Lecture Notes on Science: Fundamental Unit of Life

Introduction

• Emphasis on making science enjoyable and comprehensible
• Providing explanations for Class 9 chapters via short video sessions, covering every line of the NCERT book
• Encouragement to learn science in a fun and engaging way
• Biology Lecture 1: Fundamental Unit of Life
• Request for feedback and suggestions for next chapter

Preparation Tips

• Download slides and notes from the description or join the Telegram group
• Keep a rough notebook for noting key points during the lecture
• The session will cover previous years’ questions and important points for exams
• Personal introduction: Prashant Kirad, tutor for IIT JEE and senior classes

Fundamental Unit of Life: The Cell

Definition

• Cell is not the same as a battery cell
• All living things – you, me, trees, animals – are made of cells
• Non-living things are made of atoms

Importance of Cells

• Cells are called the Fundamental Unit of Life because all living organisms are composed of cells
• Explanation of how cells combine to form tissues, organs, organ systems, and organisms

Historical Perspective

1. Robert Hooke: Discovered dead cells in cork; coined the term “cell”
2. Antonie van Leeuwenhoek: First observed living cells
3. Robert Brown: Discovered the cell nucleus
4. Purkinje: Introduced the term “protoplasm”
5. Cell Theory: Formulated by Schleiden, Schwann, and Virchow
   • All living organisms are composed of cells
   • The cell is the basic unit of life
   • Cells arise from pre-existing cells

Types of Cells: Prokaryotic vs Eukaryotic

Prokaryotic Cells

• Small in size
• No well-defined nucleus; DNA concentrated in a nucleoid region
• Single chromosome
• Cell organelles like mitochondria, chloroplasts absent
• Example: Bacteria

Eukaryotic Cells

• Larger in size
• Well-defined nucleus with a nuclear membrane
• Multiple chromosomes
• Cell organelles present
• Example: Plant and animal cells

Cell Structure

Outline of Major Cell Components

• Cell Membrane (Plasma Membrane/PM/CM)
  • Functions as a selective barrier, allowing some substances in and out
  • Made of lipids and proteins
  • Types of transport: Passive (diffusion, osmosis) and Active
• Cell Wall (plants only)
  • Made of cellulose
  • Provides rigidity and protection
• Nucleus
  • Surrounded by a nuclear membrane with pores
  • Contains DNA in the form of chromatin or chromosomes
  • Controls cellular functions
• Cytoplasm
  • Jelly-like substance
  • Contains organelles
• Organelles
  1. Mitochondria
     • Powerhouse of the cell; produces energy (ATP)
     • Contains its own DNA and ribosomes
  2. Endoplasmic Reticulum (ER)
     • Rough ER (with ribosomes): Makes proteins
     • Smooth ER (without ribosomes): Makes lipids
  3. Golgi Apparatus
     • Modifies, sorts, and packages proteins and lipids for storage or transport
  4. Lysosomes
     • Contains digestive enzymes; breaks down waste
     • Known as the “suicidal bags” of the cell
  5. Ribosomes
     • Protein factories
     • Present in both prokaryotic and eukaryotic cells
  6. Plastids (plants only)
     • Chloroplasts: Contain chlorophyll for photosynthesis
     • Chromoplasts: Provide color to flowers/fruits
     • Leucoplasts: Store starch
  7. Vacuoles
     • Storage sacs; larger in plants

Types of Solutions - Cells in Different Solutions

• Hypertonic Solution: Higher concentration of solutes outside the cell; cell shrinks (plasmolysis)
• Hypotonic Solution: Lower concentration of solutes outside the cell; cell swells (turgid)
• Isotonic Solution: Equal concentration of solutes; no net movement of water

Cell Division

Mitosis

• Equational division; produces two identical daughter cells
• Used for growth and repair

Meiosis

• Reductional division; produces four genetically varied daughter cells
• Used in the production of gametes (sex cells)

Summary

• Importance of understanding cell structure and function
• Emphasis on practice and reviewing important points
• Encouragement to utilize resources provided and study efficiently.

Motivational Note

• Believe in your potential and capabilities
• Hard work and proper guidance will lead to success