteroid belt and Kuiper belt.
6. Describe the structure of a comet (nucleus, coma, tail).
7. What is a galaxy? Name our galaxy and describe it.
8. What is a constellation? What are zodiacs? Name any five.
9. Define light year. What is the size of the observable universe?
10. Why are meteors also called "shooting stars"?