General Biology of Protists

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Chapter 16


& Fungi

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


Organizing Organisms

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.



Amoeba proteus

Pseudopods – extensions that form when cytoplasm goes in a particular direction

Feed by phagocytosis, surrounding prey with pseudopods and digesting it

Paramecium caudatum

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

Lack chloroplasts

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

Asexual reproduction

The sprorangia make spores which disperse to start a new organism.

Sexual reproduction

2 gametangia come together to produce a zygospore


Mushrooms also make spores which disperse to start a new organism.


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