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Q65 (IAS/2014) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Plant anatomy physiology Official Key

Which one of the following is the process involved in photosynthesis?

Result
Your answer: —  ·  Correct: B
Explanation

Photosynthesis involves the conversion of light energy to chemical energy and the splitting of water molecules into hydrogen and oxygen, followed by the reduction of carbon dioxide to carbohydrates.[1] It is the process by which autotrophs take in substances from the outside and convert them into stored forms of energy, where carbon dioxide and water are converted into carbohydrates in the presence of sunlight and chlorophyll.[2]

Much of the energy initially provided by light energy is stored as redox free energy (a form of chemical free energy) in NADPH[3], and food is produced in the form of glucose, which not only serves as an instant source of energy but also gets converted into starch for storage.[4] Thus, photosynthesis converts free energy (light energy) into potential energy stored in chemical bonds of glucose.

Option A is incorrect as it describes energy release (catabolism), not energy storage. Option C describes cellular respiration, the opposite of photosynthesis. Option D incorrectly states that oxygen is taken in, whereas photosynthesis releases oxygen as a byproduct.[5]

Sources
  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > QUESTIONS > p. 82
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > 5.2.1 Autotrophic Nutrition > p. 81
  3. [3] https://www.life.illinois.edu/govindjee/paper/gov.html
  4. [4] Science-Class VII . NCERT(Revised ed 2025) > Chapter 10: Life Processes in Plants > 10.2.3 Photosynthesis: in a nutshell > p. 146
  5. [5] https://cmg.extension.colostate.edu/Gardennotes/141.pdf
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Q. Which one of the following is the process involved in photosynthesis? [A] Potential energy is released to form free energy [B] Free ene…
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Origin: Books + Current Affairs Fairness: Low / Borderline fairness Books / CA: 2.5/10 · 7.5/10
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This is a textbook 'Sitter' directly from NCERT Class X Science (Life Processes). It tests the fundamental thermodynamic definition of photosynthesis versus respiration. The strategy is simple: Master the basic energy transformations (Anabolic vs. Catabolic) rather than memorizing complex chemical formulas.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Is potential energy released to form free energy during photosynthesis?
Origin: Web / Current Affairs Fairness: CA heavy Web-answerable

Web source
Presence: 5/5
"It involves the transformation of free energy into potential energy, which is stored in the form of glucose and oxygen."
Why this source?
  • Explicitly states the direction of energy change in photosynthesis: free energy is converted into stored potential energy.
  • Directly contradicts the claim that potential energy is released to form free energy.
Web source
Presence: 5/5
"much of the energy initially provided by light energy is stored as redox free energy (a form of chemical free energy) in NADPH, to be used later in the reduction of carbon."
Why this source?
  • Describes how light energy is stored as redox free energy in NADPH and as an electrochemical proton potential during the light reactions.
  • Shows photosynthesis converts radiant energy into stored chemical/electrochemical energy rather than releasing potential energy to make free energy.

Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > QUESTIONS > p. 82
Strength: 5/5
“Let us now see what actually happens during the process of photosynthesis. The following events occur during this process – • (i) Absorption of light energy by chlorophyll.• (ii) Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.• (iii) Reduction of carbon dioxide to carbohydrates. These steps need not take place one after the other immediately. For example, desert plants take up carbon dioxide at night and prepare an intermediate which is acted upon by the energy absorbed by the chlorophyll during the day. Let us see how each of the components of the above reaction are necessary for photosynthesis.”
Why relevant

States that light energy is converted to chemical energy and water is split, indicating an energy conversion step in photosynthesis.

How to extend

A student could combine this with basic biochemistry knowledge (light reactions produce ATP/NADPH and dark reactions fix CO2) to check whether the chemical energy formed is in forms usable as cellular free energy.

Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > 5.2.1 Autotrophic Nutrition > p. 81
Strength: 5/5
“Carbon and energy requirements of the autotrophic organism are fulfilled by photosynthesis. It is the process by which autotrophs take in substances from the outside and convert them into stored forms of energy. This material is taken in the form of carbon dioxide and water which is converted into carbohydrates in the presence of sunlight and chlorophyll. Carbohydrates are utilised for providing energy to the plant. We will study how this takes place in the next section. The carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve to be used as and when required by the plant.”
Why relevant

Defines photosynthesis as converting external substances into stored forms of energy (carbohydrates) that fulfil carbon and energy needs.

How to extend

One could use the fact that stored carbohydrates can be metabolised to release energy (e.g., to make ATP) to assess whether stored potential energy is later turned into usable free energy.

Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > ATP > p. 88
Strength: 5/5
“ATP is the energy currency for most cellular processes. The energy released during the process of respiration is used to make an ATP molecule from ADP and inorganic phosphate. Endothermic processes in the cell then use this ATP to drive the reactions. When the terminal phosphate linkage in ATP is broken using water, the energy equivalent to 30.5 kJ/mol is released. Think of how a battery can provide energy for many different kinds of uses. It can be used to obtain mechanical energy, light energy, electrical energy and so on. Similarly, ATP can be used in the cells for the contraction of muscles, protein synthesis, conduction of nervous impulses and many other activities.”
Why relevant

Explains that ATP is the cellular energy currency and that energy released during respiration is used to synthesise ATP from ADP + Pi.

How to extend

Combine with the idea that photosynthesis produces carbohydrates (stored energy) to infer that those carbs might be oxidised to release energy that forms ATP (cellular free energy).

Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Decomposers or Saprophytes > p. 31
Strength: 4/5
“Energy transformation in the ecosystem occurs by means of a series of steps or levels which is referred to as food chain or food web. In brief, the plants and algae in the food chain are the primary producers. Tey use light energy to convert carbon dioxide and water into carbohydrates (long chains of sugar molecules) and eventually into other biochemical molecules needed for the support of life. Tis process of energy conversion is called photosynthesis. Organisms engaged in photosynthesis form the base of the food web. In all the ecosystems, the primary producers support the consumers — organisms that ingest other organisms as their food source.”
Why relevant

Describes photosynthesis as conversion of light energy into carbohydrates and places primary producers at the base of energy flow in ecosystems.

How to extend

Using a basic energy-flow concept (plants store light energy as chemical bonds), a student can trace whether that stored bond energy is later converted into forms usable by organisms (e.g., ATP).

Science-Class VII . NCERT(Revised ed 2025) > Chapter 10: Life Processes in Plants > 10.2.3 Photosynthesis: in a nutshell > p. 146
Strength: 4/5
“We know that water, sunlight, carbon dioxide from the air, and chlorophyll are necessary to carry out the process of photosynthesis that produces carbohydrates (Fig. 10.5). During photosynthesis, food is actually produced in the form of glucose, a simple carbohydrate. This glucose not only serves as an instant source of energy but also later gets converted into starch for storage. The word equation of photosynthesis is given below —”
Why relevant

Summarises inputs/outputs of photosynthesis and notes glucose serves as an instant energy source and is stored as starch.

How to extend

A student could use this plus knowledge that 'free energy' in cells is often ATP to investigate whether glucose from photosynthesis is ultimately used to generate ATP.

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SIMILAR QUESTIONS

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Which one of the following statements about the process of photosynthesis is correct?

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Which of the following organelles of a cell is/ are involved in photosynthesis?

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The gaseous product of a process in plants is a reirement for another vital process that releases energy. Given below are four combinations of the process and product. Identify the correct answer.