9 August 2005
An anion is a negatively charged ion, i.e., one that would be attracted to the anode in electrolysis.
The opposite of cation.
8 October 2007
Apoptosis is the death of cells that occurs as a normal and controlled part of an growth or development.
Also called programmed cell death.
Originating in the 1970s, from the Greek "apo" (from) and "ptosis" (falling/a fall), ie. "falling off."
21 February 2009
An atom, roughly 10 to the minus 8 cm in diameter, consists of a tiny, dense, positively charged nucleus made of neutrons and protons, surrounded by a cloud of negatively charged electrons.
Each chemical element consists of atoms that possess a characteristic number of protons.
Atoms are held together in molecules by sharing electrons.
10 August 2005
Atomic mass refers to the mass of an atom of a chemical element expressed in atomic mass units.
It is approximately equivalent to the number of protons and neutrons in the atom (the mass number) or to the average number allowing for the relative abundances of different isotopes.
10 August 2005
These are a unit of mass used to express atomic mass (also referred to as "atomic weight") and molecular weights, equal to one-twelfth of the mass of an atom of carbon-12. It is equal to approximately 1.66 x 10 -27 kg.
10 August 2005
The atomic number indicates the number of protons in the nucleus of an atom, which determines the chemical properties of an element and its place in the periodic table.
9 August 2005
A cation is a positively charged ion, i.e., one that would be attracted to the cathode in electrolysis.
The opposite of anion.
2 July 2009
A cytokine is any of a number of substances, such as interferon, interleukin, and growth factors, that are secreted by certain cells of the immune system and have an effect on other cells.
See also phagocyte, leukocyte, monocyte and lymphocyte.
Also refer Hostile Marital Interactions, Proinflammatory Cytokine Production, and Wound Healing.
27 November 2007
Cytoplasm is the material or protoplasm within a living cell, excluding the nucleus. Compare with protoplasm.
See Gernetic Cytobi.
14 February 2009
An electron is a stable subatomic particle with a charge of negative electricity, found in all atoms and acting as the primary carrier of electricity in solids.
- An electron's mass is about 9x10-28g,1,836 times less than that of the proton.
- Electrons orbit the positively charged nuclei of atoms and are responsible for binding atoms together in molecules and for the electrical, thermal, optical, and magnetic properties of solids.
- Electric currents in metals and in semiconductors consist of a flow of electrons, and light, radio waves, X-rays, and much heat radiation are all produced by accelerating and decelerating electrons.
9 August 2005
Hydrogen is a colorless, odourless and highly flammable gas. It is the chemical element with the atomic number 1.
- Hydrogen is the lightest of the chemical elements and has the simplest atomic structure, a single electron orbiting a nucleus consisting of a single proton.
- Hydrogen is by far the commonest element in the universe, although not on the earth, where it occurs chiefly combined with oxygen as water.
27 October 2009
Ions are atoms or molecules that carry an electric charge due to the loss or gain of one or more electrons.
See also cation and anion.
ORIGIN
Middle 19th century.
From Greek, neuter present participle of ienai meaning ‘go.’
10 August 2005
An isotope is each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.
ORIGIN
1913: coined by F. Soddy, from iso- [equal] + Greek topos ‘place’ (because the isotopes occupy the same place in the periodic table of elements).
29 December 2005
A leukocyte is a colourless cell that circulates in the blood and body fluids and is involved in counteracting foreign substances and disease.
A leukocyte is a white (blood) cell.
There are several types including lymphocytes, granulocytes, monocytes, and macrophages.
See also phagocyte.
7 November 2007
A mitochondrion is an organelle found in large numbers in skin cells, in which the biochemical processes of respiration and energy production occur.
It has a double membrane, the inner layer being folded inward to form layers (cristae).
Mitochondrial is the adjective of this noun.
The word originates in the early 20th century, in modern Latin, from the Green "mitos" meaning "thread" and "khondrion" the diminutive "khondros" meaning "granule."
10 August 2005
Molecular weight is the ratio of the average mass of one molecule of an element or compound to one twelfth of the mass of an atom of carbon-12.
10 August 2005
A neutron is a subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen.
ORIGIN
Early 20th century.
From neutral + -on.
20 February 2009
The nucleus is the central and most important part of an atom.
In biology, the nucleus a dense organelle present in most eukaryotic cells, including skin cells, and is typically a single rounded structure bounded by a double membrane that contains genetic material.
ORIGIN
Early 18th century.
From Latin, literally the word itself nucleus, meaning ‘kernel, inner part,’ diminutive of nux, nuc- ‘nut.’
29 December 2005
An organelle is any of a number of organized or specialized structures within a living cell, for example skin cells.
10 August 2005
This is a table of the chemical elements arranged in order of atomic number, usually in rows, so that elements with similar atomic structure (and hence similar chemical properties) appear in vertical columns.
29 December 2005
A phagocyte is a type of cell within the body capable of engulfing and absorbing bacteria and other small cells and particles.
Derivative:
Phagocytic (adjective).
Origin:
Late 19th Century, from the Greek phago" meaning "eating."
See also leukocyte, cytokine, monocyte and lymphocyte.
10 August 2005
A prokaryote is a microscopic single-celled organism, including the bacteria and cyanobacteria, that has neither a distinct nucleus with a membrane nor other specialized organelles. Compare with eukaryote.
10 August 2005
A proton is a stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign.
ORIGIN
1920s, from the Greek, neuter of protos meaning ‘first.’
7 July 2007
The protoplasm is the colorless material comprising the living part of a cell, including the cytoplasm, nucleus, and other organelles.
10 August 2005
Subatomic (as in "subatomic particle") simply means smaller than or occuring within an atom.