The Cell Theory Study Notes

The Cell Theory

Honors Biology

Unit 2: Cells | Topic A

Historical Context of Cell Discovery

• Understanding the beginnings of cell theory helps contextualize the study of cells, though specific scientists do not need to be remembered.

Robert Hooke's Observations

• Used a microscope to observe small organisms, particularly flies and fleas.

• Examined cork tissue, a tough, protective material found in plant stems.

• In cork tissue, he saw small boxes that resembled the rooms where monks slept, known as cells.

• Named the boxes he observed "cells," mistaking the cell walls he saw for the actual cells.

Anton van Leeuwenhoek's Discoveries

• Observed a variety of organisms using a microscope.

• Described bacteria as “animalcules,” meaning “little animals.”

• Identified diverse protists, which are single-celled eukaryotic organisms.

• Discovered microorganisms in samples such as pond water and plaque samples from his own teeth.

• Also observed yeasts (single-celled fungi) and tissues from plants and animals, identifying blood and sperm cells in animals.

Contributions from 19th Century German Scientists

• In the 1800s, three pivotal German scientists made significant contributions to the understanding of cells.

Matthias Schleiden (1838)

• Concluded that all plants are made of cells.

• His work contributed foundational knowledge about plant cells and their structures.

Theodor Schwann (1839)

• Asserted that all animals are made of cells.

• Notably stated that the cell is the basic unit of all living tissue in his book, "Mikroskopische Untersuchungen."

Rudolph Virchow (1855)

• Stated that all cells arise from pre-existing cells, emphasizing that cells come from the division of other cells rather than forming from non-living matter.

• Coined the phrase “omnis cellula e cellula,” meaning "every cell originates from another cell."

The Current Cell Theory

The Original Cell Theory

• Composed of three fundamental statements:

  • All living things are composed of one or more cells.

  • The cell is the basic unit of structure and function in living organisms.

  • Cells arise from the division of pre-existing cells.

Additions to the Current Cell Theory

• New scientific advancements have led to the expansion of the original cell theory to include:

  • Metabolism occurs in cells:

  • Metabolism consists of the collection of biochemical reactions in an organism.

  • Cells obtain energy from food, where:

    • Autotrophs create their own food.

    • Heterotrophs depend on other organisms for nutrition.

  • All organisms perform cellular respiration to convert chemical energy into usable energy, known as ATP.

    • In eukaryotic cells, this process occurs in mitochondria.

    • In prokaryotic cells, it occurs in the cytoplasm.

  • Hereditary information (DNA) is passed during reproduction/division:

  • Cells grow and perform their functions before eventually dividing, a process called cell reproduction.

  • During division, the DNA, as the genetic material, must be copied for each new cell to inherit its genetic information.

  • In animal cells, centrioles aid in dividing the DNA during mitosis, ensuring the correct distribution between the two resulting cells.

  • All cells have the same basic composition:

  • Both prokaryotic and eukaryotic cells share crucial components:

    • Cell membrane

    • Cytoplasm

    • Ribosomes

    • DNA:

    • In prokaryotic cells, DNA is located in the nucleoid region.

    • In eukaryotic cells, DNA is contained within the nucleus.