AP Biology

Lecture #47Protists

Protist Systematics & Phylogeny, I

• 1- Groups lacking mitochondria; early eukaryotic link; Giardia (human intestinal parasite; severe diarrhea); Trichomonas (human vaginal infection)

• 2- Euglenoids; autotrophic & heterotrophic flagellates; Trypanosoma (African sleeping sickness; tsetse fly)

Protozoans• Phylum Flagellates

– Flagellates have a small number of long flagella, long whiplike hairs that beats to propel the cell.

– Trypanosoma, Giardia, etc.– Some nasty parasites are flagellates, including

Giardia lamblia, which causes diarrhea and which is found in most of the surface waters of the US. Another is Trypanosoma brucei, which causes sleeping sickness in Africa. Also Trichmonas vaginalis, a sexually transmitted disease.

Protist Systematics & Phylogeny, II• Alveolata: membrane-bound

cavities (alveoli) under cell surfaces; dinoflagellates (phytoplankton); Plasmodium (malaria); ciliates (Paramecium)

Protozoans• Phylum Ciliates

– Cell covered by 1000s of tiny cilia– Swim by waving cilia. The cilia beat in a

synchronized pattern to cause movement.– Genetics: the DNA used for sexual

reproduction is stored in the small micronucleus. A copy of this information is used to run the cell: the copy is kept in the much larger macronucleus.

– Paramecium is a typical ciliate. It has a gullet to swallow food, and a contractile vacuole to get rid of excess water.

Protist Systematics & Phylogeny, III• Stamenophila: water molds/mildews

and heterokont (2 types of flagella) algae; numerous hair-like projections on the flagella; most molds are decomposers and mildews are parasites; algae include diatoms, golden, and brown forms

Protist Systematics & Phylogeny, IV

• Rhodophyta: red algae; no flagellated stages; phycobilin (red) pigment

• Chlorophyta: green algae; chloroplasts; gave rise to land plants; volvox, ulva

The second unicellular algae, Bacillariophyta, are photosynthetic autotrophs.

They have shells of silica. They make up a large portion of the world’s

phytoplankton which is Earth’s largest provider of oxygen.

Algae:

Phylum Diatoms Other photosynthetic

pigments Cells walls of silica

(silicon dioxide), finely ornamented

Variety of shapes

The third unicellular algae, Dinoflagellata, are a major component of marine phytoplankton.

These algae have at least two flagella set at right angles to each other and thick cell walls made of cellulose plates.

Blooms of dinoflagellates cause “Red Tide.”

Multicellular Algae The multicellular algae are commonly

called seaweed. They can be classified into red, brown, and green algae. All have chloroplasts, but the pigments in the chloroplasts vary, giving the different colors.

Some, like kelp, are very large and contain several different types of cells and tissues to do specialized work. These include leaves for photosynthesis, gas-filled bladders for buoyancy, the root-like holdfast, and tubes to transport nutrients throughout the body.

Algae contain the polysaccharide “agar”, which is tasteless and is used to thicken foods such as soft ice cream.

Phylum Phaeophyta is made up of the brown algae. They are found in cool saltwater along rocky coasts. Giant Kelp are the largest and most complex brown algae. They

have hold fasts and air bladders.

Protist Systematics & Phylogeny, V

• Affinity uncertain:• Rhizopods: unicellular with

pseudopodia; amoebas• Actinopods: ‘ray foot’ (slender

pseudopodia; heliozoans, radiolarians

Protozoans

• Phylum Amoeboids– Movement by cytoplasmic

streaming (Move by extensions of the cell membrane and cytoplasm called pseudopods or “False Feet”).

– Usually no fixed shape– Amoeba, – Foraminferans

• calcium carbonate shells

Protist Systematics & Phylogeny, VI

• Mycetozoa: slime molds (not true fungi); use pseudopodia for locomotion and feeding; plasmodial and cellular slime molds

Slime MoldsSlime molds have traits like both fungi and animals. During good times, they live as independent, amoeba-like cells, dining on fungi and bacteria. But if conditions become uncomfortable—not enough food available, the temperature isn't right, etc.—individual cells begin gathering together to form a single structure. The new communal structure produces a slimy covering and is called a slug because it so closely resembles the animal you sometimes see gliding across sidewalks. The slug oozes toward light. When the communal cells sense that they've come across more food or better conditions, the slug stops

Slime molds

Slime molds obtain food through decomposition of organic material

This is a slime mold--> commonly found on grass. It’s called the dog vomit slime mold – eewww, gross!

Water molds from the Phylum Oomycota are classified as protists because they have flagellated reproductive cells.

Downy mildews parasitize plants and are decomposers in freshwater ecosystems.

Isogamy = male and female gamete identical in size

“cloning” – plants identical to each other

Sexual reproduction- create variation

Protist Diversity• Parasitic & pathogenic Protists– malaria– Giardia– trypanosomes

Plasmodium

Giardia

Trypanosoma

Protozoans• Phylum Apicomplexans

– Sporozoans are animal-like protists that have part of their life cycle inside the cells of their hosts. Non-motile

– Parasites that feed on the cells and fluids of a host animal.

– They reproduce and spread by spores.– Obligate parasites

• Plasmodium causes malaria• Toxoplasma in cats

Protist Diversity• Beneficial & necessary Protists– phytoplankton• small algae + diatoms• much of the world’s photosynthesis• produces ~90% of atmospheric oxygen

– zooplankton• heterotrophic protists + animals• key ecological role at base of

marine food web

Mmmmmm!Sounds like breakfast!