Physiology of Metabolism

Abstract

Life processes are bound to a continuous turnover of matter and energy. Living organisms take up certain materials and energy from the environment, and release other materials and energy (particularly heat) into the environment. In thermodynamics (Greek therme, heat, and dynamis, power), such systems are described as open. Ultimately, the energy supplied to the biosphere is derived almost exclusively from sunlight. In the course of photosynthesis in green plants, this is transformed into chemical energy, whereby organic compounds are formed from inorganic substances. Autotrophic organisms (primary producers) are those that produce organic substances from inorganic compounds and energy. Plants using the energy of light are called photoautotrophs. Some microorganisms live chemoautotrophically, i.e., they use matter as well as energy derived from inorganic compounds. Heterotrophic organisms (consumers) live on primary producers; thus, they are dependent on organic compounds synthesized by primary producers, thereby satisfying their energy requirement. Among the heterotrophs, saprophytes feed on nonliving food sources, and parasites feed on living organisms (Table 5.1, see Sect. 8.1.1). Biotrophic parasites depend on a living host, whereas necrotrophic parasites kill their hosts.