Fermentation & Respiration in Plants 🌱
1. Three Ways Cells Handle Pyruvic Acid
- After glycolysis, cells choose one path:
- 🥛 Lactic acid fermentation (bacteria/muscles)
- 🍞 Alcoholic fermentation (yeast)
- 💨 Aerobic respiration (requires oxygen!)
2. Fermentation: Quick Energy Without Oxygen
🍞 Alcoholic Fermentation (Yeast):
- Pyruvic acid → CO₂ + Ethanol
- Enzymes: Pyruvic acid decarboxylase + Alcohol dehydrogenase
- Reaction: $$\text{Pyruvic acid} \xrightarrow{\text{decarboxylase}} \text{Acetaldehyde} \xrightarrow{\text{alcohol dehydrogenase}} \text{Ethanol}$$
🥛 Lactic Acid Fermentation (Bacteria/Muscles):
- Pyruvic acid → Lactic acid
- Enzyme: Lactate dehydrogenase
- Reaction: $$\text{Pyruvic acid} + \text{NADH} + \text{H}^+ \xrightarrow{\text{lactate dehydrogenase}} \text{Lactic acid} + \text{NAD}^+$$
🔑 Key Points:
- ⚡ Energy yield: Only 2 net ATP per glucose molecule
- ☠️ Waste products: Ethanol or lactic acid (toxic at high levels)
- 🔄 NAD⁺ recycling: NADH helps regenerate NAD⁺ to keep glycolysis going
- ⚠️ Alcohol limit: Yeast dies at ~13% alcohol – that’s why naturally fermented drinks (like wine) can’t go higher!
3. Aerobic Respiration: Maximum Energy Mode 💪
🏭 Mitochondria Powerhouse:
- Pyruvate enters mitochondria → becomes Acetyl CoA
- Enzyme: Pyruvic dehydrogenase (needs Mg²⁺, NAD⁺, CoA)
- Reaction: $$\text{Pyruvic acid} + \text{CoA} + \text{NAD}^+ \rightarrow \text{Acetyl CoA} + \text{CO}_2 + \text{NADH} + \text{H}^+$$
🔁 Krebs Cycle (TCA Cycle):
- Acetyl CoA + Oxaloacetic acid (OAA) → Citric acid
- First enzyme: Citrate synthase
- Produces per cycle: 2 CO₂, 3 NADH, 1 FADH₂, 1 ATP
💡 NEET Must-Knows:
- 🍬 Fermentation ATP: Net 2 ATP/glucose (vs 36-38 in aerobic)
- 🧪 Key enzymes:
- Alcohol fermentation: Pyruvic acid decarboxylase + Alcohol dehydrogenase
- Lactic acid: Lactate dehydrogenase
- 🚪 Mitochondrial entry: Pyruvate → Acetyl CoA via pyruvic dehydrogenase
- 🔁 Krebs starter: Acetyl CoA + OAA → Citrate (citrate synthase)
- 🍷 Alcohol limit: 13% in natural fermentation (yeast dies beyond this)
🌟 Quick Summary:
- 🌬️ Fermentation = Emergency energy without oxygen (low ATP)
- ⚡ Aerobic Respiration = Full energy release with oxygen (high ATP)
- 🏭 Krebs Cycle = Energy factory in mitochondria
- ⚠️ Yeast self-destructs at ~13% alcohol – stronger drinks need distillation!
Keep exploring the amazing world of plant respiration! You’re doing great! 🌿✨
