Final answer:
Ernst Haeckel is the scientist who proposed the addition of a kingdom for protists in 1866, making a significant contribution to the classification of life forms by expanding the traditional two-kingdom system to include unicellular organisms. option C is correct .
Step-by-step explanation:
The scientist who proposed adding a kingdom for protists was Ernst Haeckel. Initially, the concept of the phylogenetic tree contained only two kingdoms for living organisms: the kingdoms of plants and animals. It was Ernst Haeckel who, in 1866, suggested the addition of a new kingdom, Protista, to include unicellular organisms.
Later on, Haeckel also proposed another kingdom, Monera, for unicellular organisms without nuclei, such as bacteria. Robert Whittaker expanded on these ideas about a century later with a tree that included Fungi as a distinct kingdom and organized life into five kingdoms in total: Animalia, Plantae, Protista, Fungi, and Monera.
Protozoans are unicellular organisms. Historically, protozoans were called “animal” protists as they are heterotrophic and showed animal-like behaviours.
There are also parasitic protozoans which live in the cells of larger organisms. Most of the members do not have a predefined shape. For instance, an amoeba can change its shape indefinitely but a paramecium has a definite slipper-like shape. The most well-known examples of protozoans are amoeba, paramecium, and euglena. Unlike other members of this group, euglena is a free-living protozoan that has chlorophyll, which means it can make its own food.