Protists: Characteristics and Classification

• Protists are unicellular organisms that do not fit into other kingdoms.

Characteristics of Protists

• They are always unicellular, made of one eukaryotic cell which functions as a whole.
• They can be autotrophic (make their own food), heterotrophic (dependent on other animals for food), or parasitic.
• They mostly live in water, soil or other organisms.

Classification of Protists

• Classified according to how they obtain nutrients and how they move.
• Animal protists, or protozoans ("small animals"), are heterotrophs.
• Plant-like protists, or unicellular algae, are autotrophs.

How Protists Move

• Flagellates move by flagella.
• Sarcodines move by extensions of cytoplasm (pseudopodia).
• Ciliates move by cilia.
• Sporozoans do not move.

Flagellates

• Move by one or two flagella.
• Absorb food across the membrane.
• Euglena is autotrophic, has chloroplasts and a red eye-spot for detecting light.
• Trypanosoma cause sleeping sickness, transmitted by the tsetse fly.
• Trichomonas causes trichomoniasis/inflammation of the vagina, is an STD (sexually transmitted infection), greenish vaginal discharge with a bad smell.

Sarcodines

• Move by pseudopodia ("false feet"), which are live extensions of cytoplasm creating ameboid movement.
• Ingest food by surrounding and engulfing (phagocytosis), creating a food vacuole.
• Reproduce by binary fission (mitosis).
• Have a contractile vacuole to remove excess water.
• Can cause amebic dysentery in humans (diarrhea and stomach upset) from consuming contaminated water.
• Ameoba lives in the gut of humans
• Foranniniferans and Radio lavians form shells.

Ciliates

• Paramecium is an example, move using cilia.
• Possess two nuclei: macronucleus (metabolism) and micronucleus (reproduction).
• Food is ingested through the cytostome (cellular mouth), forming a food vacuole.
• The anal pore (cellular anus) removes waste.
• Contractile vacuole removes excess water.
• Reproduce by binary fission or asexually through conjugation.
• They have a rigid outer membrane (pellicle) that gives them a consistent shape, like a shoe.

Sporozoans

• Do not move independently.
• Are endoparasitic, residing inside the body.
• Utilize both sexual and asexual reproduction and need multiple hosts; generate protective spore coats.
• Malaria: Caused by sporozoan (Plasmodium), affects the liver and blood and is transmitted by mosquitoes.
• Toxoplasmosis: Caused by a sporozoan (Toxoplasma), dangerous for pregnant women causing miscarriages, sources: excrement of cats and undercooked meat.

The Amoeba

• The ameba, a protozoan in the Kingdom Protista (phylum Sarcodina), changes shape; also sometimes called Amoeba.
• These animal-like protists move/creep by pushing cytoplasm creating fingerlike extensions called pseudopodia ("false foot.")
• The cell membrane is exceptionally flexible so it can change shape.
• Amoebas reside in ponds, puddles, and can also exist inside people.
• The darker, inner cytoplasm is called endoplasm, and the clearer cytoplasm closer to the cell membrane is called ectoplasm
• The ameba consumes food when the pseudopodia extend to wrap around it which is called phagocytosis; the food becomes a food vacuole which will be disposed via lysosomes.
• It reproduces through mitosis and divides into two identical new cells, which is called binary fission.
• Contractile vacuole pump out excess water.
• Amoebas create cysts (hard wall body) in harsh conditions.
• Consuming contaminated water can lead to contracting Amebic Dysentery causing cramps and diarrhea.