Science · Class 9
The Fundamental Unit of Life
Cell organelles, plasma membrane, and prokaryotic vs eukaryotic cells.
4 sections15–25 min read6 MCQs · 2 examples
Chapter Overview
The cell is the structural and functional unit of life. This chapter covers cell theory, prokaryotic vs eukaryotic cells, plant vs animal cells, and detailed structure of plasma membrane, nucleus, cytoplasm, and cell organelles.
Cell Theory
- All living organisms are composed of cells
- Cell is the basic unit of structure and function
- All cells arise from pre-existing cells (Rudolf Virchow)
Cell Organelles
- Nucleus: controls activities; contains DNA
- Mitochondria: powerhouse — aerobic respiration, ATP
- ER: rough (ribosomes) synthesises proteins; smooth makes lipids
- Golgi: packaging and dispatch of materials
- Lysosomes: suicide bags — digestive enzymes
- Plastids (chloroplast): photosynthesis in plants
- Vacuole: large in plant cells — turgor pressure
Plasma Membrane
- Selectively permeable
- Osmosis: water movement across semipermeable membrane
- Hypotonic → swelling; hypertonic → shrinkage (plasmolysis)
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Plant vs animal cell
List two structures in plant cell not in animal cell.
- 1Cell wall (cellulose)
- 2Large central vacuole
- 3Plastids/chloroplasts
Answer
Cell wall, chloroplasts, large vacuole
Osmosis
RBC placed in distilled water — what happens?
- 1Distilled water is hypotonic
- 2Water enters cell by osmosis
- 3Cell swells and may burst (haemolysis)
Answer
Cell swells — endosmosis
Key Points to Remember
- ✓ Prokaryotes lack membrane-bound nucleus (bacteria)
- ✓ Eukaryotes have organised nucleus and organelles
- ✓ Cell wall in plants provides rigidity
Exam Tips
- • Draw labelled diagrams of plant and animal cell
- • Know functions of each organelle
- • Link osmosis to real examples (pickling, salting)
Practice MCQs — The Fundamental Unit of Life
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 6Score: 0/0
Powerhouse of the cell is: