Sugar molecules, like glucose, pass through an animal cell membrane using facilitated diffusion. This process involves the following steps:

1. Binding: Glucose binds to a specific transport protein embedded within the cell membrane. This protein is called a glucose transporter (GLUT).

2. Conformational Change: The binding of glucose triggers a conformational change in the glucose transporter. This change in shape allows the glucose molecule to move through the membrane.

3. Passage: Glucose is transported across the membrane through the channel created by the transporter protein.

4. Release: Once glucose reaches the other side of the membrane, it is released from the transporter protein. The transporter protein returns to its original conformation, ready to bind another glucose molecule.

Here's why facilitated diffusion is used instead of simple diffusion:

* Polarity: Glucose is a polar molecule, meaning it has a slightly positive and negative end. Cell membranes are primarily composed of lipids, which are nonpolar. Therefore, glucose cannot easily pass through the membrane by simple diffusion.

* Concentration Gradient: Facilitated diffusion allows glucose to move down its concentration gradient, meaning it moves from a region of high concentration to a region of low concentration. This is essential for replenishing glucose inside the cell.

In summary: Facilitated diffusion, with the help of specific transport proteins, enables the efficient transport of glucose across the cell membrane, ensuring the cell has a constant supply of this vital energy source.