Biology
Chapter 4
Board Weightage: 12 - 14 Marks in ICSE Board Exam
Photosynthesis: Light & Dark Reactions
Prescribed Textbook: Selina Concise Biology (Class 10) - Chapter 6
Canonical Link:
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📖 Syllabus Scope & Overview
Overall balanced chemical equation of photosynthesis (6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂↑), structure of chloroplast (grana for light reaction, stroma for dark reaction), Phase 1: Light-dependent phase (photolysis of water: 4H₂O → 4H⁺ + 4e⁻ + 2H₂O + O₂↑, photophosphorylation ADP + Pi → ATP, NADP reduction), Phase 2: Light-independent / Dark phase (Calvin cycle in stroma), destarching a potted plant, and experimental proofs (sunlight, chlorophyll, CO₂ necessary; O₂ evolved).
🔑 Mandatory ICSE Examiner Technical Keywords with Detailed Description
Official CISCE Evaluation Benchmark
According to CISCE board marking schemes, evaluators allocate marks based on the explicit presence of mandatory technical keywords. General or colloquial explanations fail to secure full marks. The table below details every required technical term, its scientific/academic description, the evaluator directive, and its exact model answer usage.
Mandatory Keyword #1
Core Definition
Chapter Concept: Photolysis of Water & Light Reactions
1 Mark (Structural Location / Physiological Function)
"Photolysis of water occurs in grana"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Biology (Photosynthesis: Light & Dark Reactions), "Photolysis of water occurs in grana" is an indispensable physiological term, anatomical structure, or biological process defined in the prescribed ICSE syllabus.
CISCE biology evaluators deduct marks for incorrect phonetic spelling or vague layperson descriptions. Candidates must use exact biological terminology: "Photolysis of water occurs in grana".
📝 Model Answer Application (Exact Phrasing for Board Exam):
"The physiological role of Photolysis of Water & Light Reactions is characterized by "Photolysis of water occurs in grana", ensuring proper structural and functional regulation."
Mandatory Keyword #2
Core Definition
Chapter Concept: Photolysis of Water & Light Reactions
1 Mark (Structural Location / Physiological Function)
"Oxygen evolved comes from water (H2O)"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Biology (Photosynthesis: Light & Dark Reactions), "Oxygen evolved comes from water (H2O)" is an indispensable physiological term, anatomical structure, or biological process defined in the prescribed ICSE syllabus.
CISCE biology evaluators deduct marks for incorrect phonetic spelling or vague layperson descriptions. Candidates must use exact biological terminology: "Oxygen evolved comes from water (H2O)".
📝 Model Answer Application (Exact Phrasing for Board Exam):
"The physiological role of Photolysis of Water & Light Reactions is characterized by "Oxygen evolved comes from water (H2O)", ensuring proper structural and functional regulation."
Mandatory Keyword #3
Core Definition
Chapter Concept: Photolysis of Water & Light Reactions
1 Mark (Structural Location / Physiological Function)
"Photophosphorylation: ADP + Pi -> ATP"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Biology (Photosynthesis: Light & Dark Reactions), "Photophosphorylation: ADP + Pi -> ATP" is an indispensable physiological term, anatomical structure, or biological process defined in the prescribed ICSE syllabus.
CISCE biology evaluators deduct marks for incorrect phonetic spelling or vague layperson descriptions. Candidates must use exact biological terminology: "Photophosphorylation: ADP + Pi -> ATP".
📝 Model Answer Application (Exact Phrasing for Board Exam):
"The physiological role of Photolysis of Water & Light Reactions is characterized by "Photophosphorylation: ADP + Pi -> ATP", ensuring proper structural and functional regulation."
Mandatory Keyword #4
Process & Mechanism
Chapter Concept: Photolysis of Water & Light Reactions
1 Mark (Structural Location / Physiological Function)
"Dark reaction occurs in stroma"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Biology (Photosynthesis: Light & Dark Reactions), "Dark reaction occurs in stroma" is an indispensable physiological term, anatomical structure, or biological process defined in the prescribed ICSE syllabus.
CISCE biology evaluators deduct marks for incorrect phonetic spelling or vague layperson descriptions. Candidates must use exact biological terminology: "Dark reaction occurs in stroma".
📝 Model Answer Application (Exact Phrasing for Board Exam):
"The physiological role of Photolysis of Water & Light Reactions is characterized by "Dark reaction occurs in stroma", ensuring proper structural and functional regulation."
Mandatory Keyword #5
Core Definition
Chapter Concept: Photolysis of Water & Light Reactions
1 Mark (Structural Location / Physiological Function)
"Destarching: keep plant in dark for 24-48 hours"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Biology (Photosynthesis: Light & Dark Reactions), "Destarching: keep plant in dark for 24-48 hours" is an indispensable physiological term, anatomical structure, or biological process defined in the prescribed ICSE syllabus.
CISCE biology evaluators deduct marks for incorrect phonetic spelling or vague layperson descriptions. Candidates must use exact biological terminology: "Destarching: keep plant in dark for 24-48 hours".
📝 Model Answer Application (Exact Phrasing for Board Exam):
"The physiological role of Photolysis of Water & Light Reactions is characterized by "Destarching: keep plant in dark for 24-48 hours", ensuring proper structural and functional regulation."
Complete step-by-step evaluator solutions for textbook problems and 5 generated practice sets adhering to CISCE marking schemes.
📘 Textbook Problem: Textbook Exercise 4 - Review Questions Q.5
Selina Concise Biology (Class 10) - Chapter 6 - End-of-Chapter Review
3 Marks Total
With reference to Photosynthesis: Light & Dark Reactions: (i) Define the biological process of Photolysis of Water & Light Reactions. (ii) State its exact location and physiological significance in the living organism.
Step-by-Step Marking Breakdown
Step 1: Scientific Definition with Technical Keywords: Define Photolysis of Water & Light Reactions incorporating mandatory ICSE terminology: Photolysis of water occurs in grana, Oxygen evolved comes from water (H2O), Photophosphorylation: ADP + Pi -> ATP.
1 Mark
Step 2: Anatomical / Cellular Location: State the precise anatomical site or organelle where this biological process occurs.
1 Mark
Step 3: Biological Significance / Function: Explain the physiological necessity of this process for organismal survival, homeostasis, or reproduction.
1 Mark
Final Answer: Precise scientific definition, exact organ/organelle location, and physiological function
(Units: Biological Nomenclature)
💡 Examiner Tip: Underline key technical terms in biological definitions. CISCE examiners specifically look for mandatory keywords.
🎯 Generated Set: Generated Practice Set 1 - Core Concept (2 Marks)
ICSE Class 10 Exam Blueprint - Chapter 4
2 Marks Total
Define "Photolysis of Water & Light Reactions" in the context of ICSE Class 10 Biology. State its primary characteristic or SI unit/standard symbol.
Step-by-Step Marking Breakdown
Step 1: Precise Technical Definition: Photolysis is the splitting of water molecules into hydrogen ions, electrons, and oxygen gas in the presence of light and activated chlorophyll in the grana / thylakoids: 2H₂O → 4H...
1 Mark
Step 2: Mandatory Technical Criteria: Ensure the definition contains mandatory keywords: Photolysis of water occurs in grana, Oxygen evolved comes from water (H2O), Photophosphorylation: ADP + Pi -> ATP.
1 Mark
Final Answer: Accurate scientific/scholarly definition containing all mandatory ICSE evaluation keywords.
(Units: chemical molecule)
💡 Examiner Tip: Avoid colloquial explanations. Use the exact technical definition given in prescribed CISCE curriculum.
🎯 Generated Set: Generated Practice Set 2 - Method & Application (3 Marks)
ICSE Question Bank & Specimen Framework - Biology
3 Marks Total
A system governed by "Photosynthesis Complete Chemical Equation" has standard parameters. Using the relation 6CO₂ + 12H₂O --[Light & Chlorophyll]--> C₆H₁₂O₆ + 6H₂O + 6O₂↑, calculate the required variable when other quantities are doubled. State the formula and show step-by-step substitution.
Step-by-Step Marking Breakdown
Step 1: State the Formula / Conceptual Principle: Write the primary governing equation: 6CO₂ + 12H₂O --[Light & Chlorophyll]--> C₆H₁₂O₆ + 6H₂O + 6O₂↑. Define each symbol clearly.
Formula: 6CO₂ + 12H₂O --[Light & Chlorophyll]--> C₆H₁₂O₆ + 6H₂O + 6O₂↑
1 Mark
Step 2: Mathematical / Procedural Deduction: Substitute the modified parameters: Let initial state be S₁ and new state be S₂. Set up the ratio S₂ / S₁ and simplify algebraically.
1 Mark
Step 3: Concluding Result & Interpretation: Express the final outcome clearly with proper units or scientific deduction.
1 Mark
Final Answer: Result derived directly from 6CO₂ + 12H₂O --[Light & Chlorophyll]--> C₆H₁₂O₆ + 6H₂O + 6O₂↑
(Units: chemical molecule)
💡 Examiner Tip: In derivation and numerical questions, every intermediate mathematical step carries fractional credit.
🎯 Generated Set: Generated Practice Set 3 - Comparative Analysis (3 Marks)
ICSE Exemplar Practice Paper - Biology
3 Marks Total
Differentiate between "Photolysis of Water & Light Reactions" and "Photolysis of Water & Light Reactions" on the basis of: (i) Fundamental definition/mechanism, (ii) Key working condition or formula, (iii) Real-world practical example or application.
Step-by-Step Marking Breakdown
Point 1: Conceptual Difference: Contrast the primary mechanisms: Photolysis of Water & Light Reactions focuses on Photolysis of water occurs in grana, whereas Photolysis of Water & Light Reactions emphasizes Photolysis of water occurs in grana.
1 Mark
Point 2: Quantitative / Operational Difference: Highlight differences in formulas, governing laws, operating environments, or physical behavior.
1 Mark
Point 3: Exemplary Differentiation: Provide one clear, unambiguous textbook example illustrating each concept under everyday conditions.
1 Mark
Final Answer: Three-point structured comparative table with clear opposing criteria.
(Units: Tabular points)
💡 Examiner Tip: Always construct a comparative answer in a two-column table with an explicit "Point of Difference" header column.
🎯 Generated Set: Generated Practice Set 4 - Board Standard Structured (4 Marks)
ICSE Board Marking Blueprint - Class 10
4 Marks Total
A comprehensive ICSE examination question based on "Photosynthesis: Light & Dark Reactions":
(i) State the fundamental law or rule governing "Photolysis of Water & Light Reactions". [1 Mark]
(ii) How does this concept change with temperature / pressure / time / scale? [1 Mark]
(iii) State one common mistake students make in this chapter and provide the correct scientific reasoning. [2 Marks]
Step-by-Step Marking Breakdown
Part (i): Statement of the Law: State the formal principle verbatim as recognized by CISCE syllabus committees.
1 Mark
Part (ii): Dependency Analysis: Explain the direct or inverse variation of the target variable with respect to environmental or operational factors.
1 Mark
Part (iii): Error Analysis & Correct Resolution: Identify the frequent pitfall: Students often confuse Photolysis of water occurs in grana with related quantities. The correct understanding requires strict application of Photolysis of Water & Light Reactions.
2 Marks
Final Answer: Structured 4-mark solution completely addressing parts (i), (ii), and (iii).
(Units: Multi-part breakdown)
💡 Examiner Tip: Notice the mark distribution in multi-part questions; allocate your answering time and detail strictly in proportion to allotted marks.
🎯 Generated Set: Generated Practice Set 5 - Higher Order Thinking (HOTS) (4 Marks)
ICSE High-Achiever Challenge Series - Class 10
4 Marks Total
A critical scenario-based problem in "Photosynthesis: Light & Dark Reactions": An experiment is performed under non-ideal conditions involving "Photolysis of Water & Light Reactions" and "Photolysis of Water & Light Reactions".
(a) Predict what happens to the expected outcome if the boundary condition fails.
(b) Give complete scientific justification.
(c) State the critical safeguard or correction formula to rectify the error.
Step-by-Step Marking Breakdown
Part (a): Prediction of Anomalous Outcome: Accurately predict the deviation from theoretical expectations when standard assumptions are violated.
1 Mark
Part (b): Scientific Justification: Provide a rigorous scientific explanation using first principles and mandatory keywords: Photolysis of water occurs in grana, Oxygen evolved comes from water (H2O), Photophosphorylation: ADP + Pi -> ATP, Dark reaction occurs in stroma.
2 Marks
Part (c): Correction Protocol & Mathematical Remedy: State the exact rectification formula or procedural calibration necessary to restore accuracy.
Formula: 6CO₂ + 12H₂O --[Light & Chlorophyll]--> C₆H₁₂O₆ + 6H₂O + 6O₂↑
1 Mark
Final Answer: Full scenario analysis with anomaly prediction, first-principles justification, and correction method.
(Units: HOTS Analytical Reasoning)
💡 Examiner Tip: HOTS questions in ICSE evaluate depth of conceptual understanding. Avoid superficial guessing; reason backward from core laws.