An amphipathic molecule will react in what manner when exposed to water?

An amphipathic molecule possesses both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions. When exposed to water, such molecules tend to orient themselves in a way that maximizes their interaction with the aqueous environment while minimizing their exposure to water at the hydrophobic regions. This behavior is primarily observed in the formation of micelles.

In the case of micelles, the hydrophilic heads of the amphipathic molecules face outward, interacting with the water, while the hydrophobic tails curl inwards, away from the water. This arrangement is energetically favorable and allows for a stable structure to form in an aqueous environment, thus providing a way for the hydrophobic parts to avoid contact with water.

This behavior is fundamental in biological systems, such as in the formation of cell membranes and the digestion and absorption of lipids in the gastrointestinal tract. Other options like dissolving completely, forming a gas, or combusting do not accurately represent the nature of amphipathic molecules when they interact with water. They instead demonstrate specific behaviors related to more soluble or reactive substances, which do not align with the typical interactions of amphipathic compounds in an aqueous medium.