Question

If the light is cut and carbon dioxide supply is continued then which of the following substances will disappear from photosynthesising algal cells?
A. RUDP
B. PGAL
C. RUMP
D. PGA

Answer 1

The light reaction is the first step of the photosynthesis, where light energy is trapped to produce ATP and NADPH. The second step of photosynthesis is a dark reaction, in which ATP and NADPH are used to produce glucose. This reaction is catalysed by RuBP carboxylase enzyme.

Complete answer:
Option A: During carbon fixation, the protein namely Ribulose-diphosphate combines with carbon dioxide to form phosphoglyceraldehyde.
Option B: Phosphoglyceraldehyde or PGAL plays as an intermediate source in many metabolic pathways.
Option C: Ribulose-monophosphate or RUMP helps in the synthesis of RUDP. RUDP helps in carbon fixation in dark reaction or light-independent reaction. The RUDP is synthesized when the RUMP is combined with ATP and produced.
Option D: PGA or phosphoglyceric acids is the first product of the Calvin cycle. It is a three-carbon compound.
Hence, RUDP is combined with carbon dioxide to form an intermediate product of the Calvin cycle. Their RUDp is the product which will disappear when light is cut and carbon dioxide is supplied.

Note: In some plants, cyanobacteria and in algae energy is stored in the form of sugar. It is produced in the light-independent reaction, also called the Calvin cycle or dark reaction. Thus the biosynthetic phases of the photosynthesis. In light-independent reaction, does not directly need light but uses the products i.e. ATP and NADPH produced in light reaction to fix the carbon dioxide and produced sugar molecules and other organic molecules that were necessary for the cells. The dark reaction takes place in the stroma of the chlorophyll and cytoplasm.