80. The following statements were made regarding photosynthesis:
    A. Conversion of 3-phosphoglycerate into glyceraldehyde-3-phosphate is a reduction process which utilizes ATP as well as NADH in Calvin cycle
    B. Conversion of ribulose 5-phosphate to ribulose 1,5- bisphosphate utilizes one third of the total ATP requirements of carbon fixation in Calvin cycle.
    C. Sucrose is synthesized outside the chloroplast and uses uridine triphosphate to activate glucose.                                                                                                                                                                D.Starch is a glucose polymer which is synthesized in chloroplast stroma and uses ATP

Which one of the following options represents a combination of correct statements?
(1) C and D                       (2) B and D
(3) A and C            (4) A and D

Introduction

Photosynthesis integrates complex biochemical reactions, from carbon fixation in the Calvin cycle to carbohydrate polymerization. Understanding the specific energy carriers and compartments for sucrose and starch synthesis is critical for grasping plant metabolism.

Explanation of Each Statement

A. Conversion of 3-phosphoglycerate into glyceraldehyde-3-phosphate is a reduction process which utilizes ATP as well as NADH in Calvin cycle

• Incorrect. The reduction actually uses ATP and NADPH, not NADH, in the Calvin cycle to convert 3-phosphoglycerate into glyceraldehyde-3-phosphate.

B. Conversion of ribulose 5-phosphate to ribulose 1,5-bisphosphate utilizes one third of the total ATP requirements of carbon fixation in Calvin cycle.

• Incorrect or ambiguous. While ATP is required for converting ribulose 5-phosphate to ribulose 1,5-bisphosphate during regeneration, the “one third” proportion is not a definitive or commonly cited ratio in standard plant biochemistry.

C. Sucrose is synthesized outside the chloroplast and uses uridine triphosphate to activate glucose.

• Correct. Sucrose is formed in the cytosol via a process using UDP-glucose, which is derived from glucose-1-phosphate and UTP.

D. Starch is a glucose polymer which is synthesized in chloroplast stroma and uses ATP

• Correct. Starch is synthesized from glucose units in the chloroplast using ATP to form ADP-glucose, the active glucose donor for polymerization.

Why Option (1) C and D Is Correct

Both C and D accurately detail the site and nucleotide requirements of sucrose (cytosol, UTP/UDP-glucose) and starch (chloroplast, ATP/ADP-glucose) biosynthesis, matching textbook plant physiology. A and B are incorrect based on coenzyme specifics and ambiguous ATP ratios.