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
2-2-5-polysaccharides as
Exam code:H020
Polysaccharides: Structure
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Starch, glycogen and cellulose are polysaccharides
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Polysaccharides are macromolecules (polymers) that are formed by many monosaccharides joined by glycosidic bonds in a condensation reaction to form chains
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These chains may be:
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Branched or unbranched
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Folded (making the molecule compact which is ideal for storage eg. starch and glycogen)
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Straight (making the molecules suitable to construct cellular structures e.g. cellulose) or coiled
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Starch
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Starch is constructed from two different polysaccharides:
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Amylose (10 – 30% of starch)
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Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules
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The helix shape enables it to be more compact and thus it is more resistant to digestion
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Amylopectin (70 – 90% of starch)
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1,4 glycosidic bonds between α-glucose molecules but also 1,6 glycosidic bonds form between glucose molecules creating a branched molecule
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Amylose – one of the two polysaccharides that is used to form starch (the storage polysaccharide in plants)
Amylopectin – one of the two polysaccharides that is used to form starch (the storage polysaccharide in plants)
Glycogen
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Glycogen is a polysaccharide found in animals
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It is made up of α-glucose molecules
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There are 1,4 glycosidic bonds between α-glucose molecules and also 1,6 glycosidic bonds between glucose molecules creating a branched molecule
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Glycogen has a similar structure to amylopectin but it has more branches
Glycogen, the highly branched molecule used as a storage polysaccharide in animals and fungi
Summary of Storage Polysaccharides Table
Cellulose
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Cellulose is a polysaccharide found in plants
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It consists of long chains of β-glucose joined together by 1,4 glycosidic bonds
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β-glucose is an isomer of α-glucose, so in order to form the 1,4 glycosidic bonds consecutive β-glucose molecules must be rotated 180° to each other
To form the 1,4 glycosidic bond between two β-glucose molecules, the glucose molecules must be rotated to 180° to each other
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Due to the inversion of the β-glucose molecules, many hydrogen bonds form between the long chains giving cellulose its strength
Cellulose has high tensile strength due to the many hydrogen bonds that form between the long chains of β-glucose molecules
Examiner Tips and Tricks
Be clear about the differences between starch, glycogen, and cellulose.
Polysaccharides: Function
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Starch and glycogen are storage polysaccharides because they are:
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Compact
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So large quantities can be stored
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Insoluble
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So they will have no osmotic effect, unlike glucose which would lower the water potential of a cell causing water to move into cells
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Starch
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Starch is the storage polysaccharide of plants. It is stored as granules in plastids such as amyloplasts and chloroplasts
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Plastids are membrane-bound organelles that can be found in plant cells. They have a specialised function eg. amyloplasts store starch grains
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Due to the many monomers in a starch molecule, it takes longer to digest than glucose
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The amylopectin in starch has branches that result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added for storage
Glycogen
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Glycogen is the storage polysaccharide of animals and fungi, it is highly branched and not coiled
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Liver and muscles cells have a high concentration of glycogen, present as visible granules, as the cellular respiration rate is high in these cells (due to animals being mobile)
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Glycogen is more branched than amylopectin making it more compact which helps animals store more
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The branching enables more free ends where glucose molecules can either be added or removed allowing for condensation and hydrolysis reactions to occur more rapidly – thus the storage or release of glucose can suit the demands of the cell
Cellulose
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Cellulose is the main structural component of cell walls due to its strength which is a result of the many hydrogen bonds found between the parallel chains of microfibrils
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The high tensile strength of cellulose allows it to be stretched without breaking which makes it possible for cell walls to withstand turgor pressure
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The cellulose fibres and other molecules (eg. lignin) found in the cell wall forms a matrix which increases the strength of the cell walls
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The strengthened cell walls provide support to the plant
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Cellulose fibres are freely permeable which allows water and solutes to leave or reach the cell surface membrane
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As few organisms have the enzyme (cellulase) to hydrolyse cellulose it is a source of fibre
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