Both statements are true. The protein-to-lipid ratio varies dramatically depending on physiological function (e.g., mitochondrial inner membrane is $\sim 75\%$ protein for transport/respiration, whereas the myelin sheath consists of $\sim 80\%$ lipid and only $\sim 20\%$ protein to provide high electrical insulation along axons). Reason (R) directly explains the lipid-rich nature of myelin (A).

Transport mechanisms across membranes:
Simple Diffusion: Small hydrophobic/gaseous molecules like Nitric oxide (NO) diffuse directly across the lipid bilayer (IV)
Facilitated Diffusion: Polar solutes like Glucose pass down their gradient via carrier proteins (GLUT uniporters) (I)
Primary active transport: Direct ATP-driven ion pumping, such as the $\text{Na}^+/\text{K}^+$ ATPase pump (III)
Secondary active transport: Driven by electrochemical ion gradients, such as proton-coupled Lactose permease symport (II).

The insulin receptor is a transmembrane heterotetrameric ($(\alpha\beta)_2$) Receptor Tyrosine Kinase (RTK). Upon insulin binding to the extracellular $\alpha$ subunits, the intracellular $\beta$ subunit intrinsic tyrosine kinase undergoes autophosphorylation on specific tyrosine residues.