CELL THEORY

A Brief History

Robert Hooke named the cell [1665] based on observations of the cell walls of cork tissue

Anton van Leeuwenhoek documented unicellular organisms based on observations of protozoa [1673] and bacteria [1683]

Paramecium - Protocista

Amoeba - Protocista

Matthias Schleiden proposed that cells were the fundamental units of plants based on observations of plant tissue [1838]

Plant cells

Plant Cell

Theodor Schwann proposed that cells were the fundamental units of animals based on observations of animal tissue [1839]

Blood

Sperm

Schleiden and Schwann are credited as the founders of The Cell Theory [1839]

All living things are made of cells.

Cells exhibit the fundamental characteristics of life:

Obtain energy—photosynthesis, chemosynthesis, or digestion Use energy—respire Excrete Waste Show Order Homeostasis Evolve Reproduce Move Respond to changes in environment Grow and repair damage to self

The development of the Cell Theory involved the input of numerous individuals from various nationalities over many years

Rudolph Virchow stated “omnis cellula a cellula ” [all cells arise from pre-existing cells based on observations of dividing cells [1855]

Rudolph Virchow stated “omnis cellula a cellula ” [all cells arise from pre-existing cells based on observations of dividing cells [1855]

The Cell Theory was modified to incorporate Virchow’s work

All organisms are made of cells

Cells are the smallest structural and functional unit of an organism [that carries out the life processes]

All cells come from pre-existing cells

BUT, exceptions remain:

1. Single-celled organisms ARE cells, not composed of cells; that is, they are a-cellular

2. Many cells are unique in composition—muscle cells

and fungal hyphae are multi-nucleated (i.e., more than one nucleus)

And, what about viruses?

Are not composed of cells but consist of a nucleic acid (DNA or RNA) in a protein coat

Yet conduct all of the cell processes (although with help, not independently)

SO:

Could there be an organism that does not contain a single cell?

Might there be some other fundamental unit of life? At least, in some cases?

Are the life processes sufficient criteria to distinguish between the living and the non-living?

Microscopes

Max magnification – X1000

Max Resolution 0.2um

Max magnification X1000,000

Max Resolution 0.5nm

Microscopic measurements

mm – millimeters

μm – micrometer

nm - nanometers

1m = 1000mm = 1000,000μm= 1000,000,000nm

Comaparison of Light and Electron Microscopes

Light Microscope

Human Cheek Cell Nerve Cells

Transmission Electron Microscope

Plant Cell Mitochondrion

Scanning Electron Microscope

Human Sperm Insect Head

Sizes of Biological Structures

Thickness of leaf Paramecium Sharp end of pin Plant cell Animal cell Mitochondrion Bacterium Ribosome DNA molecule Hydrogen atom

O.5mm 200μm 100 μm 40μm 20μm 1μm 0.5-1μm 20nm 2nm 0.04nm

Red and White Blood Cells

S.E. M Light Microscope