Biology


Biology, the study of life and living things, includes major divisions of molecular biology, cytology or cell biology, organism biology, ecology, and biohistory.	Sapience Home Site Map About Sapience Science Biohistory Ecology Organism types Organism biology Cytology Molecular biology

Biology, the study of life and living things, includes major divisions of molecular biology, cytology or cell biology, organism biology, ecology, and biohistory.

Science

Biohistory

Biohistory follows the same organization as studies of earth history and run parallel to it. These include the Precambrian, Paleozoic, Mesozoic, and Cenozoic eras.

Ecology

Ecology includes major divisions of behavioral ecology, population ecology, community ecology, system ecology, evolution, ecosystems, and biogeography.

Systematics

This includes the study of types of organisms, including microbes, protists, plants, fungi, and animals and their classification.

Organism biology

This includes habitat, tissues, Organ systems, morphology or biological form, life cycle, and behavior.

Cytology, or cell biology, includes study of cell structure, such as the nucleus, organelles, the cytoskeleton, and walls and membranes. It also includes cellular function and behavior such as cellular reproduction and vital functions including respiration, photosyntesis, and nutrition It also includes discussion of types of cells.

Molecular biology

Molecular biology includes study of processes and structure below the level of the cell, many of which are common to all or many forms of life. It is divided by types of compounds, including inorganic molecules, small organic molecules, carbohydrates, lipids, proteins, and nucleic acids.


History Prehistory Early prehistory including the Pliocene, early Pleistocene, early mid Pleistocene, late mid Pleistocne, and late Pleistocene might be connected. Middle prehistory including the 5th decamillennium BP, 4th decamillennium BP, 3rd decamillennium BP, and 2nd decamillennium BP can be connected. Late prehistory including the early 8th millennium BC, late 8th millennium BC, early 7th millennium BC, late 7th millennium BC, early 6th millennium BC, and late 6th millennium BC can be connected. Antiquity The 5th millennium BC including the early 5th millennium BC, early mid 5th millennium BC, mid 5th millennium BC, late mid 5th millennium BC, and late 5th millennium BC can be connected. The 4th millennium BC including the early 4th millennium BC, early mid 4th millennium BC, mid 4th millennium BC, late mid 4th millennium BC, and late 4th millenium BC can be connected. The 3rd millennium BC including the early 3rd millennium BC, early mid 3rd millennium BC, mid 3rd millennium BC, late mid 3rd millennium BC, and late 3rd millennium BC can be connected. The 2nd millennium BC including the early 2nd millennium BC, early mid 2nd millennium BC, mid 2nd millennium BC, late mid 2nd millennium BC, and late 2nd millennium BC can be connected. The 1st millennium BC including the 10th century BC, 9th century BC, 8th century BC, 7th century BC, and 6th century BC might be connected. Classical and medieval history Early classical times including the 5th century BC, 5th century BC, 3rd century BC, 2nd century BC, and 1st century BC can be considered. Late classical times including the 1st century CE, 2nd century CE, 3rd century CE, 4th century CE, and 5th century CE can be considered. Early medieval times including the 6th century, 7th century, 8th century, 9th century, and 20th century can be connected. Late medieval times including the 11th century, 12th century, 13th century, 14th century, and 15th century can be considered. c 360-320 BC. Aristotle does various studies in natural science Modern history Most of the more interesting developments in biology are modern. At the beginning in the 16th century, biology was still mostly natural history and dealt with organisms. I do not yet have details of the early 16th century, early mid 16th century, mid 16th century, late mid 16th century, or late 16th century. There were some interesting developments in the 17th century, which laid the foundations of modern organism biology and expanded systematics. I do not yet have details of the early 17th century, early mid 17th century, mid 17th century, or late mid 17th century. The late 17th century including the early 1680s, late 1680s, early 1690s, and late 1690s can be connected. 1638 Harvey publishes work giving the first correct description of the function of the heart and circulation of the blood. 1674 - 1723 Leeuwenhoek uses microscope to discover and study insects, protozoa, and bacteria. 18th century I do not yet have specifics for the early 18th century, early mid 18th century, mid 18th century, or late-mid 18th century. The late 18th century including the early 1780s, late 1780s, early 1790s, and late 1790s can be connected. Developments in the 19th century were substantial. Development of the early 19th century, early mid 19th century, mid 19th century, late-mid 19th century, and late 19th century can be examined. c. 1847 - c. 1885 Pasteur establishes bacterial origin of many diseases and infections and develops methods of treatment. 1856 - 1869 Mendel establishes foundations of genetics. 1859 Darwin publishes his "Origin of Species" Developments in the 20th century are almost too numerous to mention, but include the development of molecular biology, details of cell biology, genetics, ecology, and better understanding of biological history. These developments continue in the early 20th century, early mid 20th century, mid 20th century, and late-mid 20th century. Late 20th century The early 1980s including 1981, 1982, 1983, 1984, and 1985 can be connected. The late 1980s including 1986, 1987, 1988, 1989, and 1990 can be connected. The early 1990s including 1991, 1992, 1993, 1994, 1995, and 1996 can be connected. The late 1990s including 1996, 1997, 1998, 1999, and 2000 can be connected. Early 21st century The early 2000s including 2001, 2001, 2003, 2004, and 2005 can be connected. The late 2000s during 2006 and 2007. 2008 including the first quarter, second quarter, third quarter with July, August, and September, and fourth quarter including October and November is connected. 2009 including the first quarter 2009, second quarter 2009, third quarter 2009, and fourth quarter 2009 can be connected. 2010 including the first quarter 2010, second quarter 2010, third quarter 2010, and fourth quarter 2010 can be connected. The early 2010s can be connected. 2011 can be connected. The first quarter 2011 can be connected. January 2011 including 2011 week 1, 2011 week 2, 2011 week 3, 2011 week 4, 2011 week 5, and 2011 week 6 can be connected. February 2011 and March 2011 can be connected. The second quarter 2011 including April 2011, May 2011, and June 2011 can be connected. Its future can be considered. The near future including next month, next quarter, and next year can be connected. The middle future and far future are obscure. Sociology Peoples of the world Peoples are important to the development of biology. This can be examined from the point of view of particular nations such as Japan, Mexico, the Philippines, Vietnam, Germany, Egypt, and Ethiopia. Much of the organized study has come from Western civilization including Russia can be connected. Anglic peoples including those of the United States can be connected. Latin peoples including those of Brazil can be connected. Asiatic peoples such as those of Bangladesh have been important in the study of biology. South Asian peoples including those of India and Pakistan have been important. Oriental peoples including China have also been important. Southeast Asian peoples including those of Indonesia can also be connected. African peoples including those of Nigeria can be connected. American Indians including those of the United States and Brazil can possibly be connected. Communities Communities such as Tokyo, Seoul, Mexico City, and New York City can be connected to biology. Social structure and change Social change Particular changes and movements The agricultural revolution can be connected. The agrarian revolution including bronze age developments, early iron age developments, late iron age developments, modernization can be connected. The industrial revolution including the early industrial revolution, middle industrial revolution, and late industrial revolution can be connected. Social change factors including institutional change, cultural change, demographic change, and natural change can be connected. Social change processes including innovation, transmission, adaptation, and extinction can be connected. Social types Industrial societies can be connected. Agrarian societies can be connected. Horticultural societies can be connected. Hunting and gathering societies can be connected. Social structure including cultural structure and anthropological structure can be connected. Community and regional structure can be connected. Class structure can be connected. Institutional structure can be connected. Institutions Religion Particular religions including Abrahamic religion, Asiatic religion, secularism, and pagan religions can be connected. Religious organization including highly structured, fragmented, and loosely structured organization can be connected. Religious practice is also cnnected to biology. Religious belief can be connected to biology. Government including government structure and law can be connected. Particular governments including international govermnent, national government, and local government can be connected. Government activity including state relations, administration, and succession can be connected. Economics including economic systems, industries, and economic activities is also connected to biology. Education including research, teaching, cultural institutions, educational organization, and particular schools is vital to the study of biology. Families including marriage, parenting, kinship, and particular families seems to be indirectly connected to biology. Culture Behavioral culture including cultural events, recreation and entertainment, occupations, and customs can be connected. It also depends on conceptual culture such as language, graphic arts, literature, mathematics, applied science, and philosophy. Material culture including industrial technology, building technology, foodstuffs, clothing, transportation technology, communication technology, and other artifacts can be connected. Anthropology Particular groups will be significant. Human geography including European geography, Asian geography, African Geography, North American Geography, South American Geography, and Oceanic geography will be useful. Human ecology including the influence of earth on people, human relations with other life, and human influence on the environment will be useful. Physical anthropology including human origins, racial variation, and human dispersion may be useful in studies of biology. Demography including population change, population size and structure, deths, migration, and births may be useful in biology.Social foundations including social group behavior, social group types, social control, social interaction, and social presentation may be useful in biology. Personal studies Individuals from the biography list who have been prominent in biology include: Aristotle Darwin Pasteur Psychology including social psychology, personality, mental disorders, developmental psychology, behavior patterns, mind, and behavioral elements will be useful. The human body somewhat overlaps with parts of biology. Form and appearance, life cycle, disease, body functions, and body systems from the human perspective often provide a starting point for study of other organisms.
Other science Earth science Earth science is important in biology, as earth is the only place where life is definitely known to exist. Biology has close connections to geohistory, including the Precambrian, Paleozoic, and Mesozoic Eras. The geology of the Cenozoic Era including Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene epochs can be investigated. Physical geography is also significant. Mapping is useful. Terrestrial geography is better accessible and better known than Oceanic geography. Atmospheric sciences including atmospheric structure, meteorology, and climatology are significant to biology. Hydrospheric science including oceanography, glaciology, groundwater, and fresh water is highly significant to biology. Geology including minerals, rocks, landforms, and geologic processes is important in biology, though interior geology seems to be less so.	Links to other sites: Yahoo directory- Biology Yahoo directory- Life Sciences Yahoo directory- Ecology Wikipedia - Biology
Astronomy Cosmology and galactic astronomy include largely speculative and theoretical biology, or xenobiology. The role of stellar astronomy, including the interstellar medium, stars, star clusters, and astrocartography, is becoming less speculative with the discovery of planets outside the Solar system. Solar system astronomy is vital. Life on earth depends on the sun, Studies of the possibility of life in various planetary systems are part of active plans for scientific investigation. The inner planets, including the earth, present possiblities, Gas giant systems and outer dwarf planets also present possiblities. The role of minor bodies and the interstellar medium is somewhat speculative. Studies of the origin of life are tied indirectly to solar system history Chemistry Chemical systems involve mostly organic chemistry, and a little bit of inorganic chemistry. They use a little bit of gas chemistry, and depend most heavily on liquid chemistry. They do not include a great deal of solid chemistry. Chemical changes are also useful. Nuclear reactions including fusion, transmutation, radioactive decay, and fission have limited significance but may apply. Chemical reactions including stoichiometry, mechanical changes, electronic rearrangement, chemical thermodynamics, and chemical kinetics are essential to biology. Physical changes including freezing, boiling, sublimation, mixing, and separation are also important to the study of life. Biological substances are highly important. Most biological substances are mixtures, and while solutions are important, heterogenous mixtures are even more so. There are a great many biological compounds important in biology. Various chemical classes of compounds can be considered. Most biologically important compounds are organic. Relatively few of these are inorganic. Water is the single most important compound in biology. Most living things are composed of only a few elements. Hydrogen is an essential component, although mostly incorporated into compounds. Oxygen is also important. Physics The structure of matter is useful. Exotic forms of matter are not known to have applications in biology. Bulk matter including solids, liquids, and gases also has applictions in biology. Molecular physics including chemical bonding and the structure and behavior of molecules is extremely important at certain levels in biology. Atomic physics including a little nuclear physics but mostly electronic physics has applications. Subatomic physics including particle types and interactions has become important in biology. Quantum theory and relativity theory are less directly significant. In electromagnetism, Optics including electromagnetic waves, geometric optics, physical optics, quantum optics, and the electromagnetic spectrum is very useful. Magnetism including current elements, assemblages, Magnetic field, force, flux, and magnetic properties of matter has few direct effects on living things. Electric current is somewht useful, though most living things do not tolerate large amounts of it. Electrostatics has some connection, although living matter is for the most part electrically neutral. Thermodynamics can be applied. Classical thermodynamics involves treating living things as a thermodynamic systems and considering their states and processes. It includes minimal use of statistical mechanics. Various areas make use of mechanics. Gravitation can be connected. Deformable body gravitation, rigid body gravitation, and particle gravitation are not really applicable to biological organisms. Surface gravitation is most important. Nonrigid mechanics including wave mechanics, fluid mechanics, and deformable bodies is also useful. Rigid body mechanics including dynamic systems, static systems, rotational dynamics, and rigid body descrption and motion is also important. Particle mechanics is often too simple to describe complicated biological systems, but has some fundamental concepts. Particle systems including simplified systems, interactions, and system properties can be used in examining biology. Energetics including power,, mechanical energy, and workcan also be used. Kinetic concepts including types and cases of force, force, momentum, and mass can be applied. Kinematic concepts including types and cases of motion, acceleration, velocity, and position can be examined. Biological systems can be described as particles only under limited circumstance.

History

Prehistory

Early prehistory including the Pliocene, early Pleistocene, early mid Pleistocene, late mid Pleistocne, and late Pleistocene might be connected. Middle prehistory including the 5th decamillennium BP, 4th decamillennium BP, 3rd decamillennium BP, and 2nd decamillennium BP can be connected. Late prehistory including the early 8th millennium BC, late 8th millennium BC, early 7th millennium BC, late 7th millennium BC, early 6th millennium BC, and late 6th millennium BC can be connected.

Antiquity

The 5th millennium BC including the early 5th millennium BC, early mid 5th millennium BC, mid 5th millennium BC, late mid 5th millennium BC, and late 5th millennium BC can be connected. The 4th millennium BC including the early 4th millennium BC, early mid 4th millennium BC, mid 4th millennium BC, late mid 4th millennium BC, and late 4th millenium BC can be connected. The 3rd millennium BC including the early 3rd millennium BC, early mid 3rd millennium BC, mid 3rd millennium BC, late mid 3rd millennium BC, and late 3rd millennium BC can be connected. The 2nd millennium BC including the early 2nd millennium BC, early mid 2nd millennium BC, mid 2nd millennium BC, late mid 2nd millennium BC, and late 2nd millennium BC can be connected. The 1st millennium BC including the 10th century BC, 9th century BC, 8th century BC, 7th century BC, and 6th century BC might be connected.

Classical and medieval history

Early classical times including the 5th century BC, 5th century BC, 3rd century BC, 2nd century BC, and 1st century BC can be considered. Late classical times including the 1st century CE, 2nd century CE, 3rd century CE, 4th century CE, and 5th century CE can be considered. Early medieval times including the 6th century, 7th century, 8th century, 9th century, and 20th century can be connected. Late medieval times including the 11th century, 12th century, 13th century, 14th century, and 15th century can be considered.

c 360-320 BC. Aristotle does various studies in natural science

Modern history

Most of the more interesting developments in biology are modern. At the beginning in the 16th century, biology was still mostly natural history and dealt with organisms. I do not yet have details of the early 16th century, early mid 16th century, mid 16th century, late mid 16th century, or late 16th century.

There were some interesting developments in the 17th century, which laid the foundations of modern organism biology and expanded systematics. I do not yet have details of the early 17th century, early mid 17th century, mid 17th century, or late mid 17th century. The late 17th century including the early 1680s, late 1680s, early 1690s, and late 1690s can be connected.

1638 Harvey publishes work giving the first correct description of the function of the heart and circulation of the blood.
1674 - 1723 Leeuwenhoek uses microscope to discover and study insects, protozoa, and bacteria.

18th century

I do not yet have specifics for the early 18th century, early mid 18th century, mid 18th century, or late-mid 18th century. The late 18th century including the early 1780s, late 1780s, early 1790s, and late 1790s can be connected.

Developments in the 19th century were substantial. Development of the early 19th century, early mid 19th century, mid 19th century, late-mid 19th century, and late 19th century can be examined.

c. 1847 - c. 1885 Pasteur establishes bacterial origin of many diseases and infections and develops methods of treatment.
1856 - 1869 Mendel establishes foundations of genetics.
1859 Darwin publishes his "Origin of Species"

Developments in the 20th century are almost too numerous to mention, but include the development of molecular biology, details of cell biology, genetics, ecology, and better understanding of biological history. These developments continue in the early 20th century, early mid 20th century, mid 20th century, and late-mid 20th century.

Late 20th century

The early 1980s including 1981, 1982, 1983, 1984, and 1985 can be connected. The late 1980s including 1986, 1987, 1988, 1989, and 1990 can be connected. The early 1990s including 1991, 1992, 1993, 1994, 1995, and 1996 can be connected. The late 1990s including 1996, 1997, 1998, 1999, and 2000 can be connected.

Early 21st century

The early 2000s including 2001, 2001, 2003, 2004, and 2005 can be connected.

The late 2000s during 2006 and 2007. 2008 including the first quarter, second quarter, third quarter with July, August, and September, and fourth quarter including October and November is connected. 2009 including the first quarter 2009, second quarter 2009, third quarter 2009, and fourth quarter 2009 can be connected. 2010 including the first quarter 2010, second quarter 2010, third quarter 2010, and fourth quarter 2010 can be connected.

The early 2010s can be connected. 2011 can be connected. The first quarter 2011 can be connected. January 2011 including 2011 week 1, 2011 week 2, 2011 week 3, 2011 week 4, 2011 week 5, and 2011 week 6 can be connected. February 2011 and March 2011 can be connected. The second quarter 2011 including April 2011, May 2011, and June 2011 can be connected.

Its future can be considered. The near future including next month, next quarter, and next year can be connected. The middle future and far future are obscure.

Sociology

Peoples of the world

Peoples are important to the development of biology. This can be examined from the point of view of particular nations such as Japan, Mexico, the Philippines, Vietnam, Germany, Egypt, and Ethiopia. Much of the organized study has come from Western civilization including Russia can be connected. Anglic peoples including those of the United States can be connected. Latin peoples including those of Brazil can be connected. Asiatic peoples such as those of Bangladesh have been important in the study of biology. South Asian peoples including those of India and Pakistan have been important. Oriental peoples including China have also been important. Southeast Asian peoples including those of Indonesia can also be connected. African peoples including those of Nigeria can be connected. American Indians including those of the United States and Brazil can possibly be connected.

Communities

Communities such as Tokyo, Seoul, Mexico City, and New York City can be connected to biology.

Social structure and change

Social change

Particular changes and movements

The agricultural revolution can be connected. The agrarian revolution including bronze age developments, early iron age developments, late iron age developments, modernization can be connected. The industrial revolution including the early industrial revolution, middle industrial revolution, and late industrial revolution can be connected. Social change factors including institutional change, cultural change, demographic change, and natural change can be connected. Social change processes including innovation, transmission, adaptation, and extinction can be connected.

Social types

Industrial societies can be connected. Agrarian societies can be connected. Horticultural societies can be connected. Hunting and gathering societies can be connected.

Social structure including cultural structure and anthropological structure can be connected. Community and regional structure can be connected. Class structure can be connected. Institutional structure can be connected.

Institutions

Religion

Particular religions including Abrahamic religion, Asiatic religion, secularism, and pagan religions can be connected. Religious organization including highly structured, fragmented, and loosely structured organization can be connected. Religious practice is also cnnected to biology. Religious belief can be connected to biology.

Government including government structure and law can be connected. Particular governments including international govermnent, national government, and local government can be connected. Government activity including state relations, administration, and succession can be connected.

Economics including economic systems, industries, and economic activities is also connected to biology. Education including research, teaching, cultural institutions, educational organization, and particular schools is vital to the study of biology. Families including marriage, parenting, kinship, and particular families seems to be indirectly connected to biology.

Culture

Behavioral culture including cultural events, recreation and entertainment, occupations, and customs can be connected. It also depends on conceptual culture such as language, graphic arts, literature, mathematics, applied science, and philosophy. Material culture including industrial technology, building technology, foodstuffs, clothing, transportation technology, communication technology, and other artifacts can be connected.

Anthropology

Particular groups will be significant. Human geography including European geography, Asian geography, African Geography, North American Geography, South American Geography, and Oceanic geography will be useful. Human ecology including the influence of earth on people, human relations with other life, and human influence on the environment will be useful. Physical anthropology including human origins, racial variation, and human dispersion may be useful in studies of biology. Demography including population change, population size and structure, deths, migration, and births may be useful in biology.Social foundations including social group behavior, social group types, social control, social interaction, and social presentation may be useful in biology.

Personal studies

Individuals from the biography list who have been prominent in biology include:

Psychology including social psychology, personality, mental disorders, developmental psychology, behavior patterns, mind, and behavioral elements will be useful. The human body somewhat overlaps with parts of biology. Form and appearance, life cycle, disease, body functions, and body systems from the human perspective often provide a starting point for study of other organisms.

Other science

Earth science

Earth science is important in biology, as earth is the only place where life is definitely known to exist.

Biology has close connections to geohistory, including the Precambrian, Paleozoic, and Mesozoic Eras. The geology of the Cenozoic Era including Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene epochs can be investigated. Physical geography is also significant. Mapping is useful. Terrestrial geography is better accessible and better known than Oceanic geography. Atmospheric sciences including atmospheric structure, meteorology, and climatology are significant to biology. Hydrospheric science including oceanography, glaciology, groundwater, and fresh water is highly significant to biology. Geology including minerals, rocks, landforms, and geologic processes is important in biology, though interior geology seems to be less so.

Astronomy

Cosmology and galactic astronomy include largely speculative and theoretical biology, or xenobiology. The role of stellar astronomy, including the interstellar medium, stars, star clusters, and astrocartography, is becoming less speculative with the discovery of planets outside the Solar system. Solar system astronomy is vital. Life on earth depends on the sun, Studies of the possibility of life in various planetary systems are part of active plans for scientific investigation. The inner planets, including the earth, present possiblities, Gas giant systems and outer dwarf planets also present possiblities. The role of minor bodies and the interstellar medium is somewhat speculative. Studies of the origin of life are tied indirectly to solar system history

Chemistry

Chemical systems involve mostly organic chemistry, and a little bit of inorganic chemistry. They use a little bit of gas chemistry, and depend most heavily on liquid chemistry. They do not include a great deal of solid chemistry.

Chemical changes are also useful. Nuclear reactions including fusion, transmutation, radioactive decay, and fission have limited significance but may apply. Chemical reactions including stoichiometry, mechanical changes, electronic rearrangement, chemical thermodynamics, and chemical kinetics are essential to biology. Physical changes including freezing, boiling, sublimation, mixing, and separation are also important to the study of life.

Biological substances are highly important. Most biological substances are mixtures, and while solutions are important, heterogenous mixtures are even more so. There are a great many biological compounds important in biology. Various chemical classes of compounds can be considered. Most biologically important compounds are organic. Relatively few of these are inorganic. Water is the single most important compound in biology. Most living things are composed of only a few elements. Hydrogen is an essential component, although mostly incorporated into compounds. Oxygen is also important.

Physics

The structure of matter is useful. Exotic forms of matter are not known to have applications in biology. Bulk matter including solids, liquids, and gases also has applictions in biology. Molecular physics including chemical bonding and the structure and behavior of molecules is extremely important at certain levels in biology. Atomic physics including a little nuclear physics but mostly electronic physics has applications. Subatomic physics including particle types and interactions has become important in biology.

Quantum theory and relativity theory are less directly significant. In electromagnetism, Optics including electromagnetic waves, geometric optics, physical optics, quantum optics, and the electromagnetic spectrum is very useful. Magnetism including current elements, assemblages, Magnetic field, force, flux, and magnetic properties of matter has few direct effects on living things. Electric current is somewht useful, though most living things do not tolerate large amounts of it. Electrostatics has some connection, although living matter is for the most part electrically neutral.

Thermodynamics can be applied. Classical thermodynamics involves treating living things as a thermodynamic systems and considering their states and processes. It includes minimal use of statistical mechanics.

Various areas make use of mechanics. Gravitation can be connected. Deformable body gravitation, rigid body gravitation, and particle gravitation are not really applicable to biological organisms. Surface gravitation is most important. Nonrigid mechanics including wave mechanics, fluid mechanics, and deformable bodies is also useful.

Rigid body mechanics including dynamic systems, static systems, rotational dynamics, and rigid body descrption and motion is also important.

Particle mechanics is often too simple to describe complicated biological systems, but has some fundamental concepts. Particle systems including simplified systems, interactions, and system properties can be used in examining biology. Energetics including power,, mechanical energy, and workcan also be used. Kinetic concepts including types and cases of force, force, momentum, and mass can be applied. Kinematic concepts including types and cases of motion, acceleration, velocity, and position can be examined. Biological systems can be described as particles only under limited circumstance.

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