Answer:
D) bilayer membranes
Explanation:
Two lipidic bilayers compose the cell membrane. There are also proteins and glucans incrusted in between. Lipids are amphipathic molecules with hydrophilic heads -negatively charged phosphate group- and hydrophobic tails. Lipids are arranged with their hydrophilic polar heads facing the exterior and the interior of the cells, while their hydrophobic tails are against each other, constituting the internal part of the membrane. Membranes are fluid, which means that the composing molecules can move through them.
Lipids can easily change places with other neighboring lipids by lateral diffusion in the same layer. This is passive diffusion, which means that it does not need energy to happen.
Lipids can also diffuse transversally to the other layer but not as easily as lateral diffusion. Jumps between monolayers are infrequent as the lipidic polar heads meet the fatty acid barrier.
There are also other lipidic movements as rotational diffusion that imply the rotation of the molecule.
