Questions
5–7 questions per paper
Difficulty
Medium
Importance
Core foundation — never skip
Overview
The cell is the fundamental structural and functional unit of life, serving as the biological bedrock for all living organisms. Mastering this topic is essential for understanding advanced physiology and biotechnology, and it frequently features in board exams through comparative analysis questions.
Prokaryotic vs Eukaryotic Cells
The core distinction lies in the organization of the genetic material and the presence of membrane-bound organelles. Prokaryotes lack a defined nucleus and membrane-bound organelles, while eukaryotes contain compartmentalized structures that allow for complex cellular processes.
- Prokaryotes contain 70S ribosomes
- Eukaryotes contain 80S ribosomes in the cytoplasm
- Prokaryotic DNA is circular and naked
- Eukaryotic DNA is linear and associated with histones
- Mesosomes are characteristic of prokaryotic plasma membrane invaginations
Cell Membrane Structure
The Fluid Mosaic Model, proposed by Singer and Nicolson, best explains the architecture of the cell membrane. It describes the membrane as a lipid bilayer embedded with integral and peripheral proteins that provide flexibility and selectivity to the cell.
- Fluid Mosaic Model: Singer and Nicolson (1972)
- Phospholipids possess hydrophilic heads and hydrophobic tails
- Passive transport moves molecules along concentration gradient
- Active transport requires ATP against concentration gradient
- Plasma membrane is selectively permeable
Cell Organelles and Functions
Organelles are specialized subunits within a cell that perform specific tasks to maintain homeostasis. Exam questions often require linking the structure of these organelles to their specific metabolic functions, such as protein synthesis or energy production.
- Mitochondria: Powerhouse, site of aerobic respiration
- Lysosomes: Suicidal bags containing hydrolytic enzymes
- Golgi Apparatus: Packaging and secreting center
- Rough ER: Protein synthesis due to ribosome presence
- Smooth ER: Lipid and steroid synthesis
Formula Sheet
Fluid Mosaic Model (Singer & Nicolson)
Exam Tip
Always draw a neat, labeled diagram for organelles like mitochondria or chloroplasts, as they are high-scoring 'visual' questions in biology boards.
Common Mistakes
- Confusing the function of smooth vs rough endoplasmic reticulum
- Overlooking the presence of 70S ribosomes in eukaryotic mitochondria and chloroplasts
- Failing to distinguish between diffusion and active transport mechanisms in membrane models
More Revision Notes
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