Electrons in pigment molecules become excited (a) light strikes a thylakoid. Therefore, (a) light strikes a thylakoid is correct .
The electron transport chain (ETC) is not located in the thylakoid membrane of chloroplasts; rather, it is a component of cellular respiration and is found in the inner mitochondrial membrane in eukaryotic cells.
In photosynthesis, the light-dependent reactions occur in the thylakoid membrane of chloroplasts.
When light strikes chlorophyll and other pigments, it excites electrons, initiating a series of redox reactions in the thylakoid membrane.
This process is distinct from the electron transport chain involved in cellular respiration.
During photosynthesis, the excited electrons move through the electron transport chain in the thylakoid membrane, leading to the creation of a proton gradient.
This proton gradient, also known as the proton motive force, is then utilized by ATP synthase to generate adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate (Pi).
Additionally, the electron transport chain generates reducing equivalents, such as NADPH, which are crucial for the synthesis of organic molecules during the subsequent Calvin cycle.
It's important to clarify that the electron transport chain associated with the synthesis of ATP through a proton gradient is a component of cellular respiration and is found in the mitochondria, not in the thylakoid membrane of chloroplasts involved in photosynthesis.