Cell theory
2.1
KEY IDEAS
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cells are the basic unit of life on Earth there are two types of cells: prokaryotic and eukaryotic cells.
Cells: the building blocks of life
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In this topic, you will learn that: ✚
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For any object to be classified as living, it must have at least one cell. Cells are the smallest structural and functional units of life. Robert Hooke, an English natural philosopher of the 17th century, studied cork under a microscope (Figure 1). He identified the small square structures in the cork, and named them after the rooms (‘cells’) where monks lived in monasteries. Some living organisms are unicellular – they exist as a single cell. Other organisms are multicellular – they are composed of many cells, sometimes even trillions.
unicellular
multicellular consisting of many cells
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consisting of a single cell
Cell theory
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Before the invention of the microscope, biologists believed in a theory known as spontaneous generation. People believed that maggots appeared spontaneously from rotting meat and tadpoles appeared from a new puddle of water. Eventually this theory was disproved with experiments that showed, for example, that maggots only appeared in meat after flies had laid their eggs. In the 19th century, Louis Pasteur FIGURE 1 Robert Hooke’s microscope disproved the theory of spontaneous generation. His work demonstrated that all microorganisms arise from pre-existing ones and that if the microorganisms are isolated and destroyed in a sterile environment, no new microorganisms will grow. This became the foundation for cell theory and revolutionised the field of medicine with the development of antiseptic techniques. Cell theory specifies that: • all living organisms consist of at least one cell • all cells arise from pre-existing cells • cells are the smallest structural unit of life (Figure 2). This theory is based on both biochemical and microscopic observations and experimentation.
cell theory
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the theory that describes cells as the basic component of all living organisms
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BIOLOGY FOR VCE UNITS 1 & 2
OXFORD UNIVERSITY PRESS
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