The Open Door Web Site

 

 THE CELL THEORY

What level of complexity is necessary for life?

Aristotle (384 – 322BC)

From the C17th microscopists discovered tissues were made of cells (Hooke 1665 and Leeuwenhoek 1677).

Research in the C18th and C19th showed that tissues were made of cells and that the cells of a particular tissue had a common structure.

Xavier Bichat (1771 1802): An organ is composed of different tissues and several organs can be grouped together as an organ system (e.g. the digestive system).

An idea of hierarchy of structure developed:

Purkinje (1835) Observed a fertilised hen's egg (a single cell) could develop into an embryo (many specialised cells in a compact mass).

C19th botanists showed that plant tissues consist of many different types of cells.

THE CELL THEORY

Matthias Schleiden (1838) working on plants and Theodor Schwann (1839) working on animals came to the same basic conclusion: ... "The cell is the basic unit of living tissue."

The cell is an autonomous unit ("a citizen") grouped together to form an organism ("the society").

Rudolf Virchow (1858) a pathologist noted that all cells come from pre-existing cells. A fact that was particularly clear when studying the growth of tumours.

THE ORGANISMAL THEORY

The counter argument to the cell theory developed during the later part of the C19th.

Reichert a morphologist: Argued that an organism has a structured plan.

Strasberger a cytologist: Cells are connected in an organism sometimes by cytoplasmic bridges (plant cell plasmodesmata).

Sherrington and Pavlov neurophysiologists: Cells communicate with one another and they are co-ordinated in their actions.

SUMMARY

THE CELL THEORY

THE ORGANISMAL THEORY
1. Multicellular organisms develop from a single fertilised germ cell (the zygote). 1. Some organisms (e.g. Fungi) are not divided into cellular compartments = non-cellular. Plants have plasmodesmata = cytoplasmic bridges between neighbouring cells.
2. The basic components of the cell (viz. nucleus, mitochondria etc) are repeated in every cell, even free living unicellular organisms. 2. Certain cells lack the basic components (e.g. mature red blood cells have no nucleus). Cells in multicellular organisms are highly specialised. Unicellular organisms have a cytoplasm that is not subdivided into cells and should therefore be considered as acellular.
3. Cells can be taken from organisms and cultured away from the body. In primitive multicellular animals (e.g. sponges) and most plants whole new individuals can be cultured from isolated cells. This power of regeneration is called totipotence. 3. Remove cells from complete multicellular organisms requires elaborate life support systems to keep them alive.
  4. Homeostatic control and co-ordination is required to maintain the whole organism whether it is unicellular or multicellular.

CELL STRUCTURE AND MICROSCOPY

pdf download available

© Paul Billiet 2004