Correct Answer: Option 3, They recycle chemicals from dead organisms.

Fungi and bacteria are principal decomposers that keep the nutrient balance in ecosystems, which is essential for plant and animal growth. They play an important role in nutrient cycling, or the endless recycling of chemical elements that occurs between organisms and their nonliving surroundings. Fungi and bacteria secrete enzymes that degrade organic material into inorganic nutrients and minerals, which are then returned to the environment, ready to be absorbed by living organisms.

Option 1 is incorrect. The decomposers recycle and break down organic materials, which are returned to the abiotic environment in forms that can be used by plants, but not as energy.

Option 2 is incorrect. They release inorganic products like carbon dioxide and ammonia, not oxygen.

Option 4 is incorrect because what they synthesize are inorganic products from organic nutrients, not the other way around.