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Observing Cells
Objectives:
After completing this exercise and reading the corresponding material in your text, you should be able to 1. Prepare a wet mount slide
2. Identify structures described in this lab on slides
3. Cite examples of the wide diversity of cell types
4. Relate differences in structure among cells to functional differences

Introduction
Structurally and functionally, all living things share one common feature: all living organisms are composed of cells. The development of this concept began with Robert Hooke's seventeenth-century observation that slices of cork were made up of small units he called "cells.” Over the next 100 years, the cell theory emerged. It was formally (and independently) presented by Schleiden and Schwann in 1839, and clarified by Virchow a few years later. This theory has three principles: (1) All organisms are composed of one or more cells. (2) All life processes derive from the activities of cells. (3) All cells arise from preexisting cells. Living organisms are composed of one or many cells, and every activity that occurs in a living organism is ultimately related to metabolic processes in cells. Understanding the processes of life requires an understanding of the structure and function of the cell. Although cells vary in organization, size, and function, all share certain structural features. All are enclosed within a plasma membrane, defining the boundary of the living material. All contain a region of DNA (deoxyribonucleic acid), which forms the genetic code. Inside of the plasma membrane is watery cytoplasm, and the chemical processes inside the cell occur within this watery medium. Upon microscopic examination, we see there are two basic types of cells, prokaryotic and eukaryotic, see the table below to see a comparison of the two cell types.

Table 1. Comparison of Prokaryotic and Eukaryotic Cells

| | | | |Characteristics |Prokaryotic |Eukaryotic | | |Found loose in the cytoplasm, not bounded by |Isolated from other cytoplasmic organelles by | | |special membrane |a porous double membrane | |Genetic material | | | | |Consists of a single, circular molecule of DNA|Many linear molecules of DNA combined with | | | |histone protein form chromosomes | | |Small ribosomes (70s) |Large ribosomes (80s) | | | | | | | | | |Cytoplasmic structures | | | | |No internal membranes except photosynthetic |Endomembrane system, a system of connected | | |membranes (formed from infolding of the plasma|membranous structures | | |membrane) found in some | | | |...
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