The Protists (Kingdom Protista)

- Found in the domain eukarya.

- Protista is likely not one kingdom, it probably consists of many kingdoms. Scientists cannot agree. For our study, we are going to consider protists to be in one kingdom (The Kingdom Protista).

- Protists are generally unicellular but can be colonial like volvox. Some protists can be relatively simple

multicellular organisms (Body is a thallus).

-Protista includes a wide variety of species.

-Protists include organisms that are fungal-like, animal-like and/or plant-like. Eukaryotes that don’t belong in the other eukaryote kingdoms are often put into protista.

- Protists are the most primitive eukaryotes and are the first eukaryotes to appear in evolutionary terms.

The Kingdom Protista

A Cladogram Showing Phylogenetic Relationships Among Some Groups of Protists.

Protist groups shown are Heterokonts, Avelolates, Euglenoids, Amoebozoa and Early Protists.

Note: The kingdoms animalia (Animals), fungi and plantae (Land Plants) are shown on this cladogram.

The term “land plants” is general and includes all organisms in the plant kingdom. This includes aquatic plants such as cattails, cypress, etc.

The kingdom protista includes organisms that are fungal-like but do not fit into the kingdom fungi. Such a protist example is slime mold.

Physarum, a slime mold.

The kingdom protista includes organisms that are animal-like but do not fit into the kingdom animalia. These animal-like protists are called protozoans. Examples include amoeba and paramecium. These 2 protozoans are classified by how they move and they are found in different evolutionary groups. Amoeba move by pseudopods. Paramecium move by cilia.

An amoeba

The feathery red alga Polysiphonia.

The kingdom protista includes organisms that are plant-like (they photosynthesize) but do not fit into the kingdom plantae. Such protist example include seaweed and euglena.

Photosynthetic protists are often called algae.

- 20,000 to 30,000 known species.- Mostly Aquatic.- Single cells or clusters, filaments, sheets or 3-dimensional.- Basis of many aquatic food chains (Algae are part of phytoplankton).

Volvox Phytoplankton, which is a photosynthetic organism (generally one-celled) that is part of the plankton, a body of floating cells near the surface of fresh or saline bodies of water. Phytoplankton (grasses of the sea) make ½ of all the oxygen gas in the atmosphere.

Algae (The Photosynthetic Protists)

Algal Diversity

(a) A unicellular Micrasteria.

(b) A colonial Gonium.

(c) A colonial Volvox.

(d) Filaments of Spirogyra.

(e) Caulerpa with differentiation into rootlike, stemlike, and leaflike regions. All of these are green algae.

Seaweeds are (f) the intertidal red alga Porphya and (g) the brown alga Fucus.

(a) (b)

(c)(d)

(e) (f) (g)

Euglenoids- Usually Unicellular and Photosynthetic.

2 Euglena Cells. Note

the chloroplasts &red eyespots.

- Possess eyespot, which is a unique organelle that orients individuals to light.

- No known sexual reproduction.

- Move by 2 flagella.- No cell wall.- Found mainly in

polluted freshwater.- 1/3 of all species are

photosynthetic but the majority ingest food.

- Example: Euglena

Alveolates

Paramecium- Possess membrane-bounded sacs lying beneath the plasma membrane.

- Examples: Dinoflagellates (Cause Red Tides), formanifera, ciliates (Paramecium) and the apicomplexa.

Heterokonts- All heterokonts all

have 2 unequally sized flagella.

The Giant Kelp, a brown algae

- Includes several algal groups.

- Examples: Golden algae, brown algae (Fucus), diatoms and the oomycota (water molds, downy mildews).

- Diatoms are typically single-celled algae with silica cell walls that create vast deposits over time.

Protista and Humans- Protists cause some serious diseases like amoebic

dysentery and malaria. Malaria is caused by protozoan

parasites of the genus Plasmodium (phylum Apicomplexa). - Algae serve as medicine, food and fertilizer

– Seaweed is an important food.

– Industrial Use• Diatomite (or diatomaceous earth) is a sedimentary rock

composed of fossilized diatom cell walls. Diatomite is used in cement, stucco, plaster and abrasives.

• Agar - a polysaccharide analogous to starch and cellulose that is used in the microbiology laboratory to grow bacteria.

Protista Reproduction- Some protists carry out conjugation, a primitive form

of sexual reproduction.

- Algal life cycles include gametic, zygotic, and sporic types (See Life Cycles Slide Show). In many cases, however, asexual reproduction (by cell division, fragmentation of filaments, or mitospores) is more common than sexual reproduction.

The Kingdom Plantae (The Land Plants) Evolved from Protists

From an evolutionary perspective, red algae

and/or green algae gave rise to the land

plants (The Kingdom

Plantae).

A great wealth of molecular data support the idea that red algae, green algae, and land plants belong in the same clade. Biologist have long suspected – on the basis of cellular details, biochemistry, life cycles, and morphology – that green algae gave rise to land plants. Analyses of proteins and nucleic acids have provided overwhelming support for this suspicion and also showed that red algae belong in this clade. So are red algae and green algae, protists or plants? Maybe both or somewhat in between.

BIO 141 Botany with Laboratory

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