🌱 Respiration in Plants

Plants breathe too! Even big plants let gases move easily because:

  • Every living cell is close to the surface 🌿
  • Woody stems? Living cells hide under bark with tiny holes (lenticels)
  • Air spaces between cells help gases spread like a network 🌀

🔥 Glucose Breakdown: The Big Picture

When cells burn glucose completely:

\[ \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \longrightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Energy} \]

But cells are smart! They break glucose in small steps to trap energy as ATP 💡, not just heat. This is respiration.

🚀 Glycolysis: Sugar-Splitting Powerhouse

(From Greek: glycos = sugar, lysis = splitting)

  • 📍 Where: Cytoplasm of all living cells
  • 🧬 Pathway: EMP pathway (Embden, Meyerhof, Parnas)
  • 🍬 Start: Glucose from sucrose (photosynthesis) or stored carbs

🔬 Glycolysis Steps (Figure 12.1)

  1. Glucose → Glucose-6-phosphate (uses 1 ATP)
  2. → Fructose-6-phosphate → Fructose-1,6-bisphosphate (uses 1 more ATP)
  3. Split into two 3-carbon pieces:
    • Dihydroxyacetone phosphate
    • Glyceraldehyde-3-phosphate (PGAL)
  4. PGAL → 1,3-Bisphosphoglycerate (BPGA) (makes NADH + H⁺)
  5. BPGA → 3-Phosphoglyceric acid (makes 1 ATP per piece → so 2 total!)
  6. → Phosphoenolpyruvate (PEP) → Pyruvic acid (makes 1 more ATP per piece → 2 total!)

💡 Glycolysis Energy Tally

  • ATP used: 2 (steps 1 & 2)
  • ATP made: 4 (steps 5 & 6 for both 3-carbon pieces)
  • ✅ Net gain: 2 ATP + 2 NADH per glucose 🎉

🦠 After Glycolysis: Pyruvic Acid’s Adventure!

Pyruvic acid’s fate depends on oxygen:

  • No oxygen? → Fermentation (Anaerobic):
    • Yeast/bacteria: Pyruvic acid → Ethanol + CO₂ (Alcoholic fermentation) 🍞
    • Muscles/bacteria: Pyruvic acid → Lactic acid (Lactic fermentation) 💪
    • ⚠️ Low energy yield: < 7% of glucose’s energy → just 2 net ATP!
    • Fun fact: Yeast dies if alcohol hits ~13%. Naturally fermented drinks (like wine) max out at this! 🍷
  • Oxygen present? → Aerobic respiration:
    • Pyruvic acid enters Krebs cycle → full energy release! (requires O₂) 💨

🧪 Fermentation Reaction Quick Peek

Alcoholic:
Pyruvic acid → CO₂ + Ethanol (via enzymes pyruvic acid decarboxylase and alcohol dehydrogenase)

Lactic:
Pyruvic acid → Lactic acid (via lactate dehydrogenase)

🎯 NEET Super-Important Concepts

  1. Glycolysis ATP Math: 2 ATP used, 4 ATP made → net 2 ATP + 2 NADH per glucose.
  2. Fermentation Products: Alcohol + CO₂ (yeast) or Lactic acid (muscles/bacteria) → only 2 net ATP.
  3. Glycolysis Location & Oxygen: Happens in cytoplasm without O₂ → all living cells can do it!
  4. Key Enzymes: Hexokinase (starts glycolysis), Lactate dehydrogenase (lactic fermentation).
  5. Pyruvic Acid Fork: No O₂ → fermentation; O₂ → aerobic respiration (Krebs cycle).

Keep breathing… I mean, studying! You’ve got this 🌟