Chapter 20 The Diversity of Protists Learning Goals

. Describe what are protists . List and describe some of the major groups of protists What Are Protists?

. Most protists are single celled – Protists include any eukaryote that is not a plant, animal, or fungus – Most protists are single-celled and microscopic in size – Some are large aggregations or colonies of single-celled individuals; others are multicellular organisms Table 20-1 Table 20-1 What Are Protists?

. Protists use diverse modes of nutrition – They may ingest food – They may absorb nutrients from their surroundings – They may exhibit photosynthesis . Protists use diverse modes of nutrition – Protists that ingest food are typically predators –They use extensions of the cell membrane called pseudopods to surround and engulf prey items Pseudopods

Fig. 20-1 What Are Protists?

. Protists use diverse modes of nutrition (continued) – Protists that absorb nutrients directly from the surrounding environment are of two types –Free-living types in the soil that decompose organic dead matter –Parasites that live inside the bodies of other organisms, sometimes harming the host What Are Protists?

. Protists use diverse modes of nutrition (continued) – Some protists have photosynthetic organelles called chloroplasts – Photosynthetic protists are abundant in oceans, lakes, and ponds – They are free-floating – They sometimes live in mutually beneficial associations with other organisms: Solar energy captured by the protist is used by the host, which in turn shelters and protects the protist What Are Protists?

. Protists use diverse modes of nutrition (continued) – Photosynthetic protists are collectively known as algae – Single-celled, non-photosynthetic protists are collectively known as protozoa What Are Protists?

. Protists use diverse modes of reproduction – Most protists reproduce asexually by mitotic cell division – Some also reproduce sexually – Two individuals contribute genetic material to an offspring that is genetically different from either parent – Many protists reproduce asexually but adopt sexual reproduction during certain times of the year or under stressful circumstances (e.g., a crowded environment or a food shortage) What Are the Major Groups of Protists?

. Excavates have a feeding groove and lack mitochondria – They are named for the feeding groove, that gives the appearance of having been “excavated” from the surface of the cell – The two largest groups are the diplomonads and the parabasalids What Are the Major Groups of Protists?

. Excavates have a feeding groove and lack mitochondria (continued) – The diplomonads have two nuclei and move about by multiple flagella –The parasitic diplomonad Giardia found in freshwater streams infects human and other mammalian hosts, causing gastrointestinal disorders What Are the Major Groups of Protists?

. Excavates have a feeding groove and lack mitochondria (continued) –Giardia exist as cysts (a stage of their life cycle) in the feces of animals –When excreted, the cysts enter water systems and, if ingested, develop into adult diplomonads –In humans, the adults can cause severe diarrhea, dehydration, nausea, vomiting, and cramps Giardia: The Curse of Campers

Fig. 20-3 20.2 What Are the Major Groups of Protists?

. Excavates have a feeding groove and lack mitochondria (continued) – Parabasalids are anaerobic, flagellated protists named for the presence in their cells of a distinctive structure called the parabasal body – Parabasalids in the gut of termites digest the wood the termites eat – Another parabasalid, Trichomonas vaginalis, causes the sexually transmitted infection trichomoniasis in humans Trichomonas Causes a Sexually Transmitted Infection

Fig. 20-4 What Are the Major Groups of Protists?

. Euglenozoans have distinctive mitochondria – The folds of the inner membrane of their mitochondria appear like a stack of disks under the microscope – There are two major groups, the euglenids and the kinetoplastids Euglena, A Representative Euglenid

flagellum eyespot

contractile vacuole

stored food

nucleus

nucleolus

chloroplasts

Fig. 20-5 What Are the Major Groups of Protists?

. Euglenids are single-celled protists that live mostly in freshwater and swim by flagella –Some euglenids lack a rigid outer covering and move by wiggling, as well as by whipping their flagella –Some euglenids have a photoreceptor called an eyespot that, by shading light from only certain directions, allows the organism to determine the direction of light and move toward it for photosynthesis –Euglena is a photosynthetic representative 20.2 What Are the Major Groups of Protists?

. Euglenozoans have distinctive mitochondria (continued) – Kinetoplastids derive their name from the arrangement of their DNA into structures called kinetoplasts – A dangerous kinetoplastid is Trypanosoma, which is responsible for African sleeping sickness that is transmitted to humans by infected tsetse flies A Disease-Causing Kinetoplastid

Fig. 20-6 What Are the Major Groups of Protists?

. Stramenopiles include photosynthetic and nonphotosynthetic organisms – All members of the group have fine, hair-like projections on their flagella – Some are photosynthetic and some are not – Most are single-celled, but some are multicellular – There are three major stramenopile groups: the water molds, the diatoms, and the brown algae 20.2 What Are the Major Groups of Protists?

. The water molds, or oomycetes, are protists that are shaped as long filaments that aggregate to form cottony tufts – Many water molds are decomposers that live in water and damp soil – One species causes a disease in grapes known as downy mildew – Another oomycete has destroyed millions of avocado trees in California – Still another is responsible for late blight, a devastating disease of potatoes that caused the Irish potato famine in the mid-1800s A Parasitic Water Mold

Fig. 20-7 20.2 What Are the Major Groups of Protists?

. The diatoms are photosynthetic stramenopiles that produce protective shells of silica – These shells consist of top and bottom halves that fit together like a pillbox – Diatoms are found in fresh and saltwater – Accumulations of fossil deposits of diatoms form the “diatomaceous earth” used commercially as a mild abrasive – The diatoms form part of the phytoplankton, single-celled photosynthesizers that float passively in the Earth’s lakes and oceans Some Representative Diatoms

Fig. 20-8 What Are the Major Groups of Protists?

. The brown algae form a group of stramenopiles that have multicellular marine representatives known as seaweeds – Giant kelp from the Pacific Coast reach heights of 325 feet and can grow more than 6 inches in a single day Brown Algae, a Multicellular Protist

Fig. 20-9 What Are the Major Groups of Protists?

. Alveolates include parasites, predators, and phytoplankton – The alveolates are single-celled organisms that have distinctive, small cavities beneath the surface of their cells – The major alveolate groups are the dinoflagellates, apicomplexans, and ciliates What Are the Major Groups of Protists?

. The major alveolate groups are the dinoflagellates, apicomplexans, and ciliates (continued) – Dinoflagellates are photosynthetic and swim by means of two whip-like flagella –In large numbers they can cause “red tide,” which suffocates fish, and some produce a toxin that may be lethal to humans if dinoflagellate-infected mollusks are consumed Dinoflagellates

Fig. 20-10 A Red Tide caused by dinoflagellate

Fig. 20-11 What Are the Major Groups of Protists?

. All apicomplexans, also known as sporozoans, are parasitic, living inside bodies or cells of their hosts and lacking a means of locomotion What Are the Major Groups of Protists?

. A well-known apicomplexan is the malarial parasite Plasmodium – The Anopheles mosquito carries the parasite and passes it on to a human host – The protist develops in the victim’s liver, then enters the blood, where it reproduces rapidly in red blood cells – The release of large quantities of spores through the rupture of the blood cells causes the recurrent fever of malaria The Life Cycle of the Malaria Parasite

1 A female Anopheles mosquito bites an infected human and ingests (infected gametocytes, which become gametes human) female gametocyte

male salivary gametocyte glands male gamete

female gamete

2 Fertilization produces a zygote that enters the wall of the mosquito’s stomach

3 The zygote gives rise to sporozoites that migrate to the mosquito’s salivary glands

7 The synchronized rupture of red blood cells releases toxins and the parasites; some parasites infect more blood cells

6 Parasites multiply in the 8 Some parasites become red blood cells gametocytes, which may be ingested by another feeding Anopheles mosquito

4 The infected 5 Parasites mosquito bites an emerge from the uninfected human liver and enter and saliva containing red blood cells sporozites is injected; the sporozites enter the liver and develop through several stages

liver Fig. 20-12 20.2 What Are the Major Groups of Protists?

. The ciliates are the most complex of the alveolates, possessing many organelles, including cilia, that may cover the cell or be localized and that provide locomotion – Parameciumis is a freshwater species that has cilia over the entire cell surface – Didiniumis is a predatory ciliate 20.2 What Are the Major Groups of Protists?

. Amoebozoans inhabit aquatic and terrestrial environments; they feed and move by extending finger-shaped pseudopods – Amoebas are sometimes known as lobose amoebasto to distinguish them from other protists that have pseudopods – Amoebas are predatory and parasitic, the latter resulting in amoebic dysentery that leads to severe diarrhea An Amoeba

Fig. 20-16 20.2 What Are the Major Groups of Protists?

. Amoebozoans inhabit aquatic and terrestrial environments and feed by extending finger- shaped pseudopods (continued) – Slime molds are decomposers that inhabit the forest floor –They alternate between two phases: a mobile feeding stage and a stationary reproductive stage called a fruiting body 20.2 What Are the Major Groups of Protists?

. Slime molds are decomposers that inhabit the forest floor (continued) – Acellular slime molds form a multinucleate mass of cytoplasm called a plasmodium that engulfs bacteria and organic matter The Acellular Slime Mold Physarum

Fig. 20-17 The Life Cycle of a Cellular Slime Mold

1 When food becomes scarce, cells aggregate into a slug-like mass called a pseudoplasmodium

nucleus

fruiting bodies

3 Single, amoeba-like cells emerge from spores, 2 A pseudoplasmodium and crawl spores migrates toward light and and feed forms a fruiting body in which spores are produced

haploid (n)

Fig. 20-18 20.2 What Are the Major Groups of Protists?

. Red algae live primarily in clear tropical oceans – Red algae are multicellular, photosynthetic seaweeds that are almost exclusively marine – Their pigment, which can range in color from red to black, masks their green chlorophyll – They predominate in deep, clear waters, where their red pigments absorb the deeply penetrating blue-green light and transfer this light energy to chlorophyll for photosynthesis 20.2 What Are the Major Groups of Protists?

. Red algae live primarily in clear tropical oceans (continued) – Some species deposit calcium carbonate in their tissues and contribute to the formation of reefs – They contain gelatinous substances of commercial value, such as agar and carrageenan, and are major sources of energy for nonphotosynthetic organisms Red Algae

Fig. 20-19 Major Groups of Protists

. Green algae live mostly in ponds and lakes – These are photosynthetic protists that may be multicellular or unicellular – Some species, like Spirogyra, form thin filaments of long chains of cells –Volvoxis is a colonial green alga Green Algae

Fig. 20-20