AP BIOLOGY

Detailed explanation-1: -Glucose tends to move from an area of high concentration to an area of low concentration, a process called diffusion. Because the glucose transporter works with the concentration gradient, its process of moving glucose across the cell membrane is called facilitated diffusion.

Detailed explanation-2: -The membrane is selectively permeable because substances do not cross it indiscriminately. Some molecules, such as hydrocarbons and oxygen can cross the membrane. Many large molecules (such as glucose and other sugars) cannot.

Detailed explanation-3: -Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly. Small polar molecules, such as water and ethanol, can also pass through membranes, but they do so more slowly.

Detailed explanation-4: -GLUT4 is a glucose transporter found in fat and skeletal muscle. Insulin triggers GLUT4 to insert into the membranes of these cells so that glucose can be taken in from the blood.

Detailed explanation-5: -A special form of passive transport allows polar substances, such as glucose, salts, and amino acids, to pass through cell membranes. All cells need the food energy supplied by glucose.