Question

The assimilatory power in photosynthesis is _____ .
(a) ATP
(b) NADPH
(c) ATP and ${ NADPH }_{ 2 }$
(d) ATP, NADPH, and ${ CO }_{ 2 }$

Answer 1

Assimilatory power is the power generated in light reactions during photosynthesis. The energy providing molecules formed during these reactions that occur in the presence of light helps in carrying out the reactions in dark phase reactions.

Complete answer:
- The assimilatory power in photosynthesis is the power produced in the form of ATP and ${ NADPH }_{ 2 }$. These molecules are formed during the evolution of oxygen and the photolysis of water.
- This energy is formed during the light phase reactions in photosynthesis that takes place in direct sunlight, in the thylakoids of chloroplasts.
- Assimilatory power helps in carbon dioxide fixation to form storage carbohydrates for the plant during the dark phase reactions.

Additional information:
- The carbon dioxide formed is fixed into carbohydrates or other organic compounds through assimilatory reactions.
- Cytochrome ${b}_{6}f$ and ATP synthase work together to create ATP in a process known as photophosphorylation.
- Photosystem I complex (PS I) in the electron transport chain transfers electrons to the enzyme FNR or Ferredoxin-NADP(+) Reductase, creating a non-cyclic electron flow. The PS I releases FNR into the stroma of thylakoid, reducing ${ NADP }^{ + }$ to NADPH.
So, the correct answer is ‘ATP and ${NADPH}_{2}$’.

Note:
- Photosynthesis is also known as carbon assimilation reaction as this is an oxidation-reduction process involving a light phase and dark phase reaction where water is oxidized and ${ CO }_{ 2 }$ is reduced to carbohydrates.
- Light-dependent reactions occur due to the presence of light-absorbing pigments, mainly the chlorophylls.
- The net reactions forming light reaction is $2{ H }_{ 2 }O \ + \ 2NAD{ P }^{ + } \ + \ 3ADP \ + \ 3{ P }_{ i } \ \longrightarrow \ { O }_{ 2 } \ + \ 2NADPH \ + \ 3ATP$