Some solutes are able to pass directly through the lipid bilayer of a plasma membrane, whereas other solutes require a transport protein or other mechanism to cross between the inside and the outside of a cell. The fact that the plasma membrane is permeable to some solutes but not others is what is referred to as selective permeability.
Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply.
Small uncharged molecules like carbon dioxide, oxygen, water can diffuse freely through a lipid bi-layer, and Lipids also can cross the lipid bilayer without the aid of any transport protein or other mechanism. However, the larger polar molecules like proteins, sucrose, and ions require transport protein or another mechanism to cross these molecules through lipid bi-layer.