THERE ARE MANY DIFFERENT CELL TYPES AMONG FUNGI, PROTOZOANS AND higher plants and animals. They differ in size, form and function, degree of specialization and mean generation time. Yet at the ultrastructural level there is a sameness about cells that is almost tedious. The same basic structures—nuclei, plastids, mitochondria, endoplasmic reticulum, Golgi bodies, lysosomes—appear with predictable regularity (figure 1.1). Whether this reflects a monophylogenetic origin of higher cells or convergence in response to selection pressures will be discussed later. The immediate point is that the monopoly position of these cell organelles in nature suggests that they comprise a winning formula, that is, a formula that facilitates the existence of cells as self-replicating self-regulating systems that operate according to known chemical and physical laws. However, there is another winning formula in nature, shown by bacteria and blue-green algae. These prokaryotic cells, as they are called, are immensely successful in terms of number of species and range of environments occupied. They carry out metabolic processes that are essentially similar to those of higher (eukaryotic) cells. They have sophisticated genetic systems, they synthesize complex macromolecules, they have efficient energy transforming mechanisms, and they show growth rates that are generally much faster than those of higher cells. Yet prokaryotic cells do not have internal organelle or membrane systems comparable to those in eukaryotes. Is a two-tier system of cell organization really necessary? What is the functional value of membrane-enclosed compartments in higher cells?
KeywordsOxidative Phosphorylation Thylakoid Membrane Prokaryotic Cell Golgi Body Envelope Membrane
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- Fawcett, D. W. (1966) The Cell: An Atlas of Fine Structure. Saunders, Philadelphia.Google Scholar
- Gunning, B. E. S. & Steer, M. W. (1975) Ultrastructure and the Biology of Plant Cells. Edward Arnold, London.Google Scholar
- Gunning, B. E. S. & Steer, M. W. (1975) Plant Cell Biology, an Ultrastructural Approach. Edward Arnold, London.Google Scholar
- Hall, J. L., Flowers, T. J. & Roberts, R. M. (1974) Plant Cell Structure and Metabolism. Longman.Google Scholar
- Smith, H. (1977) The Molecular Biology of Plant Cells. Botanical Monographs, Vol. 14. Black well Scientific Publications, Oxford.Google Scholar
- Stephenson, W. K. (1979) Concepts in Cell Biology. Wiley, New York.Google Scholar