"Do electrons move?"
Toma asked while fiddling with a battery.
Rei answered. "Constantly moving. The essence of chemical reactions is electron movement."
"From where to where?"
"Redox reactions. Losing electrons is oxidation, gaining is reduction."
Kana wrote in her notebook. "Lose = oxidation, gain = reduction."
"Isn't that backwards?" Toma was confused.
"It is confusing," Milia laughed. "But reacting with oxygen means losing electrons. Hence oxidation."
Rei supplemented. "OIL RIG. Oxidation Is Loss, Reduction Is Gain."
"English mnemonic?" Kana was impressed.
"Any memorization method works. Important thing is, they always occur in pairs."
Toma asked. "Pairs?"
"If one side is oxidized, the other is reduced. Electrons don't disappear."
Milia gave an example. "Iron rusts. Iron is oxidized, oxygen is reduced."
"Fe → Fe^3+ + 3e^-," Rei wrote the equation.
"Lost three electrons."
Kana asked. "Where do those electrons go?"
"To oxygen. O2 + 4e^- → 2O^2-."
"Receiving them."
Toma understood. "Give and take."
"Yes. Exchange of electrons," Milia nodded.
Rei continued. "In living bodies, it's more complex. Electrons move step by step."
"Why?"
"If large energy is released at once, it becomes heat and is wasted. Moving gradually, efficiently recovering."
Kana imagined. "Descending stairs?"
"Perfect metaphor," Rei acknowledged. "The electron transport chain is exactly an electron staircase."
Milia drew a diagram. "Starting from NADH, going through several intermediate carriers to oxygen."
"Carriers?"
"Electron transporters. NAD, FAD, coenzyme Q, cytochromes..."
Toma counted. "How many?"
"Over five major ones," Rei answered.
"Each has different redox potential."
Kana had a question. "Redox potential?"
"Ease of receiving electrons. Higher potential means stronger attraction."
Milia supplemented. "Like water flowing from high to low places, electrons flow from low to high potential."
"So the order is determined."
Toma got excited. "Electron dominoes?"
"Relay is closer," Rei corrected. "Passing the baton."
Kana asked. "Why so complex?"
"To efficiently recover energy," Milia explained.
"Extracting energy little by little at each step."
Rei continued. "That energy pumps protons, making ATP."
Toma asked. "What if electron transport stops?"
"Death," Milia answered immediately.
Silence flowed.
"Cyanide inhibits the electron transport chain. That's why it's deadly poison."
Kana shivered. "It's that important."
Rei nodded. "Life depends on electron flow."
"Same with photosynthesis?" Toma asked.
"Reverse direction," Milia answered. "Light energy raises electrons to high energy state."
"Climbing stairs."
"And those electrons reduce carbon dioxide to make sugar."
Kana summarized. "Electrons go up and down."
"Up in photosynthesis, down in respiration. Global scale circulation."
Toma was moved. "Electrons are amazing."
Rei smiled. "But electrons themselves don't change. Just elementary particles."
"How they're used is important," Milia added.
"Life is technology for controlling electron flow."
Kana looked outside. "Invisible, but electrons are flying around everywhere."
"Inside cells, in the atmosphere too."
Toma stared at the battery. "This too is electron flow."
"Converting chemical energy to electrical energy," Rei explained.
"Same principle as life."
Milia said quietly. "Electrons are energy currency."
"And the thread of life."
Outside the window, lightning flashed. A space where electrons bounce around. That's this world.