Cell Theory

Prior to the 1600s, organisms were discerned as being complete and inseparable into smaller parts. This was due in parts to the inability to see smaller structures through optical instruments like the microscope. In 1665, Robert Hooke congregated a crude compound microscope and tested its properties on a piece of cork. He observed a honeycomb-like structure and compared the spaces inside the cork to the little rooms of a monastery, known as a cell. Because cork comprises of desiccated nonliving cells, Hooke was not able to see nuclei, organelles, or cell membranes. In 1674, Anton van Leeuwenhoek was the first to outlook a living cell under a microscope. Later researchers noted that cells could be isolated and that every single cell was a distinct structure. Further research designated that tissues were formed of cells, and the function of tissue was dependent upon the function of the cells from which it is formed. Two centuries later, in 1850, Rudolf Virchow demonstrated that diseased cells could arise from normal cells in normal tissues.

The original form of the cell theory comprised of three basic tenets:

  • All living things are composed of cells.
  • The cell is the primary functional constituent/unit of life.
  • Cells move up just from preexisting cells.

By means of advances of molecular biology, a fourth tenet has been added to the theory:

  • Cells carry genetic information in the form of deoxyribonucleic acid (DNA). This genetic parent/substance is transferred from parent to daughter cell.

Cell theory has created a fascinating dilemma with respect to viruses. Viruses are small structures that hold genetic material but are unable to reproduce on their own. This violates the third and fourth tenets of the cell theory because virions can only replicate by invading other organisms and because they may hold ribonucleic acid (RNA) as their genetic information. Therefore, viruses debated later in this chapter, are not considered living organisms.


Robert Hooke, who invented the first crude microscopes to watch at cork, is also known for his characterization of springs. Hooke’s Law, F = −kx, describes the relationship amidst elastic force, the spring constant, and the displacement of spring from equilibriumWhile Hooke’s Law does not seem on the official MCAT content lists, the related topic of elastic potential energy, U = 1/2kx², is testable content. This equation, furthermore as supplementary forms of energy, is discussed in Chapter 2 of MCAT Physics and Math Review. also

MCAT Concept Check 1.1:

Before you march on, estimate your understanding of the material alongside this question.

1. What are the four underlying tenets of cell theory?





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