More Than Half a Century Ago, Two Cell Biologists Published

Multiple Choice

More than half a century ago, two cell biologists published details of their research involving isolated membrane vesicles from chloroplasts. Normally, the fluid inside these vesicles is near neutral. In an experiment, these membrane vesicles were soaked in an acidic solution (pH 4) until the inside of the vesicle also became pH 4. Based on the details provided in this scenario, by what mechanism could hydrogen ions have crossed the vesicle membrane, and what do you think happened at the molecular level?

A) Active transport; hydrogen ions moved out of the vesicle with the help of ATP energy.
B) Pinocytosis; water moved from outside the vesicle to inside.
C) Facilitated diffusion; hydrogen ions moved into the vesicle through a channel protein.
D) Simple diffusion; hydrogen ions moved into the vesicle through a channel protein.
E) Osmosis; water moved from inside the vesicle to outside.