Plant-like protists produce almost one-half of the oxygen on the planet through photosynthesis. Other protists decompose and recycle nutrients that humans need to live. For example, medicines made from protists are used in treatment of high blood pressure, digestion problems, ulcers, and arthritis.

Cell Organelles Organelles are the ‘tiny organs’ of a cell. They are distinct, specialized structures that are adapted to fulfill the essential life functions necessary for cell survival. Some organelles (for example, the mitochondria, ribosomes, and nucleus) are found in almost all cell types.

Organelles are specialized structures that perform various jobs inside cells. The term literally means “little organs.” In the same way organs, such as the heart, liver, stomach, and kidneys, serve specific functions to keep an organism alive, organelles serve specific functions to keep a cell alive.

During protein synthesis, ribosomes assemble amino acids into proteins. Ribosomes are the cellular structures responsible for protein synthesis. When viewed through an electron microscope, free ribosomes appear as either clusters or single tiny dots floating freely in the cytoplasm.

Each eukaryotic cell has a plasma membrane, cytoplasm, a nucleus, ribosomes, mitochondria, peroxisomes, and in some, vacuoles; however, there are some striking differences between animal and plant cells.

A parasite is an organism that lives on or in another organism and feeds on it, often without killing it. A few protist species live on dead organisms or their wastes, and contribute to their decay.

Protists can reproduce asexually through binary fission, one nucleus divides; multiple fission, many nuclei divide; and budding. They can, however, also reproduce by sexual reproduction. Protists reproduce sexually through the processes of conjugation and alternation of generations.

With simple care, most will last for 5–7 days. Some cultures last longer than others. Euglena and Paramecium cultures, for example, tend to be long-lived, but Volvox is not.

The animal-like protists must “eat” or ingest food. Some animal-like protists use their “tails” to eat. The protist produces toxins which paralyze its prey. Once digested, the food material moves through the vacuole and into the cytoplasm of the protist.

Most protists can be found in moist and wet areas. They can also be found in tree trunks and other organisms.

Animal-like protists include the flagellates, ciliates, and the sporozoans.

Cell Structure Still other protists are composed of enormous, multinucleate, single cells that look like amorphous blobs of slime, or in other cases, similar to ferns. Many protist cells are multinucleated; in some species, the nuclei are different sizes and have distinct roles in protist cell function.