How is acetylcholine removed from the postsynaptic membrane?

Explanation:

Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (and humans) as a neurotransmitter.

Neurotransmitter is a chemical message released by nerve cells to send signals to other cells, such as neurons, muscle cells and gland cells.

After a neurotransmitter molecule has been recognized by a post-synaptic receptor, it is released back into the synaptic cleft. Once in the synapse, it must be quickly removed or chemically inactivated in order to prevent constant stimulation of the post-synaptic cell and an excessive firing of action potentials.

Some neurotransmitters are removed from the synaptic cleft by special transporter proteins on the pre-synaptic membrane. These transporter proteins carry the neurotransmitter back into the pre-synaptic cell, where it is either re-packaged into a vesicle and stored until it is once again needed to transmit a chemical message, or broken down by enzymes.

the correct answer is:

a population changes in response to a change in the environment.