Question

Who was the scientist who first proposed that all single-celled organisms should be put into their own kingdom?

Answer 1

Carolus Linnaeus
Ernst Haeckel
Anton van Leeuwenhoek
Charles Darwin

Answer 2

@sleepyjess

Answer 3

I say D

Answer 4

@dan815

Answer 5

Charles Darwin did not propose that all single celled organisms should be placed in their own kingdom.

First we should note that single-celled organisms are actually referred to "Protozoa".

Linnaeus identified two kingdoms: Plantae and Animalia (plants and animals basically)
To the two kingdoms, a third kingdom was added called "Protista" (protists) .

The reason for this is because as scientists began studying single-celled organisms under the microscope, they either classified them as a plant or an animal.
E.g. bacteria are single-celled organisms which can make their own food, similarly, plants can also make their own food. Therefore, bacteria was classified as a plant.
Protozoa are single-celled organisms that can move on their own, therefore, they were classified as animals.

Eventually, more single-celled organisms were identified and it became difficult to place them in either the plant or animal kingdom. To solve this problem, Ernst Haeckel (1866) created a third kingdom for all single-celled organisms, Protista.

Answer 6

Carolus Linnaeus he had rooted the classification system of the animal kingdom meaning he had separated the animal kingdom into groups and was the one with the idea to do so. So with this explanation the answer would be A . Carolus Linnaeus :)