• Cell is the basic structural & functional unit of life. Levels of organisation: cells → tissues → organs → organ systems → organism.
• History: Hooke (1665) named “cells” from cork; Schleiden & Schwann (1838) proposed cell theory; Virchow (1885) said “cells arise from pre-existing cells”.
• Observing cells: Compound microscope shows cells; electron microscope reveals ultrastructure (very fine details) up to $2\\times10^{9}$ magnification (two billion).
• Units (exact): $1\\ \\text{cm}=10\\ \\text{mm}$, $1\\ \\text{mm}=1000\\ \\mu\\text{m}$, $1\\ \\mu\\text{m}=1000\\ \\text{nm}$.
• Plant vs Animal cells: Plants have cell wall, chloroplasts, and usually one large central vacuole; animals lack cell wall & chloroplasts and have small vacuoles.
• Key organelles: Nucleus (control), ER (modifies proteins/lipids), Ribosomes (protein synthesis), Golgi (packaging/dispatch), Mitochondria (energy), Vacuoles (storage/waste), Chloroplasts (photosynthesis in plants).
• Prokaryotes (bacteria): nucleoid, no membrane-bound organelles; Eukaryotes: true nucleus & organelles.
• Micro-organisms occur everywhere (air, water, soil, bodies). Types: algae, fungi, protozoa, bacteria, viruses.
• Useful microbes: decomposition → manure; sewage treatment; nitrogen fixation (rhizobium in legume nodules); fermentation (curd, bread, idli, vinegar); antibiotics; vaccines; biogas; leather tanning; oil-spill cleanup.
• Harmful microbes: food spoilage (toxins → food poisoning), diseases in humans/plants/animals; vector-borne illnesses (malaria, dengue); material damage (fungus on damp cloth/leather/paper).
• Hygiene & prevention: eat fresh covered food, drink boiled water, cover mouth while coughing/sneezing, avoid stagnant water/garbage (mosquito control), maintain household cleanliness.

Microscopy tip: Start with 10× objective, add a drop of iodine/eosin for onion peel, cover with coverslip to avoid folds and air bubbles.

1. Who coined the term ‘cell’?
   Robert Hooke (1665).
2. Basic unit of life?
   Cell.
3. Cell components that perform specific jobs?
   Organelles.
4. Powerhouse of the cell?
   Mitochondria.
5. Site of photosynthesis in plants?
   Chloroplasts.
6. Outer rigid covering of plant cells?
   Cell wall.
7. Liquid matrix inside cell membrane?
   Cytoplasm.
8. True nucleus present in which cells?
   Eukaryotic cells.
9. Bacteria: prokaryote or eukaryote?
   Prokaryote.
10. Storage sacs inside cells?
    Vacuoles.
11. Cell control centre?
    Nucleus.
12. Protein factories of cells?
    Ribosomes.
13. Packaging & secretion organelle?
    Golgi apparatus/bodies.
14. Cell boundary in all cells?
    Plasma (cell) membrane.
15. $1\\ \\text{mm}$ equals how many micrometres?
    $1000\\ \\mu\\text{m}$.
16. $1\\ \\mu\\text{m}$ equals how many nanometres?
    $1000\\ \\text{nm}$.
17. Organism category visible only via microscope?
    Micro-organisms.
18. Curd formation uses which process?
    Fermentation by microbes.
19. Drugs that kill/restrain bacteria?
    Antibiotics.
20. Preparation that gives disease immunity?
    Vaccine.

1. Define tissue with one example.
   A group of similar cells doing a common function, e.g., xylem tissue.
2. Why do plant cells have a fixed shape?
   Due to the rigid cell wall surrounding the plasma membrane.
3. State two differences between plant & animal cells (names only).
   Cell wall & chloroplast present in plants; a large central vacuole in plants.
4. What is cytoplasm?
   The semifluid matrix between plasma membrane and nucleus containing organelles.
5. Who observed living cells first?
   Antonie van Leeuwenhoek (live bacteria/protozoa).
6. Write exact conversions used in microscopy.
   $1\\ \\text{cm}=10\\ \\text{mm}$; $1\\ \\text{mm}=1000\\ \\mu\\text{m}$; $1\\ \\mu\\text{m}=1000\\ \\text{nm}$.
7. Name two unicellular protozoa.
   Amoeba and Paramoecium.
8. What helps distribute proteins to correct destinations?
   Golgi bodies (sorting/packaging).
9. Why is mitochondrion called powerhouse?
   It generates cellular energy (ATP).
10. Name the microbe in legume root nodules.
    Rhizobium (nitrogen-fixing bacteria).
11. What is fermentation used for in food?
    Curd, idli/dosa batter rising, bread, vinegar, etc.
12. What are pathogens?
    Disease-causing micro-organisms.
13. Name two water/food-borne diseases.
    Typhoid and cholera (also gastro, hepatitis A/E).
14. Why cover mouth while coughing?
    Prevents spread of airborne pathogens.
15. Why do damp clothes grow fungus?
    Moist, humid conditions favour fungal growth.
16. State one benefit of sewage treatment by microbes.
    Decomposes organic waste, reduces pollution.
17. Why should antibiotics be taken only on prescription?
    Misuse can harm and cause resistance; follow full prescribed course.
18. What is a colony of microbes?
    A visible mass/group of many microbes living together.
19. Give one example of useful fungus.
    Yeast (baking/fermentation).
20. Give one vector that spreads diseases.
    Female mosquito (malaria, dengue, etc.).

1. State the cell theory in simple words.
   All living organisms are made of cells; cell is the basic unit of life; new cells arise from pre-existing cells.
2. How does a compound microscope help observe cells?
   It uses lenses to magnify a specimen on a glass slide; stains like iodine/eosin add contrast to see cell parts.
3. Explain why the electron microscope is used.
   To view ultrastructure (very tiny details) of organelles and viruses at very high magnification (up to $2\\times10^{9}$).
4. List four major organelles and their one-line functions.
   Nucleus—control; Mitochondria—energy; Ribosomes—protein synthesis; Golgi—packaging/secretion.
5. Differentiate: Plant vs Animal cell in two points.
   Plants have cell wall & chloroplasts; animals lack both. Plants have a large central vacuole; animals have small vacuoles.
6. Differentiate: Prokaryote vs Eukaryote.
   Prokaryotes have nucleoid & no membrane-bound organelles; eukaryotes have a true nucleus and organelles.
7. How do microbes make manure from garbage?
   They decompose organic waste (kitchen/garden) into nutrient-rich compost/manure.
8. What happens when yoghurt is added to warm milk?
   Lactic acid bacteria multiply and ferment lactose → milk sets into curd within 8–10 hours.
9. Why does bread/idli batter ‘rise’?
   Fermentation produces $\\mathrm{CO_2}$ gas that gets trapped, increasing volume and making the dough light.
10. How do antibiotics help? One caution?
    They kill/stop pathogens; take only with medical advice and complete the full course.
11. What is vaccination? Why follow schedule in infants?
    Giving a vaccine to build immunity; schedules ensure timely protection against multiple diseases.
12. Name two ways microbes help the environment.
    Nitrogen fixation in soils; sewage treatment and biogas production.
13. How does food poisoning occur?
    Microbes in stale/contaminated food release toxins (enterotoxins) causing vomiting/diarrhoea.
14. How do diseases spread through air and water?
    Air: droplets from cough/sneeze; Water: contaminated supplies with pathogens from sewage.
15. Why store leather & paper items dry?
    Moisture promotes fungal growth that spoils/damages these materials.
16. How do rhizobium bacteria help crops?
    They fix atmospheric nitrogen into nitrates in legume root nodules, enriching soil & protein content of pulses.
17. State two cleanliness habits that prevent disease.
    Eat covered fresh food; keep surroundings free of stagnant water/garbage; drink boiled water.
18. Why are viruses studied with electron microscopes?
    Viruses are much smaller than $1\\ \\mu\\text{m}$; require very high magnification/resolution.
19. What is a colony vs a unicellular microbe?
    Colony: group living together (fungal mat); unicellular microbes live singly (Amoeba, Paramoecium).
20. How do microbes survive adverse conditions?
    By forming protective coverings and suspending life processes until conditions improve.