A(n) is defined as a mechanism in a nerve terminal membrane that is responsible for removing neurotransmitter molecules from the synapse by taking them back into the neuron.

The correct answer to fill in the blank is: transporter.

Explanation:

Neurotransmitter transporters are transport proteins located in the neurons' cell membrane and with the important function of carrying the neurotransmitters across the membranes and to their specific destinations. The mechanism used by the neurotransmitter transporters is electrochemical gradients.

The specific neurotransmitter transporters that remove the molecule to put a stop to its action are located in the synaptic membrane.

the correct answer is:

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