Challenge Your Exam Readiness With Our Free STAAR Practice Questions

Plants use photosynthesis to convert carbon dioxide and water into glucose, capturing solar energy in chemical form. The process occurs in the chloroplasts of plant cells and involves light-dependent reactions in the thylakoid membranes and the Calvin cycle in the stroma. During the light-dependent reactions, water molecules are split (photolysis), releasing electrons, protons, and oxygen gas. The oxygen is not required for glucose synthesis, so it is released into the atmosphere as a byproduct. Option A, carbon dioxide, is a reactant absorbed by plants, not released. Nitrogen (B) is essential for plant proteins but not released by photosynthesis. Hydrogen (D) is generated internally during photolysis but is used to reduce NADP+ and is not released. STAAR science objectives emphasize understanding energy transformations and cycles in living systems. Recognizing that photosynthesis provides oxygen for most aerobic life is foundational. The correct answer, C, reflects mastery of plant physiology and the global role of photosynthesis in maintaining atmospheric balance.