Overview
This lecture explains the historical development of cell theory, focusing on key experiments and discoveries that led to its three major tenets.
Early Microscope Discoveries
- Anton van Leeuwenhoek invented an early microscope and observed bacteria, which he called "animacules."
- Robert Hooke used a microscope to examine cork and introduced the term "cells" after observing cell-like structures.
- Early scientists noticed both plant and animal tissues contained these cell structures.
The Three Tenets of Cell Theory
- First tenet: The cell is the basic unit of structure in life.
- Matthias Schleiden found all plants are made of cells.
- Theodor Schwann found all animals are made of cells.
- Second tenet: All living organisms are composed of cells.
The Origin of Cells Debate
- Initially, it was unclear where cells came from, especially in bacteria.
- Abiogenesis (spontaneous generation from non-living matter) was the dominant theory until the late 1800s.
- Observation: Plants produce seeds, animals reproduce, but bacteria origins were debated.
Disproving Abiogenesis
- Rudolph Virchow observed cell division in bacteria, suggesting cells come from existing cells ("Omnis cellula e cellula").
- The phrase and idea were originally proposed by Raspail and Remak, though Virchow is commonly credited.
- Some scientists still believed abiogenesis and cell division could both occur.
Pasteur’s Swan-Neck Flask Experiment
- Louis Pasteur designed the swan-neck flask experiment to test abiogenesis.
- Boiled broth stayed sterile in the swan-neck flask, disproving spontaneous generation.
- Third tenet: All cells come from preexisting cells.
Key Terms & Definitions
- Cell — The basic unit of structure and function in living organisms.
- Abiogenesis — The theory that living organisms can arise from non-living matter.
- Binary fission — The process by which bacteria divide to produce identical cells.
- Swan-neck flask experiment — Pasteur’s experiment demonstrating that life does not arise spontaneously in sterile conditions.
Action Items / Next Steps
- Review the three tenets of cell theory for future quizzes.
- Read about the experiments of Leeuwenhoek, Hooke, Schleiden, Schwann, Virchow, and Pasteur in your textbook.