Final answer:
The type of membrane protein that cannot be removed by a low ionic strength solution is an integral protein (option 1), due to its hydrophobic domains that interact with the lipid bilayer's hydrophobic interior.
Step-by-step explanation:
Proteins associated with the cell membrane are essential for various cellular functions, including transport, signaling, and cell recognition. These membrane proteins come in several forms, including integral proteins, peripheral proteins, and lipid-anchored proteins. When considering which type of protein cannot be washed away by a low ionic strength solution, integral proteins are the ones that remain firmly embedded within the cell membrane. Integral proteins span the hydrophobic interior of the lipid bilayer and interact with it through their hydrophobic domains, which essentially locks them in place.
In contrast, peripheral proteins do not have these hydrophobic domains and are not anchored in the same way, typically being attached to the surfaces of membranes and held by non-covalent bonds such as hydrogen bonding and electrostatic interactions, making them more easily removed. Unlike integral proteins, peripheral proteins are hydrophilic and can be dislodged by changes in ionic strength or pH. Similarly, lipid-anchored proteins are also attached to the membrane but via lipid moieties and can vary in their attachment strength. Therefore, the kind of membrane protein that cannot be washed free of the membrane by a low ionic strength solution is an integral protein.