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Biology_Alevel_Ocr
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4-1-communicable-diseases-disease-prevention-and-the-immune-system16 主题
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4-1-1-common-pathogens-and-communicable-diseases
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4-1-2-transmission-of-communicable-pathogens
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4-1-3-plant-defences-against-pathogens
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4-1-4-non-specific-immune-responses
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4-1-5-phagocytes
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4-1-6-blood-cells
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4-1-7-the-t-lymphocyte-response
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4-1-8-the-b-lymphocyte-response
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4-1-9-primary-and-secondary-immune-responses
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4-1-10-antibodies
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4-1-11-opsonins-agglutinins-and-anti-toxins
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4-1-12-types-of-immunity
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4-1-13-autoimmune-diseases
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4-1-14-principles-of-vaccination
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4-1-15-sources-of-medicine
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4-1-16-antibiotics
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4-1-1-common-pathogens-and-communicable-diseases
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4-2-biodiversity10 主题
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4-2-1-biodiversity
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4-2-2-sampling-to-determine-biodiversity
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4-2-3-practical-investigating-biodiversity-using-sampling
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4-2-4-measuring-species-richness-and-species-evenness
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4-2-5-simpsons-index
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4-2-6-genetic-diversity
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4-2-7-factors-affecting-biodiversity
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4-2-8-reasons-for-maintaining-biodiversity
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4-2-9-methods-of-maintaining-biodiversity
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4-2-10-conservation-agreements
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4-2-1-biodiversity
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4-3-classification-and-evolution15 主题
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4-3-1-classification-of-species
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4-3-2-binomial-system
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4-3-3-classification-of-the-three-domains
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4-3-4-classification-of-the-five-kingdoms
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4-3-5-classification-and-phylogeny
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4-3-6-evidence-of-evolution
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4-3-7-types-of-variation
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4-3-8-standard-deviation
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4-3-9-variation-t-test-method
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4-3-10-variation-t-test-worked-example
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4-3-11-spearmans-rank-correlation
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4-3-12-adaptation
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4-3-13-natural-selection
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4-3-14-evolution-of-resistance
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4-3-15-consequences-of-resistance
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4-3-1-classification-of-species
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5-1-communication-and-homeostasis4 主题
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5-2-excretion10 主题
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5-2-1-the-importance-of-excretion
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5-2-2-the-mammalian-liver-structure
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5-2-3-the-mammalian-liver-function
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5-2-4-the-liver-under-the-microscope
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5-2-5-the-mammalian-kidney-structure
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5-2-6-the-mammalian-kidney-function
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5-2-7-the-kidney-under-the-microscope
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5-2-8-osmoregulation
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5-2-9-kidney-failure
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5-2-10-excretory-products-and-medical-diagnosis
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5-2-1-the-importance-of-excretion
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5-3-neuronal-communication9 主题
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5-4-hormonal-communication4 主题
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5-5-plant-and-animal-responses16 主题
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5-5-1-plant-responses
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5-5-2-investigating-phototropism-and-geotropism
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5-5-3-plant-hormones
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5-5-4-auxins-and-apical-dominance
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5-5-5-gibberellin
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5-5-6-practical-effect-of-plant-hormones-on-growth
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5-5-7-commercial-use-of-plant-hormones
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5-5-8-mammalian-nervous-system
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5-5-9-the-human-brain
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5-5-10-reflex-actions
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5-5-11-coordination-of-responses
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5-5-12-factors-affecting-heart-rate
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5-5-13-investigating-factors-affecting-heart-rate
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5-5-14-mammalian-muscle-structure
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5-5-15-transmission-across-a-neuromuscular-junction
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5-5-16-the-sliding-filament-model
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5-5-1-plant-responses
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5-6-photosynthesis10 主题
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5-6-1-photosynthesis-and-respiration
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5-6-2-chloroplast-structure-and-function
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5-6-3-photosynthetic-pigments
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5-6-4-practical-investigating-photosynthetic-pigments-with-chromatography
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5-6-5-the-light-dependent-stage
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5-6-6-using-the-products-of-the-light-dependent-reaction
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5-6-7-the-light-independent-stage
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5-6-8-uses-of-triose-phosphate
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5-6-9-factors-affecting-the-rate-of-photosynthesis
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5-6-10-practical-investigating-factors-affecting-the-rate-of-photosynthesis
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5-6-1-photosynthesis-and-respiration
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5-7-respiration14 主题
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5-7-14-practical-respirometer
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5-7-1-the-need-for-cellular-respiration
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5-7-2-structure-of-the-mitochondrion
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5-7-3-the-four-stages-in-aerobic-respiration
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5-7-4-glycolysis
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5-7-5-the-link-reaction
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5-7-6-the-krebs-cycle
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5-7-7-the-role-of-coenzymes
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5-7-8-oxidative-phosphorylation
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5-7-9-anaerobic-respiration
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5-7-10-energy-yield-of-aerobic-vs-anaerobic-respiration
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5-7-11-practical-investigating-the-rate-of-respiration
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5-7-12-respiratory-substrates
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5-7-13-respiratory-quotient-rq
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5-7-14-practical-respirometer
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6-1-cellular-control7 主题
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6-2-patterns-of-inheritance13 主题
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6-2-1-key-terms-in-genetics
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6-2-2-variation-phenotype
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6-2-3-variation-sexual-reproduction
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6-2-4-predicting-inheritance-monohybrid-crosses
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6-2-5-predicting-inheritance-dihybrid-crosses
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6-2-6-predicting-inheritance-identifying-linkage
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6-2-7-predicting-inheritance-identifying-epistasis
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6-2-8-predicting-inheritance-chi-squared-test
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6-2-9-continuous-and-discontinuous-variation
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6-2-10-factors-affecting-evolution
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6-2-11-the-hardy-weinberg-principle
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6-2-12-isolation-and-speciation
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6-2-13-artificial-selection
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6-2-1-key-terms-in-genetics
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6-3-manipulating-genomes11 主题
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6-3-1-dna-sequencing
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6-3-2-comparing-genomes
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6-3-3-non-coding-dna-and-regulatory-genes
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6-3-4-synthetic-biology
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6-3-5-polymerase-chain-reaction
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6-3-6-electrophoresis
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6-3-7-dna-profiling
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6-3-8-genetic-engineering
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6-3-9-genetic-engineering-techniques
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6-3-10-uses-of-genetic-engineering
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6-3-11-gene-therapy
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6-3-1-dna-sequencing
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6-4-cloning-and-biotechnology14 主题
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6-4-1-natural-clones-in-plants
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6-4-2-producing-cuttings
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6-4-3-production-of-artificial-clones-in-plants
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6-4-4-uses-of-plant-cloning
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6-4-5-natural-clones-in-animals
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6-4-6-production-of-artificial-clones-in-animals
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6-4-7-uses-of-animal-cloning
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6-4-8-microorganisms-and-biotechnology
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6-4-9-microorganisms-and-food-production
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6-4-10-culturing-microorganisms
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6-4-11-batch-and-continuous-fermentation
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6-4-12-standard-growth-curve-of-microorganisms
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6-4-13-factors-affecting-the-growth-of-microorganisms
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6-4-14-immobilised-enzymes-in-biotechnology
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6-4-1-natural-clones-in-plants
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6-5-ecosystems7 主题
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6-6-populations-and-sustainability6 主题
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1-1-practical-skills-written-assessment7 主题
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1-2-practical-skills-endorsement-assessment16 主题
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1-2-1-practical-ethical-use-of-organisms
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1-2-2-practical-aseptic-techniques
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1-2-3-practical-dissection-of-gas-exchange-surfaces-in-fish-and-insects
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1-2-4-drawing-cells-from-blood-smears
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1-2-5-practical-investigating-biodiversity-using-sampling
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1-2-6-practical-data-loggers-and-computer-modelling
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1-2-7-practical-investigating-the-rate-of-diffusion
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1-2-8-practical-investigating-water-potential
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1-2-9-practical-factors-affecting-membrane-structure-and-permeability
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1-2-10-biochemical-tests-reducing-sugars-and-starch
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1-2-11-biochemical-tests-lipids
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1-2-12-biochemical-tests-proteins
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1-2-13-chromatography
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1-2-14-serial-dilutions
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1-2-15-practical-investigating-the-rate-of-transpiration
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1-2-16-practical-using-a-light-microscope
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1-2-1-practical-ethical-use-of-organisms
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2-1-cell-structure9 主题
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2-2-biological-molecules17 主题
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2-2-1-properties-of-water
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2-2-2-monomers-and-polymers
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2-2-3-monosaccharides
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2-2-4-the-glycosidic-bond
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2-2-5-polysaccharides
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2-2-6-biochemical-tests-reducing-sugars-and-starch
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2-2-7-lipids-and-ester-bonds
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2-2-8-lipids-structure-and-function
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2-2-9-biochemical-tests-lipids
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2-2-10-amino-acids-and-peptide-bonds
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2-2-11-protein-structure
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2-2-12-globular-proteins
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2-2-13-fibrous-proteins
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2-2-14-inorganic-ions
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2-2-15-biochemical-tests-proteins
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2-2-16-finding-the-concentration-of-a-substance
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2-2-17-chromatography
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2-2-1-properties-of-water
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2-3-nucleotides-and-nucleic-acids8 主题
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2-4-enzymes9 主题
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2-4-1-the-role-of-enzymes
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2-4-2-enzyme-action
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2-4-3-enzyme-activity-ph
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2-4-4-enzyme-activity-temperature
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2-4-5-enzyme-activity-enzyme-concentration
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2-4-6-enzyme-activity-substrate-concentration
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2-4-7-enzyme-activity-enzyme-inhibitors
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2-4-8-coenzymes-cofactors-and-prosthetic-groups
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2-4-9-practical-measuring-enzyme-activity
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2-4-1-the-role-of-enzymes
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2-5-biological-membranes9 主题
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2-5-1-the-cell-surface-membrane
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2-5-2-membrane-structure-and-permeability
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2-5-3-diffusion-and-facilitated-diffusion
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2-5-4-practical-investigating-the-rate-of-diffusion
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2-5-5-active-transport
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2-5-6-endocytosis-and-exocytosis
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2-5-7-osmosis
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2-5-8-osmosis-in-animal-and-plant-cells
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2-5-9-practical-investigating-water-potential
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2-5-1-the-cell-surface-membrane
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2-6-cell-division-cell-diversity-and-cellular-organisation11 主题
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2-6-1-the-cell-cycle
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2-6-2-the-stages-of-mitosis
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2-6-3-identifying-mitosis-in-plant-cells
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2-6-4-the-significance-of-mitosis
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2-6-5-the-stages-of-meiosis
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2-6-6-the-significance-of-meiosis
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2-6-7-specialised-cells
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2-6-8-the-organisation-of-cells
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2-6-9-stem-cells
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2-6-10-stem-cells-in-animals-and-plants
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2-6-11-the-use-of-stem-cells
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2-6-1-the-cell-cycle
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3-1-exchange-surfaces7 主题
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3-2-transport-in-animals12 主题
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3-2-1-the-need-for-transport-systems-in-animals
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3-2-2-circulatory-systems
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3-2-3-blood-vessels
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3-2-4-tissue-fluid
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3-2-5-the-mammalian-heart
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3-2-6-practical-mammalian-heart-dissection
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3-2-7-the-cardiac-cycle
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3-2-8-cardiac-output
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3-2-9-heart-action-initiation-and-control
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3-2-10-electrocardiograms-ecgs
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3-2-11-the-role-of-haemoglobin
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3-2-12-adult-and-fetal-haemoglobin
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3-2-1-the-need-for-transport-systems-in-animals
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3-3-transport-in-plants11 主题
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3-3-1-the-need-for-transport-systems-in-plants
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3-3-2-the-xylem-and-phloem
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3-3-3-the-xylem
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3-3-4-the-phloem
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3-3-5-transverse-sections-stems-roots-and-leaves
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3-3-6-the-process-of-transpiration
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3-3-7-transpiration-in-plants
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3-3-8-practical-investigating-the-rate-of-transpiration
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3-3-9-translocation
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3-3-10-the-mass-flow-hypothesis
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3-3-11-the-adaptations-of-xerophytic-and-hydrophytic-plants
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3-3-1-the-need-for-transport-systems-in-plants
课 27,
主题 4
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3-3-4-the-phloem
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Phloem Sieve Tube Elements & Companion Cells: Structure & Function
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The function of phloem tissue in a plant is to:
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Transport organic compounds (assimilates), particularly sucrose, from the source (eg. leaf) to the sink (eg. roots). The transport of these compounds can occur up and down the plant
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The organic compounds are dissolved in water to form sap
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Phloem is a complex tissue made up of various cell types; its bulk is made up of sieve tube elements which are the main conducting cells and companion cells
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Other cell types of phloem tissue also include parenchyma for storage and strengthening fibres
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Mature phloem tissue contains living cells, unlike xylem tissue
Structure of phloem tissue. (a) Microscope slide image and drawing of a sieve tube element and companion cell in transverse section (TS), (b) photomicrograph image and drawing of a sieve tube element and companion cell in longitudinal section (LS).
Structure of phloem tissue. (c) Transmission electron micrograph image and drawing of a sieve tube element and companion cell in transverse section (TS)
Sieve tube elements
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Sieve tube elements line up end to end to form a continuous tube
Phloem sieve tube elements structure & function table
Companion cells
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Each sieve tube element has a companion cell associated with it as companion cells control the metabolism of their associated sieve tube member
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They also play a role in loading and unloading of sugars into the phloem
Phloem companion cells structure & function table
Comparison of xylem & phloem tissue table
Examiner Tips and Tricks
Understand the difference between sieve tube elements and companion cells, and how they are different to xylem tissue. Remember that mature xylem tissue is dead, so there is no evidence of organelles, and they have lignified cell walls, whereas sieve tube elements have no lignin, do have sieve plates, and their companion cells contain nuclei and dense cytoplasm.