UNITY & DIVERSITY OF CELLS
Living Cells All Have a similar Basic Chemistry
Central Dogma !"!
Cell Theory”- all living things are made up of cells and cells arise from pre-existing
cells [proved by Louis Pasteur )
Combining cell theory with evolution principle leads us to view all life form its
beginnings to the present day as one vast family tree of individual cells.
Light Microscopes allow the examination of Cells and some of their components
Cut a very thin slice from a suitable plant or animal tissue and view it using a light
Microscopes you will see the tissue divides into thousands of small cells, they might be
closely packed or separated by an extracellular matrix: a dense material often made of
protein fibers embedded in a polysaccharides gel each cell is about 1-20 um, you will be able
to see particles moving or dividing.
The internal structure is difficult to see b/c the parts are small and transparent and mostly
colorless to solve this problem is to stain the cell with dyes.
Cell components differ slightly from one another in refractive index (the ratio of the
velocity of light in a vacuum to its velocity in a specified medium) causing light rays to be
deflected as they pass from the one medium into the other, the small differences in refractive
index can be made visible by specialized optical techniques
For light microscope cell samples are to be fixed ( preserved by pickling in a reactive
chemical solution) supported by embedding in a solid wax or resin, cut or sectioned into thin
slices, and stained before it is viewed, for electron microscopy similar procedures are required
with much thinner section and no way of looking at living wet cells.
Organelles: separate, recognizable substructures with specialized functions that are only
hazily defined with light microscope
All living thing or organisms are built from cells, small, membrane-enclosed units filled with a concentrated aqueous solution of chemicals and endowed with the ability to create copies of themselves by growing and then dividing into two chemical reactions. These differences in size shape, and chemical requirements often reflect differences in cell. Simplest cells are called solitary cells, higher organisms including ourselves are communities of themselves in an outer layer of slime, building themselves rigid cell walls, or surrounding themselves with hard, mineralized material, such as that found in bone. Cells vary enormously in appearance and function (figure 1-1 pg 3) Cell biology is the study of cells and their structure, function, and behavior. Cell biology can help us to tackle problems of life on earth, its origins, and massive diversity by evolution some modifications specialize a cell so much that they spoil its chances of leaving any decedents.