In a symport:

The correct option is both molecules cross the membrane in the same direction.

Understanding Symport:

Cotransport (or secondary active transport) is a mechanism by which two different molecules or ions are transported simultaneously across a cell membrane. Depending on the direction in which the two substances move relative to each other, cotransport systems are classified into two main types:

1. Symport: In a symport system, two different molecules or ions move across the biological membrane in the same direction at the same time.

2. Antiport: In an antiport system, two different molecules or ions are transported across the membrane in opposite directions.

Additionally, when a single molecule moves across a membrane independently of other molecules, the transport mechanism is called uniport.

Therefore, in a symport, both molecules cross the membrane in the same direction.