TABLE OF CONTENTS Cells are classified into three families: Bacteria, Eukarya, Archaea. Bacteria are denoted as prokaryotes, animal cells and fungi are called eukaryotes.
This appendix describes the characteristics and components of a cell. It also describes the process of cell reproduction.
A typical human cell is about 10 ?m across and weighs about 1 nanogram. Bacteria are single celled or unicellular whereas humans are multicellular; estimated number of cells in an adult human being is of the order of 10 14. Figure B-1 shows an enlarged view of typical human cells:
A cell contains all the information required for controlling cell functions and for transmitting this vital information to daughter cells when it divides.
Each cell is capable of independently carrying out functions that are necessary for sustenance and survival. A cell absorbs nutrition, derives energy from the nutrients required to carry out various specialized functions, and reproduces.
All cells share some common characteristics:
They undergo division.
They have a metabolic system. From nutrients, they extract energy, build components, and release byproducts.
They respond to stimuli. Stimuli may result from change in parameters such as temperature, environmental pH, or nutrient level.
Contents of a cell are encased in a cell surface membrane.
You can study the subcellular components by electron microscope. The components can be isolated by differential centrifugation after disruption of the plasma membrane. Constitutents of these isolated fractions can be determined by analysis for nucleic acids and proteins...
