Unit description Examines local and ocean climate systems and the way humans are altering the global climate, the impact that this may have on individual organisms and ecosystems, and the capacity for organisms to acclimatise or adapt to these changes. Specifically examines changes in the oceans carbon cycle, ocean acidification and ocean warming. Introductory Biology is a full course, day-by-day, teacher guide with editable PowerPoints for class notes, PDF printable version of the student book, editable Word doc assessments and keys, plus screen only PDF syllabus, pacing guide, detailed daily lesson plans and teacher version of student book. A change of one unit on the pH scale represents a change in the concentration of hydrogen ions by a factor of 10, a change in two units represents a change in the concentration of hydrogen ions by a factor of 100. Thus, small changes in pH represent large changes in the concentrations of hydrogen ions. Pure water is neutral. Download adobe flash media encoder for mac trial windows 7.
Our editors will review what you’ve submitted and determine whether to revise the article.Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work! Conrad H. Waddington
Biological development, the progressive changes in size, shape, and function during the life of an organism by which its genetic potentials (genotype) are translated into functioning mature systems (phenotype). Most modern philosophical outlooks would consider that development of some kind or other characterizes all things, in both the physical and biological worlds. Such points of view go back to the very earliest days of philosophy.
Among the pre-Socratic philosophers of Greek Ionia, half a millennium before Christ, some, like Heracleitus, believed that all natural things are constantly changing. In contrast, others, of whom Democritus is perhaps the prime example, suggested that the world is made up by the changing combinations of atoms, which themselves remain unaltered, not subject to change or development. The early period of post-Renaissance European science may be regarded as dominated by this latter atomistic view, which reached its fullest development in the period between Newton’s laws of physics and Dalton’s atomic theory of chemistry in the early 19th century. This outlook was never easily reconciled with the observations of biologists, and in the last hundred years a series of discoveries in the physical sciences have combined to swing opinion back toward the Heracleitan emphasis on the importance of process and development. The atom, which seemed so unalterable to Dalton, has proved to be divisible after all, and to maintain its identity only by processes of interaction between a number of component subatomic particles, which themselves must in certain aspects be regarded as processes rather than matter. Albert Einstein’s theory of relativity showed that time and space are united in continuum, which implies that all things are involved in time; that is to say, in development.
The philosophers who charted the transition from the nondevelopmental view, for which time was an accidental and inessential element, were Henri Bergson and, in particular, Alfred North Whitehead. Karl Marx and Friedrich Engels, with their insistence on the difference between dialectical and mechanical materialism, may be regarded as other important innovators of this trend, although the generality of their philosophy was somewhat compromised by the political context in which it was placed and the rigidity with which their later followers have interpreted it.
Philosophies of the Heracleitan type, which emphasize process and development, provide much more appropriate frameworks for biology than do philosophies of the atomistic kind. Living organisms confront biologists with changes of various kinds, all of which could be regarded as in some sense developmental; however, biologists have found it convenient to distinguish the changes and to use the word development for only one of them. Biological development can be defined as the series of progressive, nonrepetitive changes that occur during the life history of an organism. The kernel of this definition is to contrast development with, on the one hand, the essentially repetitive chemical changes involved in the maintenance of the body, which constitute “metabolism,” and on the other hand, with the longer term changes, which, while nonrepetitive, involve the sequence of several or many life histories, and which constitute evolution.
As with most formal definitions, these distinctions cannot always be applied strictly to the real world. In the viruses, for instance, and even in bacteria, it is difficult to make a distinction between metabolism and development, since the metabolic activity of a virus particle consists of little more than the development of new virus particles. In certain other cases, the distinction between development and evolution becomes blurred: the concept of an individual organism with a definite life history may be very difficult to apply in plants that reproduce by vegetative division, the breaking off of a part that can grow into another complete plant. The possibilities for debate that arise in these special cases, however, do not in any way invalidate the general usefulness of the distinctions as conventionally made in biology.
All organisms, including the very simplest, consist of two components, distinguished by a German biologist, August Weismann, at the end of the 19th century, as the “germ plasm” and the “soma.” The germ plasm consists of the essential elements, or genes, passed on from one generation to the next, and the soma consists of the body that may be produced as the organism develops. In more modern terms, Weismann’s germ plasm is identified with DNA (deoxyribonucleic acid), which carries, encoded in the complex structure of its molecule, the instructions necessary for the synthesis of the other compounds of the organism and their assembly into the appropriate structures. It is this whole collection of other compounds (proteins, fats, carbohydrates, and others) and their arrangement as a metabolically functioning organism that constitutes the soma. Biological development encompasses, therefore, all the processes concerned with implementing the instructions contained in the DNA. Those instructions can only be carried out by an appropriate executive machinery, the first phase of which is provided by the cell that carries the DNA into the next generation: in animals and plants by the fertilized egg cell; in viruses by the cell infected. In life histories that have more than a minimal degree of complexity, the executive machinery itself becomes modified as the genetic instructions are gradually put into operation, and new mechanisms of protein synthesis are brought into functional condition. The fundamental problem of developmental biology is to understand the interplay between the genetic instructions and the mechanisms by which those instructions are carried out.
In the language of genetics the word genotype is used to indicate the hereditary instructions passed on from one generation to another in the genes, while phenotype is the term given to the functioning organisms produced by those instructions. Biological development, therefore, consists of the production of phenotypes. The point made in the last paragraph is that the formation of the phenotype of one generation depends on the functioning of part of the phenotype of the previous generation (e.g., egg cell), as the mechanism that begins the interpretation of the instructions contained in the new organism’s genotype.
(Productivity is often measured by an increase in biomass, a term used to refer to the weight of all living organisms in an area. Biomass is reported in grams or metric tons.)Read More
…called the primary or secondary productivity (the former for plants, the latter for animals), is usually measured in units of energy, such as gram calories or kilojoules per square metre per year. Measures of weight—e.g., tons of carbon per square kilometre per year or gigatons of carbon per year—are also…Read More
The high level of plant production in estuaries supports a correspondingly high level of production of invertebrate animals and fish. Estuaries often contain beds of shellfish such as mussels and oysters and large populations of shrimps and crabs. Fish such as plaice and floundersRead More
Central to all biological activity within inland aquatic ecosystems is biological productivity or aquatic production. This involves two main processes: (1) primary production, in which living organisms form energy-rich organic material (biomass) from energy-poor inorganic materials in the environment through photosynthesis, and (2)…Read More
Primary productivity is the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances. The total amount of productivity in a region or system is gross primary productivity. A certain amount of organic material is used to sustain the…Read More
In the highly stressful desert environment, productivity is generally very low; however, it is also highly variable from time to time and from place to place. (For a full discussion of productivity, see biosphere: Resources of the biosphere.)Read More
Because of its importance for grazing and other grassland agricultural production, grassland productivity has been extensively investigated using various methods. However, most studies have focused only on aboveground productivity, ignoring the important subterranean component, which can be much more substantial—as much as 10…Read More
As stressful habitats for plants, mountain lands are not very productive environments. The biomass (dry weight of organic matter in an area) of the alpine vegetation on high temperate mountains, however, may be greater than it first appears because more than 10 times…Read More
Savannas have relatively high levels of net primary productivity compared with the actual biomass (dry mass of organic matter) of the vegetation at any one time. (For a full discussion of productivity, see biosphere: The photosynthetic process.) Most of this productivity is concentrated…Read More
Scrublands typically grow under conditions of high environmental stress. The typical climatic environment experienced by scrublands includes long periods of hot, dry weather in which lack of moisture is a limiting factor for plant growth. Furthermore, soil nutrient levels typically are very low.…Read More
The total aboveground biomass (dry weight of organic matter in an area) for temperate deciduous forests is typically 150 to 300 metric tons per hectare; values for temperate broad-leaved forests are generally higher, and those for sclerophyllous forests are lower. The subterranean component…Read More
Of all vegetation types, tropical rainforests grow in climatic conditions that are least limiting to plant growth. It is to be expected that the growth and productivity (total amount of organic matter produced per unit area per unit time) of tropical rainforests would…Read More
An important measure of natural ecosystems is the biological production of its plants and animals—that is, the total amount of biomass produced by living organisms within a given area in a specific period of time. In polar regions the greatest biological production occurs…Read More