Question

Which of the following summarizes photosystem I and the electron transport chain I in terms of exergonic and endergonic reactions.

- The energy of sunlight is used to power the exergonic reaction of combining ADP with P.
- The energy of sunlight is used to power the endergonic reaction of combining NADP+ with H+.
- The energy of sunlight is used to power the endergonic reaction of combining ADP with P.
- The energy of the electron from photosystem II is used to power the exergonic reaction of combining NADP+ with H+.
- The energy of sunlight is used to power the exergonic reaction of combining NADP+ with H+.
- The energy of the electron from photosystem II is used to power the endergonic reaction of combining NADP+ with H+.

Answer 1

The energy of sunlight is used in exergonic reactions at photosystem II to extract electrons from water, and in endergonic reactions at photosystem I to reduce NADP+ to NADPH. The electron transport chain connects both photosystems, creating an electrochemical gradient that powers the synthesis of ATP from ADP, also an endergonic process.

Step-by-step explanation:

The light-dependent reactions of photosynthesis involve both exergonic and endergonic reactions. When photons strike photosystem II (PSII), the energy from sunlight is used in an exergonic reaction to extract electrons from water (H2O), which are then passed down the electron transport chain (ETC) to photosystem I (PSI).

In PSI, the electrons are used in an endergonic reaction to reduce NADP+ to NADPH. This energy transfer is essential for synthesizing ATP from ADP and inorganic phosphate (P), a process known as photophosphorylation. The electrons traveling through the ETC to PSI enable the creation of an electrochemical gradient across the thylakoid membrane, which powers ATP synthase in the transformation of ADP to ATP, an example of an endergonic reaction as it requires energy input.