Dr. Paul's Virtually Biology Show.

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E

Ecology. The science which studies the interrelationships between different organisms with each other and with the non living environment.
Ecosystem. The sum of the living and non living components found in a particular area; Community plus non living environment.

Endosymbiotic hypothesis. The idea that certain organelles in eukaryotic cells such as chloroplasts, mitochondria, were orginally free living organisms that became associated with the ancestors or eukaryotes.

Effector. The part of an organism that produces a change in response to a signal or stimulus.

Electron. Electrons are lightweight negatively charged particles that surround the atom in different shells(energy levels) and orbitals(volumes of space") within the same energy level or shell. The further on average the electron is from the nucleus the more energy the electron has. This is important since the transfer of energy in chemical reactions involves the transfer of electrons.
Electron transport system(ETS).A series of proteins found in the plasma membranes of certain organelles and also in the cell membranes of many prokaryotes. These proteins carry electrons from one spot to another and as the electrons are carried the energy contained by the electrons is exploited to do work. This work is usually involved with making ATP.
Electrophoresis. A series of techniques which are used to separate proteins, nucleic acids or other biologically important compounds based on the relative distance traveled toward a positive or negative electrical charge. In gel electrophoresis a sample is placed in a gel and the various molecules in the sample allowed to migrate in an electric field. After a set amount of time a stain is applied and any patterns of banding observed. With proteins, the technique is used to separate alternate forms of proteins related to alternate forms of a gene.

Electrostatic. Refers to an attractive or repellent force involving positive and negative charges. Unlike charges attract, like charges repel. This is important in understanding how the properties of water come about and the assembly of phospholipid bi-layers among other things.

Endergonic reaction. A chemical reaction in which the products of the reaction have more energy than the starting materials.
Endocrine gland. A gland that secretes its products(usually hormones) into the blood stream.
Endomembrane system. A series of inter working organelles beginning with the nuclear envelope and including the rough and smooth endoplasmic reticulum as well as the Golgi body and various vacuoles produced by these organelles. This network functions in the synthesis and modification of proteins as well as the synthesis of lipids and other compounds for the cell. In addition this network insures that these materials get to their proper place in the cell.
Endocytosis. The process by which cells take in bulk material from the outside, usually by surrounding the material and isolating it into a vacuole or vesicle which is then brought deeper into the cell.

Endosymbiotic hypothesis. This hypothesis says that certain organelles, chiefly mitochondria and plastids, evolved from free living bacteria that became symbiotic with the ancestors of modern eukaryotic cells.

Energy. The ability to do work. This ability may be stored (Potential energy) , for example chemical energy, or be in current use to bring about movement (Kinetic energy);for example light energy is kinetic energy.

Entropy. A measure of disorder or uncertainty of a system. The second law of thermodynamics is often stated as "entropy in a closed system tends to increase."
Enzyme. An enzyme is an organic catalyst produced by living things. As catalysts the function of enzymes is to speed up chemical reactions without being destroyed by those reactions. Most enzymes are proteins but today we recognize that certain ribonucleic acids also can serve as enzymes.
Epistasis. A mode of genetic inheritance where a homozygous recessive gene pair prevents the expression of a gene pair at another locus.
Epithelial tissue. A flat tissue that covers the exterior of animals or lines the insides of glands and other cavities inside of the animal. Epithelial tissue is not penetrated by capillaries and lies on top of a nonliving membrane called a basement membrane.
Ethylene. A gaseous hydrocarbon with two carbon atoms and two hydrogen atoms. Ethylene is of interest as a plant hormone that is a also a gas. Ethylene is involved in fruit ripening and leaf fall in many plants.
Ethyl alcohol. CH3OH The product of fermentation of pyruvic acid by yeast. Also the alcohol that people some people overindulge in.
Eukaryotic. Refers to a cell that has a true nucleus in which the DNA is isolated from the rest of the cell by an envelope. Also, eukaryotic cells are characterized by the presence of membrane bound organelles such as mitochondria and chloroplasts.

Eusocial. This term refers to organisms that live in complex highly organized groups characterized by division of labor and castes either temporal or morphological. Examples include wolves, humans, all ants many bees and wasps as well as termites.

Evolution. 1. A change in the genetic make-up of a population. This change may lead to new adaptations within a species(microevolution) 2. The development of new species from pre-existing species(speciation)
Exergonic. A chemical reaction in which energy is released, the products have less energy than the starting materials.
Exocrine gland. A gland that secretes its products to the outside of the body or into an internal cavity such as the small intestine. Exocrine glands may secrete pheromones, but not always. A familiar exocrine gland is the liver which secretes bile. Sweat glands are also exocrine glands.
Experiment. A manipulation done on the natural world in order to test a hypothesis. Experiments usually involve comparing a control group with an experimental group where the two groups are as similar as possible except that the experimental group receives a treatment not given to the control group.
Exocytosis. The process by which cells send bulk material to the outside of a cell, usually by means of a vesicle which fuses with the cell membrane, releasing the vesicle's contents.
Exon. That part of the RNA transcript that will leave the nucleus of the cell for translation or for use to make tRNA.