Lecture Notes on Protista and Unicellular Organisms

Definition of Protista:
- Protista are considered the most complex single-celled organisms in this course.
- Each organism is unicellular and must perform all the functions of multiple organs found in multicellular organisms.

Habitat:
- All protists are aquatic: they can be found in both marine and freshwater environments, as well as in the tissue fluids of other organisms.
Diversity:
- Thousands of species of Protista have been described.
- However, the actual number may be significantly higher as many tropical members remain under-researched.

The growth of unicellular organisms is restricted by their size:
- When a cell's volume triples, its demand for oxygen and nutrients also increases by a factor of three.
- In contrast, the surface area of the cell membrane, through which these substances must penetrate, does not even double.

Characteristics:
- Found in freshwater environments.
- When observing Euglena under a microscope:
- Mix a drop of Euglena culture with a drop of methyl cellulose to slow down the organism, allowing for detailed observation.
- Cells are elongated and contain chloroplasts essential for photosynthesis.
- Exhibits an orange, light-sensitive spot located near the flagellum.
Flagellum Functionality:
- Determine the position of the flagellum:
- At the front, functioning like an airplane propeller, pulling the cell through water, or
- At the back, working like a boat propeller, pushing the cell through water.
Structure:
- The cell is coated with flexible, helical strips of proteinaceous material, collectively known as the pellicle.
- The movements the cell can perform are described as euglenoid motion.
Behavioral Adaptations:
- If Euglena gracilis is kept in darkness, the chloroplasts within the cells will regress, causing the organism to turn white and rely solely on external food sources for survival.
- Re-exposure to light can restore chloroplast function, returning the organism to its green color in a matter of hours.

Characteristics:
- Diatoms inhabit both marine and freshwater environments.
Cell Wall Composition:
- Composed mainly of opaline silica (SiO2) and water.
- The walls have a unique structure resembling a box with one side fitting into another, facilitating molecular transport through holes present in the structure.
Some diatom shells feature slits allowing cellular extensions.
Photosynthesis:
- Diatoms are photosynthetic organisms that contain yellow pigments such as xanthophylls and beta carotene, which mask the green chlorophyll color.
Ecological Importance:
- Diatoms play a key role as a food source in the aquatic food web and are significant as oxygen producers.

Overview:
- This phylum includes free-living, flagellated protistans that are vital in both marine and freshwater ecosystems, as well as certain parasitic forms.
Parasites:
- Notable examples include:
- Trypanosoma brucei: Causative agent of African sleeping sickness.
- Trypanosoma cruzi: Responsible for Chagas disease.
Observation:
- Trypanosoma can be viewed in a fixed and stained human blood smear.

Overview:
- Sarcodina comprises amoeboid protistans that inhabit freshwater, marine environments, and soil.
Locomotion and Feeding:
- Adults utilize temporary projections called pseudopodia to move and capture prey.
Amoeba Examples:
- Amoeba proteus: A free-living amoeba found in freshwater.
- Entamoeba histolytica: A parasite that causes amoebic dysentery.
Microscopic Examination:
- Collect samples of Amoeba from the bottom of the jar without disturbing the water, placing a drop on a slide without a cover slip due to its large size.
- Observe the movement of pseudopodia as they extend and retract creating a flow of cell contents.
- Examples:
- Left: Live Amoeba proteus (100x magnification).
- Right: Stained Amoeba showing nucleus and diatoms (stained dark pink).

Habitat:
- Primarily marine.
Shell Composition:
- Comprised of calcium carbonate (CaCO3) with holes for pseudopodia to extend through.

Characteristics:
- Ciliated protistans found in both freshwater and marine environments.
Cilia Structure:
- Cilia bear structural similarities to flagella; however, they are typically shorter and more numerous.
- Movement is synchronized to either row the cell through the water or to move the medium over the cell during feeding.
Example:
- Paramecium caudatum: A large, free-living ciliate completely covered with cilia.
Collection Technique:
- Collect organisms from the bottom of the sample jar; they favor proximity to food pellets.
- Mix specimens on a slide with methyl cellulose and carefully float a cover slip atop the fluid.

Paramecium multimicronucleatum:
- Two views of live samples.
Fixed and Stained Slide of Paramecium:
Vorticella:
- Another ciliate that attaches to surfaces using a thread-like extension capable of sudden coiling; utilizes a band of cilia to sweep in water and trap food particles to the feeding area.
Acineta:
- Ciliate featuring tentacles collected from our aquarium.

Overview:
- Group known as water molds; familiar example includes the cotton-like colonies (mycelia) observed on aquarium fish, highlighting their ecological interactions and potential impacts on aquatic life.