Cell – The Basic Unit of Life

 Cell – The Basic Unit of Life

Cells are the fundamental units of life. They are responsible for carrying out all biological processes that sustain living organisms. Some organisms, like bacteria, are unicellular (single-celled), while others, like humans, are multicellular (made up of billions or trillions of cells).



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Discovery of Cells


The term "cell" was first used by Robert Hooke in 1665 when he observed cork cells under a microscope. Later, Anton van Leeuwenhoek discovered living cells in pond water using a simple microscope.


Cell Theory


Cell theory was developed by Matthias Schleiden, Theodor Schwann, and Rudolf Virchow. It states that:


1. All living things are made up of cells.



2. The cell is the basic unit of life.



3. All cells arise from pre-existing cells.





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Types of Cells


Cells are mainly classified into two types based on their structure:


1. Prokaryotic Cells


Found in bacteria and archaea.


Do not have a nucleus; instead, DNA floats freely in the cytoplasm.


Lack membrane-bound organelles like mitochondria.


Generally smaller and simpler than eukaryotic cells.



2. Eukaryotic Cells


Found in animals, plants, fungi, and protists.


Have a nucleus that contains DNA.


Contain various membrane-bound organelles like mitochondria, Golgi apparatus, and endoplasmic reticulum.


Larger and more complex than prokaryotic cells.




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Structure of a Cell


1. Cell Membrane (Plasma Membrane)


A flexible, protective barrier surrounding the cell.


Made of phospholipids and proteins.


Controls what enters and exits the cell (selectively permeable).



2. Cytoplasm


A gel-like fluid inside the cell.


Contains organelles and helps in cellular processes.



3. Nucleus


Control center of the cell.


Contains DNA (Deoxyribonucleic Acid), which stores genetic information.


Surrounded by a nuclear membrane with nuclear pores for material exchange.



4. Mitochondria


Known as the powerhouse of the cell.


Produces ATP (Adenosine Triphosphate), the energy currency of the cell.


Contains its own DNA, allowing it to reproduce independently.



5. Ribosomes


Responsible for protein synthesis.


Found floating in the cytoplasm or attached to the rough endoplasmic reticulum.



6. Endoplasmic Reticulum (ER)


Rough ER: Has ribosomes, helps in making and transporting proteins.


Smooth ER: No ribosomes, involved in lipid synthesis and detoxification.



7. Golgi Apparatus


Modifies, packages, and distributes proteins and lipids.


Works like a post office of the cell.



8. Lysosomes (Only in Animal Cells)


Known as the suicide bags of the cell.


Contain digestive enzymes that break down waste and foreign particles.



9. Vacuoles


In plant cells: Large central vacuole stores water, nutrients, and waste.


In animal cells: Small vacuoles help in storage and waste removal.



10. Chloroplasts (Only in Plant Cells)


Contain chlorophyll, which helps in photosynthesis.


Convert sunlight into glucose (food for the plant).



11. Cytoskeleton


A network of protein filaments providing structure and movement.


Includes microtubules and microfilaments that help in cell division and intracellular transport.




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Functions of a Cell


1. Growth and Development


Cells grow in size and multiply through cell division (mitosis and meiosis).


2. Energy Production


Mitochondria produce ATP, providing energy for cellular activities.


3. Reproduction


Unicellular organisms reproduce through binary fission.


Multicellular organisms grow and develop through mitosis and meiosis.



4. Transport of Materials


Cell membrane controls the movement of substances via diffusion, osmosis, and active transport.



5. Waste Removal


Lysosomes and vacuoles help in digesting and removing waste materials.



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Cell Division


Cells divide to reproduce and grow. The two main types of cell division are:


1. Mitosis (For Growth and Repair)


Produces two identical daughter cells.


Used for growth and repair in multicellular organisms.



2. Meiosis (For Sexual Reproduction)


Produces gametes (sperm and egg cells).


Results in genetic variation.




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Differences Between Plant and Animal Cells



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Conclusion


Cells are the foundation of all life forms. Understanding their structure and functions helps us learn how organisms grow, survive, and reproduce. Every living thing, from the smallest bacteria to the largest animals, depends on the incredible work of its cells.

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