OCR a level biology Exam With Complete Answer.

Abiotic components - correct answer Components of an ecosystem that are non living Abiotic factors - correct answer Non living components of an ecosystem that effect other living organisms Acetycholine - correct answer Chemical that acts as a transmitter that diffuses across synaptic cleft Acetycholinesterase - correct answer 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) - correct answer Small group of exocrine cells in a sac like structure. in the pancreas these surround a tubule and secrete into the tubule Action potential - correct answer 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 - correct answer An intracellular enzyme that converts ATP to cyclic AMP (CAMP) ADP - correct answer Adenosine diphosphate Adrenal cortex - correct answer Outer layer of the adrenal gland Adrenal gland - correct answer 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 - correct answer Hormone released from medulla of adrenal glands which stimulates body to prepare for fight or flight Adrenal medulla - correct answer Inner layer of adrenal gland Adrenocorticotropic hormone (ACTH) - correct answer Hormone released by pituitary gland which stimulates adrenal cortex to produce corticosteroid hormones Actin and myosin - correct answer Proteins involved in muscular contraction Agar - correct answer Polysacharide of galactose obtained from seaweed which is used to thicken a medium into a gel. Agarose - correct answer Type of sugar that can incorporated into a type of agar gel Alkaloids - correct answer Organic nitrogen containing bases that have important physiological effects on animals, includes nicotine, quinine, strychnine and morphine Allele - correct answer Version of a gene Allele frequency - correct answer Propotion of a particular allele within the gene pool Allopatric speciation - correct answer Formation of 2 different species from one original one due to geographic isolation Alpha cells - correct answer Cells found in islets of langerhans that secrete glucagon Ammonification - correct answer Production of ammonia by bacterial action in the decay of nitrgenous organic matter AMP - correct answer Adeonside monophosphate Aneuploidy - correct answer Abnormal chromosome number Antagonist - correct answer Something that works against the other in opposite pairs, such as in the muscles that are arranged in opposing pairs, so one contracts and the other elongates ADH (antidiuretic hormone) - correct answer Hormone made in hypothalamus, stored and released from pituitary gland, that controls permeability of collecting duct in walls of kidneys Apical dominance - correct answer Inhibition of lateral buds fruther down shoot by chemicals produced by apicial bud at tip of plant shoot. Apoptosis - correct answer Programmed cell death Artificial selection - correct answer Selective breeding of organisms to produce desired phenotypes Ascending limb - correct answer Part of loop of Henle that carries fluid back into distal tubule in cortex ATP - correct answer Adenosine triphosphate Autoimmune response - correct answer Response in which body's immune system attacks and destroys some of its own cells. Autonomic nervous stsrem - correct answer Part of nervous system responsible for controlling involuntary motor activities of body Autoradiograms - correct answer Photographs made when photographic film is exposed to molecules labelled with radioactivity Autosomal linkage - correct answer Gene loci present on the same autosome (non sex chromosome) are often inherited together Autosome - correct answer Chromosome not concerned with sex determination Autotrophic nutrition - correct answer Nutrition where organic molecules are synthesised from inorganic molecules, i.e carbon dioxide and water. I.e photosynthesis where sunlight energy converted to chemical energy to synthesise large organic molecules from smaller inorganic ones. Chemosynthesis uses energy derived from chemical reactions (e.g nitrifying bacteria in soil) Auxins E.g IAA (indole 3 acetic acid) - correct answer Promotes cell elongation Inhibits leaf abcission Inhibits growth of side shoots- maintains apical dominance Involved in tropisms Stimulates release of ethene Involved in food ripening Cytokines - correct answer Promotes cell division Leaf expansion Delays leaf senescense Overcomes apicial dominance Ethene - correct answer Promotes food ripening Promotes abscission in deciduous trees Abscisic acid - correct answer Causes stomatal clouse when plant is streed by low water availabliity Inhbits seed germination and growth Stimulates cold protective responses I.e production of antifreeze Gibberelins - correct answer Promotes seed germination and growth of stems Triggers mobilisation of food stores in seed at germination Stimulates pollen tube growth in fertilisation Belt transcer - correct answer Continous belt or series of quadtrats used to estimate