"Oh no, I messed up again!"
Toma shouted. The solution in the test tube had turned an unexpected color.
"What did you add?" Rei asked calmly.
"Enzyme and substrate, and then... oh."
Kana peered in. "What about buffer solution?"
"I forgot," Toma scratched his head.
Rei sighed. "That's why the reaction didn't proceed. The pH collapsed."
"pH?" Kana asked.
"Hydrogen ion concentration. Enzymes only work at specific pH levels."
Toma asked curiously. "But what does buffer solution actually do?"
Rei began explaining. "It maintains constant pH even when acids or bases are added. The key is a combination of weak acid and its salt."
"How does it work?"
"For example, acetate buffer. Mix acetic acid CH₃COOH with sodium acetate CH₃COONa."
Kana took notes.
"When acid is added, acetate ions CH₃COO⁻ neutralize it. When base is added, acetic acid reacts."
"So it can absorb changes from both directions," Rei added.
Toma pondered. "But it can't maintain it perfectly, right?"
"Sharp. Buffer capacity has limits."
Rei wrote an equation on the whiteboard.
"Henderson-Hasselbalch equation. pH = pKa + log([A⁻]/[HA])"
"A⁻ is the salt, HA is the weak acid. This ratio determines buffering capacity."
Kana asked. "What's the ideal ratio?"
"One to one. pH equals pKa. That's where buffering capacity is maximum."
Toma got excited. "So what should I use for my experiment?"
Rei answered. "Depends on your target pH. For around pH 7, phosphate buffer. At pH 7.4, it's close to physiological conditions."
"7.4?"
"Human blood pH. If this goes wrong, it's dangerous."
Kana was surprised. "Blood is buffered too?"
"Yes. The carbonate buffer system is primary. Regulated by the balance of CO₂ and HCO₃⁻."
Rei continued. "Breathing is part of the buffer system. When you exhale, CO₂ decreases and pH rises."
"Living itself is buffering?" Toma's eyes lit up.
"In a sense. Proteins also work as buffers. Amino acids have both acidic and basic groups."
Kana nodded deeply. "Inside cells is buffered too?"
"Of course. Intracellular pH is strictly controlled. Membrane proteins transport ions for regulation."
Toma became serious. "Without buffers, life couldn't be maintained."
"Exactly. Many metabolic reactions produce acids or bases. Without buffering, pH would fluctuate wildly."
Rei gave an example. "Muscle exercise. Lactic acid is produced and pH drops. But the buffer system works, so it's not immediately a problem."
"What if it exceeds limits?" Kana asked.
"Acidosis or alkalosis. Serious health problems."
Toma began preparing a new solution. "This time I'll add buffer properly."
"What will you use?"
"pH 7 phosphate buffer. A mixture of KH₂PO₄ and Na₂HPO₄."
Rei nodded. "Good choice. It's the standard for biochemistry experiments."
Kana helped calculate. "What ratio?"
"Since pKa₂ is 7.2, almost equal amounts. But calculate precisely with the equation."
Toma carefully mixed the reagents. This time, buffer was included from the start.
"The reaction is proceeding!"
In the test tube, the enzyme reaction progressed smoothly. The color gradually changed.
"Thanks to the buffer," Rei said.
Kana murmured. "You can't see it, but it's working properly."
"It's life's infrastructure," Toma was impressed. "Like air, so ordinary we don't notice."
Rei said quietly. "But we understand its importance only when we lose it."
The three stared at the test tube. The transparent buffer silently supporting the chemical world.
"Thank you, buffer," Toma said softly.
Kana and Rei laughed. But that gratitude wasn't wrong.
Buffers continue working today too, in invisible places.