In-Depth Notes on Cell Theory and Cellular Biology

Introduction to Biology

  • Biology is defined as the study of life.
  • It addresses fundamental questions about living organisms:
    • How do we function?
    • Why do we behave the way we do?

Cell Facts

  1. The average human body consists of around 100 trillion individual cells.
  2. There are over 200 different types of cells found in the human body.
  3. The largest cells are nerve cells, which can exceed 1 meter in length and can be observed without a microscope.
  4. All cells in the human body share the same DNA instructions.
  5. If the DNA in a single human cell were stretched out, it would measure approximately 2 meters; thus, the average human body contains about 200 billion kilometers of DNA distributed among the 100 trillion cells.

Historical Discovery of Cells

  • Robert Hooke (1665)

    • Utilized a microscope to examine a thin slice of cork.
    • Described what he observed as tiny boxes (cells) resembling a honeycomb.
    • Initially believed cells were exclusive to plants and fungi.

  • Anton van Leeuwenhoek (1673)

    • Invented a simple microscope to observe pond water and discovered single-celled organisms, which he termed "animalcules".
    • Also observed blood cells from a variety of animals, establishing that cells exist in both plants and animals.

The Gap in Cell Development

  • 150-200 Year Interval
    • Following the discoveries of Hooke and Leeuwenhoek, there was minimal advancement in cell biology until the mid-19th century.
    • This stagnation was largely due to the prevailing belief in Spontaneous Generation, the notion that life arises from non-living matter.
    • Examples include claims that mice could originate from dirty clothes or corn husks, and maggots from rotting meat.

Challenges to Spontaneous Generation

  • Doubts began to arise regarding Spontaneous Generation, leading to its eventual disproof by Louis Pasteur, emphasizing a turning point in biological understanding.

Development of Cell Theory

  • 1838: Matthias Schleiden proposed that all plant structures are made of cells.
  • 1839: Theodor Schwann stated the same for all animal tissues.
  • 1858: Rudolf Virchow concluded that all cells arise from pre-existing cells, forming a pivotal part of cell theory.
Key Components of the Original Cell Theory
  • All organisms are composed of one or more cells.
  • The cell is the fundamental unit of life.
  • All cells arise from the division of pre-existing cells.
Modern Cell Theory Additions
  • The modern cell theory retains the original components but includes additional principles:
    • Energy flow occurs within cells.
    • Cells contain DNA which dictates the organism's characteristics and is transmitted from one generation to the next.

Types of Cells

  • Prokaryotic Cells

    • Do not have a nucleus; consist of simpler organisms such as Archaea and Bacteria.

  • Eukaryotic Cells

    • Contain a nucleus and are larger and more complex, including organisms such as protists, fungi, animals, and plants.