Photosynthesis causes the gas exchange change from S to T

Steps:

• Examine the graph or diagram showing points S and T to identify the specific change, such as rising oxygen levels or falling carbon dioxide.
• Recall that photosynthesis involves plants absorbing CO2 and releasing O2 in light.
• Match the observed increase in O2 or decrease in CO2 to the photosynthesis process.
• Eliminate options that do not produce gas changes matching the diagram.

Why B is correct:

• Photosynthesis converts CO2 and H2O into glucose and O2 using light energy (6CO2 + 6H2O → C6H12O6 + 6O2), directly causing the upward O2 trend or downward CO2 trend between S and T.

Why the others are wrong:

• A. Osmosis moves water across membranes but does not alter gas concentrations.
• C. Respiration consumes O2 and produces CO2, opposite to the change shown.
• D. Transpiration is water loss from leaves, unrelated to gas production or consumption.

Final answer: B