Looking for reliable SEBA Class 9 Science Chapter 5 (The Fundamental Unit of Life) extra questions and answers for the 2026–27 academic year? Access essential additional practice questions, organelle comparison charts, osmosis vs diffusion notes, cell division differences (mitosis vs meiosis), and high-yield exam questions designed to help you score top marks in your annual exams.
1. Who discovered cells and how?
Ans. Cells were discovered by Robert Hooke in 1665 when he observed a thin slice of cork under his self-designed primitive microscope.
2. What are cells?
Ans. Cells are the fundamental structural and functional units of life that perform all essential biological activities necessary for the survival of living organisms.
3. Define unicellular organisms.
Ans. Unicellular organisms are single-celled living beings in which a single cell independently carries out all vital life processes.
4. Give two examples of unicellular organisms.
Ans. Amoeba and Paramecium are two standard examples of unicellular organisms.
5. Define multicellular organisms.
Ans. Multicellular organisms are complex living beings composed of numerous cells that undergo division of labor to perform specialized functions.
SEBA Class 9 Science Chapter 5 Extra Questions
6. Who proposed the cell theory?
Ans. The classical cell theory was jointly formulated and proposed by Matthias Schleiden and Theodor Schwann.
7. What did Virchow state?
Ans. Rudolf Virchow expanded the cell theory by stating that all living cells arise exclusively from pre-existing cells.
8. What is the function of a cell membrane?
Ans. The cell membrane acts as a protective barrier around the cell and selectively regulates the movement of substances entering and leaving the cytoplasm.
9. What is diffusion?
Ans. Diffusion is the passive movement of substance molecules from a region of higher concentration to a region of lower concentration until uniform distribution is achieved.
10. What is osmosis?
Ans. Osmosis is the passive movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.
Class 9 Science Chapter 5 Important Questions SEBA 2026-27
11. Define nucleus.
Ans. The nucleus is a specialized double-membrane-bound organelle that contains genetic material and functions as the primary control center of cellular activities.
12. What are chromosomes?
Ans. Chromosomes are rod-like structures composed of DNA and proteins that carry genes responsible for transmitting hereditary information from parents to offspring.
13. What is cytoplasm?
Ans. Cytoplasm is the semi-fluid jelly-like matrix located between the plasma membrane and the nucleus in which all cellular organelles are suspended.
14. What are prokaryotes?
Ans. Prokaryotes are primitive single-celled organisms whose cellular structure lacks a defined nucleus enclosed by a nuclear membrane as well as membrane-bound organelles.
15. What are eukaryotes?
Ans. Eukaryotes are complex organisms whose cells possess a well-defined nucleus enclosed by a nuclear envelope along with membrane-bound organelles.
16. Name the two types of Endoplasmic Reticulum.
Ans. The two functional types of Endoplasmic Reticulum present inside the cell are Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER).
17. Why is Rough ER called ‘rough’?
Ans. Rough Endoplasmic Reticulum is designated as ‘rough’ because its outer surface is studded with numerous protein-synthesizing particles called ribosomes.
18. What is the main function of mitochondria?
Ans. The primary function of mitochondria is to generate usable chemical energy in the form of Adenosine Triphosphate (ATP) molecules through aerobic cellular respiration.
19. What is plasmolysis?
Ans. Plasmolysis is the phenomenon in which the protoplast of a plant cell shrinks away from its cell wall due to the hypertonic loss of water through exosmosis.
20. What is a cell wall?
Ans. A cell wall is a rigid, non-living outer protective layer composed of cellulose that surrounds the plasma membrane in plant cells to provide structural support, rigidity, and shape.
The Fundamental Unit of Life Class 9 SEBA Extra Question Answer
21. Differentiate between unicellular and multicellular organisms.
Ans. The key differences between unicellular and multicellular organisms are:
| Unicellular Organisms | Multicellular Organisms |
| Composed of a single cell that independently performs all vital life functions. | Composed of many specialized cells that divide labor to carry out functions. |
| Division of labor is absent at the cellular level. | Division of labor is present among specialized tissues and organs. |
| Examples include Amoeba, Paramecium, and bacteria. | Examples include plants, animals, and human beings. |
22. Explain the importance of the invention of the microscope.
Ans. The invention of the microscope allowed scientists to observe microscopic cells and single-celled organisms that are invisible to the naked human eye, ultimately establishing the field of cell biology and leading to the discovery of cellular structures.
23. State the main postulates of cell theory.
Ans. The three main postulates of cell theory state that:
- All living organisms are composed of one or more cells.
- The cell is the fundamental structural and functional unit of life.
- All living cells arise exclusively from pre-existing cells through cell division.
24. Why is the plasma membrane called selectively permeable?
Ans. The plasma membrane is termed selectively permeable because it regulates cellular entry and exit by allowing only specific substances to cross while restricting the passage of others.
25. What happens to a cell in a hypotonic solution?
Ans. When placed in a hypotonic solution, water moves into the cell across the plasma membrane via endosmosis, causing the cell to swell and gain volume.
26. What happens to a cell in a hypertonic solution?
Ans. When placed in a hypertonic solution, water exits the cell across the plasma membrane via exosmosis, causing the cell cytoplasm to shrink.
27. Define active transport with an example.
Ans. Active transport is the cellular process of moving molecules or ions across a membrane against their concentration gradient, which requires the expenditure of chemical energy in the form of ATP. An example is the active uptake of mineral ions from the soil by plant root hair cells.
28. Differentiate between prokaryotic and eukaryotic cells.
Ans. The key structural differences between prokaryotic and eukaryotic cells are:
| Prokaryotic Cell | Eukaryotic Cell |
| Lacks a defined nuclear membrane surrounding its genetic material (nucleoid). | Possesses a well-defined nucleus enclosed by a double nuclear membrane. |
| Membrane-bound organelles such as mitochondria and Golgi apparatus are absent. | Membrane-bound organelles are present throughout the cytoplasm. |
| Contains a single, circular chromosome. | Contains multiple, linear chromosomes. |
| Examples include bacteria and cyanobacteria. | Examples include plant cells, animal cells, and fungi. |
29. Describe the structure of the nucleus.
Ans. The nucleus is surrounded by a double-layered nuclear envelope containing nuclear pores that regulate transport; inside, it holds nucleoplasm, a dense region called the nucleolus, and chromatin material containing genetic instructions.
30. What is chromatin?
Ans. Chromatin is an uncoiled, thread-like network composed of DNA and histone proteins dispersed inside the nucleoplasm of a non-dividing cell.
SEBA Class 9 Science Chapter 5 Practice Notes
31. State any two functions of cytoplasm.
Ans. The cytoplasm acts as the structural matrix that supports and suspends cell organelles, while also serving as the primary site for metabolic chemical reactions within the cell.
32. Why are ribosomes important?
Ans. Ribosomes are essential cellular organelles because they act as the sites of protein synthesis, assembling amino acids into functional proteins required for cellular growth and enzymatic activities.
33. What is the function of the Golgi apparatus?
Ans. The Golgi apparatus functions in modifying, sorting, packaging, and dispatching cellular products—such as proteins and lipids—synthesised in the endoplasmic reticulum to their target destinations inside or outside the cell.
34. What are lysosomes and why are they called suicidal bags?
Ans. Lysosomes are single-membrane-bound organelles containing powerful hydrolytic digestive enzymes; they are called “suicidal bags” because if the cell gets severely damaged or undergoes metabolic failure, the lysosomes may burst and release enzymes that digest their own host cell.
35. Mention any two differences between plant and animal cells.
Ans. Two primary differences between plant and animal cells are:
| Plant Cell | Animal Cell |
| Contains a rigid outer cell wall composed of cellulose. | Lacks a cell wall entirely. |
| Contains plastids, such as chloroplasts for photosynthesis. | Lacks plastids. |
36. What is endocytosis? Give an example.
Ans. Endocytosis is the process by which a cell engulfs external food or liquid particles by folding its flexible plasma membrane inward to form a vesicle. An example is an Amoeba extending pseudopodia to capture food particles from its aquatic surroundings.
37. Why do we use stains like iodine in slide preparations?
Ans. Stains like iodine are applied during microscopic slide preparation to selectively color specific cellular components, enhancing optical contrast and making organelles visually distinguishable under a light microscope.
38. Explain the function of Smooth ER.
Ans. The Smooth Endoplasmic Reticulum (SER) synthesises lipid molecules and phospholipids essential for cell membrane biogenesis, while also assisting in the detoxification of metabolic byproducts, drugs, and poisons within liver cells.
39. Give two functions of mitochondria.
Ans. Mitochondria perform cellular respiration to generate usable chemical energy in the form of ATP molecules, and they help regulate metabolic cellular pathways using their own independent DNA and ribosomes.
40. What is the function of the cell wall in plants?
Ans. The plant cell wall provides structural support, rigidity, and shape to the cell while exerting turgor pressure to prevent the plant cell from bursting when taking in water under hypotonic conditions.
Class 9 Science Cell Structure Important Questions
🔬 Updated Extra Questions Guide Notice: This page features an extensive collection of SEBA Class 9 Science Chapter 5 (The Fundamental Unit of Life) Extra Questions and Detailed Answers updated for the 2026–27 academic session. All cell biology concepts, diagrammatic explanations, organelle functions, and cell division processes strictly follow the latest revised Assam Board (SEBA) curriculum.
💡 Master Class 9 Science Concepts:
- Having trouble understanding membrane biogenesis, why mitochondria are called powerhouses of the cell, or how plasmolysis occurs in Chapter 5? Drop your questions in the comments section below!
- Save and bookmark this guide for fast biology revision before your unit tests, mid-term, and annual examinations.
- Share this link with your classmates and WhatsApp study groups to help everyone excel!