Glucose does not efficiently diffuse directly through phospholipid bilayers. However, in the digestive tract, large quantities of glucose are moved from food, into the epithelial cells lining the small intestine, then out of these cells into the extracellular space and from there into the bloodstream. The relative concentrations of glucose in each of these compartments is as follows: Higher in the epithelial cell than in the food; Higher in the epithelial cell than in extracellular space; Higher in extracellular space than in bloodstream. Based on this information, predict the modes of transport used to move glucose 1) from food into the epithelial cell 2) From the epithelial cell into the extracellular space 3) From the extracellular space into the bloodstream.
A. Active transport; Simple diffusion; Simple diffusion
B. Active transport; Facilitated diffusion; Active transport
C. Active transport; Passive transport; Passive transport
D. Facilitated diffusion; Active transport; Passive transport

When concentration of a substance is different on either side of a semi-permeable membrane, the movement of this substance can occur by active or passive transport. Active transport occurs when the substance is moved from the region of its lower concentration to that of its higher concentration. This type of movement uses the energy to move the substance. Since the glucose concentration is higher in the epithelial cells than in the food, it will enter into the cells by the process of active transport.

The passive movement of substances is driven by concentration gradient. The glucose concentration is lower in extracellular space than epithelial cells, so glucose will be transported into the extracellular space by passive movement.

Likewise, a higher concentration of glucose in extracellular space than blood will move it passively into the bloodstream.