Biology AS OCR
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1-1-practical-skills-written-assessment AS7 主题
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1-2-practical-skills-endorsement-assessment AS16 主题
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1-2-1-practical-ethical-use-of-organisms as
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1-2-2-practical-aseptic-techniques as
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1-2-3-practical-dissection-of-gas-exchange-surfaces-in-fish-and-insects as
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1-2-4-drawing-cells-from-blood-smears as
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1-2-5-practical-investigating-biodiversity-using-sampling as
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1-2-6-practical-data-loggers-and-computer-modelling as
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1-2-7-practical-investigating-the-rate-of-diffusion as
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1-2-8-practical-investigating-water-potential as
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1-2-9-practical-factors-affecting-membrane-structure-and-permeability as
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1-2-10-biochemical-tests-reducing-sugars-and-starch as
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1-2-11-biochemical-tests-lipids as
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1-2-12-biochemical-tests-proteins as
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1-2-13-chromatography as
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1-2-14-serial-dilutions as
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1-2-15-practical-investigating-the-rate-of-transpiration as
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1-2-16-practical-using-a-light-microscope as
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1-2-1-practical-ethical-use-of-organisms as
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2-1-cell-structure AS9 主题
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2-1-2-using-a-microscope as
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2-1-3-drawing-cells as
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2-1-4-magnification-and-resolution as
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2-1-5-eukaryotic-cells as
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2-1-6-eukaryotic-cells-under-the-microscope as
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2-1-7-organelles-and-the-production-of-proteins as
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2-1-8-the-cytoskeleton as
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2-1-9-prokaryotic-and-eukaryotic-cells as
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2-1-1-studying-cells as
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2-1-2-using-a-microscope as
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2-2-biological-molecules AS17 主题
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2-2-1-properties-of-water as
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2-2-2-monomers-and-polymers as
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2-2-3-monosaccharides as
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2-2-4-the-glycosidic-bond as
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2-2-5-polysaccharides as
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2-2-6-biochemical-tests-reducing-sugars-and-starch as
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2-2-7-lipids-and-ester-bonds as
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2-2-8-lipids-structure-and-function as
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2-2-9-biochemical-tests-lipids as
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2-2-10-amino-acids-and-peptide-bonds as
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2-2-11-protein-structure as
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2-2-12-globular-proteins as
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2-2-13-fibrous-proteins as
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2-2-14-inorganic-ions as
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2-2-15-biochemical-tests-proteins as
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2-2-16-finding-the-concentration-of-a-substance as
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2-2-17-chromatography as
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2-2-1-properties-of-water as
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2-3-nucleotides-and-nucleic-acids AS8 主题
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2-4-enzymes AS9 主题
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2-4-1-the-role-of-enzymes as
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2-4-2-enzyme-action as
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2-4-3-enzyme-activity-ph as
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2-4-4-enzyme-activity-temperature as
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2-4-5-enzyme-activity-enzyme-concentration as
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2-4-6-enzyme-activity-substrate-concentration as
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2-4-7-enzyme-activity-enzyme-inhibitors as
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2-4-8-coenzymes-cofactors-and-prosthetic-groups as
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2-4-9-practical-measuring-enzyme-activity as
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2-4-1-the-role-of-enzymes as
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2-5-biological-membranes AS9 主题
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2-5-1-the-cell-surface-membrane as
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2-5-2-membrane-structure-and-permeability as
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2-5-3-diffusion-and-facilitated-diffusion as
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2-5-4-practical-investigating-the-rate-of-diffusion as
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2-5-5-active-transport as
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2-5-6-endocytosis-and-exocytosis as
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2-5-7-osmosis as
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2-5-8-osmosis-in-animal-and-plant-cells as
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2-5-9-practical-investigating-water-potential as
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2-5-1-the-cell-surface-membrane as
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2-6-cell-division-cell-diversity-and-cellular-organisation AS11 主题
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2-6-1-the-cell-cycle as
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2-6-2-the-stages-of-mitosis as
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2-6-3-identifying-mitosis-in-plant-cells as
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2-6-4-the-significance-of-mitosis as
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2-6-5-the-stages-of-meiosis as
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2-6-6-the-significance-of-meiosis as
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2-6-7-specialised-cells as
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2-6-8-the-organisation-of-cells as
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2-6-9-stem-cells as
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2-6-10-stem-cells-in-animals-and-plants as
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2-6-11-the-use-of-stem-cells as
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2-6-1-the-cell-cycle as
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3-1-exchange-surfaces AS7 主题
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3-2-transport-in-animals AS12 主题
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3-2-1-the-need-for-transport-systems-in-animals as
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3-2-2-circulatory-systems as
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3-2-3-blood-vessels as
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3-2-4-tissue-fluid as
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3-2-5-the-mammalian-heart as
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3-2-6-practical-mammalian-heart-dissection as
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3-2-7-the-cardiac-cycle as
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3-2-8-cardiac-output as
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3-2-9-heart-action-initiation-and-control as
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3-2-10-electrocardiograms-ecgs as
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3-2-11-the-role-of-haemoglobin as
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3-2-12-adult-and-fetal-haemoglobin as
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3-2-1-the-need-for-transport-systems-in-animals as
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3-3-transport-in-plants AS11 主题
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3-3-1-the-need-for-transport-systems-in-plants as
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3-3-2-the-xylem-and-phloem as
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3-3-3-the-xylem as
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3-3-4-the-phloem as
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3-3-5-transverse-sections-stems-roots-and-leaves as
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3-3-6-the-process-of-transpiration as
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3-3-7-transpiration-in-plants as
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3-3-8-practical-investigating-the-rate-of-transpiration as
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3-3-9-translocation as
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3-3-10-the-mass-flow-hypothesis as
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3-3-11-the-adaptations-of-xerophytic-and-hydrophytic-plants as
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3-3-1-the-need-for-transport-systems-in-plants as
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4-1-communicable-diseases-disease-prevention-and-the-immune-system AS16 主题
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4-1-1-common-pathogens-and-communicable-diseases as
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4-1-2-transmission-of-communicable-pathogens as
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4-1-3-plant-defences-against-pathogens as
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4-1-4-non-specific-immune-responses as
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4-1-5-phagocytes as
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4-1-6-blood-cells as
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4-1-7-the-t-lymphocyte-response as
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4-1-8-the-b-lymphocyte-response as
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4-1-9-primary-and-secondary-immune-responses as
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4-1-10-antibodies as
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4-1-11-opsonins-agglutinins-and-anti-toxins as
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4-1-12-types-of-immunity as
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4-1-13-autoimmune-diseases as
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4-1-14-principles-of-vaccination as
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4-1-15-sources-of-medicine as
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4-1-16-antibiotics as
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4-1-1-common-pathogens-and-communicable-diseases as
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4-2-biodiversity AS10 主题
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4-2-1-biodiversity as
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4-2-2-sampling-to-determine-biodiversity as
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4-2-3-practical-investigating-biodiversity-using-sampling as
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4-2-4-measuring-species-richness-and-species-evenness as
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4-2-5-simpsons-index as
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4-2-6-genetic-diversity as
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4-2-7-factors-affecting-biodiversity as
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4-2-8-reasons-for-maintaining-biodiversity as
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4-2-9-methods-of-maintaining-biodiversity as
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4-2-10-conservation-agreements as
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4-2-1-biodiversity as
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4-3-classification-and-evolution AS15 主题
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4-3-1-classification-of-species as
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4-3-2-binomial-system as
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4-3-3-classification-of-the-three-domains as
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4-3-4-classification-of-the-five-kingdoms as
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4-3-5-classification-and-phylogeny as
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4-3-6-evidence-of-evolution as
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4-3-7-types-of-variation as
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4-3-8-standard-deviation as
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4-3-9-variation-t-test-method as
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4-3-10-variation-t-test-worked-example as
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4-3-11-spearmans-rank-correlation as
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4-3-12-adaptation as
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4-3-13-natural-selection as
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4-3-14-evolution-of-resistance as
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4-3-15-consequences-of-resistance as
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4-3-1-classification-of-species as
3-2-9-heart-action-initiation-and-control as
Exam code:H020
Heart Action: Initiation & Control
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Control of the basic heartbeat is myogenic, which means the heart will beat without any external stimulus
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This intrinsic rhythm means the heart beats at around 60 times per minute
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The sinoatrial node (SAN) is a group of cells in the wall of the right atrium. The SAN initiates a wave of depolarisation that causes the atria to contract
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The Annulus fibrosus is a region of non-conducting tissue which prevents the depolarisation spreading straight to the ventricles
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Instead, the depolarisation is carried to the atrioventricular node (AVN)
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This is a region of conducting tissue between atria and ventricles
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After a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His
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This delay means that the ventricles contract after the atria
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The bundle of His is a collection of conducting tissue in the septum (middle) of the heart. The bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them
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The Purkyne fibres spread around the ventricles and initiate the depolarization of the ventricles from the apex (bottom) of the heart
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This makes the ventricles contract and blood is forced out of the pulmonary artery and aorta
Stages in the cardiac cycle table
The wave of depolarisation spreads across the heart in a coordinated manner
Worked Example
Explain the roles of the sinoatrial node, the atrioventricular node and the Purkyne fibres in a heartbeat.
Answer:
The Sinoatrial node sends out a wave of excitation and this spreads across both atria, causing atrial systole. Non-conducting tissue called the Annulus fibrosus prevents the excitation from spreading to the ventricles and so this ensures that atria and ventricles don’t contract at the same time. The Atrioventricular node then sends the wave of excitation to the ventricles after a short delay of around 0.1 – 0.2 seconds, ensuring that the atria have time to empty their blood into the ventricles. The Purkyne fibres conduct the excitation down the septum of the heart and to the apex, before the excitation is carried upwards in the walls of the ventricles. This means that during ventricular systole, the blood contracts from its base and blood is pushed upwards and outwards.
Examiner Tips and Tricks
Remember that the heart is myogenic, which means that the heart will generate a heartbeat by itself and without any other stimulation. Instead, the electrical activity of the heart regulates the heart rate.Be aware that you may sometimes see an alternative spelling of “Purkyne” as “Purkinje” they mean the exact same thing!
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