Final Answer:
The source of all carbon in living organisms is carbon dioxide, which cycles from the atmosphere and water into plants and eventually into other living things.
Step-by-step explanation:
The source of all carbon in living organisms is carbon dioxide, as it serves as the fundamental building block for organic molecules in living organisms. This carbon is utilized through processes like photosynthesis.
The phrase "which cycles from the atmosphere and water into" refers to the carbon dioxide being absorbed by plants through photosynthesis. During this process, carbon dioxide from the atmosphere and water from the soil are used by plants to produce organic compounds.
"Plants" is the next crucial part of the statement. Plants play a central role in the carbon cycle by converting carbon dioxide into organic molecules like carbohydrates. This process forms the basis of the food chain, as other organisms consume plants or organisms that have consumed plants.
The final part, "and eventually into other living things," signifies the flow of carbon through the food chain. Carbon moves from plants to herbivores and then to carnivores, eventually incorporating into various living organisms.