The Fundamental Unit of Life – Short Answer Type Questions
CBSE Class 9 Biology — Chapter 5: The Fundamental Unit of Life
50 topic-wise short-answer questions with clear, exam-focused answers — NCERT-aligned for CBSE Class 9 revision.
History & Microscope (Q1–Q6)
Q1. Who coined the term 'cell' and how did he observe it?
Robert Hooke coined 'cell' in 1665 after observing cork slices under a compound microscope; he saw box-like structures resembling small rooms.
Q2. Name the scientist who first observed living microorganisms.
Anton van Leeuwenhoek observed living microorganisms using simple single-lens microscopes and described 'animalcules'.
Q3. Write the formula for total magnification in a compound microscope.
Total magnification = (objective lens magnification) × (eyepiece magnification). Example: 40× × 10× = 400×.
Q4. What is the correct sequence of using coarse and fine adjustment knobs?
Start with the coarse adjustment knob to bring specimen into approximate focus, then use fine adjustment for sharp focus at higher magnification.
Q5. Give one precaution when placing a cover slip.
Lower the cover slip gently at an angle to avoid trapping air bubbles which obstruct viewing.
Q6. What unit is typically used to measure cells and organelles?
Cells and organelles are measured in micrometres (µm); 1 µm = 10⁻⁶ m.
Cell Theory & Basic Definitions (Q7–Q12)
Q7. State one main point of modern cell theory.
All living organisms are composed of one or more cells; the cell is the basic unit of life.
Q8. Define 'prokaryote' in one sentence.
A prokaryote is a cell lacking a membrane-bound nucleus and membrane-bound organelles (e.g., bacteria).
Q9. Define 'eukaryote' in one sentence.
A eukaryote is a cell with a true nucleus enclosed by a nuclear membrane and membrane-bound organelles (plants, animals).
Q10. What does 'cells arise from pre-existing cells' mean?
It means new cells are formed only by division of existing cells, not spontaneously (Virchow's idea).
Q11. Give typical size ranges for bacterial and plant cells.
Bacterial cells: ~1–5 µm; plant/animal eukaryotic cells: ~10–100 µm.
Q12. What is a tissue?
A tissue is a group of similar cells performing a common function (e.g., muscle tissue, xylem).
Cell Structure — Core Components (Q13–Q18)
Q13. What is the function of the nucleus?
The nucleus stores genetic material (DNA), controls cell activities, and contains nucleolus for ribosome assembly.
Q14. Describe the plasma membrane in one line.
A selectively permeable lipid bilayer with proteins that controls movement of substances into and out of the cell.
Q15. What is cytoplasm?
A jelly-like fluid (cytosol) where organelles are suspended and metabolic reactions occur.
Q16. What are ribosomes and their role?
Ribosomes are small particles (RNA + protein) where proteins are synthesised; they may be free or attached to rough ER.
Q17. Name two differences between plant and animal cells.
Plant cells have cell wall and chloroplasts and a large central vacuole; animal cells have centrioles and lysosomes and no cell wall.
Q18. What is chromatin?
Chromatin is the DNA–protein complex in the nucleus that condenses into chromosomes during cell division.
Endomembrane System & Packaging (Q19–Q24)
Q19. What is the role of rough endoplasmic reticulum (RER)?
RER, studded with ribosomes, assists in synthesis and initial folding of proteins destined for secretion or membranes.
Q20. What function does smooth ER (SER) perform?
SER is involved in lipid synthesis, detoxification and calcium storage; lacks ribosomes.
Q21. State the main function of the Golgi apparatus.
Golgi modifies, sorts and packages proteins and lipids for secretion or delivery to organelles (post office of cell).
Q22. What are vesicles?
Small membrane-bound sacs that transport materials between organelles or to the cell membrane for export.
Q23. Give one example of secretion handled by Golgi.
Secretion of digestive enzymes or hormones packaged into secretory vesicles then exocytosed from the cell.
Q24. What is the function of lysosomes?
Lysosomes contain hydrolytic enzymes for intracellular digestion, recycling worn-out organelles and breaking down pathogens.
Mitochondria & Chloroplasts (Q25–Q30)
Q25. Why are mitochondria called the powerhouse of the cell?
Mitochondria carry out cellular respiration to produce ATP, the cell's energy currency.
Q26. Where does photosynthesis occur in plant cells?
In chloroplasts — mainly in the thylakoid membranes (light reactions) and stroma (Calvin cycle).
Q27. Do mitochondria and chloroplasts contain DNA?
Yes — both contain small circular DNA and their own ribosomes, supporting endosymbiotic origin theory.
Q28. Give one structural difference between mitochondria and chloroplasts.
Mitochondria have inner folded membranes (cristae); chloroplasts have stacked thylakoids (grana) with chlorophyll.
Q29. What is the function of the central vacuole in plant cells?
Stores water, maintains turgor pressure, and stores nutrients and waste products.
Q30. Why are chloroplasts absent in animal cells?
Chloroplasts perform photosynthesis; animals obtain energy by consuming organic matter, so they do not need chloroplasts.
Cell Wall, ECM & Structural Support (Q31–Q36)
Q31. What is the main component of plant cell wall?
Cellulose — a polysaccharide that provides rigidity and support.
Q32. Name one function of extracellular matrix (ECM) in animals.
ECM provides structural support, mediates cell signalling and helps tissue organisation (e.g., collagen fibres).
Q33. How do cell walls help plants?
They provide mechanical strength, protect against pathogens and help maintain shape and turgor.
Q34. What gives cartilage its strength in animals?
Extracellular matrix rich in collagen and proteoglycans provides resilience and tensile strength.
Q35. Are fungal cell walls made of cellulose?
No — fungal cell walls are mainly composed of chitin (not cellulose).
Q36. What is plasmodesmata?
Channels through plant cell walls that connect adjacent cells for transport and communication.
Transport Across Membranes (Q37–Q41)
Q37. Define diffusion with an example.
Diffusion is movement of particles from higher to lower concentration, e.g., oxygen diffusing into cells.
Q38. Define osmosis.
Osmosis is the diffusion of water across a selectively permeable membrane from low solute to high solute concentration.
Q39. What is active transport?
Active transport moves substances against a concentration gradient using energy (ATP), e.g., sodium–potassium pump.
Q40. What happens to a plant cell in a hypertonic solution?
It loses water and undergoes plasmolysis — cell membrane pulls away from the cell wall.
Q41. How does facilitated diffusion differ from simple diffusion?
Facilitated diffusion uses membrane proteins (channels/carriers) to help transport molecules that cannot cross lipid bilayer freely; still energy-independent.
Cell Division & Growth (Q42–Q46)
Q42. Name the type of cell division that produces two identical daughter cells.
Mitosis, followed by cytokinesis, produces two genetically identical daughter cells.
Q43. Give one biological role of mitosis.
Mitosis is used in growth, tissue repair and asexual reproduction in single-celled organisms.
Q44. What is the difference between mitosis and meiosis (one line)?
Mitosis yields two identical diploid cells; meiosis produces four genetically varied haploid gametes (for sexual reproduction).
Q45. What is cytokinesis?
Cytokinesis is the physical division of the cytoplasm that completes cell division after nuclear division.
Q46. Why is controlled cell division important?
Uncontrolled cell division can lead to tumours; controlled division ensures normal growth and repair.
Specialised Cells & Tissues (Q47–Q50)
Q47. Give one feature of red blood cells related to function.
RBCs are biconcave and lack nucleus (in mammals) to increase surface area for efficient oxygen transport and carry haemoglobin.
Q48. What is the function of root hair cells?
Root hair cells increase surface area of roots to absorb water and minerals efficiently from soil.
Q49. Why do muscle cells have many mitochondria?
Muscle cells require large amounts of ATP for contraction, so they contain many mitochondria to meet energy demands.
Q50. Provide two quick tips to draw a good plant/animal cell diagram in exams.
(1) Use clear labels and show major organelles; (2) include magnification/scale if asked and write brief function notes beside labels.
Note: These short-answer Q&As are strictly aligned with NCERT Class 9 Biology Chapter 5 (The Fundamental Unit of Life). Use them for quick revision, flashcards, and timed practice. If you want this file exported as a printable PDF, collapsible Q&A, or converted into an interactive quiz, tell me which format and I'll generate it.