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Q19 (IAS/2014) Environment & Ecology › Ecology & Ecosystem Basics › Biogeochemical cycles Official Key

Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth? 1. Volcanic action 2. Respiration 3. Photosynthesis 4. Decay of organic matter Select the correct answer using the code given below.

Result
Your answer: —  Âˇ  Correct: C
Explanation

The correct answer is option C (1, 2 and 4 only).

Carbon dioxide in the atmosphere is produced by volcanic activity, respiration of plants and animals, and fossil fuel combustion by industries and transportation.[2] By process of respiration and decomposition of dead organic matter it returns back to atmosphere.[3] Therefore, volcanic action (statement 1), respiration (statement 2), and decay of organic matter (statement 4) all add carbon dioxide to the carbon cycle.

However, photosynthesis (statement 3) does the opposite. Carbon from the atmosphere moves to green plants by the process of photosynthesis, and then to animals.[3] Carbon dioxide is absorbed by producers to make carbohydrates in photosynthesis.[4] This means photosynthesis removes carbon dioxide from the atmosphere rather than adding it.

Therefore, only statements 1, 2, and 4 are processes that add carbon dioxide to the carbon cycle, making option C the correct answer.

Sources
  1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Carbon and Oxygen Cycles > p. 20
  2. [2] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Carbon and Oxygen Cycles > p. 20
  3. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > L) The Carbon Cycle > p. 19
  4. [4] https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/environmental-toxicology
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth? 1. Volcanic action 2. Respiration 3. Photosynthes…
At a glance
Origin: Books + Current Affairs Fairness: Moderate fairness Books / CA: 7.5/10 ¡ 2.5/10
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This is a classic 'Sitter' found in Class VII NCERT. It tests the fundamental definition of Carbon Sources vs. Sinks. If you get this wrong, you are failing the baseline; no advanced book is needed, just clarity on basic biological processes.

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
Does volcanic action add carbon dioxide to the carbon cycle on planet Earth?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Carbon and Oxygen Cycles > p. 20
Presence: 5/5
“tons as hydrocarbon molecules) or living and dead organic matter (2275 billion tons, as carbohydrate molecules). Carbon dioxide in the atmosphere is produced by volcanic activity, respiration of plants and animals, and fossil fuel combustion by industries and transportation.”
Why this source?
  • Explicitly states that atmospheric carbon dioxide is produced by volcanic activity alongside other sources.
  • Directly links volcanic activity to CO2 as a source in the modern carbon budget context.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Hadean Eon (4,540 – 4,000 mya) > p. 270
Presence: 5/5
“• Volcanic outgassing created the primordial atmosphere. Outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth, produced the next atmosphere.• During the Late Heavy Bombardment (4 billion years ago), a disproportionately large number of asteroids collided with the early terrestrial planets including earth.• Over time, the Earth's surface solidified leaving behind hot volatiles which resulted in a heavy CO2 atmosphere with hydrogen, nitrogen, inert gases, and water vapour.• After the formation of oceans, dissolving in ocean water removed most CO2 from the atmosphere. Some CO2 reacted with metals to form carbonates that were deposited as sediments.• The early atmosphere contained almost no oxygen.”
Why this source?
  • Describes volcanic outgassing creating a primordial, CO2‑rich atmosphere—showing volcanism releases large CO2 quantities.
  • Explains the role of volcanic degassing in adding CO2 to Earth's atmosphere over geologic time.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 11: Volcanism > 1) Exhalative (Vapour Or Fumes) > p. 142
Presence: 4/5
“• Exhalative volcanism includes the discharge of material in gaseous forms, such as steam, fumes, HCl, ammonium chloride, sulphur dioxide, carbon dioxide, carbon monoxide, hydrogen sulphide, hydrogen, nitrogen, etc.• Volcanic gases may escape through vents which are in the form of hot springs, geysers, fumaroles (openings that emit steam and volcanic gases, such as sulfur dioxide and carbon dioxide) and solfataras (fumaroles where sulphur gases are dominant).• Exhalative volcanism indicates the volcano is reaching its extinction. Associated landforms are called sinter mounds, cones of precipitated minerals and mud volcanoes.”
Why this source?
  • Lists carbon dioxide among gases discharged in exhalative volcanism and emitted from fumaroles and vents.
  • Provides mechanistic detail on how volcanic systems emit CO2 to the surface/atmosphere.
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Statement analysis

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Statement analysis

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