A2 Biology Progress Test 1

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  • A2 Biology progress test 1
    • nerves
      • resting potential
        • sodium-potassium pumps active
          • this is against concentration gradient
            • ATP required
        • 3 Na+ moved out for every 2K+ moved in
        • membrane does allow some to leak through
          • leakier to K+ than Na+
        • more positive on the outside than inside
          • creates a positive charge on outside
          • difference in charge creates the resting potential
        • -70mV
      • structure
        • part after cell body is the axon
        • part before cell body is the dendron
        • myelin
          • made up of Schwann cells
            • mostly lipid with some proteins
            • gaps known as nodes of Ranvier
              • allows for salutatory conduction
                • increased speed
                • action potential jumps between nodes of Ranvier
          • 1/3 are myelinated
      • action potential
        • membranes of neurones also have other protein channels as well as the ion pumps
          • some of these are voltage-gated
            • they open and close depending on the potential difference across the membrane
            • at resting potential they are closed
          • some channels are caused to open and close depending on stimuli
            • 1-the Na+ ions can now flow back into the cell
              • can do this as an electrical gradient is set up
              • resting potential is now removed
                • no overall charge
                  • membrane is depolarised
        • all-or-nothing law
          • either an action potential is generated or not no matter how big stimuli is
          • frequency of action potentials tells us the difference between a strong or soft touch
      • synapses
        • gap is called synaptic cleft
        • impulse crosses the synapse
          • action potential arrives at the membrane of the presynaptic neurone
            • transmitter substance is released into cleft and diffuses across it
              • happens via exocytosis
              • presynaptic neurone has many vesicles containing the neurotransmitter
              • Ca2+ channels open causing vesicles to move
              • plasma membrane of postsynaptic neurone has receptor proteins
                • neurotransmitters are complementary to this and bind with the receptors
                • this allows Na+ ions to rush into the postsynaptic neurone, depolarising the membrane to start the AP
    • Hormones
      • endocrine
        • endocrine system transmits info from one cell or organ to another
          • travel in blood plasma
            • go to target cells
            • gland produces and secretes the hormones
      • exocrine
        • secrete substances into a duct
          • carried to another part of the body
      • 1st and 2nd messengers
        • affect target cells by attaching to a specific receptor molecule
          • this sets into action a series of events within the cell
    • energy flow
      • abiotic factors involve non-living parts of the environment
      • biotic factors involve other living organisms
      • trophic level is the level at which an organism is in the food chain
        • most energy is wasted and transferred elsewhere, will not move to the next organism
          • can be lost due to
            • unedible parts
            • primary will use the energy in bodily functions
            • the primary used up the energy in movement
            • the primary loses energy on excretion
          • less than 10% energy transfer when mammal eats mammal
            • energy lost as heat to maintain body temp.
          • we can manipulate energy levels from producer to consumer by
            • harvesting animal before adulthood
            • treat with steroids
            • selective breeding
            • treat with antibiotics
            • maintain constant temp.
            • limit movement
            • supply food
      • nitrogen cycle
        • geochemical
          • lightning
            • breaks down n=-n to form nitrates
            • add nitrates to soil to improve fertility
          • haber process
            • makes ammonium ions to improve fertility of soils
          • volcanic activity
            • releases vast quantities of energy to break n=-n
          • ocean currents
            • dead organic matter cant decompose
              • currents may lift the matter to be exploited in shallow water
        • biological
          • nitrogen fixation
            • bacteria in root nodules of lugumes
              • risobium
            • bacteria is anaerobic so the root nodule becomes anaerobic as the enzyme releases leghaemoglobin to take up o2
            • nostoc is free-living nitrogen fixing bacteria in the soil
              • use ammonium ions
          • denitrifying bacteria
            • Untitled
      • succession
        • primary succession
          • development of a community from bare ground
            • pioneer community
              • algae and lichens begin to live on the bare rock
            • the erosion of rock and build up of dead and rotting organisms produces soil for mosses and ferns to grow
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