absorption: the movement of digested food molecules through the wall of the intestine into the blood or lymph. accommodation: the change of shape of the lens, in order to focus on objects at different distances. active site: the part of an enzyme molecule into which its substrate fits. active transport: the movement of ions in or out of a cell through the cell membrane, from a region of their lower concentration to a region of their higher concentration against a concentration gradient, using energy released during respiration. adrenaline: a hormone secreted by the adrenal glands, which prepares the body for ‘flight or fight’. aerobic respiration: the release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen. allele: any of two or more alternative forms of a gene. alveolus (plural: alveoli): an air sac in the lungs, where gas exchange occurs. amino acids: molecules that can link together in long chains to form proteins; they contain carbon, hydrogen, oxygen and nitrogen, and sometimes sulfur. amniotic fluid: secreted by the amnion, which supports and protects a developing fetus. amylase: an enzyme which breaks down starch to maltose. anaemia: an illness caused by a lack of haemoglobin. anaerobic respiration: the release of a relatively small amount of energy by the breakdown of food substances in the absence of oxygen. antagonistic muscles: muscles that work as a pair – for example, one may cause extension and the other flexing of a joint. …
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