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16.6 General Biology of Protists
There are four kingdoms in the Domain Eukarya.
Protista, Fungi, Plantae and Animalia
All organisms in Eukarya have organelles including a nucleus.
Protists vary in size from microscopic to macroscopic (very large)
Most protists are unicellular, but they are very complex
Most organisms in Protista reproduce by asexual reproduction
Organisms can be categorized by how they obtain nutrients
Heterotrophs – organisms that consume food and digest it inside their bodies.
Autotrophs – organisms that make their own food using photosynthesis. While we think of plants as doing photosynthesis, some protists and some bacteria can also do photosynthesis. Cyanobacteria make a significant amount of atmospheric oxygen.
Decomposers – digest food outside their body and absorb the nutrients across the cell wall.
Types of Protists
Protists can be separated into 3 categories based on their nutrition
Protozoa consume food (heterotrophs) and digest it internally. Also they typically can move.
Algae that can do photosynthesis (autotrophs). Underscoring the debate over how to categorize protists, some sources list algae as plants, but your book lists them as protists.
Slime molds that absorb nutrients that were digested outside their body.
Pseudopods – extensions that form when cytoplasm goes in a particular direction
Feed by phagocytosis, surrounding prey with pseudopods and digesting it
The most structurally complex and specialized of all protozoans
The majority are free-living, some are parasitic
Green algae are ancestral to plants
Green algae (Approximately 7,500 species)
Not always green
Inhabit a variety of environments
Oceans, freshwater, snowbanks, bark of trees, backs of turtles
Phytoplankton are microscopic autotrophs that live in water. They produce about half of the oxygen available in the atmosphere and form the basis of
Algae can form colonies of loosely organized independent cells or end-to-end chains of cells that form filaments.
Volvox, a colonial green alga
A Volvox colony is a hollow sphere with thousands of cells in a single layer on the outside
The cells are usually connected by strands of cytoplasm
Smaller daughter colonies are contained within the ball
Spirogyra, multicellular, filamentous algae
Forms long filaments of cells end-to-end
Can reproduce asexually and sexually
Has a chloroplast that performs photosynthesis
Stores glucose in a pyrenoid
16.8 A Fungus Is Not a Plant
Fungi (domain Eukarya)
Fungi are heterotrophs that release digestive enzymes into the external environment and digest their food outside the body, then absorb nutrients across their cell walls. They play an important role as decomposers.
Fungal cells are different from plant cells
Fungi are adapted to life on land by producing windblown spores
Yeast are single-celled fungi
They are added to bread dough, wine and beer
Bread mold is also a fungus, Rhizopus stolonifer
The sprorangia make spores which disperse to start a new organism.
2 gametangia come together to produce a zygospore
Mushrooms also make spores which disperse to start a new organism.