"Why do batteries work?"
Kana asked abruptly.
Rei thought for a moment before answering. "Because electrons move. It's a redox reaction."
"Redox... I'm always confused about that."
Milia quietly approached and wrote in her notebook. "OIL RIG: Oxidation Is Loss, Reduction Is Gain."
"Oxidation loses electrons. Reduction gains electrons," Rei translated.
"But why do electrons move?" Kana asked the essential question.
"Because it's energetically favorable," Rei drew a diagram on the board. "Electrons want to go where energy is lower."
Milia supplemented. "Like water flowing downhill."
"Just as water flows from high to low places, electrons flow from high to low potential."
Kana wrote in her notebook. "So who gives electrons and who receives them?"
"That's determined by ionization tendency and electronegativity," Rei explained.
"Metals lose electrons easily. Especially sodium and potassium."
"Conversely, oxygen and fluorine gain electrons easily."
Milia began preparing experimental equipment. "Demonstration?"
"Let's do it," Rei agreed.
Milia took out copper and zinc plates, connecting them with a salt bridge. The voltmeter needle moved.
"Zinc loses electrons, and copper ions gain electrons," Rei explained.
"Zn → Zn²⁺ + 2e⁻, this is oxidation."
"Cu²⁺ + 2e⁻ → Cu, this is reduction."
Kana got excited. "Electrons are moving through the circuit!"
"Yes. This electron flow is electric current."
Milia wrote another example. "Cellular respiration."
"Cellular respiration?" Kana asked back.
"Glucose is oxidized and oxygen is reduced. Energy is extracted in the process."
"The source of life's energy."
Rei explained in detail. "Electrons are extracted from glucose and passed to NADH and FADH2."
"They're passed stepwise to oxygen in the electron transport chain."
"Stepwise?"
"If transferred all at once, energy escapes as heat. By transferring gradually, it's stored as ATP."
Milia drew a diagram. A complex electron transport chain.
"Complex I, II, III, IV. Electrons are passed at each."
"Like a bucket brigade," Kana said.
"Good analogy," Rei acknowledged. "At each stage, protons are pumped out of the membrane. That proton gradient drives ATP synthesis."
"Electron movement indirectly creates energy..."
Milia said quietly. "Electrons are the currency of life."
"Electrons are the currency of life," Rei translated.
Kana asked seriously. "What about photosynthesis?"
"Same principle," Rei answered. "Light energy excites electrons to higher energy levels."
"Chemical energy is fixed as those electrons descend."
Milia supplemented. "Photosystem II → Photosystem I. The electron's journey."
"Water is oxidized producing oxygen, and NADPH is reduced."
Kana's face showed understanding. "Redox reactions are stories about electrons."
"Yes. Who transfers electrons to whom, and by what route."
"Designing that route is biochemistry's sophistication."
Milia wrote final words in her notebook. "Life is orchestrated electron transfer."
"Life is organized electron transfer."
Kana closed her notebook. Invisible electron flows are occurring countless times in the body right now. The reason electrons leap out is the flow of energy itself.