Therefore evidence of mutagenic activity in vivo may indicate that a substance has a potential for carcinogenic effects. It is made up of four layers. California Academy of Sciences. Weizmann Institute - Science Art Gallery. Susan B Anthony VM. To prepare for careers in the field of energy and natural resource systems, students must attain academic skills and knowledge, acquire technical knowledge and skills related to energy and natural resources and the workplace, and develop knowledge and skills regarding career opportunities, entry requirements, and industry expectations. In vitro alternatives that have been scientifically validated and accepted shall be used to make classification decisions.
Systems Biology in Toxicology and Environmental Health
The climate of a region depends on a number of factors, especially latitude. A latitudinal band of the surface with similar climatic attributes forms a climate region. There are a number of such regions, ranging from the tropical climate at the equator to the polar climate in the northern and southern extremes.
Weather is also influenced by the seasons, which result from the Earth 's axis being tilted relative to its orbital plane. Thus, at any given time during the summer or winter, one part of the Earth is more directly exposed to the rays of the sun. This exposure alternates as the Earth revolves in its orbit. At any given time, regardless of season, the northern and southern hemispheres experience opposite seasons.
Weather is a chaotic system that is readily modified by small changes to the environment , so accurate weather forecasting is limited to only a few days. Water is a chemical substance that is composed of hydrogen and oxygen and is vital for all known forms of life.
Additionally, a minute amount of the Earth's water is contained within biological bodies and manufactured products. An ocean is a major body of saline water , and a principal component of the hydrosphere. More than half of this area is over 3, meters 9, feet deep. Average oceanic salinity is around 35 parts per thousand ppt 3. Though generally recognized as several 'separate' oceans, these waters comprise one global, interconnected body of salt water often referred to as the World Ocean or global ocean.
The major oceanic divisions are defined in part by the continents , various archipelagos , and other criteria: Smaller regions of the oceans are called seas, gulfs , bays and other names. There are also salt lakes , which are smaller bodies of landlocked saltwater that are not interconnected with the World Ocean.
A lake from Latin lacus is a terrain feature or physical feature , a body of liquid on the surface of a world that is localized to the bottom of basin another type of landform or terrain feature; that is, it is not global and moves slowly if it moves at all.
On Earth, a body of water is considered a lake when it is inland, not part of the ocean, is larger and deeper than a pond, and is fed by a river. It is not known if Titan's lakes are fed by rivers, though Titan's surface is carved by numerous river beds. Natural lakes on Earth are generally found in mountainous areas, rift zones , and areas with ongoing or recent glaciation.
Other lakes are found in endorheic basins or along the courses of mature rivers. In some parts of the world, there are many lakes because of chaotic drainage patterns left over from the last Ice Age. All lakes are temporary over geologic time scales, as they will slowly fill in with sediments or spill out of the basin containing them.
A pond is a body of standing water , either natural or man-made, that is usually smaller than a lake. A wide variety of man-made bodies of water are classified as ponds, including water gardens designed for aesthetic ornamentation, fish ponds designed for commercial fish breeding, and solar ponds designed to store thermal energy. Ponds and lakes are distinguished from streams via current speed.
While currents in streams are easily observed, ponds and lakes possess thermally driven micro-currents and moderate wind driven currents. These features distinguish a pond from many other aquatic terrain features, such as stream pools and tide pools. A river is a natural watercourse ,  usually freshwater , flowing toward an ocean, a lake, a sea or another river.
In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, and rill; there is no general rule that defines what can be called a river. Many names for small rivers are specific to geographic location; one example is Burn in Scotland and North-east England. Sometimes a river is said to be larger than a creek, but this is not always the case, due to vagueness in the language.
Water within a river is generally collected from precipitation through surface runoff , groundwater recharge, springs , and the release of stored water in natural ice and snowpacks i. A stream is a flowing body of water with a current , confined within a bed and stream banks. In the United States, a stream is classified as a watercourse less than 60 feet 18 metres wide.
Streams are important as conduits in the water cycle , instruments in groundwater recharge , and they serve as corridors for fish and wildlife migration.
The biological habitat in the immediate vicinity of a stream is called a riparian zone. Given the status of the ongoing Holocene extinction , streams play an important corridor role in connecting fragmented habitats and thus in conserving biodiversity. The study of streams and waterways in general involves many branches of inter-disciplinary natural science and engineering, including hydrology , fluvial geomorphology , aquatic ecology , fish biology , riparian ecology , and others.
Ecosystems are composed of a variety of abiotic and biotic components that function in an interrelated way. Variations of these factors will initiate dynamic modifications to the ecosystem.
Some of the more important components are: Central to the ecosystem concept is the idea that living organisms interact with every other element in their local environment. Eugene Odum, a founder of ecology, stated: A smaller unit of size is called a microecosystem. For example, a microsystem can be a stone and all the life under it.
A macroecosystem might involve a whole ecoregion , with its drainage basin. Wilderness is generally defined as areas that have not been significantly modified by human activity. Wilderness areas can be found in preserves, estates, farms, conservation preserves, ranches, national forests , national parks , and even in urban areas along rivers, gulches, or otherwise undeveloped areas.
Wilderness areas and protected parks are considered important for the survival of certain species , ecological studies, conservation , and solitude. Some nature writers believe wilderness areas are vital for the human spirit and creativity,  and some ecologists consider wilderness areas to be an integral part of the Earth's self-sustaining natural ecosystem the biosphere.
They may also preserve historic genetic traits and that they provide habitat for wild flora and fauna that may be difficult or impossible to recreate in zoos , arboretums , or laboratories. Although there is no universal agreement on the definition of life, scientists generally accept that the biological manifestation of life is characterized by organization , metabolism , growth , adaptation , response to stimuli , and reproduction.
Properties common to terrestrial organisms plants, animals, fungi , protists , archaea , and bacteria are that they are cellular, carbon-and-water-based with complex organization, having a metabolism, a capacity to grow, respond to stimuli, and reproduce. An entity with these properties is generally considered life. However, not every definition of life considers all of these properties to be essential.
Human-made analogs of life may also be considered to be life. From the broadest geophysiological point of view, the biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere rocks , hydrosphere water , and atmosphere air. Over nine-tenths of the total biomass on Earth is plant life, on which animal life depends very heavily for its existence. The origin of life on Earth is not well understood, but it is known to have occurred at least 3.
Once life had appeared, the process of evolution by natural selection resulted in the development of ever-more diverse life forms. Species that were unable to adapt to the changing environment and competition from other life forms became extinct.
However, the fossil record retains evidence of many of these older species. Current fossil and DNA evidence shows that all existing species can trace a continual ancestry back to the first primitive life forms.
When basic forms of plant life developed the process of photosynthesis the sun's energy could be harvested to create conditions which allowed for more complex life forms. The incorporation of smaller cells within larger ones resulted in the development of yet more complex cells called eukaryotes.
With the ozone layer absorbing harmful ultraviolet radiation , life colonized the surface of Earth. The first form of life to develop on the Earth were microbes, and they remained the only form of life until about a billion years ago when multi-cellular organisms began to appear.
They include Bacteria, Fungi , Archaea , and Protista. These life forms are found in almost every location on the Earth where there is liquid water, including in the Earth's interior. The combination of a high mutation rate and a horizontal gene transfer  ability makes them highly adaptable, and able to survive in new environments, including outer space. However, some microorganisms are pathogenic and can post health risk to other organisms.
Originally Aristotle divided all living things between plants, which generally do not move fast enough for humans to notice, and animals. In Linnaeus ' system, these became the kingdoms Vegetabilia later Plantae and Animalia. Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these are still often considered plants in many contexts.
Bacterial life is sometimes included in flora,   and some classifications use the term bacterial flora separately from plant flora. Among the many ways of classifying plants are by regional floras , which, depending on the purpose of study, can also include fossil flora , remnants of plant life from a previous era. People in many regions and countries take great pride in their individual arrays of characteristic flora, which can vary widely across the globe due to differences in climate and terrain.
Regional floras commonly are divided into categories such as native flora and agricultural and garden flora , the lastly mentioned of which are intentionally grown and cultivated. Some types of "native flora" actually have been introduced centuries ago by people migrating from one region or continent to another, and become an integral part of the native, or natural flora of the place to which they were introduced.
This is an example of how human interaction with nature can blur the boundary of what is considered nature. Another category of plant has historically been carved out for weeds. Though the term has fallen into disfavor among botanists as a formal way to categorize "useless" plants, the informal use of the word "weeds" to describe those plants that are deemed worthy of elimination is illustrative of the general tendency of people and societies to seek to alter or shape the course of nature.
Similarly, animals are often categorized in ways such as domestic , farm animals , wild animals , pests , etc. Animals as a category have several characteristics that generally set them apart from other living things. Animals are eukaryotic and usually multicellular although see Myxozoa , which separates them from bacteria, archaea , and most protists. They are heterotrophic , generally digesting food in an internal chamber, which separates them from plants and algae.
They are also distinguished from plants, algae, and fungi by lacking cell walls. With a few exceptions—most notably the two phyla consisting of sponges and placozoans —animals have bodies that are differentiated into tissues. These include muscles , which are able to contract and control locomotion, and a nervous system , which sends and processes signals.
There is also typically an internal digestive chamber. The eukaryotic cells possessed by all animals are surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells , bones , and spicules , a framework upon which cells can move about and be reorganized during development and maturation, and which supports the complex anatomy required for mobility. Although humans comprise only a minuscule proportion of the total living biomass on Earth, the human effect on nature is disproportionately large.
Because of the extent of human influence, the boundaries between what humans regard as nature and "made environments" is not clear cut except at the extremes. Even at the extremes, the amount of natural environment that is free of discernible human influence is diminishing at an increasingly rapid pace.
The development of technology by the human race has allowed the greater exploitation of natural resources and has helped to alleviate some of the risk from natural hazards. In spite of this progress, however, the fate of human civilization remains closely linked to changes in the environment.
There exists a highly complex feedback loop between the use of advanced technology and changes to the environment that are only slowly becoming understood. Humans have contributed to the extinction of many plants and animals.
Humans employ nature for both leisure and economic activities. The acquisition of natural resources for industrial use remains a sizable component of the world's economic system. Agriculture was first adopted around the 9th millennium BCE. Ranging from food production to energy, nature influences economic wealth. Although early humans gathered uncultivated plant materials for food and employed the medicinal properties of vegetation for healing,  most modern human use of plants is through agriculture.
The clearance of large tracts of land for crop growth has led to a significant reduction in the amount available of forestation and wetlands, resulting in the loss of habitat for many plant and animal species as well as increased erosion. Beauty in nature has historically been a prevalent theme in art and books, filling large sections of libraries and bookstores. That nature has been depicted and celebrated by so much art, photography, poetry, and other literature shows the strength with which many people associate nature and beauty.
Reasons why this association exists, and what the association consists of, are studied by the branch of philosophy called aesthetics. Beyond certain basic characteristics that many philosophers agree about to explain what is seen as beautiful, the opinions are virtually endless.
An early tradition of landscape art began in China during the Tang Dynasty — The tradition of representing nature as it is became one of the aims of Chinese painting and was a significant influence in Asian art. Although natural wonders are celebrated in the Psalms and the Book of Job , wilderness portrayals in art became more prevalent in the s, especially in the works of the Romantic movement.
British artists John Constable and J. Turner turned their attention to capturing the beauty of the natural world in their paintings. Before that, paintings had been primarily of religious scenes or of human beings. William Wordsworth 's poetry described the wonder of the natural world, which had formerly been viewed as a threatening place.
Increasingly the valuing of nature became an aspect of Western culture. A common classical idea of beautiful art involves the word mimesis , the imitation of nature. Also in the realm of ideas about beauty in nature is that the perfect is implied through perfect mathematical forms and more generally by patterns in nature.
As David Rothenburg writes, "The beautiful is the root of science and the goal of art, the highest possibility that humanity can ever hope to see". Some fields of science see nature as matter in motion, obeying certain laws of nature which science seeks to understand. Matter is commonly defined as the substance of which physical objects are composed. It constitutes the observable universe. The visible components of the universe are now believed to compose only 4.
The remainder is believed to consist of The behavior of matter and energy throughout the observable universe appears to follow well-defined physical laws. These laws have been employed to produce cosmological models that successfully explain the structure and the evolution of the universe we can observe. The mathematical expressions of the laws of physics employ a set of twenty physical constants  that appear to be static across the observable universe.
Outer space, also simply called space , refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. Outer space is used to distinguish it from airspace and terrestrial locations.
There is no discrete boundary between the Earth's atmosphere and space, as the atmosphere gradually attenuates with increasing altitude. Outer space within the Solar System is called interplanetary space , which passes over into interstellar space at what is known as the heliopause.
Outer space is sparsely filled with several dozen types of organic molecules discovered to date by microwave spectroscopy , blackbody radiation left over from the big bang and the origin of the universe, and cosmic rays , which include ionized atomic nuclei and various subatomic particles.
There is also some gas, plasma and dust , and small meteors. Additionally, there are signs of human life in outer space today, such as material left over from previous manned and unmanned launches which are a potential hazard to spacecraft.
Some of this debris re-enters the atmosphere periodically. Although the Earth is the only body within the solar system known to support life, evidence suggests that in the distant past the planet Mars possessed bodies of liquid water on the surface. At present though, most of the water remaining on Mars is frozen. If life exists at all on Mars, it is most likely to be located underground where liquid water can still exist.
Conditions on the other terrestrial planets, Mercury and Venus , appear to be too harsh to support life as we know it. But it has been conjectured that Europa , the fourth-largest moon of Jupiter , may possess a sub-surface ocean of liquid water and could potentially host life. Astronomers have started to discover extrasolar Earth analogs — planets that lie in the habitable zone of space surrounding a star , and therefore could possibly host life as we know it.
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