Limiting Factor Principle in Photosynthesis

Steps:

• Identify graphs showing photosynthesis rate vs. factors like light or CO2; limitation occurs where rate rises with increasing CO2.
• Locate points on rising curve portions, indicating CO2 as the scarcest resource.
• Exclude plateau points, where rate is constant due to other limits like light or temperature.
• Match points 2 and 5 to rising sections based on standard saturation curves.

Why C is correct:

• Points 2 and 5 lie on the ascending part of the CO2 response curve, where rate is directly proportional to CO2 concentration per the limiting factor law.

Why the others are wrong:

• A includes point 3 on the plateau, limited by light, not CO2.
• B includes point 1 at zero rate (no limitation applicable) and point 6 on plateau.
• D includes point 6 on plateau, where CO2 is in excess.

Final answer: C