Cell Theory The modern cell theory , one of the fundamental generalizations of biology, holds that: • All organisms are composed of one or more cells. • New cells come from pre-existing cells; lifeforms today have descended in unbroken continuity from the first primitive cells that arose on earth more than 3.5 billion years ago. • Hereditary information passes from parent cell to daughter cell. • The fundamental biochemical reactions of life take place within cells. Methods of studying cells Microscopes. Cytology —the scientific study of cells—has progressed simultaneously with the development of better, more powerful microscopes and cell preparation techniques. Light microscopes , invented in the 1500s, today can magnify in the range of 100x to 1000x and are at the maximum of their resolving power at about 0.2 m (micrometer = Φ 1 / 1,000,000 meter). They are limited
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