Biology Cell Theory and Discovery

The Cell as the Smallest Living Entity

• The origin of the term "cell" is attributed to Robert Hooke in 1665.
• Hooke described "tiny boxes" observed in cork but believed them to exist only in plants and fungi.
• Anton van Leeuwenhoek, a Dutch tradesman and scientist, pioneered microscopy and crafted over 25 hand-made microscopes.
• He is credited with the discovery of unicellular microorganisms, blood cells, protozoans, bacteria, vacuoles, spermatozoa, and striated muscle fibers.

History of Cell Discovery

• In 1838, Matthias Schleiden, a German botanist, concluded that all plant parts are made of cells.
• In 1839, Theodor Schwann, a German physiologist, stated that all animal tissues are made of cells.
• Rudolf Virchow, a German physician, rejected the prevailing theory of spontaneous generation and proposed that cells arise from pre-existing cells.

Cell Theory

• The Cell Theory postulates:
  • All organisms consist of one or more cells (Schleiden & Schwann).
  • The cell is the basic structural unit of all organisms (Schleiden & Schwann).
  • All cells arise from pre-existing cells – "omnis cellulae cellula" (Virchow).
• The Cell Theory establishes the cell as the fundamental unit of life and the basis for reproduction.

Microscopy in Cell Biology

• Microscopy played a pivotal role in the development of the Cell Theory.
• Pioneering studies utilized light microscopes.
• Techniques such as brightfield, phase contrast, differential interference contrast, and fluorescence microscopy have all contributed to the understanding of cellular structures.
• Confocal microscopy allows for the generation of 3D images of living cells.
• Time-lapse imaging, a technique that allows for the observation of cellular processes in real time, provides deeper insights into cell movement and function.
• Super high-resolution microscopy achieves resolutions below 100 nanometers, making it possible to study structures at the nanometer scale.
• Electron microscopy (SEM and TEM) provides detailed images of cellular structures at a higher magnification than light microscopy but only on dead cells.

Viruses and Prions

• Viruses, prions, and viroids are not considered living entities because they do not:
  • Use their own energy
  • Grow on their own
  • Respond to stimuli
  • Reproduce independently
• Viruses are infectious particles containing genetic material surrounded by a protein coat, capable of infecting all organisms.
• Prions are infectious proteins that can cause neurodegenerative diseases.
• Viroids are infectious RNA molecules that mainly infect plants.

Key Facts

• The cell is the smallest unit that can be definitively said to be alive.
• Cells are bound by a plasma membrane, contain cytoplasm, have genetic material, and have the ability to synthesize proteins.
• Eukaryotic cells contain membrane-bound organelles.
• Living entities harness energy, respire, grow and develop, reproduce, and respond to stimuli.
• The first cell is thought to have arisen by the enclosure of self-replicating RNA and associated molecules within a membrane composed of phospholipids.
• Antibodies are used in immunocytochemistry (cells) and immunohistochemistry (tissues) to detect specific proteins.
• The confocal microscope allows for the generation of 3D images of cellular structures.
• Super high-resolution microscopy allows for imaging at the nanoscale, providing insights into cellular structures and processes.
• Cells are the building blocks of all living organisms, from tissues to organs, to organ systems, finally resulting in an organism.