# 1.9 Prokaryotic and Eukaryotic Cells Two primary types of structurally different cells have evolved: **prokaryotic cells** and **eukaryotic cells**. Prokaryotic cells include organisms like *archaea*, *bacteria*, and *cyanobacteria*, while all other forms of life (plants, animals, fungi, protists) are composed of eukaryotic cells. --- ### Comparison of Prokaryotic and Eukaryotic Cells | Feature | Prokaryotic Cells | Eukaryotic Cells | | :--- | :--- | :--- | | **Nucleus & Organelles** | A true nucleus and other membrane-bound organelles are **absent**. | A true nucleus and other membrane-bound organelles (e.g., mitochondria, ER) are **present**. | | **Organism Complexity** | Always **unicellular**. | Can be **unicellular** or **multicellular**. | | **Genetic Material (DNA)** | DNA is located in the cytoplasm in a region called the nucleoid. It consists of one primary **circular chromosome** and may have smaller DNA rings called **plasmids**. | DNA is stored within the membrane-bound **nucleus**. It is organized into multiple, linear, **double-stranded chromosomes**. | | **Ribosomes** | Ribosomes are **70S** in size, composed of 30S and 50S subunits. | Ribosomes are larger, **80S** in size, composed of 40S and 60S subunits. | | **Locomotive Structures** | If present, structures like flagella are composed of repeated **flagellin** protein, a hook, and a motor complex. | If present, structures like cilia and flagella are more complex, composed of microtubules in a '9+2' arrangement, **dynein** motor proteins, and are covered by the plasma membrane. | | **Cell Division** | Divide by a simpler process called **binary fission**. | Divide by more complex processes: **mitosis** (for growth and repair) and **meiosis** (for sexual reproduction). | --- ### Summary Table | Feature | Prokaryotes | Eukaryotes | | :--- | :--- | :--- | | **Nucleus** | Absent | Present | | **Organelles** | Absent (membrane-bound) | Present (membrane-bound) | | **DNA Form** | Circular chromosome + plasmids | Linear chromosomes | | **Ribosome Size** | 70S | 80S | | **Division** | Binary Fission | Mitosis & Meiosis | **Biological Significance:** The prokaryotic/eukaryotic distinction is a fundamental division in biology, forming the basis for the classification of life into Domains (Bacteria, Archaea, and Eukarya). This structural difference dictates the complexity and functional capabilities of an organism.