transport across cell membranes

• Polar substances cant pass through the phospholipid bilayer
• because the cell surface membrane contains a hydrophobic center hydrophobic molecules such as steroid hormones can easily pass through the cell membrane
• hydrophobic centre prevents hydrophilic water-soluble molecules from easily passing through
• hydrophilic substances are polar so they have a charge
• water molecules can pass through even though there polar because they are small