Concept:The term "ecosystem" was first introduced by the British ecologist Sir Arthur George Tansley in 1935.Explanation:Tansley proposed the word in his paper on vegetational concepts. An ecosystem is the basic ecological unit where living organisms interact with each other and their physical environment. Before Tansley, the term "biocoenosis" was used. Other notable contributions: Ernst Haeckel coined the word "ecology", and Eugene Odum wrote the book "Fundamentals of Ecology". Hanns Reiter gave the concept of ecology, but not the term ecosystem.Answer:D. Tansely