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.

Let's analyze which of the given processes add carbon dioxide (CO2) to the carbon cycle:

1. Volcanic action: Volcanic eruptions release significant amounts of CO2 and other gases into the atmosphere from the Earth's interior. This is a natural process that adds carbon dioxide to the carbon cycle. This statement is correct.

2. Respiration: All living organisms (plants, animals, and microorganisms) respire, breaking down organic compounds to release energy. A byproduct of this process is CO2, which is released into the atmosphere or water. This statement is correct.

3. Photosynthesis: Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight to convert CO2 and water into glucose (sugar) and oxygen. Therefore, photosynthesis removes CO2 from the atmosphere, rather than adding it. This statement is incorrect.

4. Decay of organic matter: When dead plants and animals, and their waste products, decompose, microorganisms (bacteria and fungi) break down the organic material. This decomposition process involves respiration by the decomposers, which releases CO2 into the atmosphere or soil. This statement is correct.

Therefore, volcanic action, respiration, and decay of organic matter add carbon dioxide to the carbon cycle.