Biology / A2 level
Membrane ion gradients and selective channels support resting potentials and action potentials.
Membrane ion gradients and selective channels support resting potentials and action potentials. An action potential propagates through local electrical changes; myelination alters how efficiently distant regions of axon are activated.
Chemical synapses release neurotransmitter that binds postsynaptic receptors. Summation influences whether a new action potential occurs. Hormonal and plant signalling use different mechanisms, including growth responses associated with auxin distribution; a response is a regulated process rather than a conscious choice by the tissue.
An impulse travels 0.6 m in 0.02 s. Find mean propagation speed.
Divide distance by time: 0.6/0.02=30 m/s.
Using the worked example as supplied data, predict the effect of changing one condition. Draw a labelled model, record your reasoning and identify a variable that would need controlling. No human, animal or microbial experiment is required.
Related simplified PhET model. Explain what it represents and what the living system does differently.
Neurotransmitter molecules
Electrical activity triggers chemical release; the transmitter diffuses and binds receptors.
30 m/s
Divide distance by time: 0.6/0.02=30 m/s.
No
Action potentials are approximately all-or-nothing; stimulus intensity is often encoded through firing frequency and recruitment.