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23 Cards in this Set
- Front
- Back
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Why do organisms need to respond to the environment?
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To avoid harmful environments, to ensure conditions are optimal, to avoid predators and to find a mate.
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What are the features of a good communication system?
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A specific, rapid system which covers the whole body and enables long term and short term responses.
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Outline the process of cell signalling.
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One cell releases a chemical that is detected by another cell triggering a response.
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What is Homeostasis?
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The maintenance of the internal environment at a constant state despite external changes.
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What is negative feedback?
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A process that brings about a reversal of any change in conditions. It ensures that an optimum steady state can be maintained.
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What is Positive Feedback?
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A process that increases any change detected by receptors.
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What is an Ecotherm?
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An organism that relies on external sources of heat to regulate body temperature.
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Describe adaptations of ectotherms.
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Expose body to sun, orientate body away from sun, Hide in burrow, Alter body shape, increase breathing movements.
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What is an Endotherm?
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An organism that relies on internal sources of heat to maintain body temperature.
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Describe adaptations of Endotherms when the temperature is too hot.
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Secrete more sweat, panting, hairs lie flat, vasodilation, decreased metabolism, no spontaneous contractions.
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Describe adaptations of endotherms if temperature is too cold.
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Less sweat secretes, no panting, hairs stand up, vasoconstriction, increased metabolism, shivering.
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What are Sensory Receptors?
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Specialised cells which act as transducers and detect changes in the environment.
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How is resting potential maintained?
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Sodium-Potassium pumps actively pump Na ions out of the neurone, the neurone is impermeable to them so they cannot re-enter. The pump moves Potassium ions into the neurone but they can leave the neurone though K ion channels. The membrane is polarised, the outside is more positively charges than the inside.
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Describe Depolarisation during an Action potential.
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Sodium ion channels open so ions diffuse in depolarising the membrane. Voltage-gated Sodium ion channels open so the neurone becomes more positively charges compared to the outside.
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Describe repolarisation during an Action Potential.
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The Potential difference reaches +40mV so Na channels close and Voltage-Gated Potassium ion channels open and K ions diffuse out of the neurone.
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Describe hyperpolarisation during an Action Potential.
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The potential difference overshoots slightly. Then the original PD is restored to resting state.
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What does frequency of transmission indicate?
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A higher intensity stimulus will generate more generator potentials, action potentials and more vesicles are released at the synapse. The brain can determine the intensity of the stimulus from the frequency.
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What is the All or Nothing Principle?
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A neurone either conducts an action potential or does not. It must exceed the threshold value but all action potentials are of the same magnitude (+40mV)
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What is the Myelin sheath?
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An electrical insulator made up of Schwann cells. Depolarisation only occurs at the nodes of Ranvier so the Neurone's cytoplasm cinducts enough electrical charge to depolarise the next node.(Saltatory conduction)
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What are the advantages of Myelinated neurones?
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Action potentials are transmitted much faster and over longer distances.
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Describe events at the synapse.
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An action potential arrives causing calcium ion channels to open and ions to diffuse in which causes vesicles to move and fuse with the membrane. Acetylcholine is released into the cleft and binds to receptors on Na ion channels creating a generator potential.
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How is Acetylcholine removed from the synaptic cleft?
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Acetylcholinesterase hydrolyses it to choline and ethanoic acid.
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What is the role of Synapses?
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Convergence, Divergence, Transmission in one direction only, filtering low level signals, summation, acclimatization.
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