Answer:
d. Ligand-gated ion channels
Explanation:
a.Intracellular receptor: it's activated through second messengers since its activation and actions happen only inside the cell there's no distribution of ions on opposite sides of the membrane.
b.G-protein-coupled receptor: these receptors bind specific ligands at the cell surface (hormones and neurotransmitters) to relay the signal across the membrane. This means they act as a messager, there's no distribution of ions.
c.Phosphorylated receptor tyrosine kinase dimer: works as a messenger as well, it propagates a signal through the plasma membrane when it allows tyrosine to be trans phosphorylated.
d. Ligand-gated ion channels open to allow ions such as Na+, K+, Ca2+ or Cl- in response to the binding of a chemical messenger, one example of this kind of channel in action is when a neurotransmitter binds to a receptor located on the postsynaptic neuron, opening ion channels, this lead to a flow of ions across the cell membrane that turns into a depolarization or a hyperpolarization by changing the distribution of ions on opposite sides of the membrane.
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