Understanding the difference between prokaryotic and eukaryotic cells is key to mastering biology basics and is often a popular topic in competitive exams. These two cell types form the foundation of all life, from simple bacteria to complex organisms like humans. While prokaryotic cells represent the simpler, primitive structures of life, eukaryotic cells make up the more advanced and organized forms of life. Knowing their unique characteristics, functions, and how they differ is essential for exam success and a deeper grasp of biological sciences.
Cell-Introduction
- Biotic parts of the environment include all living things, from tiny bacteria to tall Sequoia trees. But at the smallest level, all living things comprise the same basic building block – the cell.
- The cell is called the structural and functional unit of all living things. The word “cell” comes from Latin, meaning “small room,” it was first discovered by Robert Hooke, an English scientist, in 1665.
- He compared the cells he saw to honeycomb cells because they looked similar in structure.
Prokaryotic and Eukaryotic Cells
- Advancements in science and technology have helped us understand cells better, revealing more about their structure and parts.
- In the 1950s, scientists introduced the concepts of prokaryotic and eukaryotic cells, building on early work by French biologist Edouard Chatton in 1925.
- Cells differ greatly in structure based on their classification, so prokaryotic and eukaryotic cells have many unique characteristics. Read on to discover what sets these two types of cells apart.
Difference between Prokaryotic and Eukaryotic Cells
Even though these two types of cells are quite different, they do share a few things. For example, both have cell membranes and ribosomes. But that’s about where the similarities stop. Here’s a simple list of differences between prokaryotic and eukaryotic cells:
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Type of Cell | Always unicellular | Can be unicellular or multicellular |
| Cell Size | 0.2 μm – 2.0 μm in diameter | 10 μm – 100 μm in diameter |
| Cell Wall | Usually present; chemically complex | Present in plants and fungi; chemically simpler |
| Nucleus | Absent; DNA in nucleoid region | True nucleus with a nuclear membrane |
| Ribosomes | Present; smaller in size (70S) and spherical | Present; larger in size (80S) and linear |
| DNA Arrangement | Circular DNA | Linear DNA organized into chromosomes |
| Mitochondria | Absent | Present |
| Cytoplasm | Present, but lacks membrane-bound organelles | Present with various membrane-bound organelles |
| Endoplasmic Reticulum | Absent | Present |
| Plasmids | Commonly found | Rarely found |
| Lysosomes & Centrosomes | Absent | Usually present |
| Cell Division | Binary fission | Mitosis (for growth) or meiosis (for reproduction) |
| Flagella | Smaller, simpler structure | Larger and more complex structure |
| Reproduction | Asexual | Both asexual and sexual |
| Examples | Bacteria and Archaea | Plants, animals, fungi, protists |
In summary, prokaryotic cells are simpler and lack a true nucleus, while eukaryotic cells are more complex, with a nucleus and various membrane-bound organelles.
Prokaryotic Cell
- The term “prokaryote” originates from the Greek words “pro” (meaning “before”) and “karyon” (meaning “kernel”), translating to “before nuclei.”
- Prokaryotes are one of the oldest groups of organisms on Earth, with fossil records dating back 3.5 billion years.
- These early organisms thrived in extreme environments, adapting over time and possibly giving rise to more complex eukaryotic life forms.
Key Characteristics of Prokaryotic Cells
- Simplicity and Size: Prokaryotic cells are generally smaller and simpler than eukaryotic cells.
- Lack of Membrane-Bound Organelles: Prokaryotes do not have a nucleus or other membrane-bound organelles.
- Reproduction: Reproduction occurs through binary fission, a simple division process.
Structural Components of Prokaryotic Cells
- Capsule: A protective layer surrounding the cell, preventing phagocytosis (being engulfed by eukaryotic cells).
- Pilus (Attachment Pili): Hair-like structures on the cell’s surface, helping the cell adhere to surfaces. The pilus also aids in resisting removal from these surfaces, crucial for bacteria.
- Cell Wall: Located below the capsule, providing strength and rigidity to the cell.
- Plasma Membrane: A barrier within the cell that separates the interior contents from the external environment.
- Cytoplasm: A gel-like substance within the cell, supporting cellular growth and housing other cell components.
- Ribosomes: Small structures essential for protein synthesis.
- Mesosomes: Folded structures within some prokaryotic cells that assist in cellular respiration.
- Plasmids: Small, circular DNA molecules that can carry extra genetic information beneficial for the cell.
- Flagella: Tail-like structures that assist with movement, allowing the cell to navigate its environment.
Examples of Prokaryotes
- Bacteria: Commonly found in various environments, from soil to human bodies.
- Archaea: Often found in extreme conditions, such as hot springs and salt lakes.
- Kingdom Monera: All members of this kingdom are prokaryotic.
Eukaryotic Cell
- The term “eukaryotes” comes from the Greek words “eu” (meaning “good”) and “karyon” (meaning “kernel”), translating to “good” or “true nuclei.”
- Eukaryotes are larger and more complex than prokaryotes, encompassing almost all major kingdoms of life, except for Kingdom Monera.
Key Characteristics of Eukaryotic Cells
- Cell Wall: Provides support and protection to the plasma membrane. (Note: Present in plant cells but absent in animal cells.)
- Plasma Membrane: Surrounds the cell, controlling the entry and exit of substances.
- Nucleus: Contains DNA, which stores all genetic information. The nucleus is encased in a nuclear membrane and houses the nucleolus, which is essential for protein synthesis.
- Mitochondria: Known as the “powerhouses” of the cell, they generate energy used by the cell.
- Chloroplasts: Found only in plant cells, these organelles are responsible for photosynthesis, converting sunlight into energy.
- Endoplasmic Reticulum (ER): Assists in the transportation of materials within the cell. It comes in two forms: rough ER (with ribosomes) and smooth ER (without ribosomes).
Other Organelles:
Eukaryotic cells contain various organelles that perform specific functions, including:
- Ribosomes: Essential for protein synthesis.
- Lysosomes: Contain digestive enzymes to break down waste.
- Golgi Bodies: Modify and package proteins for secretion.
- Cytoplasm: Gel-like substance where organelles are suspended.
- Chromosomes: Structures that carry genetic information.
- Vacuoles: Storage structures for nutrients and waste.
- Centrosomes: Play a role in cell division.
Examples of Eukaryotes
Eukaryotes include almost every unicellular organism with a nucleus and all multicellular organisms, such as plants, animals, fungi, and protists.
Frequently Asked Questions
A prokaryotic cell is a basic type of cell that lacks a nucleus and does not contain membrane-bound organelles. These cells are always unicellular, meaning they exist as individual organisms.
Eukaryotic cells are characterized by having a true nucleus and membrane-bound organelles. These cells can exist as either unicellular organisms or multicellular organisms.
A typical eukaryotic cell ranges in size from about 10 to 100 micrometers (µm) in diameter. However, some specialized eukaryotic cells, such as certain types of eggs, can be larger, while others, like some yeast cells, can be smaller.
Prokaryotic and eukaryotic cells differ significantly in their structure and organization. Prokaryotic cells, which include bacteria and archaea, are typically smaller and simpler in structure, lacking a true nucleus and membrane-bound organelles. Their genetic material is located in a nucleoid region and is usually circular and not associated with histones.
In contrast, eukaryotic cells, which encompass animals, plants, fungi, and protists, are larger and more complex, containing a defined nucleus that houses linear DNA organized around histone proteins, as well as various membrane-bound organelles such as mitochondria and the endoplasmic reticulum. These structural differences lead to distinct functions and processes within the two cell types, such as cellular respiration and protein synthesis.
The part that is absent in prokaryotic cells is a true nucleus. In prokaryotes, the genetic material is not enclosed within a membrane; instead, it is located in a region called the nucleoid. Additionally, prokaryotic cells lack membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus, which are present in eukaryotic cells.
