Class 11 Biology Chapter 8: Cell - The Unit of Life
Complete Study Notes for Average Students
📚 Chapter Overview
This chapter is fundamental to understanding biology as it deals with cells - the basic structural
and functional units of all living organisms. This chapter carries 15 marks weightage in CBSE
exams, making it extremely important for your preparation.
🎯 Learning Objectives
By the end of this chapter, you should be able to:
Understand cell theory and its postulates
Differentiate between prokaryotic and eukaryotic cells
Identify various cell organelles and their functions
Compare plant and animal cells
Understand plasma membrane structure and functions
📖 1. Discovery of Cell and Cell Theory
Historical Timeline
1665: Robert Hooke - First used the term "cell" while observing cork under microscope
1674: Anton van Leeuwenhoek - First to observe living cells (bacteria, protozoa)
1833: Robert Brown - Discovered nucleus in plant cells
1838: Matthias Schleiden - Proposed that all plants are made of cells
1839: Theodor Schwann - Extended cell theory to animals
1855: Rudolf Virchow - Added "Omnis cellula-e-cellula" (all cells arise from pre-existing
cells)
Cell Theory Postulates ⭐ EXAM IMPORTANT
1. All living organisms are composed of one or more cells
2. Cell is the basic structural and functional unit of life
3. All cells arise from pre-existing cells
Memory Trick: All organisms are Cells, Cell is Basic unit, Cells from Pre-existing cells = ACCBCP
, 🦠 2. Types of Cells
A. Prokaryotic Cells
Definition: Cells that lack a well-defined nucleus and membrane-bound organelles.
Characteristics:
No true nucleus - genetic material freely floating in cytoplasm (nucleoid region)
No membrane-bound organelles
Small size (1-5 μm)
Circular DNA
70S ribosomes
Cell division by binary fission
Examples: Bacteria, Archaea
Structure:
Cell wall (peptidoglycan in bacteria)
Plasma membrane
Cytoplasm
Nucleoid (genetic area)
Ribosomes
Plasmids (extra DNA)
Flagella (for movement)
Pili (for attachment)
B. Eukaryotic Cells
Definition: Cells with a well-defined nucleus enclosed by nuclear membrane and contain
membrane-bound organelles.
Characteristics:
True nucleus with nuclear envelope
Membrane-bound organelles
Larger size (10-100 μm)
Linear DNA
80S ribosomes
Cell division by mitosis/meiosis
Complete Study Notes for Average Students
📚 Chapter Overview
This chapter is fundamental to understanding biology as it deals with cells - the basic structural
and functional units of all living organisms. This chapter carries 15 marks weightage in CBSE
exams, making it extremely important for your preparation.
🎯 Learning Objectives
By the end of this chapter, you should be able to:
Understand cell theory and its postulates
Differentiate between prokaryotic and eukaryotic cells
Identify various cell organelles and their functions
Compare plant and animal cells
Understand plasma membrane structure and functions
📖 1. Discovery of Cell and Cell Theory
Historical Timeline
1665: Robert Hooke - First used the term "cell" while observing cork under microscope
1674: Anton van Leeuwenhoek - First to observe living cells (bacteria, protozoa)
1833: Robert Brown - Discovered nucleus in plant cells
1838: Matthias Schleiden - Proposed that all plants are made of cells
1839: Theodor Schwann - Extended cell theory to animals
1855: Rudolf Virchow - Added "Omnis cellula-e-cellula" (all cells arise from pre-existing
cells)
Cell Theory Postulates ⭐ EXAM IMPORTANT
1. All living organisms are composed of one or more cells
2. Cell is the basic structural and functional unit of life
3. All cells arise from pre-existing cells
Memory Trick: All organisms are Cells, Cell is Basic unit, Cells from Pre-existing cells = ACCBCP
, 🦠 2. Types of Cells
A. Prokaryotic Cells
Definition: Cells that lack a well-defined nucleus and membrane-bound organelles.
Characteristics:
No true nucleus - genetic material freely floating in cytoplasm (nucleoid region)
No membrane-bound organelles
Small size (1-5 μm)
Circular DNA
70S ribosomes
Cell division by binary fission
Examples: Bacteria, Archaea
Structure:
Cell wall (peptidoglycan in bacteria)
Plasma membrane
Cytoplasm
Nucleoid (genetic area)
Ribosomes
Plasmids (extra DNA)
Flagella (for movement)
Pili (for attachment)
B. Eukaryotic Cells
Definition: Cells with a well-defined nucleus enclosed by nuclear membrane and contain
membrane-bound organelles.
Characteristics:
True nucleus with nuclear envelope
Membrane-bound organelles
Larger size (10-100 μm)
Linear DNA
80S ribosomes
Cell division by mitosis/meiosis
