Biology AS AQA
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1-1-biological-molecules-carbohydrates11 主题
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1-1-1-biological-molecules-key-terms
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1-1-2-biological-molecules-reactions
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1-1-3-monosaccharides
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1-1-4-glucose
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1-1-5-the-glycosidic-bond
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1-1-6-chromatography-monosaccharides
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1-1-7-disaccharides
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1-1-8-starch-and-glycogen
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1-1-9-cellulose
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1-1-10-biochemical-tests-sugars-and-starch
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1-1-11-finding-the-concentration-of-glucose
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1-1-1-biological-molecules-key-terms
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1-2-biological-molecules-lipids3 主题
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1-3-biological-molecules-proteins5 主题
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1-4-proteins-enzymes12 主题
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1-4-1-many-proteins-are-enzymes
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1-4-2-enzyme-specificity
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1-4-3-how-enzymes-work
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1-4-4-required-practical-measuring-enzyme-activity
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1-4-5-drawing-a-graph-for-enzyme-rate-experiments
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1-4-6-using-a-tangent-to-find-initial-rate-of-reaction
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1-4-7-limiting-factors-affecting-enzymes-temperature
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1-4-8-limiting-factors-affecting-enzymes-ph
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1-4-10-limiting-factors-affecting-enzymes-enzyme-concentration
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1-4-11-limiting-factors-affecting-enzymes-substrate-concentration
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1-4-12-limiting-factors-affecting-enzymes-inhibitors
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1-4-14-control-of-variables-and-uncertainty
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1-4-1-many-proteins-are-enzymes
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1-5-nucleic-acids-structure-and-dna-replication8 主题
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1-5-2-nucleotide-structure-and-the-phosphodiester-bond
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1-5-3-dna-structure-and-function
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1-5-4-rna-structure-and-function
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1-5-5-ribosomes
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1-5-6-the-origins-of-research-on-the-genetic-code
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1-5-8-the-process-of-semi-conservative-replication
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1-5-9-calculating-the-frequency-of-nucleotide-bases
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1-5-10-the-watson-crick-model
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1-5-2-nucleotide-structure-and-the-phosphodiester-bond
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1-6-atp-water-and-inorganic-ions4 主题
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2-1-cell-structure7 主题
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2-2-the-microscope-in-cell-studies4 主题
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2-3-cell-division-in-eukaryotic-and-prokaryotic-cells8 主题
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2-4-cell-membranes-and-transport9 主题
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2-4-1-the-structure-of-cell-membranes
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2-4-3-the-cell-surface-membrane
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2-4-4-diffusion
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2-4-5-osmosis
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2-4-7-osmosis-in-animal-cells
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2-4-9-required-practical-investigating-water-potential
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2-4-10-active-transport-and-co-transport
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2-4-11-adaptations-for-rapid-transport
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2-4-13-required-practical-factors-affecting-membrane-permeability
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2-4-1-the-structure-of-cell-membranes
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2-5-cell-recognition-and-the-immune-system7 主题
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2-6-vaccines-disease-and-monoclonal-antibodies6 主题
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3-1-adaptations-for-gas-exchange6 主题
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3-2-human-gas-exchange14 主题
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3-2-5-the-alveolar-epithelium
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3-2-1-the-human-gas-exchange-system
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3-2-2-dissecting-the-gas-exchange-system
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3-2-3-microscopy-and-gas-exchange-surfaces
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3-2-4-investigating-gas-exchange
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3-5-5-investigating-heart-rate
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3-5-6-blood-vessels
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3-5-7-capillaries-and-tissue-fluid
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3-5-8-cardiovascular-disease-data
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3-2-10-risk-factor-data
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3-2-11-correlations-and-causal-relationships
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3-2-6-ventilation-and-gas-exchange
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3-2-8-the-effects-of-lung-disease
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3-2-9-pollution-and-smoking-data
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3-2-5-the-alveolar-epithelium
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3-3-digestion-and-absorption5 主题
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3-4-mass-transport-in-animals6 主题
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3-5-the-circulatory-system-in-animals4 主题
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3-6-mass-transport-in-plants6 主题
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4-1-dna-genes-and-chromosomes10 主题
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4-2-dna-and-protein-synthesis3 主题
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4-3-genetic-diversity-mutations-and-meiosis7 主题
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4-4-genetic-diversity-and-adaptation6 主题
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4-5-species-and-taxonomy4 主题
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4-6-biodiversity9 主题
2-5-2-antigens
Exam code:7401
Antigens
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All cells, including human cells and microorganisms, have unique markers called antigens
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Antigens are macromolecules found on cell membranes, bacterial walls, or viral surfaces
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Glycolipids and glycoproteins on membranes often act as antigens
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They enable cell-to-cell recognition and help the body distinguish between self and non-self cells
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Antigens can be classified as:
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Self antigens – produced by the body’s own cells and do not trigger an immune response
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Non-self antigens – found on foreign cells (e.g. pathogens, incompatible blood cells) and stimulate an immune response
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Antigen variability
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Some pathogens (e.g. cold and flu viruses) show antigen variability due to frequent genetic mutations
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Their surface antigens change, so existing lymphocytes and memory cells can no longer bind due to there being no complementary receptors
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This prevents a secondary immune response, so the host becomes infected again
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Antigenic variability explains why individuals can catch a cold or flu repeatedly despite past exposure
Examiner Tips and Tricks
You should be able to use this concept of antigenic variability to explain why vaccines for the flu must be updated regularly
Responses