NCERT Class 11 Science — Chapter 1: Photosynthesis in Higher Plants

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Assertion (A): The biosynthetic phase of photosynthesis is often referred to as the dark reaction. Reason (R): This phase takes place in the stroma of the chloroplasts where enzymatic activity is high.

Official previous-year question

Verified 1 Aug 2026.

Options

ABoth A and R are true and R is the correct explanation of A
BBoth A and R are true but R is NOT the correct explanation of A
CA is true but R is false
DA is false but R is true

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Solution

The correct option is Both A and R are true but R is NOT the correct explanation of A

Explanation

Photosynthesis consists of two primary phases: the photochemical phase (light reaction) and the biosynthetic phase (dark reaction). These phases occur in different parts of the chloroplast and have distinct dependencies on light energy.

Analysis of Assertion (A): Correct. The biosynthetic phase is conventionally referred to as the "dark reaction." This nomenclature is used because this phase does not directly depend on the presence of light. Instead, it utilizes the products of the light reaction (ATP and NADPH) to drive the synthesis of carbohydrates.

Analysis of Reason (R): Correct. The biosynthetic phase takes place in the stroma of the chloroplasts. The stroma contains the necessary enzymes (such as RuBisCO) required for the reduction of carbon dioxide and the synthesis of sugars.

Justification for

Both A and R are true but R is NOT the correct explanation of A

: While both the assertion and the reason are factually true, the reason provided (location in the stroma) is not the explanation for why it is called the "dark reaction." The term "dark reaction" is derived from the process's independence from direct light, not its location within the chloroplast.

Key Takeaway: The dark reaction (biosynthetic phase) occurs in the stroma and is light-independent, relying on ATP and NADPH produced during the light reaction in the thylakoids.

Your note

More from Chapter 1: Photosynthesis in Higher Plants

Consider the following statements about autotrophic nutrition: 1. It is characteristic of green plants and some bacteria. 2. It involves conversion of chemical energy into light energy. 3. Heterotrophs ultimately depend on it. Which of the statements given above are correct?

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Assertion (A): In aquatic plants, bubbles of oxygen are formed around the green parts during active photosynthesis. Reason (R): Photosynthesis requires light energy to split water molecules, releasing oxygen.

hard

With reference to Julius von Sachs’ contributions, consider the following statements: 1. Photosynthetic products are stored primarily as proteins. 2. Chlorophyll is confined to distinct cellular bodies. 3. Non-green parts are not involved in carbohydrate synthesis. Which of the statements given above is/are correct?

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Consider the following statements about oxygen evolution in photosynthesis: 1. It is always replaced by sulphur production in all autotrophs. 2. It arises from the oxidation of water. 3. It is derived from carbon dioxide in higher plants. Which of the statements given above is/are correct?

hard

With reference to the role of photosynthesis in the biosphere, consider the following statements: 1. It is responsible for releasing carbon dioxide into the atmosphere. 2. It is the primary source of food for all living forms. 3. It is the only pathway of ATP generation in plants. Which of the statements given above is/are correct?

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The correct option is Both A and R are true but R is NOT the correct explanation of A

Explanation

Justification for

Both A and R are true but R is NOT the correct explanation of A

Key Takeaway: The dark reaction (biosynthetic phase) occurs in the stroma and is light-independent, relying on ATP and NADPH produced during the light reaction in the thylakoids.