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 ?

The carbon cycle involves the continuous exchange of carbon between the atmosphere and organisms. Photosynthesis is a process where green plants and phytoplankton consume carbon dioxide from the atmosphere to produce glucose, thereby acting as a carbon sink rather than a source [6]. Conversely, respiration in both plants and animals releases carbon dioxide back into the atmosphere as glucose is broken down for energy [3]. The decay of organic matter by decomposers like bacteria also releases stored carbon as CO2 [1]. Additionally, geological processes such as volcanic action contribute to the cycle by releasing CO2 stored in the Earth's crust and mantle back into the atmosphere [6]. Therefore, while photosynthesis removes CO2, respiration, decay, and volcanic eruptions are primary natural processes that add carbon dioxide to the Earth's carbon cycle.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > L) The Carbon Cycle > p. 19
2. [4] https://www.energy.gov/science/doe-explainsthe-carbon-cycle
3. [6] https://pmc.ncbi.nlm.nih.gov/articles/PMC4564695/
4. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 14: Marine Organisms > The Carbon Cycle and climate change > p. 208