Protist Habitats and Movement

• Protists are eukaryotes, but not land plants, animals, or fungi.
• They are diverse in biological and ecological characteristics due to being an artificial assemblage of phylogenetically unrelated groups.
• Protists have varied cell structures, reproductive strategies, nutrition, and habitats.
• Single-celled protists are usually motile, with diverse transportation structures.

Habitats of Protists

• Protists commonly exist in aquatic environments like freshwater, marine environments, damp soil, and snow.
• Some protist species are parasites, while others live on dead organisms or wastes, contributing to decay.

Protist Movement

• The majority of protists are motile and use varied modes of movement.
• Some protists use one or more flagella, which rotate or whip, to move.
• Other protists are covered in rows or tufts of cilia, which beat coordinately for swimming.
• Still other protists form pseudopodia to anchor to a substrate and pull themselves forward.
• Taxis refers to the movement toward or away from a stimulus.
• Phototaxis refers to the movement toward light.
• Movement toward light is achieved through the coupling of locomotion strategy with a light-sensing organ.
• Protists can be subdivided into three categories: algae, protozoa, and slime molds.

Phylum Chlorophyta: Green Algae

• Green algae is the most abundant group of algae and shares similar features with land plants, especially in chloroplast structure.
• The chlorophytes exhibit great diversity of form and function.
• Chlorophytes primarily inhabit freshwater, damp soil, and are a common component of plankton.
• Chlorophyta is divided into unicellular, filamentous, and colonial green algae.

Phylum Euglenida: Euglenoids

• Autotrophs, heterotrophs, mixotrophs and parasites ranging in size from 10 to 500 μm
• Euglenoids move through aquatic habitats using two flagella.
• Flagella guide euglenoids toward light sources sensed by an eyespot.
• Euglena includes mixotrophic species with photosynthetic capability only in the presence of light.
• In the dark, the chloroplasts of Euglena shrink, cease functioning, and the cells consume organic nutrients.

Phylum Rhizopoda: Amoebas

• Most amoebas have threadlike or needle-like pseudopodia, which are used to trap and engulf food particles and direct movement.
• Pseudopods project from anywhere and anchor to a substrate, then the amoeba transports its cytoplasm into the pseudopod, thereby moving the entire cell.

Phylum Kinetoplastea: Flagelletes

• The Kinetiplastea phylum is named after the kinetoplast, a DNA mass within the single, oversized mitochondrion.
• The phylum includes trypanosomes which are parasitic and cause African sleeping sickness and Chaga's disease.

Phylum Ciliophora - Ciliates

• Ciliates, that include Paramecium, are protists that range from 10 to 3,000 µm in length and are covered in rows, tufts, or spirals of tiny cilia.
• By beating cilia synchronously ciliates coordinate movements and ingest food particles.
• Paramecium includes protists that have organized their cilia into a plate-like primitive mouth, called an oral groove, which is used to capture and digest bacteria.
• Food captured in the oral groove enters a food vacuole, where it combines with digestive enzymes.
• Waste particles are expelled by an exocytic vesicle that fuses at a specific region on the cell membrane, called the anal pore.
• Paramecium also uses contractile vacuoles, which are osmoregulatory vesicles.
• Contractile vacuoles fill with water by osmosis and then contract to squeeze water from the cell.

Phylum Apicomplexa - Apicomplexans

• Plasmodium must colonize both a mosquito and a vertebrate to complete their life cycle.
• In vertebrates, the parasite develops in liver cells, infects red blood cells, and the blood cell is destroyed after asexual replication.
• P. falciparum causes 50% of all malaria cases in humans and is the primary cause of disease-related fatalities in tropical regions.

Phylum Oomycota - Oomycetes

• Protist parasites of terrestrial plants that destroy crops.
• Phytophthora infestans is an oomycete that causes potato late blight, rotting potato stalks into black slime.
• Potato blight of P. infestans caused the Irish potato famine in the nineteenth century, causing approximately 1 million deaths and 1 million emigrations.
• Late blight continues to wipe out 70% of potato crops when no pesticides are applied.