What are Protists? –the “Junk Drawer” kingdom
• A protist is a member of a group of eukaryotic organisms which have a membrane-bound nucleus.
• Most protists reproduce asexually, though some can reproduce sexually
• Protists are extremely diverse and share characteristics with plants, animals, and fungi but are not classified as any of these groups
What are Protists?• General characteristics-
– Most are unicellular, but some, such as the giant kelp, are multicellular & can grow to be as big as 100 meters
– Live in moist surroundings– Some move and some don’t– Some can make their own food, while others are
consumers or decomposers– They are classified by how they obtain food
• Scientists classify protists as plant-like, animal-like, or fungus-like based on which group they most resemble.
Three kinds of Protists-
• Plant-like
• Animal-like
• Fungus-like
Plant-like Protists
• Like plants, these protists use chlorophyll for photosynthesis – (takes place in chloroplasts)
• Almost all live in water• Examples include:
– Algae– Diatoms– Dinoflagellates– Euglenoids
Plant-like Protists- Algae• Algae are plant-like protist that
perform photosynthesis. They can be either multicellular or unicellular.
• Red algae
– Used to make ice cream, marshmallows & shampoo
• Brown algae
– Known as “seaweed”
• Green algae
Plant-like Protists- Diatoms
• A type of microscopic plantlike protist with a hard outer wall is a diatom
– Unicellular with glasslike cell walls– Used in silver polish, toothpaste & insulation
Plant-like Protists- Dinoflagellates
• Dinoflagellates are unicellular plantlike protists that use flagella to move.
– They have many pigments so they come in several colors
– They have 2 flagella that allow them to swirl around as they move
– They glow in the dark & look like fireflies at night
Plant-like Protists- Euglenoids• A Euglenoid is a unicellular plant-like
protist that has a flagellum at one end of its body. It has no cell wall. Instead it has a rigid rubbery coat called a pellicle.
• Euglenoids
– Have eyespots that
respond to changes in
light• Tell the euglena when to perform photosynthesis
– Produce food by photosynthesis
The importance of Algae• Algae provide food for
animals and animal-like protists, and provide shelter for many aquatic organisms such as sea otters.
• They are plant-like but have holdfasts rather than roots.
• Algae can help remove pollution from the water.
•Pollution can be a food source for algae, allowing the population of algae to increase quickly.•This overproduction can lead to Red Tides, which can be dangerous to other aquatic animals & humans
Algae are thought to cause Red Tides
Animal-like Protists: Protozoans
• Protozoans are protists that resemble tiny animals
• Protozoans are unicellular and mostly live in wet environments.
• Protozoans do not have chloroplasts and cannot make their own food.– They are consumers and some are parasites
Animal-like Protists- Ciliates
• Cilia are short, hair-like structures that grow on the surface of some protists.
• Protists with cilia are called Ciliates.
• Cilia cover the surface of the cell and move a protist through water.
• Ciliates reproduce asexually, but they can exchange some genetic material through a process called conjugation.
Animal-like Protists- Ciliates
• A paramecium is a protist with cilia and two types of nuclei.
• A paramecium gets its food by forcing water into the oral groove in its side.
Animal-like Protists- Flagellate
• A Flagellate is a type of protozoan with one or more flagella.
• Flagellates eat decaying matter.
Animal-like Protists- Sarcodines• Sarcodines are animal-like protists with
no specific shape.
• An amoeba is one common Sarcodine.
• An amoeba moves and obtains nutrients by using pseudopods, which means temporary or false foot.
• Amoeba form pseudopods by slowly pushing their cytoplasm against the soft, flexible cell membrane.
Animal-like Protists: Protozoa cont’• Amoeba use their pseudopods to engulf
their food and form a food vacuole
• They are found in soil, salt & fresh water, and use a contractile vacuole to get rid of excess water
Fungus-like Protists• Funguslike protists share many
characteristics with fungi.
• Slime molds are funguslike protists composed of cell material and nuclei floating in a slimy mass.
• Most slime molds absorb nutrients from other organic matter in their environment.
Funguslike Protists • A water mold is a
funguslike protist that lives as a parasite or feeds on dead organisms.
• Slime molds and water molds usually reproduce sexually when environmental conditions are harsh or unfavorable.
• Funguslike protists play a valuable role in the ecosystem by breaking down dead plants and animals, making nutrients available for living organisms.
• Many funguslike protists attack and consume living plants.
• Water mold destroyed more than half of Ireland’s potato crop in 1845
Importance of Funguslike Protists