A study was conducted to understand the factors controlling the rate at which molecules or ions travel across cell membranes. An artificial membrane was created that was composed of a phospholipid bilayer only. The speed at which various substances crossed this membrane was measured
Some substances can pass through an actual cell membrane much faster than they passed through the artificial membrane in this study Which of the following statements best explains this
finding?
1. Actual cell membranes have a much thicker phospholipid bilayer than the artificial membrane does.
2. Actual cell membranes have a variety of proteins embedded in the membrane that are absent in the artificial membrane.
3. Hydrophobic substances spend more time between the two layers of phospholipid in the artificial membrane than they do between the layers in an actual membrane.
4. Hydrophilic substances upend more time attached to the polar region of the phospholipids in the artificial membrane than they do attached to the polar region of the phospholipids
in an actual membrane