Cell Theory — Overview & Parts

Three Points of Modern Cell Theory

1. All living things are made of one or more cells.

2. The cell is the smallest unit of life in all organisms.

3. All living cells come from the division of pre-existing cells.

Cell theory says that cells are the smallest unit of life. In other words, this means that you cannot break down a cell into smaller parts and still call it living. For example, you can break down a whole organism such as a human into smaller components like organ systems, organs, and tissues. All of these components are still considered living. Plant and animal tissues can then be broken down further into cells, but that is the furthest life can be broken down.

What Did We Think Before?

This theory tells us that all cells come from existing cells. Your first thought might be, "Of course. Where else would cells come from?"

But before a few key experiments in the 1800s, scientists and society supported an idea called spontaneous generation. According to this hypothesis, living organisms could by produced by non-living things.

For example, it was believed that maggots sprouted directly from rotting meat, fleas were produced by dust, and salamanders came directly from mud.

The idea of spontaneous generation was replaced by cell theory, which states that all cells come from existing cells, not from non-living things. This process is also called biogenesis. Recall that bio means "living" and genesis has to do with how things are produced. Biogenesis means that living things must come from other living things.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Cell}}$ : The simplest form of life and the basic unit of structure and function

$\color{#8925AE}{\text{Cell Theory}}$ : The theory that all living things are made up of cells, cells are the most basic unit of life, and new cells are made from old cells

$\color{#8925AE}{\text{Eukaryote}}$ : Eukaryotic cells contain a nucleus and membrane-bound organelles

$\color{#8925AE}{\text{Prokaryote}}$ : Prokaryotic cells do not contain a nucleus or membrane-bound organelles

Cell Theory Has Three Main Parts:

• All living organisms are composed of cells.

• Cells are the basic unit of structure and organization in living organisms.

• All cells are made from already-existing cells.

(Video) The Wacky History of Cell Theory - Lauren Royal-Woods

by TED-Ed

In the video above, Lauren Royal-Woods explains the history of cell theory. It involved the work of many scientists. First, Antonie van Leeuwenhoek discovered tiny bacteria and protozoa living on his teeth. He shared his findings with Robert Hooke, who looked at cork cells under a compound microscope. The shape of the cork cell walls gave him the idea to call these compartments "cells". He shared his findings with the Royal Society. This discovery also began the field of cell biology, which is the study of cells.

After the discovery of the cell, in the 1800s, botanist Matthias Schleiden and Theodore Schwann made further discoveries by looking at plant and animal cells. Both Schleiden and Schwann came to the conclusion that all organisms are made of cells. Rudolf Virchow did further research to show that all cells come from other cells (an idea he borrowed from Robert Remack).