E                       Biological TERMS  

ecological community All the populations of living things that inhabit a given area. The term also is used to mean a collection of populations in a given area that potentially interact with each other.

ecological dominant A species that is abundant and obvious in a given community. In any community, a few species, usually plants, will dominate in numbers.

ecology The study of the interactions that living things have with each other and with their environment.

ecosystem A community of living things and the physical environment with which they interact.

ectopic pregnancy An abnormal pregnancy in which the blastocyst attaches inside the uterine tube or to the cervix, rather than in the normal position in the dorsal uterine wall. The embryo usually does not survive in this type of pregnancy.

ectothermic Having an internal temperature that is controlled largely the by temperature of the external environment. For example, lizards are ectothermic and often bask in the sun to warm up.

effector A muscle or gland that responds to instructions received from a motor neuron, thus effecting change in the body.

efferent division The division of the peripheral nervous system that carries motor commands from the central nervous system (CNS), towards the effectors (muscles and glands).

electrical charge A quantity of unbalanced electricity. For a molecule, the electrical charge is written as one or more times that of an electron. Electrical charge enables some types of chemical bonds to occur.

electron A basic constituent of an atom that has negative electrical charge. Electrons are distributed in an atom at a distance from the nucleus. Electrons interact to form chemical bonds between atoms, and the electronic structure determines the chemical properties of an atom.

electron transport chain (ETC) The third stage of cellular respiration, occurring within the inner membrane of the mitochondria, in which the majority of the ATP are formed. In this process, electrons are transported along a chain of molecules, providing energy to pump hydrogen ions against their concentration gradient. When these hydrogen ions return down their concentration gradient, the energy released drives the synthesis of up to 32 ATP per molecule of glucose.

electronegativity The measure of the strength of attraction a molecule has for electrons. A molecule with higher electronegativity will tend to pull electrons away from molecules with lower electronegativity.

element A substance that cannot be reduced to any simpler set of components through chemical processes. An element is defined by the number of protons in its nucleus.

embryo A developing organism. In humans, the developing organism from the time a zygote undergoes its first division through the end of the eighth week of development.

embryo sac The mature female gametophyte plant, consisting of seven cells produced by the megaspore. These cells include the egg and the central cell, which contains two nuclei.

embryology The study of how animals develop, from fertilization to birth. Comparing embryology in different organisms can provide insights into their evolutionary relationships.

embryonic stem cell A cell from the blastocyst stage of an embryo that is capable of giving rise to almost all of the cells or tissues in the body.

emigration The movement of individuals out of a population. The individuals that leave remove their alleles from the gene pool of that population.

emulsification The breaking of a large droplet into many small droplets, greatly increasing the surface area on which digestive enzymes can act.

endergonic Denoting a chemical reaction in which the products contain more energy than the reactants, so energy is stored in the reaction. Energy must be put into such a reaction to make it go.

endocrine gland A gland that releases its materials directly into surrounding tissues or into the bloodstream, without using ducts. Many hormones are produced by endocrine glands.

endocrine system The organ system that sends signals throughout the body using hormones, which generally travel through the blood. This system consists of the endocrine glands and other organs that produce hormones.

endocytosis The process by which the plasma membrane folds inward and pinches off, bringing relatively large materials into the cell enclosed inside a vesicle.

endomembrane system The network of organelle membranes and the membrane-bound transport vesicles that bud from them and fuse with them.

endometrium The tissue lining the interior of the uterus in mammals, which thickens in response to progesterone secretion during ovulation and is shed during menstruation. If pregnancy occurs, this tissue houses the embryo.