Answer:
The buildup of high H+ concentration in the intermembrane space of the mitochondria and thylakoid space in chloroplasts is significant because it drives the synthesis of ATP. ATP is the cell's main energy currency, and it is used to power all of the cell's activities.
In mitochondria, the buildup of H+ concentration is caused by the electron transport chain. The electron transport chain is a series of proteins that transfer electrons from electron donors to electron acceptors. As the electrons are transferred, protons are pumped out of the mitochondrial matrix into the intermembrane space. This creates a proton gradient, with a higher concentration of protons in the intermembrane space than in the mitochondrial matrix.
The proton gradient drives the synthesis of ATP through chemiosmosis. Chemiosmosis is a process in which the energy of the proton gradient is used to drive the synthesis of ATP. The proton gradient is dissipated when protons flow back into the mitochondrial matrix through ATP synthase. ATP synthase is a protein complex that uses the energy of the proton gradient to drive the synthesis of ATP from ADP and Pi.
In chloroplasts, the buildup of H+ concentration is caused by the light reactions of photosynthesis. The light reactions are a series of reactions that use light energy to produce ATP and NADPH. As part of the light reactions, protons are pumped out of the thylakoid space into the stroma. This creates a proton gradient, with a higher concentration of protons in the thylakoid space than in the stroma.
The proton gradient drives the synthesis of ATP through chemiosmosis, in a similar way to how it drives the synthesis of ATP in mitochondria. The proton gradient is dissipated when protons flow back into the thylakoid space through ATP synthase. ATP synthase uses the energy of the proton gradient to drive the synthesis of ATP from ADP and Pi.
The synthesis of ATP is essential for all living cells. ATP is used to power all of the cell's activities, including cell growth, cell division, and cell movement. The buildup of H+ concentration in the intermembrane space of the mitochondria and thylakoid space in chloroplasts is a key step in the synthesis of ATP.