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Chapter 19: Protists

Chapter worksheet

Ch. 19.1 Introduction to Protists

Protists form a diverse group of organisms that are subdivided based on their method of obtaining nutrition.


Classified more easily by what they are not than by what they are. More than 200,000 species.
All protists are eukaryotes. Some reproduce by mitosis while others exchange genetic material.

Classifying Protists

Divided into three groups:

  1. Animal-like Protists (Protozoans): Heterotrophs that usually ingest bacteria, algae, or other protozoans.
    Examples: ciliates, amoebas, apicomplexans, and zooflagellates
  2. Plantlike Protists (Algae): Autotrophic by means of photosynthesis. Unicellular or multicellular.
    Examples: Euglenoids, diatoms, dinoflagellates, several algae
  3. Funguslike Protists: Heterotrophic by absorbing nutrients from other organisms. Not fungus because they contain centrioles, and cell wall composition is different.
    Examples: Slime molds, water molds, and downy mildews


Typically found in damp or aquatic environments. Some have symbiotic relationships.
Microsporidia- protozoans that cause disease in insects. Used as a natural insecticide.

Origin of Protists

Endosymbiotic theory (large prokaryote engulfing a small prokaryote) may have been the first protist.

Grouping protists by nutrition is convenient but does not consider evolutionary history. Scientists are still trying to understand evolutionary history.

Mitochondria became a part of protist cells early in evolutionary process. Algae the only protists with chloroplasts and capable of photosynthesis.

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Ch. 19.2 Protozoans: Animal-like Protists

Protozoans are animal-like, heterotrophic protists


One characteristic used to further classify protozoans into different phyla is their method of movement.
Phylum Ciliophora are animal-like protists that have numerous short, hairlike projections called cilia. Cilia is used for movement as well as to move food particles into the cell.
Some ciliates have cilia covering their entire plasma membrane, while others have groups of cilia covering parts of their membrane.

There are more than 7000 species of ciliates.


Genus Paramecium is a unicellular protozoan. Enclosed by a layer of membrane called a pellicle. Ectoplasm is beneath the pellicle and contains trichocysts. Trichocysts- elongated, cylindrical bodies that can discharge a spinelike structure.


Cilia completely cover the organism and is used for movement and feeding. Food particles enter the cilia-lined oral groove and are guided to the gullet. At the gullet it is then enclosed in a food vacuole where enzymes break the particle down.
Waste products are excreted through the anal pore.

Contractile Vacuole

Paramecia live in a hypotonic environment, water constantly enters the cell by osmosis.
Contractile vacuoles- collect the excess water from the cytoplasm and expel it from the cell.
Paramecia often have two or three contractile vacuoles to maintain homeostasis.

Reproduction in Ciliates

All known ciliates have two kinds of nuclei: macronucleus and micronucleus. Both contain genetic information for the cell. The Macronucleus controls the everyday functions of the cell. The micronucleus is used for reproduction.

Ciliates reproduce asexually by binary fission. The macronucleus elongates and splits.
Genetic variation is maintained by undergoing conjugation- a sexual process in which genetic information is exchanged.
Conjugation is considered a sexual process but NOT sexual reproduction because new organisms are not formed.

During conjugation:

  1. Two paramecia form a cytoplasmic bridge and their diploid micronuclei undergo meiosis
  2. Three of the new micronuclei dissolve, the remaining one undergoes mitosis.
  3. One micronucleus from each cell is exchanged and the cells separate.
  4. The macronucleus disintegrates in each paramecium, and the micronuclei combine to form a new, diploid macronucleus.


Animal-like protists that use pseudopods for feeding and locomotion. Pseudopod- a temporary extension of cytoplasm. Use pseudopods by surrounding and enveloping prey into a food vacuole.
Digestive enzymes are then used to breakdown the captured organism.

Mostly saltwater, some fresh, and some parasites.

Amoeba Structure

Have outer membrane and thick cytoplasm called ectoplasm. Wastes and undigested food exit cell through membrane by diffusion.

Foraminiferans and Radiolarians are amoebas that have tests. Test- a hard, porous covering similar to a shell, which surrounds the cell membrane. Most are marine.

Foraminiferans have tests made of calcium carbonate, while Radiolarians have tests made of silica.

Amoeba Reproduction

Reproduce asexually by dividing into two identical cells. During harsh environmental conditions, some amoebas will form cysts to survive until environmental conditions improve.


Animal-like protists known as sporozoans because they produce spores at some point in their life cycle. Spores are reproductive cells that form without fertilization. Sporozoans lack contractile vacuoles and methods of locomotion.

All are parasitic and get nutrients from a host. Organelles at one end of the organism are specialized for penetrating host cells ad tissues.

Life cycle has both asexual and sexual stages. Often two or more hosts are required.

Plasmodium are the sporozoans responsible for the greatest number of human deaths. Plasmodium transmits malaria in humans and are transmitted by female Anapheles mosquitoes.
Greatest impact is in tropical and subtropical regions that favor mosquitoes, and preventative measures are too costly.


Animal-like protists called flagellates because they use flagella for movement. Flagella are long, whip-like projections that protrude from the cell. Many are parasites.

At least three species from the genus Trypanosoma cause infectious diseases in humans that often are fatal: Chagas' disease (American sleeping sickness), East African sleeping sickness, and West African sleeping sickness.

American Sleeping Sickness

The zooflagellates are similar to the sporozoans that cause malaria; they have two hosts in their life cycle and insects spread the diseases. The Reduviid bug feeds on human blood, zooflagellates reproduce in the gut of the insect, during feeding the parasite is passed through its feces and enters human through the wound or mucus membranes, it then multiplies in the bloodstream where it can damage the heart, liver, and spleen.

African Sleeping Sickness

Life cycle similar to the one that cases American sleeping sickness. Host insect is Tse-tse fly, when it bites it transfers parasite in its saliva. Cause fever, inflammation of the lymph nodes, and damage to the nervous system.

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Ch. 19.3 Algae: Plant-like Protists

Algae are plantlike, autotrophic protists that are the producers for aquatic ecosystems.

Characteristics of Algae

Plantlike because they contain photosynthetic pigments. Different from plants because they lack roots, leaves, or other structures typical of plants.

The primary pigments of algae are found in chloroplasts. Many algae use the pigment chlorophyll which gives them their green color but many have a second pigment that allow them to absorb light energy in deep water.
As water depth increases, much of the sunlight's energy is absorbed by water; the secondary pigments allow algae to absorb light energy from wavelengths that are not absorbed by the water.
Because of these pigments, algae are found in a variety of colors.

Diversity of Algae

Many algae exist as single cells, while others are huge multicellular organisms.
Phytoplankton are vital in aquatic ecosystems as providers of the food web. They also produce much of the oxygen in Earth's atmosphere.

Algologists use three criteria to classify: type of chlorophyll & secondary pigments, method of food storage, and composition of the cell wall.


Phylum Bacillariophyta. Consists of two unequal halves in which one fits inside the other.

Photosynthetic autotrophs the use chlorophyll and secondary pigments called carotenoids giving diatom a golden-yellow color.
Diatoms store their food as oil instead of carbohydrates which gives them bouyancy. Oil is less dense so this allows diatom to float closer to the surface where they can carry on photosynthesis.

Reproduce sexually and asexually.
Both separated halves create a new half that can fit inside the old one producing a smaller diatom. This process continues until the new diatom created is 1/4 of its original size, sexual reproduction is then triggered and gametes are produced. The gametes fuse to form a zygote that develops into a full-sized diatom. The cycle then repeats.

After the diatoms die, their silica shells accumulate on the ocean floor to form sediment known as diatomaceous earth. This collected and used as: an abrasive, a filtering agent, tooth polishes, and metal polishes.


Phylum Pyrrophyta are unicellular and have two flagella at right angles to one another causing them to spin as they move through the water.
Some have cell walls made of thick cellulose plates, others are bioluminscent.
Bioluminscent- they emit light.
Most are marine.

Algal Blooms

When food is plentiful and conditions are favorable, dinoflagellates reproduce in great numbers causing an algal bloom.
Blooms can be harmful by depleting the nutrients in water; the dinoflagellates then die and when they decompose the oxygen supply in the water is depleted; fish and other marine organisms then suffocate.

Red Tides

Caused by dinoflagellates that have a red photosynthetic pigment when they bloom. These can be lethal because some dinoflagellates produce a potentially lethal nerve toxin.
Shellfish feed by filtering particles from the water, toxins can build up in the tissues of the shellfish.
People can become seriously ill or die when consuming these toxic shellfish.


Phylum Euglenophyta are unicellular and plantlike. Have characteristics of both plants and animals.
Most contain chloroplasts and photosynthesize, when light is not available some can ingest other protists. Some are parasitic.

Have a tough outer covering called a pellicle; similar to a paramecium. Pellicle allows them to crawl in mud when there isn't enough water to swim.
Have flagella, contractile vacuole, and an eyespot which is a light-sensitive receptor that helps orient the euglenoid toward light.


Phylum Chrysophyta (Yellow-green algae and golden-brown algae) have yellow and brown carotenoids that give them a golden brown color.
Most are unicellular but some form colonies. Colony- a group of cells that join together to form a close association.
Most have two flagella at one end. All are photosynthetic but some can absorb nutrients, some ingest food.
Reproduce asexually and sexually; although sexual is rare.

Brown Algae

Phylum Phaeophyta are large, multicellular plantlike algae. The brown color is from a pigment called fucoxanthin. Kelp is one of the 1500 species.
Structures: thallus (body), blades (flat, leaflike structure), stipe (stalklike), holdfast (rootlike), and bladder (filled with air to keep in sunlight).

Green Algae

Phylum Chlorophyta contain chlorophyll, has cell walls, stores food as carbohydrates.
Most found in fresh water, damp ground, tree trunks, snow, and even fur of some animals.

Variety of growth patterns:

  1. Symmetrically divided cells with two identical sides connected by a bridge. Desmids
  2. Long, thin, multicellular filaments. Spirogyra
  3. Colonial. Volvox

Single cells held together by gelatinlike secretion called cytoplasmic strands. Each cell has flagella. Daughter colonies form inside.

Red Algae

Phylum Rhodophyta are multicellular. Red color from pigments called phycobilins that enable the algae to absorb green, violet, and blue light that can penetrate water to depths of 100 m or more.

Uses for Algae

Algae are nutritious because they contain high levels of protein, minerals, trace elements, and vitamins.
Used as food supplements, and stabilizers or to improve texture of processed foods without adding fats.

Life Cycles of Algae

Algae can alternate between spore-producing forms and gamete-producing forms.
Can reproduce sexually as well as asexually.
Green algae can reproduce asexually by fragmentation in which a multicellular individual breaks into separate pieces that will grow into an individual organism.

Alternation of Generations

A life cycle that takes two generations to complete a life cycle. Organisms alternate between asexual reproduction of a diploid form and haploid sexually reproducing form.

Haploid and Diploid Generations

Haploid form is called the gametophyte because it produces gametes. Begins as spores ending with male and female gametes. Gametes from two different organism combine to form a diploid zygote which develops into sporophyte which creates spores.

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Ch. 19.4 Funguslike Protists

Obtain their nutrition by absorbing nutrients from dead or decaying organisms.

Slime Molds

Protists that have some characteristics of fungi; both use spores to reproduce, both feed on decaying organic matter, and both absorb nutrients through their cell walls.
Differ in cell wall composition: fungi walls are chitin, slime mold walls are made of cellulose.

Slime molds are found in a variety of colors, usually exist in damp places where decaying matter is found.
Divided into two groups: acellular and cellular.

Acellular Slime Molds

Phylum Myxomycota are considered acellular because they go through a phase in their life cycle in which it is a mass of cytoplasm with multiple nuclei.

  1. Life begins as spores (when conditions are harsh-drought)
  2. Spore produces a small mass of cytoplasm (amoeboid, or flagellated- both gametes that are haploid)
  3. Two gametes combine to form zygote that forms a plasmodium (feeding stage)
  4. When food or moisture becomes limited the slime mold develops spore-producing structures
  5. Spores are produced by meiosis and dispersed by the wind.

    Plasmodium- a mobile mass of cytoplasm that contains may diploid nuclei but no separate cells.

Cellular Slime Molds

Phylum Acrasiomycota are single amoeba-like cells that have no flagella and reproduce by spores.

  1. When food is plentiful, the slime mold reproduces rapidly by sexual reproduction.
  2. Two haploid amoebas unite to form a zygote.
  3. Zygote develops into a giant cell which undergoes meiosis, followed by several divisions by mitosis.
  4. Giant cell ruptures and releases new haploid amoebas.
  5. When food is scarce the amoeba-like cells reproduce asexually giving off a chemical call acrasin.
  6. Acrasin draws amoeba-like cells together to form a sluglike colony that function like a single organism.
  7. Sluglike form eventually forms a fruiting body that produces spores.

Water Molds and Downy Mildew

Phylum Oomycota mostly live in water or damp places. Some absorb nutrients from surrounding water or soil while others obtain their nutrients from other organisms.

Like fungi, water molds envelop their food sources with a mass of threads breaking down the tissue and absorbing the nutrients through their cell walls.
Unlike fungi, water molds cell walls have cellulose, and water molds produce flagellated cells.

Downy mildews affect potatoes in Ireland in the 19th century causing widespread famine and emigration to the U.S.

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