Biology - Chapter 8: Cell – The Unit of Life

Understanding Cell Types, Structure, and Organelles

1. Cell Theory

Cell theory was proposed by Schleiden and Schwann and later modified by Rudolf Virchow.

🔬 Key Principles:

All living organisms are made of one or more cells.
The cell is the basic structural and functional unit of life.
Omnis cellula e cellula → All cells arise from pre-existing cells.

2. Cell Structure Comparison

Feature	Prokaryotic Cell	Eukaryotic Cell
Nucleus	❌ Absent	✅ Present
Ribosomes	70S	80S (Cytoplasm), 70S (Organelles)
Organelles	❌ Absent	✅ Present (Mitochondria, ER, etc.)

💡 Quick Concept: Prokaryotes = Simple (No nucleus) Eukaryotes = Complex (With nucleus)

3. Important Questions & Answers

Q1. Difference between prokaryotic and eukaryotic cells?

Answer: Prokaryotic cells lack a true nucleus and membrane-bound organelles, whereas eukaryotic cells have a well-defined nucleus and organelles.

Q2. What is the Fluid Mosaic Model?

Answer: Proposed by Singer and Nicolson (1972), it describes the plasma membrane as a lipid bilayer with proteins floating like a mosaic. It is semi-permeable.

Fluid Mosaic Model

Q3. Why is mitochondria called the powerhouse of the cell?

Answer: Mitochondria produce energy in the form of ATP during cellular respiration.

Q4. Difference between plant cell and animal cell?

Answer:

Plant cells have cell wall and plastids
Animal cells do not have these structures
Plant cells have large vacuole

Q5. Difference between RER and SER?

Answer:
• RER: Has ribosomes, helps in protein synthesis
• SER: No ribosomes, helps in lipid synthesis

Q6. Why are lysosomes called suicidal bags?

Answer: Because they contain digestive enzymes that can destroy the cell if released.

Q7. Types of chromosomes based on centromere position?

Answer:
• Metacentric
• Submetacentric
• Acrocentric
• Telocentric

Types of Chromosomes

🔥 Exam Booster: Mitochondria = ATP production RER = Protein SER = Lipid Lysosome = Digestion

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