Bioenergetics | Best 11th Class Biology Notes | Federal Board

Chapter 4 :

BIOENERGETICS

4.1 PHOTOSYNTHESIS

⚗️ Chemical Process (Redox Reaction)

Equation:
6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O
(Light & Chlorophyll Required)
CO₂ → Reduced (Glucose)
H₂O → Oxidized (O₂)

🔆 4.1.1 Role of Light

Spectrum: 380–750 nm
Action Spectrum:
- Most Effective: 🟦 Blue (430 nm) & 🟥 Red (670 nm)
- Efficiency depends on pigment absorption 🌈

🎨 4.1.2 Photosynthetic Pigments

(Located in Thylakoid Membranes)

Pigment Type	Function	Absorption Peaks
Chl-a (Bluish-green)	Primary pigment	400-470 nm (blue-violet), 630-660 nm (red)
Chl-b (Yellowish-green)	Accessory pigment	Similar to Chl-a
Carotenoids (β-carotene, xanthophylls)	Accessory, photoprotection	430-500 nm

Chl-a Structure:
- Head: Porphyrin ring w/ Mg²⁺
- Tail: Hydrophobic phytol chain

🔬 4.1.4 Photosystems & Electron Transport Chain (ETC)

Component	Function	Peak Absorption
PS-II (P680)	1st in ETC, splits H₂O	680 nm
PS-I (P700)	2nd in ETC, reduces NADP⁺ → NADPH	700 nm
ETC	Transfers e⁻, pumps H⁺ → ATP production	N/A

Water photolysis → e⁻ + H⁺ + O₂
ATP via Chemiosmosis

💧 4.1.5 CO₂ & H₂O Roles

Molecule	Role
CO₂	Enters Calvin Cycle (C-fixation)
H₂O	e⁻ donor (PS-II), O₂ source

🔬 Van Niel Experiment:

H₂O (¹⁸O) → O₂ (¹⁸O) ✅
CO₂ (¹⁸O) → No labeled O₂ ❌

⚙️ 4.1.7 Mechanism of Photosynthesis

🌞 Light Reactions (Thylakoid)

Products: ATP + NADPH + O₂

🌑 Dark Reactions (Stroma)

Calvin Cycle: CO₂ → G3P → Glucose

⚡ 4.1.8 Light Reactions (Photochemical Phase)

(a) Non-Cyclic Photophosphorylation (Z-Scheme)

Steps:
1️⃣ PS-II (P680) absorbs light → e⁻ excited → passed to acceptor.
2️⃣ H₂O Splitting → O₂ + e⁻ (replaces lost e⁻ in PS-II).
3️⃣ ETC: PQ → Cytochrome b6-f → PC → creates proton gradient.
4️⃣ ATP Synthase: H⁺ flow → ATP produced (Chemiosmosis).
5️⃣ PS-I (P700) absorbs light → e⁻ excited → transferred to Ferredoxin (Fd).
6️⃣ NADPH Formation: NADP⁺ + e⁻ + H⁺ → NADPH.

✅ Outcome: 1 ATP + 1 NADPH per e⁻ pair

(b) Cyclic Photophosphorylation

Only PS-I used, e⁻ cycles back
ATP made, No NADPH/O₂
Purpose: Extra ATP for Calvin Cycle

🌿 4.1.9 Calvin Cycle (C₃ Pathway)

(Occurs in Stroma)

Phase	Reaction
1️⃣ Carbon Fixation	CO₂ + RuBP → 3-PGA (via RuBisCO)
2️⃣ Reduction	3-PGA → G3P (ATP, NADPH used)
3️⃣ Regeneration	5 G3P → 3 RuBP (ATP used)

✅ Inputs: 3 CO₂ + 9 ATP + 6 NADPH
✅ Outputs: 1 G3P + 9 ADP + 6 NADP⁺

🌵 4.1.10-12 C₃ vs. C₄ vs. CAM Plants

Feature	C₃ 🌾	C₄ 🌿	CAM 🌵
CO₂ Fixation	Calvin Cycle	C₄ → Calvin	Night storage (Malate)
Stomata Open	Day	Day	Night
Efficiency	Moderate	High (hot climates)	Extreme drought resistance

4.2 CELLULAR RESPIRATION

Goal: Break down Glucose → ATP
Types:
- Aerobic: High ATP (O₂ required)
- Anaerobic: Low ATP (e.g., Fermentation)

4.2.3 Aerobic Respiration Stages

Stage	Location	Key Outputs
Glycolysis	Cytoplasm	2 ATP, 2 NADH
Link Reaction	Mitochondria	2 NADH, 2 CO₂
Krebs Cycle	Mitochondrial Matrix	6 NADH, 2 FADH₂, 2 ATP, 4 CO₂
ETC	Inner Mitochondrial Membrane	32 ATP, H₂O

✅ Total ATP: ~36 ATP/glucose

⚡ 4.2.7 ETC & Chemiosmosis

(Inner Mitochondrial Membrane)
1️⃣ NADH/FADH₂ donate e⁻ → ETC.
2️⃣ H⁺ pumped → Proton Gradient.
3️⃣ ATP Synthase: H⁺ flow → ATP made.
4️⃣ O₂ (final e⁻ acceptor) → H₂O formed.

✅ ATP Yield:

1 NADH → 3 ATP
1 FADH₂ → 2 ATP
Total: ~32 ATP/glucose

⚠️ 4.3 Photorespiration

Cause	Effect	Solution
High O₂, Low CO₂	RuBisCO binds O₂ → Glycolate (waste)	C₄ & CAM Pathways

📌 Key Takeaways

✅ Chl-a = Central pigment; Carotenoids = Protectors/accessories
✅ RuBisCO fixes CO₂ but also binds O₂ (photorespiration)
✅ C₄/CAM plants prevent photorespiration via CO₂ concentration strategies
✅ ETC = Major ATP source via proton gradient
✅ G3P bridges Photosynthesis & Respiration

Exercise | Chapter 4: Bioenergetics | Class 11 Biology

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Class 11 Biology Notes | Chapter 4: Bioenergetics (FBISE, Best for Exams)