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.

The question asks which processes add carbon dioxide (CO2) to the carbon cycle on Earth. 1. Volcanic action releases various gases trapped within the Earth's mantle and crust, including significant amounts of carbon dioxide, into the atmosphere. This is a natural process that adds CO2. 2. Respiration is the metabolic process by which organisms (plants, animals, microbes) convert biochemical energy from nutrients into adenosine triphosphate (ATP), releasing waste products. Aerobic respiration uses oxygen and releases carbon dioxide. This process adds CO2 to the atmosphere/environment. 3. Photosynthesis is the process used by plants, algae, and cyanobacteria to convert light energy into chemical energy, via synthesizing sugars from carbon dioxide and water. This process *removes* CO2 from the atmosphere, storing carbon in organic matter. 4. The decay of organic matter (decomposition) by microorganisms breaks down dead plants and animals. This process releases the carbon stored in the organic matter back into the environment, primarily as carbon dioxide (if oxygen is present) or methane. This adds CO2. Therefore, Volcanic action, Respiration, and Decay of organic matter (1, 2, and 4) add carbon dioxide to the carbon cycle.