28 Protists

Living Small Even a low-power microscope can reveal a great variety of organisms in a drop of pond water Protist is the informal name of the group of mostly unicellular eukaryotes Advances in eukaryotic systematics have caused the classification of protists to change significantly

Concept 28.1: Most eukaryotes are single-celled organisms Protists are eukaryotes Eukaryotic cells have organelles and are more complex than prokaryotic cells It is important to bear in mind that The organisms in most eukaryotic lineages are protists, and Most protists are unicellular

Protists, the most nutritionally diverse of all eukaryotes, include Photoautotrophs, which contain chloroplasts Heterotrophs, which absorb organic molecules or ingest larger food particles Mixotrophs, which combine photosynthesis and heterotrophic nutrition

Mitochondria and plastids are derived from prokaryotes that were engulfed by the ancestors of early eukaryotic cells Mitochondria evolved once by endosymbiosis of an alpha proteobacterium Plastids evolved later by endosymbiosis of a photosynthetic cyanobacterium The plastid-bearing lineage of protists evolved into photosynthetic protists, red and green algae

Membranes are represented as dark lines in the cell. Figure 28.3 Dinoflagellates Membranes are represented as dark lines in the cell. Secondary endosymbiosis Red alga Cyanobacterium Plastid 1 2 3 Primary endosymbiosis Stramenopiles Nucleus Secondary endosymbiosis Plastid Heterotrophic eukaryote One of these membranes was lost in red and green algal descendants. Figure 28.3 Diversity of plastids produced by endosymbiosis Euglenids Secondary endosymbiosis Green alga Chlorarachniophytes

Red Algae Red algae are reddish in color due to an accessory pigment called phycoerythrin, which masks the green of chlorophyll Red algae are usually multicellular; the largest are seaweeds Red algae are the most abundant large algae in coastal waters of the tropics Plants are descended from the green algae

► Bonnemaisonia hamifera Figure 28.21 ► Bonnemaisonia hamifera 20 cm 8 mm ◀ Dulse (Palmaria palmata) ▼ Nori Figure 28.21 Red algae

Similarities and Differences in the Protist Kingdom All are eukaryotes (cells with nuclei). Live in moist surroundings. Unicellular or multicellular. Autotrophs, heterotrophs, or both. Some can move - others cannot.

Three categories of Protists: Animal- Like Plant – Like Fungus -like

Animal-like Protists (Protozoans) Unicellular Heterotrophs Four groups based on movement: Pseudopods: False feet zooflagelletes: Have flagella Ciliates: Have cilia Sporozoans: Mostly parasitic

Pseudopods Reproduce by mitosis Contractile vacuole - collects extra H2O & expels it from cell Thin cell membrane and no definite shape. E.g Amoeba Form pseudopods to surround & trap food. Then form a food vacuole to break down food in the cytoplasm.

Pseudopods also called ‘false feet’ Cell membrane pushes in one direction & the cytoplasm flows into the bulge. This allows the protozoan to move, dragging the rest of the cell behind it. Pseudopod Movement PUSH FLOW DRAG

Ciliates Cilia - hairlike structures - help organisms move, get food and sense environment. Multicellular with 2 nuclei. 1 nuclei controls everyday functions and 1 nuclei is for reproduction. Reproduce by mitosis or conjugation. Oral groove lined with cilia - moves H20 containing food into food vacuole at end of oral groove. Food vacuole breaks down food and sends through cell. Anal pore sends out waste. Example of protozoan w/ cilia: paramecium.

(a) Feeding, waste removal, and water balance. Figure 28.17a Contractile vacuole Oral groove Cell mouth Cilia 50 μm Micronucleus Food vacuoles Macronucleus Figure 28.17a Structure and function in the ciliate Paramecium caudatum (part 1) (a) Feeding, waste removal, and water balance.

The original macro- nucleus disintegrates. Diploid micronucleus Figure 28.17b-2 Compatible mates Conjugation Asexual reproduction MEIOSIS Haploid micronucleus Diploid micronucleus The original macro- nucleus disintegrates. Diploid micronucleus MICRO- NUCLEAR FUSION Figure 28.17b-2 Structure and function in the ciliate Paramecium caudatum (part 2, step 2) (b) Conjugation and reproduction.

zooflagellates Use long whiplike part called flagella to move. These usually live inside other organisms.

Sporozoans Mostly parasites Feed on cells & body fluids of hosts Sporozoans like Plasmodium (causes malaria) have more than 1 host: mosquitoes and then humans

Funguslike Protists Like animals, they are heterotrophs Like plants, they have cell walls Reproduce by spores (tiny cells that can grow into a new organism) Not in fungi kingdom because they can move at one point in their lives. Example are water or slime molds.

Plantlike Protists Better known as algae Autotrophs Size: unicellular to very large Contain different pigments so they come in different colors. Euglena: special type of algae -when there is no sunlight they become heterotrophic.

Concept 28.6: Protists play key roles in ecological communities Protists are found in diverse aquatic and moist terrestrial environments Protists play two key roles in their habitats: that of symbiont and that of producer Some protist symbionts benefit their hosts Dinoflagellates nourish coral polyps that build reefs Wood-digesting protists inhabit the gut of termites

Some protists are parasitic Plasmodium causes malaria Pfiesteria shumwayae is a dinoflagellate that causes fish kills Phytophthora ramorum causes sudden oak death P. infestans causes potato late blight, which contributed to the Irish famine of the 19th century

Photosynthetic Protists Many protists are important producers that obtain energy from the sun In aquatic environments, photosynthetic protists and prokaryotes are the main producers In aquatic environments, photosynthetic protists are limited by nutrients These populations can explode when limiting nutrients are added

Prokaryotic producers Figure 28.29 Other consumers Herbivorous plankton Carnivorous plankton Figure 28.29 Protists: key producers in aquatic communities Prokaryotic producers Protistan producers

Biomass of photosynthetic protists has declined as sea surface temperature has increased Growth of phytoplankton communities relies on nutrients delivered from the ocean bottom through the process of upwelling Warm surface water acts as a barrier to upwelling

If sea surface temperature continues to warm due to global warming, this could have large effects on Marine ecosystems Fishery yields The global carbon cycle

Fungi Kingdom

Nutrition and Ecology Fungi are heterotrophs and absorb nutrients from outside of their bodies Fungi use enzymes to break down a large variety of complex molecules into smaller organic compounds The versatility of these enzymes contributes to fungi’s ecological success

Fungi exhibit diverse lifestyles Decomposers: Fungi are efficient decomposers of organic material including cellulose and lignin. They perform essential recycling of chemical elements between the living and nonliving world. Mutualists: Fungi form mutualistic relationships with plants, algae, cyanobacteria, and animals. They help break down plant material in the guts of cows and other grazing mammals. Many species of ants use the digestive power of fungi by raising them in “farms” Parasites: Each year, 10% to 50% of the world’s fruit harvest is lost due to fungi. Some fungi that attack food crops are toxic to humans

(b) Tar spot fungus on maple leaves Figure 31.24 (b) Tar spot fungus on maple leaves Figure 31.24 Examples of fungal diseases of plants (a) Corn smut on corn (c) Ergots on rye

Eukaryotes Use spores to reproduce Heterotrophs that feed on other organic matter like plants Need warm, moist places to grow Examples: yeast, molds, mildew, and mushrooms

Fungi –Method of Nutrition Use a structure called hyphae to get their food, except yeast Hyphae: threadlike, cytoplasm-filled tubes with nuclei Shape of fungi depends on how hyphae is used. The fungal hyphae grows into food then secrete digestive chemicals into food & absorb it Stolons – horizontal hyphae Rhizoids- hyphae forming rootlike structures

Reproduction in Fungi Produce thousands of spores with a protective covering: carried by water and air. spores land in a warm, moist place they form more fungi When there is plenty of moisture, fungi reproduce asexually by releasing spores. When conditions are not good, they reproduce sexually.

YEAST: Yeast are unicellular, they reproduce by budding. A well fed cell grows from the body of the mother cell and breaks off from the mother.

Practical Uses of Fungi Humans eat many fungi and use others to make cheeses, alcoholic beverages, and bread Some fungi are used to produce antibiotics for the treatment of bacterial infections For example, the ascomycete Penicillium

Genetic research on fungi is leading to applications in biotechnology For example, scientists are using Saccharomyces to study homologs of the genes involved in Parkinson’s and Huntington’s diseases Insulin-like growth factor can be produced in the fungus Saccharomyces cerevisiae Gliocladium roseum, a fungus that produces hydrocarbons similar to diesel fuel, could be used to produce biofuels