# 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.

1.9 Prokaryotic And Eukaryotic Cells | Cells And Sub Cellular Organelles | Biology 11