Light limitation occurs where photosynthesis rate rises linearly with light intensity

Steps:

• Recall the light response curve: rate increases proportionally with light at low intensities (light-limited), then plateaus.
• Examine graph points: identify those on the initial steep, linear upward slope.
• Point 1 is at low light with rising rate; point 5 shows similar linear increase before plateau.
• Confirm other points: 2, 3, 4, 6 are either transitional or on the flat plateau where CO2 or enzymes limit rate.

Why B is correct:

• In the light-limited phase, rate follows the law of limiting factors, directly proportional to light intensity (rate = k × light, where k is constant).

Why the others are wrong:

• A: Points 3 and 6 are on the plateau, limited by CO2, not light.
• C: Point 2 is transitional, not purely light-limited; includes incorrect pairing.
• D: Points 2, 4, and 6 are on or past the plateau, limited by other factors.

Final answer: B