undergo processing by metabolism.
The correct answer is electrons.
Electron transport chain refers to an array of complexes, which mediates electrons from electron donors to electron acceptors through redox reactions, and combines the transfer of electrons with the transfer of protons through a membrane.
This produces an electrochemical proton gradient, which instigates the production of ATP. The ultimate electron acceptor in the electron transport chain is oxygen in aerobic respiration and sulfate in anaerobic respiration.
Cacti grow in the desert, which is a very hot climate. Not the best for both gaining and maintaining water supplies, due to the fact that water becomes vapour very quickly in conditions such as a desert (unless we're talking about polar deserts).
Keeping their stomata closed during the day stops water vapour from escaping their cells. While this does inhibit growth and stop new water molecules from entering, it allows the cactus to maintain a healthy amount of water within itself.
