AP Bio Free Response Question for Vacuole pH

This question is from the 2019 AP Biology Exam. Be sure to include specific vocabulary and try not to write more than four sentences.

FAQ Writing Samples & Feedback

Free Response Practice Submission 1

a) The K+/H+ transport protein is responsible for the increase in the pH of the vacuole during flower opening. It changes the pH of the vacuole by moving the H+ ions in and out of it, and pH is a measure of the concentration of H+ ions (inverse relationship). b) The changing concentrations of the K+ and H+ ions due to the transport protein causes the vacuole to swell with water due to changing its tonicity. Since there is a greater concentration of K+ ions inside the vacuole than outside, it is hypertonic and has less water potential. Thus, water will enter into it (movement from high to low concentration) and cause it to swell.

Teacher feedback

You received 1/2 points for your response to part A. While the K+/H+ transport protein is responsible for the increase in pH, you needed to specifically say that the pH increases because the transport protein pumps H+ ions OUT of the vacuole. The proton pump is what is responsible for bringing the H+ ions back in. You received 1/1 points for your response to part B. You did an awesome job of explaining the hypertonic environment created.

Free Response Practice Submission 2

a) The K+/H+ transport protein is responsible for the increase in the pH because it removes H+ ions from inside the vacuole and thus decreases the concentration of H+ ions inside the vacuole leading to its increase in pH. b)The activation of the transport protein will cause more K+ ions to flow into the vacuole which will decrease the solute potential and water will flood into the vacuole since the water potential inside is lower than the pressure outside. Water always moves from high potential to low potential or from low concentration of solute to high concentration of solute. The increased solute inside the vacuole makes it hypertonic to the outside and water will flood in.

Teacher feedback

You received 2/2 points for your answer to part a by successfully naming the transport protein AND how it leads to a decrease in pH by removing protons from the vacuole.

You received 1/1 points for your answer to part b by successfully describing the change in water potential due to the transport protein.

Free Response Practice Submission 3

A.) The K+/H+ transport protein moves H+ ions out of the vacuole which increases its pH.

B.) The K+/H+ transport protein moves K+ ions into the vacuole. This makes the cell hypertonic because the concentration of the solute K+ is increasing inside the vacuole.

Teacher feedback

You received 2/2 points for your answer to part A by successfully naming the protein AND how it facilitates the change in pH.

You received 1/1 points for your answer to part B by explaining that the movement of potassium leads to a hypertonic environment.