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electron acceptor A molecule that forms part of the electron transport system
that transfers electrons ejected by chlorophyll during photosynthesis. Part of the
energy carried by the electrons is transferred to ATP, part is transferred to
NADPH, and part is lost in the transfer system.
electron transport 1) A series of coupled oxidation/reduction reactions where
electrons are passed like hot potatoes from one membrane-bound
protein/enzyme to another before being finally attached to a terminal electron
acceptor (usually oxygen or NADPH). ATP is formed by this process. 2)
coupled series of oxidation/reduction reactions during which ATP is generated
by energy transfer as electrons move from high reducing state to lower
reducing state. |
electrostatic attraction The attraction between atoms of opposite charge that
holds the atoms together in ionic bonds.
element A substance composed of atoms with the same atomic number; cannot
be broken down in ordinary chemical reactions.
elongation During protein synthesis, the growth of the polypeptide chain
through the addition of amino acids; the second step in translation. |
embryo Term applied to the zygote after the beginning of mitosis that produces
a multicellular structure.
embryo sac Alternate term applied to the angiosperm female gametophyte
contained within a megaspore.
emphysema Lung disease characterized by shortness of breath, often
associated with smoking.
endergonic Chemical reactions that require energy input to begin.
endochondral ossification The process by which human bones form from
cartilage.
endocrine system One of eleven major body organ systems in animals; a
system of glands that works with the nervous system in controlling the activity
of internal organs, especially the kidneys, and in coordinating the long-range
response to external stimuli.
endocytosis The incorporation of materials from outside the cell by the
formation of vesicles in the plasma membrane. The vesicles surround the
material so the cell can engulf it.
endoderm The inner layer of cells in embryonic development that gives rise to
organs and tissues associated with digestion and respiration. Also, the inner
tissue layer in þatworms.
endodermis A layer of cells surrounding the vascular cylinder of plants.
endometrium The inner lining of the uterus.
endoplasmic reticulum (ER) A network of membranous tubules in the
cytoplasm of a cell; involved in the production of phospholipids, proteins, and
other functions. Rough ER is studded with ribosomes; smooth ER is not.
endoskeleton An internal supporting skeleton with muscles on the outside; in
vertebrates, consists of the skull, spinal column, ribs, and appendages.
endosperm A food storage tissue that provides nutrients to the developing
embryo in angiosperms; formed from the triploid cell produced when a sperm cell
fertilizes the central cell. Some endosperm is solid (as in corn), some is liquid
(as in coconut).
endosymbiosis Theory that attempts to explain the origin of the DNA-
containing mitochondria and chloroplasts in early eukaryotes by the engulfing of
various types of bacteria that were not digested but became permanent
additions to the ancestral "eukaryote".
endothermic A reaction that gives off energy. The product is in a lower
energy state than the reactants.
endotherms Animals that have the ability to maintain a constant body
temperature over a wide range of environmental conditions.
endothermy The internal control of body temperature; the ability to generate
and maintain internal body heat.
energy The ability to bring about changes or to do work.
energy flow The movement of energy through a community via feeding
relationships.
energy of activation The minimum amount of energy required for a given
reaction to occur; varies from reaction to reaction.
entropy The degree of disorder in a system. As energy is transferred from one
form to another, some is lost as heat; as the energy decreases, the disorder in
the system&emdash;and thus the entropy&emdash;increases.
enzymes Protein molecules that act as catalysts in biochemical reactions.
epidermis 1. The outermost layer of skin consisting of several layers of
epithelial cells&emdash;notably, keratinocytes&emdash;and, in the inner layer of
the epidermis, basal cells and melanocytes. 2. The outer layer of cells in the plant
body, often covered by a waxy cuticle.
epididymis A long, convoluted duct on the testis where sperm are stored.
epiglottis A þap of tissue that closes off the trachea during swallowing.
epinephrine A hormone produced by the adrenal medulla and secreted under
stress; contributes to the "Þght or þight" response.
epistasis The masking of the effects of one gene by the action of another,
example: widow's peak masked by the baldness gene.
epithelial tissue Cells in animals that are closely packed in either single or
multiple layers, and which cover both internal and external surfaces of the
animal body. Also referred to as epithelium.
eras One of the major divisions of the geologic time scale. [ Pobierz całość w formacie PDF ]