Question

Although the net equation for photosynthesis indicates that the process can be measured in terms of either ${\mathbf{O}}_{\mathbf{2}}$produced or ${\mathbf{CO}}_{\mathbf{2}}$ fixed, in practice, these measurements are not necessarily equivalent. Explain.

Short answer

The equation of photosynthesis can be measured in terms of${\mathrm{CO}}_2$ and${\mathrm{O}}_2$.

Step-by-step solution

Reactions of photosynthesis

The reaction of photosynthesis is as follows;

$6{\mathrm{CO}}_2+6{\mathrm{H}}_2\mathrm{O}\to \mathrm{light}\mathrm{energy}\to {\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$

The reaction of the Calvin cycle is as follows;

$3{\mathrm{CO}}_2+9\mathrm{ATP}+6\mathrm{NADPH}\to \mathrm{GAP}+9\mathrm{ADP}+8\mathrm{Pi}+6{\mathrm{NADP}}^{+}$

The above reactions were independently linked to ATP and NADPH

• The light-dependent reactions were measured with${\mathrm{O}}_2$ that is produced by PS II

$6{\mathrm{CO}}_2+6{\mathrm{H}}_2\mathrm{O}\to \mathrm{light}\mathrm{energy}\to {\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$

• The light-independent reactions were measured with ${\mathrm{CO}}_2$that is fixed by the Calvin cycle.

$3{\mathrm{CO}}_2+9\mathrm{ATP}+6\mathrm{NADPH}\to \mathrm{GAP}+9\mathrm{ADP}+8\mathrm{Pi}+6{\mathrm{NADP}}^{+}$

Flow of electrons in light reactions and ATPproduction.

The light-dependent reactions are measured in terms of${\mathrm{O}}_2$ production by PS II and light-independent reactions are measured in terms of ${\mathrm{CO}}_2$production fixed by the Calvin cycle. They are not related directly to NADPH and ATP. Thus, it may lead to an increase in O₂production formed without increasing${\mathrm{CO}}_2$ fixation.