Light Independent Reactions in Photosynthesis

Question 5 • PA Human Anatomy & Physiology A 2026-2027 SMITH IC

Which is an important difference between light-dependent (L-D) and light-independent (L-IND) reactions in photosynthesis?

Answer

The L-D reactions need CO2 and light energy, and the L-IND reactions needs water and O2.

The L-D reactions require light energy and water, and the L-IND reactions require ATP, NADPH, and CO2.

The L-D reactions can only occur during daylight, and the L-IND reactions can only occur during the night.

The L-D reactions need water and CO2, and the L-IND reactions need CO2 and light.

Explanation

Light-dependent reactions use light energy to split water, releasing oxygen and producing ATP and NADPH. The light-independent reactions (Calvin cycle) use ATP and NADPH to incorporate CO2 into sugars. Therefore, choice B correctly identifies the requirements of both stages. Light-independent reactions do not have to occur only at night; they can proceed whenever the needed materials are available.

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