3.1 Cell Theory

Overview

• The development of cell theory was influenced by the work of many scientists and advancements in microscopy.

• The cell theory serves as a unifying concept in biology.

Historical Contributions

• Many scientists contributed to cell theory:

  • Robert Hooke (1665):

    • First to identify and name cells by observing the cell walls of dead plant material.

    • Used the term "cells" based on the resemblance of cork cells to small rooms.

    • Fig. Hooke's observations of cell walls.

  • Antonie van Leeuwenhoek:

    • Improved microscopy techniques and was the first to observe and draw microscopic organisms (termed "animalcules") in pond water.

    • Fig. Leeuwenhoek's observations of microscopic life.

The Three Principles of Cell Theory

1. All organisms are made of cells.

   • Cells are the fundamental building blocks of all living organisms.

2. All existing cells are derived from other living cells.

   • Cells reproduce by division, confirming their origin from pre-existing cells.

3. The cell is the most basic unit of life.

   • Propounds the idea that cell functions are vital for life processes.

Types of Cells

• There are two primary types of cells:

  • Prokaryotic Cells:

    • Lack a nucleus and most internal structures of eukaryotic cells.

    • Characteristics include:

      • Microscopic size (0.1-5 micrometers).

      • Enclosed by a membrane and filled with cytoplasm.

      • Capable of asexual reproduction.

      • Example: Bacteria (shown in colored SEM at a magnification of 8800x).

  • Eukaryotic Cells:

    • Contain a nucleus and membrane-bound organelles.

    • Characteristics include:

      • Larger size (10-100 micrometers).

      • Can be unicellular or multicellular.

      • Can reproduce asexually or sexually.

Comparative Summary of Prokaryotic and Eukaryotic Cells

• Prokaryotic Cells:

  • No true nucleus.

  • Lack membrane-bound organelles.

  • Include cell walls and can have structures like capsules, pilus, and flagella.

  • Ribosomes are present.

• Eukaryotic Cells:

  • Have a defined nucleus.

  • Contain multiple membrane-bound organelles (e.g., mitochondria, Golgi apparatus, endoplasmic reticulum, lysosomes).

  • Can have high complexity in structure/function compared to prokaryotic cells.