Cell : Organelles And Their Functions
Introduction:
Good day, everyone. Today, we are going to discuss the structural organisation of a cell, which is the basic unit of life. According to the NCERT curriculum in the chapter titled “The Fundamental Unit of Life“, the cell is the smallest functional and structural unit of an organism, capable of performing all life processes. All living organisms, from the simplest bacteria to complex multicellular organisms like humans, are made up of cells. Let’s delve into the details of cellular organisation, its structure, and the functions of its components.
1. Discovery of the Cell:
- Robert Hooke discovered dead cells in a thin slice of cork under a primitive or old microscope in 1665.
- Anton van Leeuwenhoek discovered living cells in the pond water by using an improved microscope in 1674.
- Robert Brown discovered and named the cell nucleus in 1831.
- The Cell Theory, proposed by Matthias Schleiden and Theodor Schwann in 1838-39, states that:
- All living organisms are composed of cells.
- The cell is the basic unit of life.
- All cells arise from pre-existing cells, as expanded or added by Rudolf Virchow in 1855.
2. Types of Cells:
Cells are classified into two main types:
- Prokaryotic Cells: These lack a well-defined nucleus and membrane-bound organelles. Examples include bacteria and archaea.
- Eukaryotic Cells: These cells have a true nucleus and membrane-bound organelles. Examples include plants, animals, fungi, and protists.
| Feature | Prokaryotic cell | Eukaryotic cell |
|---|---|---|
| Nucleus | Absent (Nucleoid region present) | Present (Well-defined, membrane-bound nucleus) |
| Size | Smaller (0.1 – 5.0 µm) | Larger (10 – 100 µm) |
| Cell Type | Unicellular (mostly) | Multicellular or unicellular |
| Organelles | No membrane-bound organelles (e.g., mitochondria, ER) | Membrane-bound organelles (e.g., mitochondria, ER) |
| Ribosomes | Smaller (70S type) | Larger (80S type, except in mitochondria and chloroplasts) |
| Examples | Bacteria, Archaea | Plants, Animals, Fungi, Protists |
3. Types of Organisms:
There are two types of organisms:
- Unicellular Organisms: Organisms that consist of a single cell. Example: Amoeba, bacteria, Paramoecium, and Chlamydomonas.
- Multicellular Organisms: Organisms with multiple cells. Example: fungi, plants, and animals.
4. Structural Organization of the Cell:
Cells are made up of various structures and organelles, each performing specific functions. Below are the main components of a eukaryotic cell.
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- Structure: The plasma membrane is a thin, flexible barrier membrane made of a lipid bilayer with embedded proteins.
- Function: Regulates movement of substances in and out of the cell, maintains cell shape, and facilitates communication between cells.
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Cell Wall (in Plant Cells):
- Structure: Composed of cellulose in plants, found only in plant cells, fungi, and some bacteria.
- Function: Provides structural support and protects the cell.
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- Structure: The control centre of the cell, surrounded by the nuclear envelope.
- Function: Stores genetic material and controls cell activities.
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- Structure: A jelly-like fluid filling the cell.
- Function: Site for most cellular processes and reactions.
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- Structure: A network of membranous tubules and sacs.
- Function: Rough ER aids in protein synthesis, while Smooth ER helps in lipid synthesis and detoxification.
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- Structure: Flattened sacs.
- Function: Modifies, sorts, and packages proteins and lipids.
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- Structure: Double-membrane-bound organelles.
- Function: Produce energy (ATP), known as the powerhouses of the cell.
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- Structure: Small non-membrane-bound structures.
- Function: Sites of protein synthesis.
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Lysosomes (in Animal Cells):
- Structure: Membrane-bound vesicles containing digestive enzymes.
- Function: Break down cellular waste and foreign substances.
- Structure: Large membrane-bound sacs.
- Function: Store nutrients and maintain turgor pressure in plant cells.
- Plastids (in Plant Cells):
- Structure: Organelles found in plant cells and some algae.
- Function: Chloroplasts are involved in photosynthesis.
- Structure: A network of protein filaments.
- Function: Provides mechanical support and facilitates cell movement.
5. Cell Division and Growth:
- Mitosis: Cell division that results in two genetically identical daughter cells.
- Meiosis: Cell division that results in four genetically diverse cells with half the chromosome number.
6. Functions of a Cell:
The cell is a functional unit of life, performing essential functions for survival, including metabolism, growth, reproduction, response to stimuli, and transportation of substances.
7. Why Do Cells Change States?
The three types of solutions that impact cell behaviour:
- Isotonic Solution: Equal solute concentration as inside the cell, cell remains stable.
- Hypotonic Solution: Lower solute concentration, cell gains water and swells.
- Hypertonic Solution: Higher solute concentration, cell loses water and shrinks.
Conclusion: In short, the cell is a complex yet beautifully organised structure that functions as the foundation of life. Each organelle within the cell has a specific function that contributes to the cell’s overall health and survival. Understanding the structural organisation of the cell helps us appreciate how life works at the microscopic level and how different components come together to form a functional, living unit.
