Biology AS Edexcel Snab Revision
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lifestyle-health-and-risk as19 主题
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diet-and-health interpreting-data-on-risk-factors
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diet-and-health treatment-of-cvd
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diet-and-health energy-budgets-and-diet
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diet-and-health monosaccharides
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diet-and-health the-glycosidic-bond
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diet-and-health disaccharides
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diet-and-health polysaccharides
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diet-and-health lipids-and-ester-bonds
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diet-and-health reducing-risk-factors-of-cvd
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diet-and-health practical-vitamin-c-content
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the-circulatory-system the-need-for-a-circulatory-system
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the-circulatory-system the-importance-of-water-in-transport
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the-circulatory-system mammalian-heart-structure-and-function
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the-circulatory-system blood-vessels-structure-and-function
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the-circulatory-system cardiac-cycle
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the-circulatory-system investigating-heart-rate
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the-circulatory-system atherosclerosis
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the-circulatory-system blood-clotting
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diet-and-health cardiovascular-disease
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diet-and-health interpreting-data-on-risk-factors
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genes-and-health as28 主题
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gas-exchange-cell-membranes-and-transport properties-of-gas-exchange-surfaces
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gas-exchange-cell-membranes-and-transport ficks-law-of-diffusion
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gas-exchange-cell-membranes-and-transport the-mammalian-lung
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gas-exchange-cell-membranes-and-transport cell-membranes
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gas-exchange-cell-membranes-and-transport practical-investigating-membrane-permeability
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gas-exchange-cell-membranes-and-transport diffusion-and-facilitated-diffusion
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gas-exchange-cell-membranes-and-transport active-transport
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gas-exchange-cell-membranes-and-transport osmosis
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nucleic-acids nucleotides-and-phosphodiester-bonds
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nucleic-acids dna-structure
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nucleic-acids rna-structure
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proteins transcription
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proteins translation
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proteins nature-of-the-genetic-code
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proteins amino-acids-and-peptide-bonds
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proteins levels-of-protein-structure
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proteins globular-proteins-structure-and-function
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proteins fibrous-proteins-structure-and-function
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proteins the-role-of-enzymes
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proteins mode-of-enzyme-action
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proteins enzyme-and-substrate-concentrations
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inheritance dna-replication
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inheritance mutations
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inheritance inheritance-key-terms
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inheritance pedigree-diagrams
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inheritance monohybrid-crosses
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inheritance chi-squared-test
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inheritance genetic-screening
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gas-exchange-cell-membranes-and-transport properties-of-gas-exchange-surfaces
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voice-of-the-genome as19 主题
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cell-structure-and-organisation cell-theory
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cell-structure-and-organisation eukaryotic-cells
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cell-structure-and-organisation prokaryotic-cells
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cell-structure-and-organisation organisation-of-cells
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cell-structure-and-organisation microscopy
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cell-structure-and-organisation magnification-calculations
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cell-structure-and-organisation recognising-organelles
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cell-division the-cell-cycle
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cell-division mitosis
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cell-division practical-identifying-mitosis-in-plant-cells
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reproduction-and-inheritance mammalian-gametes
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reproduction-and-inheritance fertilisation-in-mammals
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reproduction-and-inheritance genes-and-linkage
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reproduction-and-inheritance meiosis-source-of-genetic-variation
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differentiation-and-variation stem-cells
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differentiation-and-variation stem-cells-in-medicine
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differentiation-and-variation cell-differentiation
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differentiation-and-variation epigenetics
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differentiation-and-variation phenotypes-and-variation
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cell-structure-and-organisation cell-theory
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biodiversity-and-natural-resources as19 主题
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biodiversity the-variety-of-life
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biodiversity measuring-biodiversity-within-a-habitat
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biodiversity comparing-biodiversity-between-habitats
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biodiversity ecological-niches-and-adaptations
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biodiversity natural-selection
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biodiversity hardy-weinberg-equation
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biodiversity reproductive-isolation
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biodiversity classification
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biodiversity conservation-of-biodiversity
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resources-from-plants plant-cell-structure
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resources-from-plants plant-stems
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resources-from-plants importance-of-water-and-inorganic-ions-to-plants
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resources-from-plants starch-and-cellulose-structure-and-function
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resources-from-plants plant-fibres
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resources-from-plants practical-identifying-tissue-types-within-stems
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resources-from-plants tensile-strength-plant-fibres
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resources-from-plants development-of-drug-testing
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resources-from-plants antimicrobial-properties-of-plants
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resources-from-plants sustainability-and-plant-materials
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biodiversity the-variety-of-life
gas-exchange-cell-membranes-and-transport ficks-law-of-diffusion
Exam code:8BN0
Fick’s Law of Diffusion
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Fick’s Law relates the rate of diffusion to the concentration gradient, the diffusion distance and the surface area
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This relationship can be represented by the following equation, where ∝ means “proportional to”
rate of diffusion format('truetype')%3Bfont-weight%3Anormal%3Bfont-style%3Anormal%3B%7D%3C%2Fstyle%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22math1502cc2c94be1a7c4ca7ef25b8b%22%20font-size%3D%2216%22%20text-anchor%3D%22middle%22%20x%3D%228.5%22%20y%3D%2216%22%3E%26%23x221D%3B%3C%2Ftext%3E%3C%2Fsvg%3E){kind=small}
(surface area x concentration difference)format('truetype')%3Bfont-weight%3Anormal%3Bfont-style%3Anormal%3B%7D%3C%2Fstyle%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22math13cec07e9ba5f5bb252d13f5f43%22%20font-size%3D%2216%22%20text-anchor%3D%22middle%22%20x%3D%229.5%22%20y%3D%2216%22%3E%26%23xF7%3B%3C%2Ftext%3E%3C%2Fsvg%3E){kind=small}
thickness of membrane
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Proportionality means the rate of diffusion will double if:
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The surface area or concentration difference doubles
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The diffusion pathway halves
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Fick’s Law can be written as an equation which can be used to calculate the rate of diffusion
Rate = P x A x ((C1 – C2)T)
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Where
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P = A permeability constant that is a quantitative measure of the rate at which a particular molecule can cross a particular membrane
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A = surface area
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C1 – C2 = the difference in concentration between two areas
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T = thickness of the exchange surface
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Worked Example
A sample of alveolar epithelium tissue from a mammal is 1.5 
m thick and has a surface area of 3 m2. The concentration of oxygen in the alveolus is 1.8 x 10-16 mol m-3 and the concentration of oxygen in the blood is 7.5 x 10-17 mol m-3. The permeability constant for oxygen across alveolar epithelium is 0.012 molecule s-1.
Calculate the rate of diffusion across the section of alveolar epithelium.
Answer:
Step 1: Substitute numbers into the equation
Rate = P x A x ((C1 – C2) T)
Rate = 0.012 x 3 x ((1.8 x 10-16 – 7.5 x 10-17)1.5)
Step 2: Complete the calculation
Rate = 0.012 x 3 x (1.05 x 10-16 1.5)
Rate = 0.012 x 3 x 7 x 10-17
Rate = 2.52 x 10-18 molecules <img alt=”straight mu” data-mathml='<math class=”wrs_chemistry”><semantics><mi mathvariant=”normal”>μ</mi><annotation encoding=”application/vnd.wiris.mtweb-params+json”>{“language”:”en”,”fontFamily”:”Times New Roman”,”fontSize”:”18″}</annotation></semantics></math>’ height=”22″ role=”math” src=”data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20xmlns%3Awrs%3D%22http%3A%2F%2Fwww.wiris.com%2Fxml%2Fmathml-extension%22%20height%3D%2222%22%20width%3D%2211%22%20wrs%3Abaseline%3D%2216%22%3E%3C!–MathML%3A%20%3Cmath%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%20class%3D%22wrs_chemistry%22%3E%3Cmi%20mathvariant%3D%22normal%22%3E%26%23x3BC%3B%3C%2Fmi%3E%3C%2Fmath%3E–%3E%3Cdefs%3E%3Cstyle%20type%3D%22text%2Fcss%22%2F%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22Times%20New%20Roman%22%20font-size%3D%2218%22%20text-anchor%3D%22middle%22%20x%3D%225.5%22%20y%3D%2216%22%3E%26%23x3BC%3B%3C%2Ftext%3E%3C%2Fsvg%3E” style=”vertical-align:-6px;width:11px;height:22px” w
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