Biology Chapter 3: Cells

Study Notes

Robert Hooke first observed plant cells in the late 1600s with a primitive microscope.
In the 1830s, Matthias Schleiden and Theodor Schwann formulated that all living organisms are made of cells.
Rudolf Virchow later asserted that cells come only from pre-existing cells.

A cell is the fundamental structural and functional unit of all living organisms.
Organism activity is reliant on the collective and individual functions of its cells.
Cell activities are influenced by their shape and the number of subcellular components.
Cells originate only from other cells, confirming cellular continuity.

Cells include over 250 distinct types in the human body, showcasing variations in shape, size, and function.
Example cell types include:
- Disc-shaped red blood cells.
- Branching nerve cells.
- Cubelike kidney tubule cells.
Cell lengths range from 2 micrometers in small cells to over a meter in nerve cells.

Human cells comprise three main components:
- Plasma membrane: Selectively permeable barrier and outer cell boundary.
- Cytoplasm: Intracellular fluid containing organelles that carry out specific functions.
- Nucleus: Central organelle regulating cell activities.

Extracellular materials are crucial and exist outside of cells, contributing to body mass.
Types of extracellular materials include:
- Body fluids: Interstitial fluid, blood plasma, and cerebrospinal fluid serve as transport and dissolving media.
  - Interstitial fluid nourishes cells with essential compounds and waste removal.
- Cellular secretions: Aid digestion and provide lubrication (e.g., saliva, mucus).
- Extracellular matrix: A protein and polysaccharide-rich substance that organizes and supports cells, particularly abundant in connective tissues.

A generalized cell represents a composite cell concept that encompasses the essential features and functions common to all cell types, regardless of specific characteristics.