The cell is the basic living unit of the human body. It is called a dynamic cell because it constantly performs activities such as respiration, growth, adaptation, reproduction, and communication. Each cell contains specialized structures called organelles that work together to maintain life. Understanding these structures helps us understand how the human body functions at the microscopic level.
Cell Membrane
The cell membrane is a thin, flexible barrier that surrounds the cell. It is made of a phospholipid bilayer with embedded proteins.
Functions
- Maintains the shape of the cell
- Controls entry and exit of substances
- Helps in cell communication and signaling
- Protects internal organelles
Cytoplasm
The cytoplasm is a semi-fluid material that fills the inside of the cell. It contains water, salts, enzymes, and all cellular organelles.
Functions
- Supports organelles
- Site of many chemical reactions
- Helps in transport of molecules
Nucleus
The nucleus is the control center of the cell. It contains genetic material (DNA) arranged in chromosomes.
Functions
- Controls cell activities
- Stores and protects genetic information
- Regulates cell growth and reproduction
The nucleus contains:
- Nuclear membrane – protects the nucleus
- Nucleoplasm – fluid medium
- Nucleolus – produces ribosomes
Endoplasmic Reticulum (ER)
The ER is a network of membranes found throughout the cell.
Types
- Rough ER: has ribosomes and helps in protein synthesis
- Smooth ER: synthesizes lipids and detoxifies chemicals
Ribosomes
Ribosomes are small structures either floating in the cytoplasm or attached to the rough ER.
Function
- Produce proteins needed for cell growth and repair
Golgi Apparatus
The Golgi apparatus looks like flattened sacs arranged in layers.
Functions
- Modifies, packages, and transports proteins
- Forms lysosomes and secretory vesicles
Mitochondria
Known as the “powerhouse of the cell,” mitochondria generate energy in the form of ATP.
Functions
- Energy production
- Regulation of metabolism
- Participates in cell death (apoptosis)
Lysosomes
Lysosomes contain digestive enzymes.
Functions
- Break down waste materials and damaged organelles
- Defend against invading microbes
Peroxisomes
Small organelles that contain enzymes for detoxification.
Functions
- Break down fatty acids
- Neutralize harmful substances
Cytoskeleton
The cytoskeleton is a network of protein fibers (microtubules, microfilaments, and intermediate filaments).
Functions
- Maintains cell shape
- Helps in movement of the cell
- Supports organelle positioning
Centrosome and Centrioles
Centrosomes help organize microtubules and are essential during cell division.
Cell Inclusions
These are stored nutrients or pigments inside the cell.
Examples
- Glycogen
- Lipids
- Melanin
Cell Division
Cells multiply through two processes:
1. Mitosis
Produces identical cells for growth and repair.
2. Meiosis
Occurs in reproductive organs and produces gametes.
Detailed Notes:
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