RAYCROFT ! Notes - Cell - Student Page 1
BIOLOGY 12 - CELL STRUCTURE & FUNCTION: Chapter Notes
THE CELL THEORY
• although different living things may be as unlike as a violet and
an octopus, they are all built in essentially the same way. The
most basic similarity is that all living things are composed of
one or more cells. This is known as the Cell Theory.
• our knowledge of cells is built on work done with microscopes
• English scientist
Robert Hooke in 1665 first described cells
from his observations of cork slices. Hooke first used the word
"cell".
• Dutch amateur scientist Antonie van Leeuwenhoek
discovered microscopic animals in water
• German scientists Schleiden and Schwann in 1830's were first
to say that all organisms are made of one or more cells.
• German biologist
Virchow in 1858 stated that all cells come from the division of pre-existing cells.
• Cells are the building blocks of life.
The Cell Theory can be summarized as:
1. All living organisms are made up of one or more cells
2. The cell is the basic unit of life
3. All cells come from the division of pre-existing cells
• cells come in many shapes and sizes, although most are microscopic:
• most cells are small, about 0.001 cm in length (1/100 of a mm, or 10 µm).
• the smallest cells of the microorganism mycoplasma are 0.3 µm in size
• Some cells are large. e.g. some giant algal cells may be several centimeters long. A chicken's egg is a
single cell.
• 40,000 red blood cells would fill the letter "O" on a page of type. You produce about 2.5 million new
red blood cells every second! Each square cm of your skin contains about 150,000 skin cells.
• Human beings are composed of about 50 to 100 trillion cells.
• cells
carry on all the processes associated with life, such as reproducing and interacting with the
environment.
Microscopy
• The study of cell structure includes the fields of CYTOLOGY (for
cells) and HISTOLOGY (for tissues), whereas the function of cells is
studied in CELL PHYSIOLOGY, BIOCHEMISTRY, and
CYTOGENETICS.
• The first instrument used in studying cell structure was the light
microscope, which remains an important tool today. The
TRANSMISSION ELECTRON MICROSCOPE and the SCANNING
ELECTRON MICROSCOPE have vastly increased our knowledge.
• Before an object can be viewed, it is necessary to stain the material
and cut it into samples thin enough for a light beam or an electron
beam to penetrate them.
• First, the tissue is treated, to "fix" the structures so they will not be
altered by the staining and slicing. Usually this is done by using
chemicals such as ALCOHOL and FORMALDEHYDE.
• Stains have been developed that react differently with different cell
structures, depending on their chemical composition or enzymatic
activity. The use of stains containing radioactive atoms, known as AUTORADIOGRAPHY, often involves
feeding cells specific compounds with radioactive atoms and then observing the distribution of radioactive
events on a photographic film emulsion.
Relative Powers of Microscopes
1. Compound Light Microscope: maximum resolving power = 200 nm (maximum useful magnification =
~1000 X)
2. Transmission Electron Microscope: maximum resolving power = 0.5 nm nm (maximum useful
magnification = >30,000 X)
3. Scanning Electron Microscope: Gives vivid 3-D images, but less magnification than transmission EM
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