Unit 4 Notes
The Protists
Eukaryotic Cells
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Cell Wall – only some eukaryotes have cell walls, such as plants – purpose is to provide strength and
rigidity to the cell.
Cell (Plasma) Membrane – consists of the phospholipid bilayer; purpose is to allow substances into and out
of the cell.
Cytoplasm – jelly-like substance that fills the inside of the cell.
Chromosome – made from chromatin and located in the nucleus of the cell; purpose is reproduction. Can
have multiple chromosomes.
Nucleus – large structure in the center of the cell; purpose is to control the activities of the cell.
Mitochondrion – located in the cytoplasm of the cell; its purpose is to produce the energy (ATP) for the
cell.
Chloroplasts – located only in plant and algae cells; contains chlorophyll pigment used in photosynthesis.
Endoplasmic Reticulum – can be either smooth or rough; purpose of smooth is to produce phospholipids,
fats, and steroids for use by the cell; purpose of rough is to provide a site for protein synthesis and to
synthesize proteins to be secreted by cell.
Ribosomes – involved in protein synthesis.
Golgi Apparatus – packages cell products for secretion from cell.
Lysosomes – membrane-enclosed packets that contain digestive enzymes
Cilia – on outside of cell; purpose is to either move the cell itself, or to move substances over and around
the cell.
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Introduction
Over 100,000 species of protists are currently known to exist and another 35,000 species are recognized by their
fossils. The word “protist” comes from the Greek word meaning “very first”, and this is so because the protists
are considered to be the first eukaryotes to appear on the earth.
Protists are classified in large groups based on
whether they are most like plants, animals, or fungi.
I. Protozoa – Animal-like Protists
The word “protozoa” comes from two root words: proto, which means “first”, and zoa, which means “animal”.
Protozoa lack cell walls, are unicellular, heterotrophic, and are usually motile. Most are found in aquatic
environments or in moist soil. They can exist in two forms:
a. trophozoite – under ideal conditions, this is the active, feeding form
b. cyst – under difficult conditions, this is a dormant form which can withstand harsh conditions
Protozoa are important because they work with other microbes to decompose the remains of dead animals and
plants and recycle nutrients. In addition, many species are a major part of aquatic food chains.
Protozoa are classified into 4 groups based on what type of movement they exhibit:
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1. Amoebas – move by pseudopods (pieces of cytoplasm that can extend outward in different shapes); no
definite form and constantly changing shape. Also known as sarcodines, amoebas are heterotrophic, and
reproduction occurs through mitosis. Representative species of amoebas include:
a. Foraminifera – these have hard, shell-like casings called tests. Their shells are made of calcium
carbonate with pores through which the pseudopods move in and out. The remains of foraminifera
build up on the ocean floor and are found frequently in fossils.
b. Heliozoa – freshwater amoebas encased in hardened capsules of silicon dioxide that resemble the
sun.
c. Radiolaria – found in the sea, they have glassy skeletons of silicon dioxide, and also contribute to
the ocean sediment.
d. Entamoeba histolytica – important to humans; causes amoebiasis. This sickness is transmitted by
contaminated food and water, and causes intestinal ulcers and sharp appendicitis-like pain.
2. Flagellates – move by flagella. Representative species include:
a. Euglena – freshwater microbe; has a nucleus and two flagella. It is important because it is
autotrophic in sunlight (can undergo photosynthesis); heterotrophic in the dark.
b. Volvox – this is a colony of cells instead of one individual cell, all living in a ball. Each cell has its
own function for the good of the whole colony, such as feeding, or reproduction.
c. Trypanosoma brucei – transmitted by the tsetse fly, this causes African Sleeping Sickness. It
invades the brain tissue of humans, causing a coma-like condition.
d. Giardia lamblia – also called “beaver fever”, found in contaminated water, especially in mountain
streams and lakes. It causes nausea, cramping, and a foul-smelling watery diarrhea in humans. Very
common.
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e. Trichomonas vaginalis – causes trichomoniasis, which is a sexually-transmitted disease that affects
over 2 million Americans each year. Causes intense itching, burning, and a frothy fish-smelling
discharge from the vagina. Mostly affects women.
3. Ciliates – move by hairlike cilia all around their bodies. Cilia sway like wheat in a field to cause
movement, and have some sensory function. An example is:
a. Paramecium – enclosed by a pellicle, or outer layer. Undergoes conjugation, which is a form of
sexual behavior where 2 paramecium exchange genetic information.
4. Sporozoa – exist as a spore; have no means of movement. Also known as Apicomplexans, these protozoa
are parasitic and of the 4 groups of protozoans, cause the most damage to humans. Examples:
a. Plasmodium – this is the organism that causes malaria, a blood disease that affects over 300 million
people worldwide annually. Transmitted by the bite of a mosquito, the parasites are injected into the
bloodstream and destroy red blood cells, causing waves of intense cold followed by waves of intense
fever.
b. Toxoplasma gondii – causes toxoplasmosis, a blood disease often transmitted by cats. Causes an
illness where you have extreme fatigue.
c. Pneumocystis jirovecci – causes a pneumonia which mostly affects AIDS patients.
d. Cryptosporidium coccidi – found in contaminated drinking water, it is an intestinal parasite which
causes mild to severe diarrhea.
II. Algae – The Plant-like Protists
These protists can be either unicellular or multicellular. Can be either autotrophic or heterotrophic, and have
many characteristics similar to green plants.
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1. Unicellular Algae – can undergo photosynthesis; makes up the microbial population in the ocean known as
phytoplankton. These generate as much as 80% of the world’s oxygen. Also, ½ of the world’s organic
matter is produced by these. They are classified into 6 divisions (see chart above):
a. Euglenophyta (Euglenoids)– no cell wall. Are unicellular, freshwater algae. Can be autotrophic or
heterotrophic.
b. Pyrrophyta (Dinoflagellates) – cell wall made of cellulose. Dinoflagellates are unicellular
photosynthetic algae. Several species are luminescent and give off light when disturbed.
Dinoflagellates are subject to population explosions whenever conditions are favorable. This
“bloom” is sometimes called a “red tide” because the algae are red in color and are so numerous that
the water appears reddish. They give off a toxin that is poisonous to humans and animals, and the
toxin concentrates in shellfish, making them inedible to humans during a red tide.
c. Chrysophyta (Diatoms) – cell wall of silica, which looks like glass. Diatoms are unique because
they store their food in a light, less-dense oil form that allows them to float on top of water to be
closer to sunlight. Diatoms are an important freshwater and marine food source; when dead, their
shells often accumulate in large layers known as diatomaceous earth, which is still used as an
abrasive and for filtering purposes.
d. Chlorophyta (Green Algae) – cell wall of cellulose. The "green algae" is the most diverse group of
algae, with more than 7000 species growing in a variety of habitats. The green algae contain two
forms of chlorophyll, which they use to capture light energy. Often found attached to rocks in the
ocean and are exposed at low tide.
e. Phaeophyta (Brown Algae) – cell wall of cellulose. Many of the world's familiar seaweeds and
kelps are members of Phaeophyta. There are approximately 1,500 species.
f. Rhodophyta (Red Algae) - cell wall of cellulose. Most marine red algae have soft and delicate
bodies, however, some become strongly calcified and contribute significantly to the growth of coral
reefs in tropical seas. Because of the permanent nature of the structures that they produce, coralline
algae have a rich fossil record that extends back as far as 700 million years. Commercial agar used as
a culture medium for bacteria is produced from several genera of red algae. The so-called Irish moss
is the source of carrageenin, a substance widely used as a stabilizing agent in emulsions and in ice
cream.
III. Slime & Water Molds – The Fungus-like Protists
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1. Slime Molds – Slime molds resemble plants because cells have cell walls enclosed with cellulose, but also
resemble animals because at some point in their life cycle, they have flagella which allow them to move.
They are called slime molds because they are slimy and have a threadlike structure similar to fungi. They
live in moist terrestrial habitats, such as on decaying wood or fresh cow dung.
2. Water Molds – play an important role in the decomposition and recycling of decaying matter. Their greatest
impact on humans, however, comes from the many species of water mold which are parasites on flowering
plants. These include root rotting fungi, seedling dampening mold, blister rusts, white rusts, and the downy
mildews that affect grapes, lettuce, corn, cabbage, potatoes, and many other crop plants. Two examples that
have caused major problems in the past:
a. Phytophthora infestans – responsible for the Irish potato famine in the mid-1800’s; ruined potato
crop
b. Pfiesteria piscicida – also called “the cell from hell”, it is responsible for destroying the fish
population off of the coast of North Carolina by causing toxic lesions on the fish.
Pfiesteria piscicida
Phytophthora infestans
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