ELEMENTS OF GENERAL BIOLOGY

Outline: Autotrophs and Heterotrophs. How the Organisms Take In Energy. Photosynthesis: Using Energy for Making Food. Light and Dark Reactions. Glycolysis and Fermentation. The Role of Pigments. Respiration in the Cell: Aerobic and Anaerobic. Genetics is the Study of Heredity. Mendel and His Experiments. Punnett Square. The Chromosome Theory. Heredity and Regularity of Variability. The Role of Environment in Development and Manifestation of Traits. Twins. Sex-Linked Traits. Genetic Disorders. Blood Groups. The Beginnings of Selection and Breeding. Genetic Engineering. Growth as a Basic Life Process. DNA. Mitosis. Asexual and Sexual Reproduction. Parthenogenesis and Embryogenesis. Classification and identification. Different methods of classification. Naming organisms. Five kingdoms and their subdivisions. Tool for identification.

2.1. Introduction to Cell Biology

Charles Darwin faced a dilemma. In his great book On the Origin of Species, published in 1859, he proposed the theory of natural selection to explain the gradual appearance and disappearance of different forms of animals and plants over long periods of time. But he realized that the fossil record, on which he based his theory, was incomplete, especially for the beginning of life. The oldest fossils that had been found in Darwin’s time were complex organisms in rocks dated at about 550 million years ago (the Cambrian period). Where were the missing Precambrian fossils? These would surely provide a link to the origin of life. Conditions on Earth were probably suitable for the emergence of life by 4 billion years ago, about 600 million years after Earth began to form. But until recently there was no evidence for life older than the Cambrian. By the turn of the twentieth century, there was evidence for fossilized clumps of algae (simple aquatic photosynthetic organisms) in rocks at the base of the Grand Canyon that were close to 1 billion years old. It took nearly another century to push the clock of life back nearer to its origins. In 1993, geologist J. William Schopf found fossilized chains of cylindrical objects, quite similar in size and shape to contemporary cyanobacteria (“blue-green algae”), in rocks in Western Australia that he dated an astonishing 3.5 billion years old. He then used a chemical analysis method called laser Raman spectroscopy to show that these objects apparently contain carbon deposits that are chemical signatures of life. Rounded or cylindrical objects in the Earth’s rocks or in a meteorite from Mars get scientists excited because they realize that life is not just a bunch of macromolecules. Rather, life is macromolecules that can perform unique functions because they are enclosed in a structural compartment that is separate from the external environment. This separation allows living things to maintain a constant internal environment (homeostasis). The water-insoluble phospholipid structure that defines and contains cells is called the plasma membrane. It and its functions are so important. Subsequent pages will be devoted to the chemical activities that take place inside all cells.

Date: 2014-12-22; view: 954