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अध्याय 11: उच्च पादपों में प्रकाश-संश्लेषण (Photosynthesis in Higher Plants)

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झारखण्ड बोर्ड (JAC) • कक्षा XI • Biology • अध्याय 11

अनुमानित समय: 45 Mins

प्रगति: अध्ययनरत

उच्च पादपों में प्रकाश-संश्लेषण (Photosynthesis in Higher Plants)

In Class 11 Biology, "Photosynthesis in Higher Plants" provides an authoritative, curriculum-verified master resource aligned with the 2026–27 NCERT syllabus.

अध्याय CBT ऑनलाइन टेस्ट दें सभी अध्याय देखें

प्रस्तावना अध्याय अवधारणाएँ अध्याय सारांश स्व-मूल्यांकन अभ्यास टेस्ट दें

☀️ Have You Ever Wondered?

How can a green leaf capture photons of sunlight traveling across 150 million kilometers of space and convert that electromagnetic cosmic energy into sweet sugar molecules that fuel all animal life on Earth? Light reactions, the Z-scheme, and the Calvin Cycle.

यह अध्याय क्यों महत्वपूर्ण है

In Class 11 Biology, "Photosynthesis in Higher Plants" provides an authoritative, curriculum-verified master resource aligned with the 2026–27 NCERT syllabus.

अध्ययन से पूर्व (आवश्यक ज्ञान)

Chloroplast structure from Chapter 8.
Photosynthesis basics from Class 10.
Photons and energy.

इस अध्याय के लक्ष्य

Explain Photosynthetic Pigments: Chlorophyll a (chief pigment), Chlorophyll b, Xanthophylls, Carotenoids (absorption and action spectra).
Explain Light Reaction (Photochemical phase): Photosystem-I ($P_{700}$) and Photosystem-II ($P_{680}$), Photolysis of water ($2\text{H}_2\text{O} \to 4\text{H}^+ + 4e^- + \text{O}_2$), and the Z-scheme of Non-Cyclic vs Cyclic photophosphorylation.
Explain Chemiosmotic Hypothesis (Peter Mitchell): Proton gradient across thylakoid membrane driving ATP-Synthase ($CF_0-CF_1$).
Explain Dark Reaction (Biosynthetic phase): The $C_3$ Calvin Cycle (Carboxylation by RuBisCO, Reduction, Regeneration of RuBP; $18\text{ ATP} + 12\text{ NADPH}$ per glucose).
Analyze the $C_4$ Hatch-Slack Pathway (Kranz anatomy, PEP-case in mesophyll, RuBisCO in bundle sheath; avoids wasteful Photorespiration).
State Blackman's Law of Limiting Factors.

अध्याय रूपरेखा एवं प्रगति

1 1. Light Reaction & The Z-Scheme

2 2. Chemiosmotic ATP Synthesis

3 3. $C_3$ Calvin Cycle vs. $C_4$ Kra...

सम्पूर्ण सैद्धांतिक एवं वैचारिक अध्ययन

1. Light Reaction & The Z-Scheme

Light harvesting complexes in thylakoid membranes:
• Non-Cyclic Photophosphorylation: Light strikes PS-II ($P_{680}$), exciting electrons. The electron vacancy is replenished by the Photolysis of Water ($2\text{H}_2\text{O} \to 4\text{H}^+ + 4e^- + \text{O}_2 \uparrow$ on inner thylakoid face). Electrons cascade through plastoquinone, cytochrome $b_6f$, and plastocyanin to PS-I ($P_{700}$), reducing $\text{NADP}^+$ to $\text{NADPH}$ and generating $\text{ATP}$.
• Cyclic: PS-I alone operates ($>680\text{ nm}$ light), producing ATP only.

2. Chemiosmotic ATP Synthesis

Peter Mitchell proved ATP synthesis is driven by a Proton Gradient ($\Delta pH$) across the thylakoid membrane:
• High $[H^+]$ in Thylakoid Lumen (due to water splitting and $H^+$ pumping from stroma).
• Protons rush through the transmembrane $CF_0-CF_1$ ATP-Synthase channel back into the stroma, spinning the molecular catalytic head to synthesize ATP from ADP + Pi!

3. $C_3$ Calvin Cycle vs. $C_4$ Kranz Anatomy

$C_3$ Pathway (Calvin Cycle): Primary $\text{CO}_2$ acceptor is $5C$ RuBP, catalyzed by RuBisCO to form $3C$ 3-PGA. Photorespiration ($C_2$ cycle): At high temperature/oxygen, RuBisCO binds $O_2$ instead of $\text{CO}_2$, wasting $25\%$ ATP and producing zero sugar!
$C_4$ Pathway (Maize, Sugarcane): Overcomes photorespiration using Kranz Anatomy (concentric bundle sheath cells with agranal chloroplasts). Primary $\text{CO}_2$ fixation by PEP carboxylase (never binds $O_2$!) in mesophyll → forms $4C$ Oxaloacetate → pumps malate into bundle sheath where high $\text{CO}_2$ concentration saturates RuBisCO!

Photosynthesis in Higher Plants - Key Biological & Anatomical Model

अध्याय का सार संक्षेप एवं 10 मुख्य निष्कर्ष

मुख्य बिंदु 1

Water Photolysis: Manganese-calcium enzyme complex splitting water into oxygen and protons.

मुख्य बिंदु 2

Z-Scheme: Non-cyclic electron transport path generating NADPH and ATP reducing power.

मुख्य बिंदु 3

Chemiosmotic Thylakoid Gradient: Proton accumulation in lumen driving rotary ATP synthase.

मुख्य बिंदु 4

RuBisCO Dual Affinity: World's most abundant enzyme binding both CO2 and O2.

मुख्य बिंदु 5

Kranz Anatomy: Structural bundle sheath adaptation eliminating wasteful photorespiration in C4 plants.

स्व-मूल्यांकन अभ्यास (Check Your Understanding)

मूल वैचारिक स्पष्टता की जांच के लिए नैदानिक प्रश्न। पहले स्वयं हल करें, फिर उत्तर देखें।

Describe the three main stages of the Calvin Cycle ($C_3$ Pathway). How many ATP and NADPH molecules are required to synthesize one molecule of glucose?

उत्तर एवं व्याख्या देखें

उत्तर: Stages: (1) Carboxylation: Fixation of $\text{CO}_2$ onto RuBP catalyzed by RuBisCO to form two molecules of 3-PGA, (2) Reduction: Phosphorylation and reduction of 3-PGA using ATP and NADPH to form triose phosphates, (3) Regeneration of RuBP: Multi-step rearrangement requiring 1 ATP. For one molecule of glucose ($6\text{ CO}_2$ fixed): $18\text{ ATP}$ and $12\text{ NADPH}$ are consumed.
Carboxylation, Reduction, Regeneration; requires 18 ATP and 12 NADPH per glucose.

What is 'Kranz Anatomy'? Explain how $C_4$ plants completely avoid the wasteful process of Photorespiration.

उत्तर एवं व्याख्या देखें

उत्तर: Kranz anatomy is a specialized internal leaf structure in $C_4$ plants (maize, sugarcane) where large bundle-sheath cells form concentric wreaths around vascular bundles, lacking grana and intercellular spaces. Primary $\text{CO}_2$ fixation occurs in mesophyll cells via PEP carboxylase, which has zero affinity for oxygen. $4C$ malic acid is transported into bundle sheath cells and decarboxylated, releasing a high concentration of $\text{CO}_2$ around RuBisCO, completely suppressing its oxygenase activity.
Bundle-sheath wreath cells with PEP-case in mesophyll pumping CO2 to RuBisCO.

Explain the Chemiosmotic Hypothesis of ATP synthesis in chloroplasts proposed by Peter Mitchell.

उत्तर एवं व्याख्या देखें

उत्तर: ATP synthesis is driven by a proton concentration gradient across the thylakoid membrane. Protons accumulate inside the thylakoid lumen due to: (1) Splitting of water in the lumen, (2) Proton pumping across cytochrome $b_6f$ complex, (3) Removal of protons from the stroma to form NADPH. When protons diffuse back into the stroma through the $CF_0-CF_1$ ATP synthase enzyme channel, the released conformational energy synthesizes ATP from ADP and Pi.
Proton accumulation in lumen powers CF0-CF1 ATP synthase during exit.

Differentiate between Cyclic and Non-Cyclic Photophosphorylation on the basis of: (i) Photosystems involved, (ii) Photolysis of water, (iii) Products formed.

उत्तर एवं व्याख्या देखें

उत्तर: (i) Cyclic involves only Photosystem-I ($P_{700}$); Non-cyclic involves both PS-I and PS-II ($P_{680}$). (ii) In cyclic, photolysis of water does NOT occur; in non-cyclic, photolysis of water occurs, releasing oxygen. (iii) Cyclic produces only ATP; non-cyclic produces both ATP and NADPH.
PS-I only vs both PS-I/II; no water splitting vs water splitting; ATP only vs ATP + NADPH.

State Blackman's Law of Limiting Factors in photosynthesis.

उत्तर एवं व्याख्या देखें

उत्तर: If a chemical process is affected by more than one factor, then its rate is governed by the pace of the factor which is nearest to its minimum value: it is the factor which directly affects the process if its quantity is changed.
Rate is determined by the factor nearest to its minimum value.

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