Question 7a
Abscisic acid (ABA) is a weak acid represented by the structure ABA-H. It can dissociate, releasing positively charged H+ ions (protons) and forming negatively charged ABA− ions, as shown below:
ABA-H ⇌ ABA− + H⁺
Key Observations from Research:
- The non-dissociated form, ABA-H, is capable of moving in and out of chloroplasts, while the dissociated form, ABA−, cannot cross chloroplast membranes.
- Light exposure enhances the uptake of protons (H+ ions) into the grana within chloroplasts.
Question: Based on this information, predict how light affects the pH level of the stroma.
In light conditions, protons (H+ ions) are actively taken into the grana, reducing the concentration of H+ ions in the stroma. This leads to a rise in pH in the stroma (the stroma becomes less acidic).