Lecture Notes: Biology Lecture on the Fundamental Unit of Life

Introduction

• Presenter: Samriddhi, Biology mentor and educator at Physics Wala
• Audience: 9th-grade students
• Series: Sprint Series - Lecture 1 on Biology
• Topic: Fundamental Unit of Life
• Objective: Quickly cover core chapters with one-shot learning approach

Basic Concepts

Definition of Cell

• Structural and fundamental unit of life
• Comprises functional aspects of living organisms
• Discovered by Robert Hooke in 1665
• Cells may be single (unicellular) or multiple (multicellular)

Discovery of Cells

• Robert Hooke (1665): First discovered and named 'cell' through a self-designed microscope
• Antonie van Leeuwenhoek (1674): First observed living cells
• Robert Brown (1831): Discovered the nucleus
• Jan Evangelista Purkinje (1839): Introduced the term 'protoplasm'

Cell Theory Expansion

• Matthias Schleiden and Theodor Schwann (1838-39): Formulated the cell theory
  • Schleiden: All plants are composed of cells
  • Schwann: All animals are composed of cells
• Rudolf Virchow: Extended cell theory with the concept 'Omnis cellula e cellula' (All cells arise from pre-existing cells)

Structural Organization in Living Organisms

• Hierarchy: Cell → Tissue → Organ → Organ System → Organism
• Examples: Brain, heart, kidneys, lungs, pancreas, etc.
• Structure: Cells form tissues, tissues form organs, organs form systems

Cell Components

Plasma Membrane (Cell Membrane)

• Outer boundary of the cell
• Semi-permeable and controls the entry/exit of substances
• Made of lipids (phospholipids) and proteins (Fluid Mosaic Model by Singer and Nicolson)
• Processes: Diffusion, Osmosis, Active Transport

Cell Wall

• Found in plant cells, bacteria, and fungi (not in animal cells)
• Provides structure and protection
• Made of cellulose (plants), peptidoglycan (bacteria), and chitin (fungi)

Nucleus

• Control center of the cell
• Contains DNA and is responsible for cell activities
• Components: Nuclear membrane with pores (nuclear envelope), nucleoplasm, chromatin (scattered DNA), chromosomes (condensed DNA during cell division), nucleolus (RNA synthesis)

Cytoplasm

• Jelly-like substance filling the cell
• Site of various cellular activities and contains organelles

Organelles

Endoplasmic Reticulum (ER)

• Network of membranes
• Types: Rough ER (RER) with ribosomes, Smooth ER (SER) without ribosomes
• Functions: Protein synthesis (RER), lipid synthesis (SER), detoxification (SER in liver cells)

Golgi Apparatus

• Stack of membrane-bound sacs (cisternae)
• Processes, sorts, and packages proteins and lipids
• Involved in the formation of lysosomes

Lysosomes

• Contain digestive enzymes
• Also known as 'suicide bags' for their role in autolysis

Vacuoles

• Storage sacs
• Larger in plant cells (up to 90% of cell volume); smaller in animal cells
• Store nutrients, waste products, and help maintain turgor pressure

Mitochondria

• Powerhouse of the cell; site of ATP production through aerobic respiration
• Double-membraned with inner membranes folded into cristae
• Contain their own DNA and ribosomes

Plastids (in plant cells)

• Types: Chloroplasts (photosynthesis), Chromoplasts (pigmentation), Leucoplasts (storage)
• Contain their own DNA and ribosomes

Ribosomes

• Sites of protein synthesis
• Found in both prokaryotic and eukaryotic cells

Types of Cells

Prokaryotic Cells

• Primitive cells without a defined nucleus (e.g., bacteria)
• DNA located in nucleoid region
• Lack membrane-bound organelles, except ribosomes

Eukaryotic Cells

• Complex cells with a well-defined nucleus (e.g., plant and animal cells)
• Contain membrane-bound organelles

Cell Division

Mitosis

• Equatorial division leading to two genetically identical daughter cells
• Chromosome number remains the same
• Occurs in growth and repair of tissues

Meiosis

• Reductional division leading to four genetically unique daughter cells
• Chromosome number is halved
• Used in the formation of gametes (sperm & eggs)

Questions and Practice

1. Explain the role of tonoplasts.
2. Differentiate between slime and plasma.
3. Describe the process of osmosis using examples.
4. Compare and contrast prokaryotic and eukaryotic organisms.

Homework Questions:

• What happens when a dried apricot is immersed in pure water and then in sugar solution?
• Explain the changes in the size and structure of red blood cells in different solutions.
• Discuss the protective role of the plasma membrane.

Reminder: Ensure all important points, tables, and flowcharts discussed in the lecture are noted down for better understanding and revision.