Question

If a chemical was to block the transport of electrons from ferredoxin to NADP+ reductase how would that affect the process of photosynthesis (i.e. what would still be produced, what wouldn’t be produced, would the plant live, etc)?

Answer 1

NADPH is produced in the last steps of electron transfer as ferredoxin (Fd) transfers electrons to ferredoxin-NADP + oxidoreductase (FNR). This chemical equation is given as;

2 reduced ferredoxin + NADP+ + H+ 2 oxidized ferredoxin + NADPH

The NADPH is then used as a reducing equivalent in the reactions of the Calvin cycle.

The Calvin cycle refers to the light-independent reactions in photosynthesis that take place in three key steps. The Calvin cycle converts carbon dioxide and other compounds into glucose. Overall chemical equation for the Calvin cycle is given as;

3 CO2 + 6 NADPH + 5 H2O + 9 ATP → glyceraldehyde-3-phosphate (G3P) + 2 H+ + 6 NADP+ + 9 ADP

  + 8 Pi (inorganic phosphate)

Here each G3P molecule is of 3 carbons. To make one glucose molecule (which can be created from 2 G3P molecules) it requires 6 turns of the Calvin cycle.

Thus, lack of NADPH completely restricts the Calvin cycle. There will be no glucose production.

In glycolysis, the first step of respiration, the glucose molecule is broken down into two smaller molecules called pyruvate, and a little energy is released in the form of ATP.

When the chemical blocks transport of electrons from ferredoxin to FNR, the rate of respiration will be more than the rate of photosynthesis. The energy consumed will be more than the energy produced. Since, plants are autotrophs, they don't have external source of nutrition for gaining this energy. It will eventually die.