Cell Theory:
Cell Theory is a fundamental concept in biology that states:

1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of life.
3. All cells arise from pre-existing cells.

Cell Structure:
Cells have various structures, including:

• Cell Membrane: A protective barrier that regulates what enters and exits the cell.
• Nucleus: Contains genetic material (DNA) and controls cell activities.
• Cytoplasm: The jelly-like substance where cellular processes occur.
• Organelles: Specialized structures (e.g., mitochondria, ribosomes) that perform specific functions.

Cell Function:
Cells perform essential functions such as:

• Metabolism: Chemical reactions that provide energy and build cellular components.
• Reproduction: Cells divide to produce new cells for growth and repair.
• Response to Stimuli: Cells can react to environmental changes.

Types of Cells:
Cells can be classified into two main types:

1. Prokaryotic Cells: Simple, unicellular organisms (e.g., bacteria) without a nucleus or membrane-bound organelles.
2. Eukaryotic Cells: More complex, can be unicellular or multicellular (e.g., plants, animals, fungi) with a defined nucleus and organelles.

This overview highlights the essential concepts of cell theory, structure, function, and the types of cells, forming the foundation of cellular biology.