Respiration in Plants

Beginner - Story Mode Topper - Revision

1. Do Plants Breathe? The Logic of No Nose

Imagine you make sugar in kitchen but never eat it. Useless right? Plant makes glucose in leaf, but to grow roots, make flowers, it needs to break that glucose and release energy. That breaking is respiration. Not breathing through nose, but burning food inside every cell to make ATP battery.

Plants have no nose, no lungs. Every cell needs oxygen. How? Small holes - stomata in leaves, lenticels in bark. Oxygen enters by diffusion, no pump needed because distance is short. Same hole where CO2 went in for photosynthesis, now O2 comes in for respiration. Daytime both happen, night only respiration. That's why at night plants take O2. Think of stomata as both entrance gate and exit gate, guarded by guard cells.

Part 1A - Do Plants Breathe? No Special Organs

Part 1B - Stomata & Lenticels Zoom - Guard Cells

Revision: Respiration = breaking C-C bonds to release ATP. No special organs, stomata + lenticels + general surface diffusion. O2 in CO2 out. Photosynthesis stores, respiration releases.

2. Glycolysis - The Starter Pack That Never Fails

Think glucose as 6-chocolate bar. You can't eat whole, you break into 2 pieces of 3. Glycolysis does same. Occurs in cytoplasm, needs no oxygen, so oldest pathway on earth, found in every cell from bacteria to you.

Story in 4 acts: Act1 Invest: Spend 2 ATP to make glucose ready. Act2 Split: Cut 6C into two 3C G3P. Act3 Payback x2: Each 3C makes 2 ATP +1 NADH. So 2x3C =4 ATP +2 NADH. Act4 Result: Net you spent 2, made 4, profit 2 ATP +2 NADH +2 Pyruvate. Enzyme hexokinase, phosphofructokinase key regulatory are checkpoints. If you have enough ATP, PFK stops, like shop closed when fridge full. Fate: Pyruvate goes to mitochondria if O2 present else fermentation.

Part 2A - Glycolysis EMP 10 Steps Overview

Part 2B - Energetics & PFK Regulation Zoom

Revision: Site cytoplasm, common to aerobic & anaerobic, 10 steps EMP. Glucose 6C →2 Pyruvate 3C. Use 2 ATP produce 4 ATP +2 NADH. Net 2 ATP +2 NADH. Key PFK hexokinase pyruvate kinase.

3. Fermentation - Jugaad When No Oxygen

Imagine current goes off, you use power bank. Fermentation is power bank mode. When mitochondria can't get O2, cell says okay, I'll just squeeze little energy from glycolysis itself, but I need to recycle NADH back to NAD+ else glycolysis stops.

Two jugaads: Yeast says - Pyruvate → Ethanol + CO2 makes bread fluffy beer bubbly, enzyme pyruvic decarboxylase + alcohol dehydrogenase. Your muscle says - Pyruvate → Lactate, enzyme lactate dehydrogenase, you feel cramps because lactate + acid. Both make only 2 ATP from glycolysis and no more. Less than 7% energy of glucose released, rest still in ethanol lactate.

Part 3A - Fermentation Alcoholic vs Lactic

Part 3B - NAD+ Regeneration Zoom - Why Only 2 ATP

Revision: Anaerobic cytoplasm incomplete oxidation. Alcoholic Pyruvate→Acetaldehyde→Ethanol+CO2 yeast. Lactic Pyruvate→Lactate muscle bacteria. Net 2 ATP only NADH→NAD+ regeneration.

4. Aerobic - Link Reaction The Door to Mitochondria

Pyruvate is made outside cytoplasm but big party is inside mitochondria. To enter it must change dress. Link reaction is bouncer at mitochondrial gate.

Pyruvate 3C carried into matrix. Enzyme Pyruvate dehydrogenase complex PDH needs 5 cofactors NAD+ CoA TPP FAD Lipoate. Reaction Pyruvate+CoA+NAD+→Acetyl CoA 2C+CO2+NADH. CO2 first release you breathe out. Acetyl CoA now can enter Krebs. Happens twice per glucose so 2 NADH+2 CO2 made here. If O2 absent this step blocked.

Part 4A - Link Reaction PDH Complex 5 Cofactors

Part 4B - Acetyl CoA Entry Gate Zoom

Revision: Matrix oxidative decarboxylation PDH. Pyruvate 3C→Acetyl CoA 2C+CO2+NADH. 2 times per glucose =2 NADH. Acetyl CoA connecting link.

5. TCA Cycle - The Circular Business

Imagine a shop that borrows 4 rupees OAA, adds 2 rupees from customer Acetyl CoA to make 6 rupees product Citrate, sells things releases CO2 earns NADH FADH2 and at end returns 4 rupees back to start. That's cycle, profit is energy carriers.

Krebs 1937 circle 8 steps: 1 Citrate synthase makes Citrate 6C from OAA 4C+Acetyl 2C. 2 Aconitase to Isocitrate. 3 Isocitrate DH gives α-KG 5C+CO2+NADH. 4 α-KG DH makes Succinyl CoA 4C+CO2+NADH. 5 Succinyl CoA synthetase makes Succinate+GTP 1 ATP. 6 Succinate DH makes Fumarate+FADH2 only enzyme in inner membrane. 7 Fumarase makes Malate. 8 Malate DH makes OAA back+NADH. Per acetyl 3 NADH 1 FADH2 1 GTP 2 CO2. For 1 glucose x2 =6 NADH 2 FADH2 2 ATP 4 CO2.

Part 5A - Krebs TCA 8 Steps Circular Map

Part 5B - Per Acetyl Counting 3 NADH 1 FADH2 Zoom

Revision: Matrix 8 enzymes OAA acceptor citrate first product. 3 NADH steps 3,4,8 1 FADH2 step6 1 GTP step5 2 CO2 steps3,4. Regulated by ATP ADP NADH NAD+. Succinate DH membrane bound.

6. ETS & Oxidative Phosphorylation - Power Plant

NADH and FADH2 are like charged batteries. They need to be discharged to make ATP. ETS is power plant where electrons flow like water from high to low and energy used to pump protons and then make ATP.

Inner membrane has 5 complexes: Complex I NADH DH pumps 4H+, Complex II Succinate DH no pump, CoQ mobile, Complex III bc1 pumps 4H+, Cytochrome c mobile, Complex IV Cytochrome oxidase pumps 2H+ + O2→H2O. H+ piles up in intermembrane space high concentration. They want to go back to matrix but only way is through Complex V ATP synthase rotating turbine. When H+ flows it rotates and makes ADP+Pi→ATP. This is chemiosmosis Peter Mitchell idea. O2 final acceptor makes water. If cyanide blocks Complex IV everything stops - death. 1 NADH≈2.5 ATP 1 FADH2≈1.5 ATP old books say 3 and 2.

Part 6A - ETS Complex I to IV Electron Flow

Part 6B - ATP Synthase Turbine Chemiosmosis Zoom

Revision: Inner membrane cristae electrons I→III→IV for NADH II→III→IV for FADH2 O2→H2O proton gradient Complex V ATP synthase chemiosmosis. Inhibitors Cyanide Azide Complex IV Rotenone Complex I Antimycin III Uncoupler 2,4-DNP. Yield 2.5/1.5 new 3/2 old.

7. Balance Sheet, Amphibolic & RQ - Final Tricks

Now account book: How much ATP from 1 glucose? Glycolysis 2 ATP+2 NADH≈5 Link 2 NADH≈5 Krebs 2 ATP+6 NADH≈15+2 FADH2≈3 = ~32 ATP practical. Why not 38? Because transporting NADH from cytoplasm to mitochondria costs proton leak membrane leak. But exam still sometimes asks 38 theoretical 32 actual in eukaryotes.

Respiration not only breaking catabolism but also making raw materials. If you need amino acids α-KG leaves cycle OAA leaves to make glucose. So cycle is amphibolic both ways like road two-way. RQ is detective test to know what is burning: RQ=CO2 out/O2 in. Carbs fully oxidized so RQ=1 6CO2/6O2. Fat needs more O2 so RQ ~0.7 tripalmitin. Protein ~0.9. Organic acid like malate >1 succulents at night 0 because no CO2 released they fix CO2. NEET loves this germinating fatty seeds RQ <1 leaf with organic acid >1.

Part 7A - Balance Sheet 38 vs 32 Practical ATP

Part 7B - RQ Table & Amphibolic Pathway Zoom

Revision: Balance 10 NADH x2.5=25 2 FADH2 x1.5=3 4 ATP direct =32 new /38 old. Amphibolic catabolic+anabolic Krebs intermediates withdrawn. RQ=CO2/O2 Carb 1 Fat 0.7 Protein 0.9 Organic acid >1 Succulent dark 0.