Why does the pH of the cell become more basic during photosynthesis?

Answer 1

During the light reactions of photosynthesis, protons (H+) are ferried into the thylakoid space using the energy from the excited electrons in Photosystems 680 and 700. H+ causes buildup of hydronium (H3O+) ions in water, which are acidic.

Answer 2

A chloroplast is made of a couple of chambers, separated by membranes. The outside of the chloroplast is surrounded by a double membrane, and the space directly inside this double membrane is called the Stroma. In the Stroma, there are stacks of membranous structures called Grana (singular Granum). This membrane is called the thylakoid membrane, and the space inside is called the thylakoid space. In order for the Chloroplast to produce ATP, which is the first step in producing Glucose (if you're in high-school, your textbook may not tell you this), the first step is for hydrogen ions to move from the stroma into the thylakoid space. So as hydrogen ions move into the thylakoid space from the stroma, hydrogen ions move from the cytosol into the stroma. This decreases the hydrogen ion concentration in the cytosol, which is expressed by raising the pH, which is what it means for the pH to become more basic.

Answer 3

Water does not photosynthesise. Plants do. The water will be the same pH after a plant has photosythesised in it as it was before photosyntheis took place.