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Organisms Response to Environments summary pages
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Unit 6: Organisms Respond to Changes in Their Internal and External Environments summary pages for AQA A level biology
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OrganismsRespond to
Changes in Their
Internal and
External
Environments
Introduction
● Homeostasis:
● The maintenance of a stable internal environment despite external
fluctuations.
● Control Systems:
● Coordination and regulation of physiological processes to achieve and
maintain homeostasis.
The Nervous System
Structure of Neurons
, ● Neuron Types:
● Sensory Neurons: Transmit sensory information to the central nervous
system (CNS).
● Motor Neurons: Transmit signals from the CNS to effectors (muscles
or glands).
● Interneurons: Located in the CNS, connect sensory and motor neurons.
● Parts of a Neuron:
● Dendrites: Receive signals.
● Cell Body: Contains the nucleus.
● Axon: Conducts signals away from the cell body.
Transmission of Nerve Impulses
● Resting Potential:
● Neurons are negatively charged at rest.
● Sodium-potassium pump maintains ion concentration gradients.
● Action Potential:
● A rapid, temporary change in membrane potential.
● Triggered by a stimulus reaching a threshold.
● Propagation:
● Action potentials travel along the axon.
● Synaptic Transmission:
● Neurotransmitters transmit signals between neurons.
The Endocrine System
Hormones
● Chemical Messengers:
● Produced by endocrine glands, released into the bloodstream.
● Travel to target cells, eliciting a response.
● Examples:
● Insulin (pancreas), adrenaline (adrenal glands).
Feedback Mechanisms
● Negative Feedback:
● Reverses a change to maintain homeostasis.
● Example: Regulation of blood glucose levels by insulin and glucagon.
● Positive Feedback:
● Amplifies a response, often leading to an endpoint.
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