OCR a level biology | 328 Questions and Answers with complete solution

Abiotic components - Components of an ecosystem that are non living Abiotic factors - Non living components of an ecosystem that effect other living organisms Acetycholine - Chemical that acts as a transmitter that diffuses across synaptic cleft Acetycholinesterase - Enzyme in synaptic cleft that breaks down acetycholine. After it has triggered an action potential in the post synaptic neurone, acetycholine must be broken down otherwise it would remain in the synaptic cleft and continue to open sodium ion channels in the post synaptic membrane causing action potentials Acinus (plural acini) - Small group of exocrine cells in a sac like structure. in the pancreas these surround a tubule and secrete into the tubule Action potential - A brief reversal of teh potential across the membrane of a neurone causing a peak of +40mV compared to the resting potential of -60mV Adenyl cyclase - An intracellular enzyme that converts ATP to cyclic AMP (CAMP) ADP - Adenosine diphosphate Adrenal cortex - Outer layer of the adrenal gland Adrenal gland - One of the pair of glands lying above kidneys, which release adrenaline and a number of hormones known as corticoids (or corticosteroids) such as aldosterone Adrenaline - Hormone released from medulla of adrenal glands which stimulates body to prepare for fight or flight