Cells

A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Unicellular organisms fall into two general categories: prokaryotic organisms and eukaryotic organisms. All prokaryotes are unicellular and are classified into bacteria and archaea. Many eukaryotes are multicellular, but many are unicellular such as protozoa, unicellular algae, and unicellular fungi. Unicellular organisms are thought to be the oldest form of life, with early protocells possibly emerging 3.8–4 billion years ago.

Although some prokaryotes live in colonies, they are not specialised cells with differing functions. These organisms live together, and each cell must carry out all life processes to survive. In contrast, even the simplest multicellular organisms have cells that depend on each other to survive.

Most multicellular organisms have a unicellular life-cycle stage. Gametes, for example, are reproductive unicells for multicellular organisms. Additionally, multicellularity appears to have evolved independently many times in the history of life.

Some organisms are partially unicellular, like Dictyostelium discoideum. Additionally, unicellular organisms can be multinucleate, like Caulerpa, Plasmodium, and Myxogastria.

EUKARYOTIC:

10x bigger than prokaryotic. Thought to have evolved from prokaryotes. More organisationally complex than prokaryotic cells. Staggering differences in shape and size that vary from amoebas to whales, from red algae (among the first eukaryotics) to dinosaurs.


 * Eukaryotic Cells
 * Animal (eat and digest)
 * Plant (produce their own food by photosynthesis)
 * Fungi (break down dead waste, decomposed organisms)
 * Protist (mostly unicellular, most diverse and numerous) (NO GENERALIZATIONS) (plant like, algae like, animal like, mysterious)

Characteristics of Protists
A few characteristics are common between protists.


 * 1) They are eukaryotic, which means they have a nucleus.
 * 2) Most have mitochondria.
 * 3) They can be parasites.
 * 4) They all prefer aquatic or moist environments.

Classification of Protists
For classification, the protists are divided into three groups:


 * 1) Animal-like protists, which are heterotrophs and have the ability to move.
 * 2) Plant-like protists, which are autotrophs that photosynthesize.
 * 3) Fungi-like protists, which are heterotrophs, and they have cells with cell walls and reproduce by forming spores.

But remember, protists are not animals, nor plants, nor fungi

protozoa - ingest food, motile

algaea/plantlike - manufacture food by photosynthesis

fungal like - digest food from environment

PROKARYOTIC:


 * Prokaryotic
 * Bacteria
 * Archaea (adapt, survive, and thrive in extreme environments)