Which statement best describes open versus closed ecosystems and why most real ecosystems resemble open systems?

• A. Open systems exchange energy with surroundings.
• B. Closed systems exchange energy and matter with surroundings.
• C. Most real ecosystems are open because they exchange energy and matter with the environment.
• D. Real ecosystems do not exchange energy or matter with the environment.

Answer: (C)

The main idea is that ecosystems are open systems because they continuously exchange both energy and matter with their surroundings. Energy from the sun enters, flows through the food web, and is ultimately lost as heat—so energy is not confined inside the system. At the same time, matter moves in and out: nutrients and water enter, waste and heat leave, organisms migrate, and nutrients cycle through decomposition and uptake. Because these exchanges never stop and boundaries aren’t perfectly sealed, natural ecosystems are open rather than closed. That’s why the statement describing open systems as exchanging energy and matter with the environment is the best fit.