Category: Biology Dictionary E

Eyes Definition Eyes are animal organs that are specialized for sight. These may be as simple as proteins or cells which can tell light from darkness – like the “eyes” found in many microorganisms – or they may be complex assemblies of lenses, filters, light-sensitive tissues, nerves, and support structures. Most animals, including humans, have […]

Extremophile Definition Extremophiles are organisms that have evolved to survive in environments once thought to be entirely uninhabitable. These environments are inhospitable, reaching extreme conditions of heat, acidity, pressure, and cold that would be fatal to most other life forms. Because extremophiles live on extreme ends of the spectrum, they can indicate the range of […]

Extracellular Matrix Definition The extracellular matrix can be thought of as a suspension of macromolecules that supports everything from local tissue growth to the maintenance of an entire organ. These molecules are all secretions made by neighboring cells. Upon being secreted, the proteins will undergo scaffolding. Scaffolding, in turn, is a term used to describe […]

Extracellular Fluid Definition Extracellular fluid is the term for the many fluids that exist in an organism outside of cells of the organism, but sealed within the body cavities and vessels. Extracellular fluid that travels in the circulatory system is blood plasma, the liquid component of blood. As the oxygen and nutrients from blood are transferred […]

Extirpation Definition Extirpation (also known as ‘local extinction’) describes the situation in which a species or population no longer exists within a certain geographical location. Unlike extinction, whereby a species no longer exists anywhere, extirpation means that at least one other population of the species still persists in other areas. Most species of plants and animals have a […]

Extinction Definition Extinction is a term applied to a known species, of which there are no known living individuals. Some species which have suffered extinction are known only from their fossilized remains. Others were at one point known to humans, but are gone now. Still others suffered directly at the hands of humans, driven to extinction. An extinct species, […]

External Respiration Definition External respiration is the process of exchanging oxygen, carbon dioxide, and other blood solutes with the external environment. Respiration in whole is the process of delivering oxygen to the cells to extract the energy from sugars in oxidative phosphorylation in the mitochondria. This process uses oxygen, and produces carbon dioxide, as well as a number of […]

Experimental Group Definition In a comparative experiment, the experimental group (aka the treatment group) is the group being tested for a reaction to a change in the variable. There may be experimental groups in a study, each testing a different level or amount of the variable. The other type of group, the control group, can show […]

Exoskeleton Definition An exoskeleton is the rigid covering found on the exterior of many animals, particularly invertebrates such as arthropods and mollusks. Much like the internal endoskeleton of vertebrates, the exoskeleton is responsible for supporting the structure of an animal’s body. The exoskeleton also provides protection against attack from predators, and accidental damage of the soft internal organs. Furthermore, due to the […]

Exon Definition An exon is a coding region of a gene that contains the information required to encode a protein. In eukaryotes, genes are made up of coding exons interspersed with non-coding introns. These introns are then removed to make a functioning messenger RNA (mRNA) that can be translated into a protein. Exon Structure Exons […]