Chapter 21

Kingdom Protista• This kingdom is also called the

protozoan group.

• proto = first

• zoan = animals

Characteristics of Protozoans• Unicellular• Mostly microscopic• All symmetries represented (oval, spherical, etc…)• No organs or tissues, but some specialized organelles; nucleus may be single or multiple• Free-living, commensalism,

mutualism, parasitism all present

Binary Fission

• Binary means “two”• Fission means “splitting”• So Protists that reproduce this way are

literally splitting in two.

Characteristics of Protozoans• Locomotion by pseudopodia, flagella, cilia, and

direct cell movements.• Simple endo- or exo- skeleton, but most are

naked.• Nutrition of all kinds: autotrophic, heterotrophic,

saprozoic (using nutrients dissolved in the surrounding medium

• Aquatic (marine or freshwater) or terrestrial (in moist soil or leaf litter)

• Reproduction asexually by budding, fission, or cysts, and sexually by conjugation or syngamy (union of male and female gametes to form a zygote.)

The First Eukaryotes• Protists are thought to be the first

eukaryotes.• They evolved about 1.5 billion years

ago.• Thought to have formed through the

process of Endosymbiosis.

Endosymbiosis

Two important features of eukaryotes that formed first in protists:• Sexual reproduction

• Multicellularity

What’s the unifying theme of protists?• They are all eukaryotic organisms

that can’t be classified as plants, animals, or fungi. (all of the “leftover eukaryotes”)

• They do not form embryos during early development.

Alternation of Generations:• As with some plants, some protists go

through an alternation of generations.

• This means that there is a diploid form (has two copies of each chromosome) and another form that is haploid (has only one copy of each chromosome).

Alternation of Generations:• The diploid, spore producing phase is

called the sporophyte.

• The haploid, gamete producing phase is called the gametophyte.

Alternation of Generations:

Sporophyte• The adult sporophyte produces

reproductive cells called sporangia, which produces haploid spores by meiosis.

• These spores grow into multicellular haploid gametophytes.

Sporangia

Gametophyte• The mature gametophytes produce

haploid gametes that fuse and complete the life cycle by dividing through mitosis to form a new diploid sporophyte.

Conjugation• This is the temporary union of two

protists to exchange nuclear material.

Conjugation in paramecium

AmeobasAmeboid Movement:• Members of the phylum Rhizopoda

move by using flexible cytoplasmic extensions called pseudopodia.

• pseudo = false

• podia = feet

Foraminifera• Typically live in sand or attach

themselves to other organisms or on rocks.

• Characterized by their porous shells, called tests. These shells are made of calcium carbonate.

• Long, thin projections of cytoplasm extend through the pores of the tests, in order to catch prey and aid in swimming.

Foraminifera

Foraminifera

Algae• These protists are strict

photoautotrophs.• Multicellular and unicellular forms• Major portion of marine plankton

Algae• Green – (Phylum Chlorophyta) Contain

the same pigments found in the chloroplasts of plants.

• Red – (Phylum Rhodophyta) Mostly multicellular. Have pigment that absorbs light waves that penetrate deep water.

• Brown – (Phylum Phaeophyta) Mostly marine. Kelp is an example of this phylum.

Halosphaera-green algae

Red Algae

Brown Algae

Diatoms• Phylum Bacillariophyta• Photosynthetic • Unicellular• Double shelled• Move by secreting chemicals through

holes in their shells, enabling them to glide

• Sexual reproduction

Diatoms• Sexual reproduction involves

separating the shell in halves, and each new diatom generates a new half. The shell becomes too small, after successive “halvings”.

• Then the diatom slips out of its shell, grows to normal size, regenerates a new shell, and begins the cycle of reproduction again.

Flagellates• These are protists that move using

flagella

Three kinds of Flagellates:• Dinoflagellates• Euglenoids• Kinetoplastids

Dinoflagellates• Freshwater and marine• Have an exterior coat made of cellulose• Various unusual shapes• Usually twin flagella, which beat within

two grooves around the body at right angles to one another.

• Responsible for “Red Tides”• Usually reproduce asexually• Can be heterotrophic or autotrophic, or

both.

Dinoflagellates

Red Tide

Euglenoids• Freshwater protists with two flagella.• About one-third of these are

photosynthetic• The other two-thirds are heterotrophic• Has a light sensitive organ called the

“eyespot”• Has a flexible protein scaffold called a

pellicle, which allows it to change shape• Reproduce by mitosis

Euglenoids

Kinetoplastids• Unicellular• Heterotrohpic• Have at least one flagella, but some

have thousands• Most reproduce asexually, but some

sexually• Example is the trypanosomes, like the

one that causes African Sleeping Sickness

Kinetoplastids

Ciliates• Have large numbers of cilia (short hair

like projections from the cell membrane, which provide movement for the organism)

• Unicellular heterotrophs• Also have a pellicle• Micronuclei and macronuclei• Reproduce sexually and asexually• Paramecium is an example

A closer look at paramecium:

Protistan Molds:• These are heterotrophs with some

mobility• Once thought to be fungi, because of

their similar appearance• Contain different carbohydrates than

fungal cell walls.• Carry out mitosis, unlike fungi

Cellular slime molds• Resemble amoebas• Move through the soil ingesting

bacteria• During times of stress, they form

aggregations called slugs• Then the aggregates form stalked

structures which contain spores• These spores, when released, form new

amoeba like organisms

Cellular slime molds

Plasmodial slime molds• These stream along as a mass of

cytoplasm that looks like an oozing slime• They feed on bacteria• Contains many nuclei, but they are not

separated by cell walls• Also creates spores in unfavorable

conditions• Spores can grow into amoeboid cells or

flagellated cells, which can fuse into diploid zygotes

Plasmodial slime molds

Plasmodial slime molds

Other molds• Oomycetes is a phylum of water molds,

white rusts, and downy mildews• Often grow on dead animals in freshwater • All members of the group are parasitic or

detritivores (feed on dead organisms)• Unusual because they have two flagella,

with one facing forward and the other facing backward.

Water molds

Oomycetes• These organisms are responsible for

the failure of potato crops in Ireland in 1845 – 1850

• This crop failure led to a famine that killed about 1 million people!

Sporozoans• Parasitic protists that form spores during

their reproduction cycle• Nonmotile, unicellular • Malaria is a disease caused by sporozoans• Cryptosporidium is a sporozoan which

causes disease, it infected water supplies in several cities in the US in 1980s and 1990s. It comes from pet feces.

Cryptosporidium

Protists and Humans• Protists cause many human diseases• They also cause disease in livestock,

which affects us , because of our food supply

Beneficial Protists• Cattle could not digest the cellulose in

hay without the sporozoans which normally live in their digestive tract.

• Protists, which make up a large part of the plankton in the ocean, support the food chain.

• Many protists are also detritivores, which means they recycle chemicals back into the environment.

Protists from cow guts

Malaria• Almost 3 million people die each year

of Malaria, a sporozoan disease• Most of these victims are children• Symptoms include fever, chills,

sweating, confusion, and great thirst• Victims die of anemia, kidney failure

or brain damage, unless the disease is treated

Malaria Life Cycle

1. Mosquito infects human with sporozoites.

2. Sporozoites travel to the liver, where they become merozoites.

3. Merozoites are released into the blood, where they infect red blood cells. They are now called trophozoites.

4. Another mosquito bites the infected human, picking upthe trophozoites, which have now turned into gametocytes.

5. Inside the mosquito, the gametocytes combine to once again begin the life cycle as sporozoites.

Treating and preventing Malaria• In the 17th century, Quinine, a chemical

derived from the bark of the cinchona tree, was discovered to be a remedy for Malaria.

• Malaria can also be controlled by reducing mosquito populations. This is done by spraying pesticides, which kill mosquitoes, getting rid of their breeding places, and introducing animals that will eat mosquito larvae, like the mosquito fish.

Mosquito PredatorMosquito fish eat mosquito larvae. This helps to control the mosquitoPopulation.

Making a Malaria Vaccine• For a vaccine to work, it has to

stimulate the body’s immune system to recognize and attack specific molecules on the parasites.

• However, Plasmodium goes through several stages inside the human body. In addition, during one stage, it hides in the liver, where the immune system can’t find it.

• Therefore, the body’s immune system must recognize a protein present in all stages of the parasite’s development.

Making a Malaria Vaccine

•The EndThe “Microbe Astronomer”