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The cell is the fundamental structural and functional unit of all living organisms. All life forms, from unicellular bacteria to complex multicellular organisms, are made up of cells. The concept that “all living things are composed of cells” forms the cornerstone of biology and is crucial for NEET aspirants. Studying cell structure and function helps understand physiology, genetics, and biochemistry in detail.
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The discovery of the cell dates back to 1665 when Robert Hooke observed cork cells under a microscope. Later, Anton van Leeuwenhoek discovered living cells such as bacteria and protozoa. The cell theory, proposed by Schleiden and Schwann, states:
All living organisms are made up of cells.
The cell is the basic unit of life.
All cells arise from pre-existing cells (Virchow).
This theory is the foundation of modern biology.
Cells are broadly classified into prokaryotic and eukaryotic cells:
1. Prokaryotic Cells:
Lack a true nucleus.
DNA is present in a nucleoid region.
Example: Bacteria and Archaea.
No membrane-bound organelles.
2. Eukaryotic Cells:
Have a well-defined nucleus enclosed by a nuclear membrane.
Contain membrane-bound organelles.
Example: Plant and animal cells.
Cells are composed of several key structures called organelles, each with specific functions.
1. Plasma Membrane (Cell Membrane):
A selectively permeable membrane that separates the cell from its environment.
Controls the movement of substances in and out of the cell.
Composed of a phospholipid bilayer with proteins.
2. Cytoplasm:
Jelly-like substance filling the cell.
Supports organelles and serves as the site of metabolic reactions.
3. Nucleus:
The control center of the cell.
Contains genetic material (DNA).
Surrounded by a nuclear envelope with pores for material exchange.
Nucleolus inside the nucleus is responsible for ribosome synthesis.
4. Mitochondria:
Known as the “powerhouse of the cell.”
Site of cellular respiration and energy (ATP) production.
5. Endoplasmic Reticulum (ER):
Network of membranous tubules.
Rough ER has ribosomes; involved in protein synthesis.
Smooth ER lacks ribosomes; involved in lipid synthesis.
6. Golgi Apparatus:
Packaging and transport center of the cell.
Modifies proteins and lipids for secretion or storage.
7. Lysosomes:
Contain digestive enzymes for breaking down waste and foreign materials.
8. Ribosomes:
Sites of protein synthesis.
Free ribosomes float in the cytoplasm, while attached ribosomes are on the rough ER.
9. Vacuoles:
Storage organelles containing water, nutrients, or waste.
Larger in plant cells for maintaining turgor pressure.
10. Cytoskeleton:
Network of protein filaments.
Provides shape, support, and facilitates intracellular transport.
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present, made of cellulose | Absent |
| Vacuole | Large, central | Small or absent |
| Plastids | Present (chloroplasts, chromoplasts, leucoplasts) | Absent |
| Shape | Fixed, rectangular | Irregular, flexible |
The cell performs various essential functions to sustain life:
Nutrition: Cells absorb nutrients and convert them into energy.
Respiration: Mitochondria carry out cellular respiration to produce ATP.
Excretion: Lysosomes and cell membrane remove waste products.
Reproduction: Cells divide by mitosis or meiosis for growth and reproduction.
Communication: Cells communicate through signaling molecules.
Transport: Plasma membrane regulates substance movement in and out of the cell.
Cell division is essential for growth, repair, and reproduction. There are two main types:
1. Mitosis:
Produces two identical daughter cells.
Involved in growth and repair.
2. Meiosis:
Produces four genetically different gametes.
Essential for sexual reproduction.
Understanding cell structure and function is crucial for NEET aspirants because:
Many questions in NEET are based on organelles, their functions, and cell division.
Foundation for genetics, molecular biology, and biotechnology.
Helps in understanding diseases related to cell malfunction.
| Organelle | Structure | Function |
|---|---|---|
| Nucleus | Double membrane | Controls cell activities, stores DNA |
| Mitochondria | Double membrane | ATP production, cellular respiration |
| ER | Network of membranes | Protein and lipid synthesis |
| Golgi apparatus | Flattened sacs | Modifies, packages proteins/lipids |
| Lysosomes | Vesicles with enzymes | Digestion and waste removal |
| Ribosomes | Small particles | Protein synthesis |
| Vacuole | Membrane-bound sac | Storage and turgor |
The cell, as the unit of life, forms the foundation of biology. A thorough understanding of cell structure, organelles, and their functions is essential for NEET and Class 11 exams. By studying the cell in detail, students gain insights into complex biological processes, paving the way for success in NEET. StudentBro.in provides concise and student-friendly notes for effective revision.
