Cell Theory and Homeostasis

Study Notes

Aristotle introduced the spontaneous generation theory, suggesting life could arise from non-living matter.
Homeostasis is the ability of cells to maintain internal balance amid changing external conditions.
Cells, especially immune cells, employ membranes for protection against pathogens.

Zacharias Janssen created the first primitive microscope, enabling observation of tiny life forms.
Robert Hooke first identified and named cells by examining cork under a microscope.
Francesco Redi conducted experiments disproving spontaneous generation by demonstrating that maggots originate from flies, not decaying meat.
Anton Van Leeuwenhoek crafted his own microscope, observing single-celled organisms for the first time.
Matthias Schleiden proposed that all plants consist of cells, marking a fundamental unit of life.
Theodor Schwann extended this concept to animals, affirming that all living organisms are composed of one or more cells.
Rudolf Virchow introduced the idea that all cells come from preexisting cells, completing the cell theory.

Composed mainly of phospholipids forming a phospholipid bilayer; this creates a selective barrier.
Polar phosphate "heads" face outward while nonpolar fatty acid "tails" face inward.
Fluid mosaic model describes the membrane's structure with embedded proteins, carbohydrates, and cholesterol.
Key protein types:
- Channel Proteins: Form openings for specific substances to cross the membrane.
- Carrier Proteins: Change shape to transport substances across the membrane.
- Cell Recognition Proteins: Identify pathogens and initiate immune responses.
- Receptor Proteins: Bind specific molecules to trigger cellular responses.

A network of protein filaments providing structural support from the nucleus to the plasma membrane.
Composed of three main components:
- Microtubules: Made of alpha- and beta-tubulin, they maintain cell shape and facilitate chromosome movement during division.
- Microfilaments: Comprised of actin, they form a dense structure that supports shape and movement.
- Intermediate Filaments: Made of various proteins and provide mechanical strength; keratin reinforces the strength in skin cells.
The cytoskeleton is dynamic, adapting to internal and external changes.

A semi-fluid solution called cytosol, containing water, inorganic, and organic molecules.
Provides a medium for organelles and cellular components.

A rigid layer surrounding most prokaryotic cells (e.g., bacteria, archaea).
Bacterial cell walls contain peptidoglycan; plant cell walls are primarily cellulose; fungal cell walls consist of chitin.
Maintains cell shape and prevents excessive water absorption, protecting cells from bursting.