NOTES FOR BIOLOGY 1002

SECTIONS 004, 005, 006

Spring 2006

DR. STEVEN POMARICO

CHAPTER 22

PROTISTIANS

The Kingdom Protist represents an unusual mix of organisms.

The organisms found in this kingdom are all eukaryotes and most are single-celled for most of their life-cycle.

Remember the eukaryotic differences:

         Nucleus (with a double membrane)

         Organelles

         2 or more chromosomes (DNA + proteins)

Since the organisms of the kingdom Protista are eukaryotic cells, they are clearly different from the Bacteria and Archaea.

The differences between the protists and the rest of the eukaryotes are not quite as clear.

Protists can be organized into three general groups

         Plant-like protists - Autotrophic (photosynthetic)

         Fungus-like protists - Heterotrophic (decomposers)

         Animal-like protists - Heterotrophic (hunters and symbiotic)

The animal-like protists>

         Protozoans are heterotrophic protists, which actively seek and ingest their food (either food particles or other organisms)

One type of protozoan are the flagellated protozoans

         -One flagellum

         -Both free living and symbiotic species

Some of the symbiotic species are parasitic. Including kinetoplastids like

                   Trypanosoma (See fig 22.4) - causing sleeping sickness

                   and

         Parabasilids like Trichomanas (See fig 22.5)

and

         Diplomonads like Giardia (See fig 22.5) - causing diarrhea etc.

Another type of protozoan are the amoeboid protozoans

The amoeboid protozoans are also known as amoebae (See fig 22.6)

         -No visible special structures for movement (i.e., flagella) instead move and                    engulf food-using pseodopods

One type of amoeboid protozoans are the rhizopods

         This group includes:

-Naked (no covering) amoebas - Most are free living though some can be parasitic - amoebic dysentery

- Amoebas with one type of protective shells (See fig. 22.6)

Foraminiferans or forams - make CaCO₃ shells

A second type of amoeboid protozoans are the actinopods

         This group includes amoebas with glass-like silica protective shells

                   Radiolarians and Heliozoans (See fig. 22.6)

The actinopods are often found with phytoplankton. Phytoplankton are the photosynthetic eukaryotes at the base of most aquatic food webs.

A third type of protozoans are the cilates (See fig 22.7)

         -Most species are solitary freshwater

         -Have aveoli (singular aveolus) for membrane support

         -Use cilia for movement and feeding

         Cilia are short hair-like filaments that are made of protein.

These cilia may be a uniform covering of the organism or can be localized in patches

The ciliates are the most complex of the protozoa with an internal structure that includes an oral groove, an anal pore, a contractile vacuole and two types of nuclei.

These two different nuclei have different functions:

         The macronucleus handles all the day-to-day business and the

                    micronucleus functions in sexual reproduction (See fig 22.8).

The last type of protozoans we’ll consider are the sporozoans:

         -All are parasites which have a mobile stage called a sporozoite

                   This group includes:

- Toxoplasma that vectors through cats.

- Plasmodium that causes malaria

Phytoplankton are responsible for most of the photosynthesis (and most of the oxygen production) of the planet.

One type of phytoplankton are the dinoflagellates:

         -Most are marine

         -2 flagella, one at the end and one in an equatorial groove (see fig 19-19)

         -May have a cellulose cell wall

Members of this group are responsible algal blooms some of which result in red tides which result in massive fish kills along the Gulf coast (See fig 22.12).

Some species of plant-like protists (the “seaweeds”) have been placed in the in the past

Kingdom Plantae. This is indicative of the state of flux that surrounds the Kingdom Protist.

A second type of phytoplankton are the stramenopiles. This group includes

         - chrysophytes

         - brown algae

          The chrysophytes include:

- golden algae

- yellow-green algae

- diatoms

- coccolithophores.

The characteristics of the diatoms:

         -May be freshwater or marine

         -Have glass-like “shells” with perforation to allow for exchange of substances

         -About 5,600 described living species and more than 35,000 extinct species

                   (Based on “shell” morphology)

The characteristics of the brown algae

                   -Marine

                   -Deep water to tidal (See fig 22.17)

                   -“Brown” color caused by accessory pigments

                   -Cell wall has added polysaccharides

                   -Giant kelp forest

                   -Gas-bladders to keep the plant extending toward the surface.

An ancestral stramenopile which are not photosynthetic and therefore not phytoplankton are the oomycotes.

The oomycotes include:

- water molds

- downy mildew

These organisms are characterized by filamentous bodies and mobile flagellated gametes.

A third type of phytoplankton are the green algae.

The characteristics of the green algae:

                   -Some marine and many freshwater species

                   -Unicellular and colony forms

                   -Typical chloroplasts

                   -Probably an ancestor of land plants

-Cell wall only has cellulose

A fourth type of phytoplankton are the red algae.

The characteristic of the red algae

                   -Mainly marine but some fresh water

                   -Deep water

                   -Red color caused by accessory pigments

                   -Cell wall has added polysaccharides

                   -Held upright by CaCO₃

                   -Supports the deep water food web

                   -Used in cosmetics, ice cream, paint, sushi

The last type of phytoplankton we’ll consider, the euglenoids, is sometimes grouped with the protozoans.

The characteristic of the euglenoids:

                   -Most are freshwater

                   -Have 1-3 flagella

                   -Primarily photosynthetic but can switch to heterotrophic in the dark

                   -Lack a rigid cell wall

                   -Have a photoreceptor called an eyespot

                   -Named after Euglena (See fig. 22.3)

The remaining protistans we’ll consider are unicellular decomposers known as slime molds..

         The slime molds are divided into 2 general types:

                   Acellular slime molds

                   Cellular slime molds

         The slime molds have a two-part life cycle in which the cells of many “individuals” form an interactive aggregate which is almost multicellular.

Both types of slime molds have:

         -a mobile feeding stage

         -a stationary reproductive stage with a fruiting body that produces                      spores.

Acellular slime molds are also known as plasmodial slime molds

This name comes from the plasmodium, which is the mobile feeding stage of this organism life cycle.

In this mobile stage the cells go through mitosis but not cytokinesis. This results in an acellular organism which looks like a very large multi-nucleated “cell”.

This plasmodium moves through decaying material, engulfing bacteria and food particles.

In harsh environmental conditions (dry) the plasmodium forms a mound and produces a stalked fruiting body that produces haploid spores.

The cellular slime molds have many similarities to the acellular slime molds, but there are some differences.

         -Individual solitary cells characterize the mobile feeding stage.

                   Amoeboid movement using pseudopodia

-During times of environmental stress, a signal causes the cells aggregate into a pseudoplasmodium but remain individual cells.

         -This aggregate of cells is still mobile and migrates to a suitable spot for the                    formation of the fruiting body