Final answer:
Membrane proteins can diffuse laterally in the lipid bilayer, and the statement is true. There are two main types of membrane proteins: integral and peripheral, both of which contribute to the transportation of molecules across the cell membrane.
Step-by-step explanation:
Membrane proteins can indeed diffuse laterally in the lipid bilayer, so the correct answer to the question is (a) True. This lateral mobility allows membrane proteins to interact with specific target molecules in the cell or to be clustered in particular regions of the membrane as needed for cell function. The two primary types of membrane proteins are integral proteins, which are embedded within the hydrophobic portion of the lipid bilayer, and peripheral proteins, which bind more loosely to the surface of the membrane, often attached to integral proteins or lipid polar head groups.
Integral proteins, like channel proteins and carrier proteins, perform vital roles in transport across the membrane by allowing certain ions and molecules which cannot pass through the hydrophobic core of the lipid bilayer on their own to do so. For example, channel proteins form pores through which ions can pass down their concentration gradient, while carrier proteins undergo conformational changes to transport specific molecules across the membrane.
It is essential to highlight that while the lipid bilayer presents a barrier to the diffusion of polar molecules and ions due to its hydrophobic nature, the presence of transport proteins allows for regulated movement of substances. These proteins are not static but are in constant motion within the plane of the membrane, a concept known as the fluid mosaic model of cell membranes.