📌Definition Table

Term	Definition
Prokaryote	Single-celled organism lacking a membrane-bound nucleus and organelles. Includes Bacteria and Archaea.
Plasmid	Small, circular DNA molecule separate from chromosomal DNA, often carrying extra genes like antibiotic resistance.
Nucleoid	Region in a prokaryotic cell where the circular DNA is located, not enclosed by a membrane.
Pilus (pili)	Hair-like appendages on prokaryotes used for attachment or DNA transfer during conjugation.
Binary Fission	Asexual reproduction process in prokaryotes where the cell divides into two identical cells.

📌Introduction

Prokaryotic cells are the most ancient and structurally simple forms of life, appearing on Earth over 3.5 billion years ago. They lack a true nucleus and membrane-bound organelles, yet they perform all essential life functions such as metabolism, growth, and reproduction. Their compact and efficient structure allows them to thrive in diverse environments, from deep-sea vents to the human gut. Understanding prokaryotic cell structure is key to microbiology, biotechnology, and medicine, as many prokaryotes are either beneficial (e.g., nitrogen-fixing bacteria) or harmful (pathogens).

📌 Structure of Prokaryotic Cells

• Cell wall composed of peptidoglycan (in Bacteria) or other polymers (in Archaea), providing shape and protection.
• Plasma membrane controls movement of substances in and out of the cell.
• Nucleoid contains a single, circular DNA molecule, the main genetic material.
• Plasmids carry extra genes, often conferring survival advantages.
• Ribosomes (70S) are the sites of protein synthesis.
• Flagella enable motility, powered by a rotary motor mechanism.
• Pili and fimbriae assist in attachment to surfaces and in conjugation.

🧠 Examiner Tip: Always specify 70S ribosomes when describing prokaryotic cells in IB exams, as it’s a common marking point.

📌 Reproduction & Gene Transfer

• Prokaryotes reproduce asexually via binary fission, producing genetically identical cells.
• DNA is replicated starting at a single origin of replication before cell division.
• Conjugation allows DNA transfer between prokaryotes via pili.
• Transformation occurs when prokaryotes absorb foreign DNA from the environment.
• Transduction uses viruses (bacteriophages) to transfer genetic material between cells.
• These methods contribute to rapid adaptation and evolution in bacterial populations.

🧬 IA Tips & Guidance: For a lab investigation, bacterial growth curves can be measured under different environmental conditions, linking cell structure to survival.

📌 Specialized Structures in Some Prokaryotes

• Capsule: protective layer preventing desiccation and aiding immune evasion.
• Endospores: dormant, resistant structures for surviving extreme conditions.
• Thylakoid membranes in cyanobacteria for photosynthesis.
• Magnetosomes for orientation in magnetic fields.
• Gas vesicles for buoyancy control in aquatic environments.
• Plasma membrane infoldings to increase surface area for metabolic processes.

🌐 EE Focus: An EE could explore structural adaptations of extremophile prokaryotes and how these allow survival in extreme environments.

📌 Functions of Prokaryotic Cells

• Maintain homeostasis through selective permeability of the plasma membrane.
• Perform metabolism, including respiration, fermentation, and photosynthesis (in some species).
• Protect against environmental stress through cell wall and capsule formation.
• Engage in symbiotic relationships (e.g., gut microbiota in humans).
• Adapt rapidly to environmental change via high mutation rates and horizontal gene transfer.
• Act as decomposers, nitrogen fixers, and producers in ecosystems.

❤️ CAS Link: A CAS project could involve creating public awareness materials on antibiotic resistance, linking bacterial gene transfer to public health.

📌 Microscopy in Prokaryotic Studies

• Light microscopes allow observation of general shape and arrangement of cells.
• Electron microscopes reveal internal details, such as ribosomes and nucleoid structure.
• Staining techniques (Gram staining) differentiate bacterial cell wall types.
• Fluorescence microscopy can highlight specific proteins or DNA sequences.
• Time-lapse microscopy can show binary fission in real time.
• Microscopy is essential for taxonomy, pathology, and research into cell function.

🔍 TOK Perspective: Our understanding of prokaryotic cells depends heavily on technological advancements in microscopy — without these tools, much of modern microbiology would not exist.

📝 Paper 2: Be ready to draw and label a prokaryotic cell, distinguish between Bacteria and Archaea, and describe binary fission and horizontal gene transfer mechanisms.