📌Definition Table

Term	Definition
Resolution	The ability of a microscope to distinguish two points as separate.
Magnification	The process of enlarging an image compared to the actual size of the specimen.
Gram Staining	A method to classify bacteria based on cell wall composition.
Light Microscope (LM)	Microscope that uses visible light to magnify images, suitable for living specimens.
Electron Microscope (EM)	Uses electron beams for much higher resolution images, requires dead specimens.

📌Introduction

Comparing prokaryotic and eukaryotic cells reveals key differences in complexity, structure, and evolutionary history. Prokaryotes are smaller, lack membrane-bound organelles, and have circular DNA, while eukaryotes are larger, contain multiple organelles, and have linear chromosomes within a nucleus. These differences are closely linked to their functions, reproductive methods, and ecological roles. Microscopy — from simple light microscopes to advanced electron microscopes — has been the key tool in uncovering these distinctions, enabling scientists to study cell ultrastructure in detail and validate theories such as endosymbiosis.

📌 Prokaryotic vs Eukaryotic Differences

• Size: Prokaryotic cells are typically 0.1–5 μm; eukaryotic cells are 10–100 μm.
• DNA: Prokaryotes have a single circular chromosome in a nucleoid; eukaryotes have multiple linear chromosomes in a nucleus.
• Ribosomes: Prokaryotic ribosomes are 70S; eukaryotic cytoplasmic ribosomes are 80S.
• Organelles: Prokaryotes lack membrane-bound organelles; eukaryotes have many specialised ones.
• Reproduction: Prokaryotes divide by binary fission; eukaryotes divide by mitosis or meiosis.
• Cell wall: Present in most prokaryotes (peptidoglycan in bacteria) and some eukaryotes (cellulose in plants, chitin in fungi).

🧠 Examiner Tip: IB questions often award marks for correct, concise comparison tables of prokaryotic vs eukaryotic structures — memorise at least three clear differences.

📌 Light Microscopy

• Uses visible light to illuminate the specimen.
• Magnification up to ~1000× with resolution of ~200 nm.
• Suitable for living specimens, stained slides, and dynamic processes.
• Common stains: methylene blue, iodine, crystal violet.
• Inexpensive and accessible for most labs.
• Limited in resolving very small structures like ribosomes.

🧬 IA Tips & Guidance: Light microscopes are excellent for IA work — choose appropriate stains and measure field of view to calculate actual specimen size.

📌 Electron Microscopy

• Transmission Electron Microscope (TEM) passes electrons through the specimen for internal details at ~0.1 nm resolution.
• Scanning Electron Microscope (SEM) scans specimen surface to produce 3D images.
• Requires specimens to be fixed, dehydrated, and coated in metals (gold, platinum).
• Cannot be used on living specimens.
• Essential for viewing organelles like mitochondria, ER, and ribosomes in detail.
• More costly and requires specialised training.

🌐 EE Focus: An EE could investigate how resolution differences between light and electron microscopy influence the discovery of cellular structures.

📌 Fluorescence and Confocal Microscopy

• Uses fluorescent dyes or proteins (e.g., GFP) to highlight specific cell components.
• Confocal microscopy uses laser scanning to produce sharp, 3D reconstructions.
• Allows visualisation of dynamic processes in living cells.
• Common in molecular biology and medical research.
• Can be combined with electron microscopy for correlative studies.
• Offers greater specificity than traditional staining methods.

❤️ CAS Link: A CAS project could involve creating microscopy workshops for younger students, showing how to prepare slides and interpret images.

📌 Importance of Microscopy in Cell Theory

• Discovery of cells in the 17th century relied on light microscopy.
• Electron microscopy in the 20th century revealed organelles and ultrastructure.
• Led to the formulation and refinement of cell theory.
• Validated endosymbiotic theory by showing bacterial-like features in mitochondria/chloroplasts.
• Continues to drive research in cell biology, microbiology, and nanotechnology.
• Demonstrates how technology influences scientific progress.

🔍 TOK Perspective: Microscopy shows how technological limitations shape what we can know — improvements often lead to paradigm shifts in biology.

📝 Paper 2:
Be prepared to compare prokaryotic and eukaryotic cells in a table, draw labelled diagrams, and explain the advantages and limitations of light vs electron microscopy.