Matter is cycled between plants and animals through eating, breathing, and decomposition, so the same atoms (like carbon and nitrogen) are used over and over instead of being “used up.”

Quick Scoop

1. Start with plants

  • Plants take in carbon dioxide from the air and water from the soil and use sunlight to make sugars in photosynthesis. These sugars contain carbon, hydrogen, and oxygen atoms that become plant matter like leaves and stems.
  • Plants also take in minerals such as nitrogen from the soil, which become part of their proteins and other nutrients.

2. Animals eat plants (and other animals)

  • When animals eat plants, they take in the atoms in plant sugars, proteins, and fats, adding that matter to their own bodies (muscles, bones, organs).
  • Carnivores then eat herbivores, passing the same atoms along the food web as matter moves from plant → herbivore → carnivore.

3. Breathing and waste return matter

  • Through cellular respiration, animals break down food molecules and release carbon dioxide back into the air when they breathe , returning carbon to the atmosphere.
  • Animals also release matter in their wastes (urine and feces), which add nutrients such as nitrogen and phosphorus back to the soil and water.

4. Decomposers close the loop

  • When plants and animals die, decomposers like bacteria and fungi break their bodies down into simpler substances, returning carbon, nitrogen, and other elements to the soil and air.
  • These recycled nutrients in the soil are then absorbed again by plant roots, restarting the cycle of matter between plants and animals.

5. Big-picture idea

  • Matter is conserved: the total amount of atoms does not change; they just move between air, soil, plants, animals, and decomposers in biogeochemical cycles (like the carbon and nitrogen cycles).
  • This cycling of matter is what allows ecosystems to keep functioning over long periods of time without constantly needing new material from outside Earth.

In short, plants build food from air and water, animals eat that food, and decomposers break everything back down so plants can use the same atoms again—an endless recycling loop of matter between plants and animals.