Chapter 7
Protists
What is a Protist
• Diatoms are only one of the vast varieties of protists
• Protists are eukaryotes that cannot be classified as
animals, plants, or fungi
• Most protists are unicellular, but some are multicellular
• Some are heterotrophs, autotrophs, or both
• Some cannot move, while others zoom around
• Scientists divide protists into three categories:
– Animal-like protists
– Plant-like protists
– Fungus-like protists
Animal-Like Protists
• Like animals, animal-like protists are
heterotrophs, and most are able to move from
place to place to obtain food
• But unlike animals, animal-like protists, or
protozoans, are unicellular
• Protozoans can be classified into four groups,
based on the way they move and live
Animal-Like Protists
• Protozoans with Pseudopods
– Amoeba’s belong to the group protozoans called sarcodines
– Sarcodines move and feed by forming pseudopods temporary
bulges of the cell
– Ex: amoeba’s use pseudopods to move away from bright light
– Sarcodines also use pseudopods to trap food by extending a
pseudopod on each side of the food particle
– Protozoans that live in fresh water, such as amoebas, have a
problem; small particles like those of water, pass easily through
the cell membrane into the cytoplasm
– If excess water were to build up inside the cell, the amoeba
would burst
– Fortunately, amoebas have a contractile vacuole a structure that
collects the extra water and then expels it from the cell
Animal-Like Protists
• Protozoans with Cilia
– Ciliates have structures called cilia, which are hair-like
projections from cells that move with a wave-like
motion
– Ciliates use their cilia to move and obtain food
– The cells of ciliates, like paramecium, are complex
– They have 2 contractile vacuoles that expel water
from the cell
– More than one nucleus
• One to control the everyday tasks of the cell
• One to function in reproduction which is asexually by binary
fission but can produce by conjugation
Animal-Like Protists
• Protozoans with Flagella use long, whip-like
flagella to move
• Some of these protozoans live inside the
bodies of other organisms
• Symbiosis is a close relationship in which at
least one of the species benefits
• Mutualism is when both partners benefit from
living together
Animal-Like Protists
• Protozoans that are Parasites
– They are all parasites that feed on the cells and
body fluids of their hosts
– Many of these parasites have more than one host
– Malaria
Plant-like Protists
• Plantlike protists, which are commonly called algae, are extremely
diverse
• Like plants, algae are autotrophic
• Algae play a significant role in many environments
• Ex: algae that live near the surface of ponds, lakes, and oceans are
an important food source for other organisms in the water
• In addition, much of the oxygen in Earth’s atmosphere is made by
these algae
• Algae vary greatly in size, some are unicellular or multicellular,
some live in colonies, some become specialized to perform certain
functions such as reproduction, different colors such as green,
yellow, red, brown, orange, or even black
Plantlike Protists
• Diatoms
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–
–
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Unicellular with beautiful glasslike cell walls
Some float, other attach to objects
Diatoms are a food source for heterotrophs
They can move by oozing chemicals out of slits in their
cell walls, then they glide in the slime
– When they die their cell walls collect on the bottoms
of oceans & lake
• Over time they form layers of a coarse substance called
diatomaceous which makes a good polishing agent used in
household scouring products
• Used as an insecticide
Plantlike Protists
• Dinoflagellates
– Unicellular algae surrounded by stiff plates that
look like a suit of armor
– Different colors
– Have 2 flagella that help them move
– Glow in the dark
Plantlike Protists
• Eugleniods
– Green, unicellular algae that are found in fresh
water
– Have one animal like characteristic – can be
heterotrophs under certain conditions but when
sunlight is available, most are autotrophs
– Whip-like flagellum to help them move
Plantlike Protists
• Red Algae
– Multicellular seaweeds
– Grow more than 260 m below the ocean
– People uses
• Ice cream
• Hair conditioner
• Can be eating fresh, dried, or toasted
Plantlike Protists
• Green Algae
– Very diverse
– Unicellular
– Some form colonies which make them
multicellular
– Live in fresh or salt water, on land
– Contain the same type of chlorophyll as most
plants on land
Plantlike Protists
• Brown Algae
– Commonly called seaweed
– Other colors include: green, yellow, or orange
– Fig 22
– Found along the Atlantic coast
– Giant kelp
– Some people eat brown algae
– Used in pudding
Fungus-like Protists
• Spore is a tiny cell that is able to grow into a new
organism
• Like fungi, fungus-like protists are heterotrophs,
have cell walls, and use spores to reproduce
• Able to move
• Three types:
– Slime molds
– Water molds
– Downy mildews
Fungus-like Protists
• Slime Molds
– Brilliantly colored
– Live on forest floors
– Ooze along the surfaces of decaying materials,
feeding on bacteria
– Some are so small you need a microscope to see
them
– Fig 23
Fungus-like Protists
• Water Molds & Downy Mildews
– Live in water
– Grow as tiny threads that look like fuzz
– Fig 24
– Attack many food crops such as potatoes, corn,
and grapes