Step-by-step ICSE solutions and marking scheme for Photosynthesis: Light & Dark Reactions from Selina Concise Biology (Class 10) - Chapter 6 and 5 generated practice problem sets.

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Biology Chapter 4 1 Textbook + 5 Generated Exercises 12 - 14 Marks in ICSE Board Exam

Photosynthesis: Light & Dark Reactions — Solved Textbook & 5 Practice Sets

Prescribed Reference Textbook: Selina Concise Biology (Class 10) - Chapter 6

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📘 Prescribed Textbook Solved Exercise (Selina Concise Biology (Class 10))

Primary Curriculum Benchmark

Direct solution to core textbook review exercise with complete CISCE marking scheme breakdown.

Textbook Exercise 4 - Review Questions Q.5 Selina Concise Biology (Class 10) - Chapter 6 - End-of-Chapter Review

3 Marks Allotted

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 ICSE Evaluator Marking Key

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 Verified Answer: Precise scientific definition, exact organ/organelle location, and physiological function (Key Units: Biological Nomenclature)

💡 Examiner Directive: Underline key technical terms in biological definitions. CISCE examiners specifically look for mandatory keywords.

🎯 5 Generated Practice Exercises with Step-Marking

CISCE Syllabus Graded Set

Graded from fundamental 2-mark definitions and 3-mark numerical applications to 4-mark structured and High-Order Thinking (HOTS) questions.

Generated Practice Set 1 - Core Concept (2 Marks) Difficulty: Easy

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 Directive: Avoid colloquial explanations. Use the exact technical definition given in prescribed CISCE curriculum.

Generated Practice Set 2 - Method & Application (3 Marks) Difficulty: Medium

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 Directive: In derivation and numerical questions, every intermediate mathematical step carries fractional credit.

Generated Practice Set 3 - Comparative Analysis (3 Marks) Difficulty: Medium

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 Directive: Always construct a comparative answer in a two-column table with an explicit "Point of Difference" header column.

Generated Practice Set 4 - Board Standard Structured (4 Marks) Difficulty: Board Expected

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 Directive: Notice the mark distribution in multi-part questions; allocate your answering time and detail strictly in proportion to allotted marks.

Generated Practice Set 5 - Higher Order Thinking (HOTS) (4 Marks) Difficulty: Hard

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 Directive: HOTS questions in ICSE evaluate depth of conceptual understanding. Avoid superficial guessing; reason backward from core laws.

🔑 Mandatory ICSE Examiner Technical Keywords Required in Solutions

Required for Step-Marking Credit

CISCE evaluators check for the explicit usage of mandatory technical terminology when scoring reasoning questions and step derivations. The table below outlines each key term, its technical description, the examiner marking directive, and the exact model answer phrasing expected in ICSE board examination solutions.

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 Examiner Directive & Marking Rubric:

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 Solutions):

"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 Examiner Directive & Marking Rubric:

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 Solutions):

"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 Examiner Directive & Marking Rubric:

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 Solutions):

"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 Examiner Directive & Marking Rubric:

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 Solutions):

"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 Examiner Directive & Marking Rubric:

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 Solutions):

"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."

⚖️ CISCE Evaluation Directives for Biology

Step-Mark Allocation: Every sub-step, formula statement, and intermediate substitution carries independent marks. Writing final answers without formula yields zero in Section B numericals.

Mandatory SI Units: In ICSE Science and Mathematics, omitting SI units or writing incorrect unit exponents causes automatic 1/2 mark deduction per problem.

Examiner Technical Vocabulary: CISCE evaluators look for exact prescribed terms in definitions and reasoning questions. General paraphrasing often loses full credit.

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