The correct answer is (d). An ecosystem is a functional unit that includes all living organisms and the physical environment in which they live. It is not a closed system, as it exchanges energy and matter with its surroundings.
(a) An ecosystem represents all living organisms and physical environment in any given space-time unit. This is true, as an ecosystem is a functional unit that includes all living organisms and the physical environment in which they live.
(b) An ecosystem is a functional unit. This is true, as an ecosystem is a system in which living organisms interact with each other and with the physical environment.
(c) An ecosystem has its own productivity. This is true, as an ecosystem is a system in which energy is converted from one form to another and matter is cycled.
(d) An ecosystem is a closed system. This is false, as an ecosystem is not a closed system, as it exchanges energy and matter with its surroundings.