Unicellular and multicellular environments may vary. Multi-cellular organisms are able to do more functions, and unicellular is one-cell, so their functions are limited, although some unicellular ones such as thermophiles and photosynthetic bacteria can thrive in any environment with sun or heat. Multi-cellular ones like animals, can be found anywhere active, although different types exist in different places.
There are a number of intermediate steps between unicellular and multicellular organisms. Probably the most clear "midway" point is the colonial organism of which the extant Volvox (link below) is one of the best examples. (Admittedly Volvox itself is only 200 million years to present old, so it is not a remnant of this transition, but is similar to what scientists surmise was part of the transition that led to the development of multicellular organisms.) In a colonial organism, numerous unicellular organisms work in tandem to achieve goals (similar to how geese fly in flocks even though each is autonomous). The required communication would select cells that more effectively communicate with each other, leading to cells that can function as part of the same organism.
Organisms evolved from being unicellular to multicellular. So unicellular came first.
Single celled organisms are the type of organism that developed first. More complex multi-cellular organisms developed not long after this.
Simple prokaryotes
sponges
unicellular
Sponges
D.Sponges
Lichenaria is an organism formed from the fusion of algae and fungi.
It's the organism that causes something; for example, the causative organism for a staph infection is a type of bacterium.
A Redwood is not an organism, however it is a type of tree. There are three types of redwoods: the giant sequoia, the dawn redwood, and the coast redwood.
The first organ to develop in the embryo is the heart. In a fetus, there is a brain, but it isn't fully developed and can't understand signals from the nervous system. Therefore the first functional organ would be the heart. But the first thing to start developing in a fetus is the nervous system. ( no that isn't an organ )
sponges -apex
D.Sponges
Whatever organism first developed sensitivity to light. We have no way of knowing what that was.
unicellular
Two-word name was first developed by Carolus Linnaeus. He chose two words from Latin for naming an organism. First word referred to Genus of organism and second word referred to species of organism.
Which person developed a system of organism classification that is still in use today?
The first type of organisms to live in a new habitat are called pioneers. This is an organism that is forging the way for other life to be able to live comfortably in the new habitat.
Trilobites
amoeba
Bacteria would always be the first link in a food chain. This is simply because it is so small and is, essentially, everywhere.
phytoplankton
which type of organism grow in pus