IB Biology HL C3.1 Integration of body systems questions

Twenty-four participants learned to choose one of two buttons to obtain a reward. On each trial, one of two shapes appeared on a screen while one of two tones was played. There were four shape–tone combinations, and the correct button depended on the combination: neither the shape alone nor the tone alone predicted the correct button. Participants received feedback during four training blocks. Twenty-four hours later, they completed a test without feedback or further practice. With two possible buttons, chance performance is 50%.

The graph shows the mean percentage of correct choices in each block and at the 24-hour test. Means are rounded to the nearest whole percentage point.

During a controlled observation, blood CO₂ is raised briefly and then allowed to fall. The measurements are:

Which statements are consistent with the data and feedback control of ventilation?

I. The initial CO₂ increase can lower blood pH by increasing blood acidity.
II. The fall in pH causes brainstem chemoreceptors to signal the diaphragm and intercostal muscles to reduce ventilation.
III. Increased ventilation can remove CO₂ from the blood, raising pH and reducing chemoreceptor stimulation so ventilation falls.