The Variety of Life - Chapter 10 AQA AS Biology

Chapter 10 AS AQA Biology - unit 2

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  • Created by: H.N
  • Created on: 30-11-12 20:40
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  • The Variety of Life
    • starch
      • role
        • energy storage
        • insoluble - doesn't draw H20 into cell by osmosis
        • unbranched chain wound into a tight coil - very compact - a lot packed into small space
        • when hydrolysed forms alpha-glucose - easily transported + readily used in respiration
      • found in plants but never found in animal cells
      • structure
    • Glycogen
      • structure
        • similar to starch - but shorter chains + highly branched
        • small granules -  mainly in the liver and muscles
        • compact
      • role
        • shorter chains - more readily hydrolysed  to alpha-glucose
          • important for energy release in animals
        • good for storage
    • Heamoglobin
      • structure
        • Primary - 4 polypeptide chains
        • secondary - chains coiled into helix
        • tertiary - chain folded into a precise shape
        • quaternary -  polypeptides linked to form a spherical molecule
          • heam group - Fe2+  ion - can combine with a single 02
            • i.e. a single heamoglobin molecule can carry 4 02 molecules
        • large protein with a quarternary structure
      • role
        • to transport oxygen
          • readily associate with 02 at gas exchange surface
          • readily dissociates from 02 at tissues
        • changes its affinity in different conditions
          • (low p02) presence of C02 - heam molecule binds more loosely to 02 = RELEASES 02
            • releases 02 = unloading/Dissociating
          • (high p02) Presence of 02 - binds more closely to 02 = O2 ATTACHES TO IT
            • combines with 02 = Loading/Associating
        • high affinity for 02 - take up more easily, releases less easily
        • low affinity for 02 - takes up less easily, releases it more readily
      • oxygen dissociation curves
        • further to LEFT= greater affinity for 02 (organisms in low 02 environments)
        • further to RIGHT = lower affinity for 02 (organisms that are v. active - high 02 demand)
        • greater the C02 conc = more easily hemoglobin releases 02
          • dissociation curve shifts down - Bohr effect
            • saturation of blood lower at given p02
        • Gas exchange surface - C02 constantly removed=pH raised, higher affinity for 02
          • 02 is LOADED
        • In the tissues - C02 produced by respiring cells = pH of blood (in tissues) lowered, lower affinity for 02
          • 02 is UNLOADED
    • Cellulose
      • structure
        • made of monomers of beta- glucose
        • each beta glucose rotated 180 degrees
        • straight, unbranched chains that run parallel to one another
          • H bonds form cross-linkages between adjacent chains - adds strength
        • molecules group together = microfibrils = fibres
      • role
        • provides rigidity to the cell wall
        • maintain a turgid state to provide maximum surface area for photosynthesis
    • plant cell structure
      • leaf palisade cell
        • function - carry out photosynthesis
        • many chloroplasts - arranged to get max. light
        • large vacuole - pushes cytoplasm/chloroplasts to edge of cell
      • Chloroplasts
        • disc-shaped
        • main features
          • the chloroplast envelope
            • double membrane - surrounds organelles + controls entry/exit of materials
          • the grana
            • stacks of thylakoids -  containing chlorophyll
              • 1st stage of photosynthesis occurs here
          • the stroma
            • fluid-filled matrix
              • 2nd stage of photosynthesis occurs here
              • possesses all enzymes needed for this
        • contain DNA + ribosomes  - manufacture proteins for photosynthesis
      • cell wall
        • no. of polysaccharides
        • thin layer (middle lamella) - marks boundary between adjacent cell walls
        • functions
          • provide mechanical strength - cell doesn't burst
          • allow water to move along it
      • differences between animal + plant cells
        • animal- no cell wall (only cell-surface membrane)
        • Chloroplasts in plants not animals
        • Vacuole present in plants - rarely animals
        • plants - starch grain for storage / animals- glycogen granules for storage

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