Resolution and the Microscopic World
Light Microscopy (LM)
- Resolution Limit: ~200 nm
- Constraint: Light wavelength
Electron Microscopy (EM)
- Resolution Limit: ~0.1 nm
- Constraint: Electron wavelength
- Precision: Cellular Ultrastructure
- Reveals compartmentalization and fine organelle detail
- Visible: Ribosomes, Lysosomes, and ER architecture
Comparative Ultrastructure: Plant vs. Animal Cells
Animal cell (stained, ×1100) – 10 μm
plasma membrane | cytoplasm | mitochondrion | vesicle | nucleus | nuclear envelope | chromatin | nucleolus | glycogen granules
Moss leaf cell (×450)
vacuole | plasma membrane | cell wall | tonoplast | chloroplast | nucleus | nuclear envelope | cytoplasm | cell wall of adjacent cell
Ultrastructural Markers: Plantae
- Chloroplasts: Photosynthetic site
- Large Vacuole: Osmotic turgidity
- Storage: Carbohydrate as Starch
Ultrastructural Markers: Animalia
- Centrioles: Spindle assembly
- Cholesterol: Membrane fluidity
- Storage: Carbohydrate as Glycogen
Cellular Ultrastructure: Comparative Summary
| Organelle | Prokaryote | Animal Cell | Plant Cell |
|---|---|---|---|
| Nucleus | Nucleoid only | Present | Present |
| Mitochondria | Absent | Present | Present |
| Ribosomes | 70S | 80S | 80S |
| Cell Wall | Peptidoglycan | Absent | Cellulose |
Nature of Science
Micrograph interpretation is limited by:
- Staining artifacts
- 2D sectioning of 3D structures
Academic Review Objectives
- Evaluate factors influencing vacuole visibility across cell types.
- Analyze mitochondrial morphology variations due to sectioning angles.
Eukaryotic Compartmentalization
- Localized chemical environments
- Enhanced metabolic efficiency
Eukaryotic cells significantly exceed prokaryotic size limits due to surface area-to-volume efficiency.
The Nucleus
- Double-membrane nuclear envelope
- Pores for selective molecular traffic
- Nucleolus: Ribosome biogenesis
Chromatin Structure
DNA associated with histone proteins
Cellular Ultrastructure: Energy & Waste
Mitochondria
- ATP synthesis site
- Cristae maximize surface area
- Contains 70S ribosomes and DNA
Lysosomes
- Hydrolytic enzyme compartments
- Breakdown of metabolic waste
Ultrastructure: The Endomembrane System
- Rough ER: Protein synthesis mediated by membrane-bound 80S ribosomes.
- Smooth ER: Biosynthesis of lipids and essential metabolic detoxification.
- Golgi Apparatus: Post-translational modification, sorting, and packaging.
- Vesicles: Coordinated transport between compartmentalized organelles.
Functional Pathway: rER → Transport Vesicle → Golgi → Secretory Vesicle
Note: Compartmentalization is essential for specialized metabolic efficiency.
Prokaryotic Cell Architecture
- Peptidoglycan Cell Wall: structural integrity & osmotic protection
- Nucleoid Region: naked genophore DNA; no histones / nuclear envelope
- 70S Ribosomes: protein synthesis
- External Appendages: Pili (adhesion), Flagella (locomotion)
- Plasmids: small circular DNA; often antibiotic resistance
- IBDP Biology | Aligned with IBDP Biology syllabus
Ultrastructural analysis of Escherichia coli bacterium
Learn More about 1 Cell biology – 1.2 Ultrastructure of cells ,
Original IB DP Lessons
