A few questions about Photosynthesis?

Question

1.Where is the light energy needed to excite electrons?

2.Where do the water molecules split?

3.What is the location where hydrogen ions diffuse from a high to low concentration?

4.The highest concentration of protons occurs where?

Answer 1

Hello Ethan,

See my comments below.

1.Where is the light energy needed to excite electrons?

Can you clarify your question? Are you asking where does the light come from that excites electrons in the reaction centers during photosynthesis? If so, the light comes from the sun, but artificial lighting can work (i.e. think indoor plants). The photons of light travel into the plant and react with reactions centers in the chloroplast --> thylakoid membranes--> reaction centers.

2.Where do the water molecules split?

If you are referring to subcellular location where this occurs, it occurs in the chloroplast organelle. In the chloroplast, there are grana stacks and lamellae composed of thylakoid membranes. The inside of these membranes are referred to as the lumen of the thylakoid or thylakoid space. The water splitting occurs inside the lumen of the thylakoid at photosystem II; remember, unintuitively, PSII occurs first in the Z-scheme.

If you are asking about the molecular mechanism, you are asking one of the most important questions in biology and, as far as I know, it has yet to be answered. So, good for you for asking an important question. See recent commentary in Nature Magazine from James Barber from the Imperial College of London. Barber (2017) A mechanism for water splitting and oxygen production in photosynthesis.

3.What is the location where hydrogen ions diffuse from a high to low concentration?

I’m assuming you are referring to photosynthesis based on your last two questions, in which case this occurs at the multi-protein complex called ATP synthase. Protons travel from the thylakoid lumen (high), to the stroma (low). This is different for mitochondria, in which case make sure to make a distinction when you are asking questions.

4.The highest concentration of protons occurs where?

I’m assuming your referring to photosynthesis based on your last questions in which case the protons (hydrogen ions) move from the thylakoid lumen (high) to the stroma (low). Highest concentration occurs in the thylakoid space.