Consider the following: 1. Photosynthesis 2. Respiration 3. Decay of organic matter 4. Volcanic action Which of the above add carbon dioxide to the carbon cycle on Earth ?

1. Statement 1 (Photosynthesis) is incorrect: Photosynthesis is the process by which plants, algae, and some bacteria use sunlight, water, and carbon dioxide (CO2) to create their own food (energy) and release oxygen. It removes CO2 from the atmosphere, thus taking it out of the active carbon cycle, rather than adding to it. 2. Statement 2 (Respiration) is correct: Respiration is the process by which organisms (plants, animals, microbes) break down organic compounds to release energy for life processes. This process consumes oxygen and releases CO2 into the atmosphere, adding it to the carbon cycle. 3. Statement 3 (Decay of organic matter) is correct: When organisms die, decomposers (like bacteria and fungi) break down the organic matter. This decomposition process involves respiration by the decomposers, which releases CO2 (and methane in anaerobic conditions) into the atmosphere, returning carbon to the cycle. 4. Statement 4 (Volcanic action) is correct: Volcanoes release various gases trapped within the Earth's mantle, including significant amounts of CO2. This geological process adds carbon from the Earth's interior to the atmosphere and thus to the carbon cycle. Therefore, respiration, decay of organic matter, and volcanic action add CO2 to the carbon cycle.