A-Level Biology · Topic 6
Responding to the environment: nerves, muscles and homeostasis: every key term you need (+ practice quiz)
16 flashcard terms for A-Level Biology Topic 6, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
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Taxis vs kinesis Taxis is directional movement towards or away from a stimulus; kinesis is a non-directional change in turning rate or speed.
Resting potential About -70 mV inside the axon, maintained by the sodium-potassium pump and the membrane's greater permeability to potassium.
Action potential Depolarisation when voltage-gated sodium channels open, then repolarisation as potassium channels open. All-or-nothing above threshold.
Refractory period A brief interval when sodium channels cannot reopen. It ensures impulses travel one way and limits their frequency.
Saltatory conduction In myelinated axons the impulse jumps between nodes of Ranvier, so transmission is far faster than in unmyelinated ones.
Cholinergic synapse Calcium influx triggers vesicles to release acetylcholine, which binds receptors on the postsynaptic membrane and depolarises it.
Summation Several small impulses combine to reach threshold — spatial from different neurones, temporal from one neurone firing rapidly.
Sliding filament theory Myosin heads bind actin, pull, detach using ATP and reset. The filaments slide past each other, so the sarcomere shortens.
Slow vs fast twitch fibres Slow fibres are aerobic, rich in myoglobin and fatigue-resistant; fast fibres contract powerfully but rely on anaerobic respiration.
Negative feedback A change from the set point triggers a response that reverses it. The basis of temperature, glucose and water regulation.
Ultrafiltration High pressure in the glomerulus forces small molecules through the basement membrane into the Bowman's capsule, retaining cells and proteins.
Selective reabsorption Glucose and most water return to the blood in the proximal convoluted tubule, whose cells have microvilli and many mitochondria.
Loop of Henle Sets up a salt gradient in the medulla by counter-current multiplication, letting the collecting duct reabsorb water.
Antidiuretic hormone Released when blood water potential falls. Makes the collecting duct more permeable to water by inserting aquaporins.
Insulin and glucagon Insulin lowers blood glucose by promoting uptake and glycogenesis; glucagon raises it through glycogenolysis and gluconeogenesis.
Second messenger model Adrenaline binds a surface receptor, activating adenylate cyclase to make cyclic AMP, which activates enzymes inside the cell.
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