The correct option is C Assertion is true but reason is false
Ecosystem is the functional unit of nature where the living organisms interact with each other and with the surrounding environment.
Ecosystem is considered as an open system. An open system can exchange both energy and matter with its surroundings.
Ecosystem receives input in the form of solar energy and matter (inorganic nutrients). There is a transfer of energy and matter amongst various components of the ecosystem. During this circulation of energy in the ecosystem, a part of energy is lost, therefore a regular input of energy is essential for maintaining the ecosystem.
Ecosystems give output in the form of heat (energy loss) and waste matter.
Hence, assertion is true but reason is false.