🌬️ Respiratory Quotient (RQ)

When plants do aerobic respiration, they use oxygen (O2) and release carbon dioxide (CO2). The respiratory quotient is the ratio of CO2 released to O2 used:

\[ RQ = \frac{\text{volume of CO}_2\text{ evolved}}{\text{volume of O}_2\text{ consumed}} \]

RQ changes based on what fuel (substrate) the plant is breaking down!

🍚 RQ for Carbohydrates (like glucose)

When plants fully break down carbohydrates, RQ = 1. Here’s why:

\[ \ce{C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy} \]

\[ RQ = \frac{6\ \ce{CO2}}{6\ \ce{O2}} = 1.0 \]

Equal CO2 out and O2 in → perfect 1:1 ratio! ✨

🥑 RQ for Fats (like tripalmitin)

Fats need more oxygen to break down → RQ < 1. Example:

\[ \ce{2(C51H96O6) + 145O2 -> 102CO2 + 98H2O + energy} \]

\[ RQ = \frac{102\ \ce{CO2}}{145\ \ce{O2}} ≈ 0.7 \]

Less CO2 produced per O2 used → RQ is low (0.7).

🥚 RQ for Proteins

Proteins give an RQ around 0.9 – between carbs and fats!

💡 Important Reality Check!

Plants never use only one type of fuel! They mix carbs, fats, and proteins together during respiration. 🌈

🌱 Quick Summary of Plant Respiration

  • 🌿 No lungs needed! Plants exchange gases through stomata (leaf pores) and lenticels (stem spots) by diffusion.
  • ⚡ Cellular respiration = Breaking food molecules to release energy. Glucose is the favorite fuel! But fats/proteins work too.
  • 🔁 Glycolysis: First step in cytoplasm → 1 glucose → 2 pyruvic acid molecules.
  • 🧪 Without oxygen? Pyruvate becomes lactic acid or alcohol (fermentation). Happens in microbes/grains!
  • 💨 With oxygen? Pyruvate goes to mitochondria → becomes acetyl CoA (releases CO2).
  • 🔄 Krebs’ cycle: Happens in mitochondria. Makes NADH + H+ and FADH2 → used to create ATP (energy!).

📌 Must-Know for NEET

  1. RQ values: Carbs=1.0, Fats≈0.7, Proteins≈0.9
  2. Gas exchange in plants: Occurs via stomata/lenticels (no organs like animals!)
  3. Glycolysis location & output: Cytoplasm → 2 pyruvate per glucose
  4. Krebs’ cycle site: Mitochondrial matrix (makes energy carriers)
  5. Fermentation vs aerobic: Anaerobic = no O2 (lactic acid/alcohol), Aerobic = O2 needed (full energy release)