What does the law of conservation of matter state in biological systems?

• A. Matter is conserved; energy is recycled.
• B. Atoms are created and destroyed during metabolism.
• C. Energy flows, not recycled; matter is not conserved.
• D. Matter is conserved; atoms are cycled through organisms and the environment; energy flows, not recycled.

Answer: (D)

In biology, matter cannot be created or destroyed in chemical reactions; it is conserved and continually recycled through organisms and the environment. Atoms move through ecosystems—carbon cycles between CO2 in the air, organic molecules in plants and animals, and back again; nitrogen moves through soil, water, and living beings; water continually changes form and location. Energy, however, enters the system as sunlight and is transformed as it moves through food chains. With each transfer, some energy is lost as heat and is not reused to drive new work in the same way matter is recycled. So, the idea that matter is conserved and atoms are cycled through organisms and the environment, while energy flows and is not recycled, best captures how biological systems work.