Animal Physiology
Animal physiology is the study of how animals work, and investigates the biological processes that occur for animal life to exist. These processes can be studied at various levels of organization from membranes through to organelles, cells, organs, organ systems, and to the whole animal. Animal physiology examines how biological processes function, how they operate under various environmental conditions, and how these processes are regulated and integrated. The study of animal physiology is closely linked with anatomy (i.e., the relationship of function with structure) and with the basic physical and chemical laws that constrain living as well as nonliving systems. Although all animals must function within basic physical and chemical constraints, there is a diversity of mechanisms and processes by which different animals work. A comparative approach to animal physiology highlights underlying principles, and reveals diverse solutions to various environmental challenges. It can reveal similar solutions to a common problem, or modifications of a particular physiological system to function under diverse conditions. The discipline of animal physiology is diverse and here the major areas of research and investigation are outlined.
TROPICAL SOILS | Humid Tropical☆
S.W. Buol, in Reference Module in Earth Systems and Environmental Sciences, 2013
Chemical and Mineralogical Composition of Soils
Of the chemical elements essential for plant and animal physiology, only carbon, oxygen, and hydrogen, are derived directly from air and water. Nitrogen and to some extent sulfur are derived from the air but must be present as inorganic ions in the soil before they can be utilize by plants. The other essential elements are obtained from the dissolution of minerals in the soil. Essential element bearing minerals are derived from the geologic material within which the soil is formed. An inadequate supply of any essential element limits plant growth. The most frequent limitations result from insufficient plant-available nitrogen, phosphorus, potassium, calcium, or magnesium.
Practically no nitrogen is present in soil minerals. Nitrogen enters the soil as ammonium and nitrate dissolved in rainwater or via fixation from the air by nitrogen-fixing microbes in the soil. Some nitrogen-fixing microbes in the soil are symbiotic and the nitrogen they extract from the air is incorporated into their legume plant host. Other nitrogen-fixing microbes are not symbiotic, and the nitrogen they extract from the air is incorporated into their cells. Nitrogen is also present in the organic residues of dead organisms in and on the surface layers of soil. Plants do not ingest the organic forms of nitrogen but as microbes in the soil decompose organic residues and exhaust carbon dioxide to the air inorganic forms of nitrogen are released into the soil solution and become available to growing plants, leach into the groundwater during periods of excessive rainfall, or return to the air as nitrogen gas during periods when the soil is saturated with water. Plant-available nitrogen contents in soil are transient and closely related to the nitrogen content in the organic residue and the rate at which the residue is decomposing.
Phosphorus is present in only a few minerals in the soil. Apatite, a soluble calcium phosphate mineral capable of supplying plant-available phosphorus, is the most common source of phosphorus and most abundant in soil formed in limestone. Iron and aluminum phosphate minerals are extremely insoluble and do not release phosphorus rapidly enough for rapid plant growth. Soils with high iron and aluminum contents tend to absorb phosphate applied as fertilizer and decrease its availability to plants. This is a serious problem in attempts to fertilize food crops in many soils in the tropics.
Potassium is present in mica and feldspar minerals. These minerals are rather easily decomposed in the soil environment and consequently are sparse in soils formed in siliceous materials and sediments that have been repeatedly transported and deposited on the land surface.
Calcium and magnesium are most abundant in carbonate minerals associated with limestone and some carbonate rich sandstone. Carbonate minerals are also relatively unstable when subjected to weathering and therefore most abundant in soils formed directly from limestone, some sandstone, and recently deposited sediments derived from carbonate rich rock.
