To determine what is required for the light-dependent reactions in photosynthesis, let's first review what these reactions involve.
Photosynthesis occurs in two main stages:
1. Light-dependent reactions
2. Light-independent reactions (Calvin cycle)
The light-dependent reactions take place in the thylakoid membranes of the chloroplasts and rely on light energy to drive the process. Let's break down the components involved in these reactions:
- Water ([tex]$H_2O$[/tex]) is utilized in the light-dependent reactions. It is split into oxygen, protons, and electrons through a process known as photolysis. The electrons are used to replace those lost by chlorophyll in Photosystem II, and the protons contribute to the generation of a proton gradient that is used to produce ATP.
- ATP and [tex]$NADPH$[/tex] are products of the light-dependent reactions. ATP provides energy, while [tex]$NADPH$[/tex] provides reducing power for the subsequent Calvin cycle.
- [tex]$CO_2$[/tex] is not involved in the light-dependent reactions. Instead, it is utilized in the Calvin cycle (light-independent reactions) to form glucose.
Given this information, the one that is required for the light-dependent reactions in photosynthesis is:
[tex]$H_2 O$[/tex]
