Question

Suppose the interior of the thylakoids (lumen) of isolated chloroplasts were made acidic and then transferred in dark to a $pH=8$ solution, what would be likely to happen?

• A. The isolated chloroplast will make $ATP$
• B. The Calvin cycle will be activated
• C. Cyclic photophosphorylation will occur
• D. The isolated chloroplast will reduce $NAD{P}^{+}$ to $NADPH+H^{+}$

Answer 1

The correct option is A The isolated chloroplast will make $ATP$

The acidic lumen of the thylakoids will have a higher concentration of H${}^{+}$ ions. When these are transferred to basic pH of 8, the H${}^{+}$ will tend to move outside due to their concentration gradient, which is higher in the lumen and lower in the surrounding. The thylakoids bear ATP synthases that will use the proton motive force H${}^{+}$ ions and will make the ATP. So, an isolated chloroplast is capable of synthesizing the ATP when the lumen is made acidic and the outer medium is made alkaline.

Hence, the correct answer is 'The isolated chloroplast will make ATP'