Algae and Protist Biology PDF

## Green Algae - Green algae are named for their grass-green chloroplasts (chlorophylls a, b). - Plants are descended from green algae. - The two main groups are chlorophytes and charophyceans. - Chlorophytes include unicellular, colonial, and multicellular forms. ## Red Algae and Green Algae - Re...

## Green Algae - Green algae are named for their grass-green chloroplasts (chlorophylls a, b). - Plants are descended from green algae. - The two main groups are chlorophytes and charophyceans. - Chlorophytes include unicellular, colonial, and multicellular forms. ## Red Algae and Green Algae - Relatives of Land Plants - Red algae and green algae are the closest relatives of land plants. - Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont. - The photosynthetic descendants of this ancient protist evolved into red algae, green algae, and glaucophytes. - Land plants are descended from green algae relatives that evolved from the cyanobacterial endosymbiont protist. - Archaeplastida is a supergroup used by some scientists that includes red algae, green algae, charophytes, glaucophytes, and land plants. ## Life Cycle: Porphyra This image depicts a life cycle diagram of a red alga, *Porphyra*, with labels indicating: - **Sporophyte (2n)**: The diploid generation (has two sets of chromosomes). - **Zygote (2n)**: The product of fertilization; a diploid cell formed by the union of two gametes. - **Meiosis**: The process by which a diploid cell divides into four haploid cells (n). - **Germinating Spore (n)**: A haploid cell produced by meiosis that can develop into a new organism. - **Gametophyte (n)**: The haploid generation (has one set of chromosomes). - **Male Gametes**: Haploid sperm cells. - **Female Gametes**: Haploid egg cells. - **Fertilization**: The fusion of a male and female gamete to form a zygote. The diagram exhibits these stages clearly, suggesting that *Porphyra* undergoes an alternation of generations, a common reproductive cycle in plants and some algae. ## Red Algae - Red algae are reddish in color due to the accessory pigment called phycoerythrin, which masks the green of chlorophyll. This allows them to absorb blue light and reflect and transmit red light. - Their color varies from greenish-red in shallow water to dark red or almost black in deep water. - Red algae are usually multicellular; the largest are seaweeds. - Red algae are the most abundant large algae in coastal waters of the tropics. ## Forams - Foraminiferans, or forams, are named for their porous, generally multi-chambered shells, called **tests** made of calcium carbonate. - Pseudopodia extend through the pores in the test. - Foram tests in marine sediments form an extensive fossil record. The image attached shows a micrograph of a foram, highlighting the multichambered test that gives these protists their name. ## Rhizarians - Rhizarians are a diverse group of protists defined by their DNA similarities. - DNA evidence supports Rhizaria as a monophyletic clade. - Amoebas move and feed by pseudopodia; some but not all belong to the clade Rhizaria. - Rhizarians include forams and radiolarians. This slide includes two micrographs labelled a and b, depicting a foram and a radiolarian, respectively. ## Radiolarians - Marine protists called radiolarians have tests fused into one delicate piece, usually made of silica like the diatoms. - Radiolarians use their pseudopodia to engulf microorganisms through phagocytosis. - The pseudopodia of radiolarians radiate from the central body. ## Oomycetes - Oomycetes include water molds, white rusts, and downy mildews. - They were once considered fungi based on morphological studies. - Most oomycetes are decomposers or parasites. - They have filaments (hyphae) that facilitate nutrient uptake convergently with fungi. - Their ecological impact can be great, as in *Phytophthora infestans* causing potato blight. ## Alternation of Generations - A variety of life cycles have evolved among the multicellular algae. - The most complex life cycles include an alternation of generations, the alternation of multicellular haploid and diploid forms. - Heteromorphic generations are structurally different, while isomorphic generations look similar. ## Diatoms - Diatoms are unicellular algae with a unique two-part, glass-like wall of hydrated silica. - Diatoms are a major component of phytoplankton and are highly diverse. - Diatoms usually reproduce asexually, and occasionally sexually. The image accompanying this text shows a diatom with the two-part glass-like wall that characterizes it. ## Ciliates - Ciliates, a large varied group of protists, are named for their use of cilia to move and feed. - They live as solitary cells in fresh water. - They have large macronuclei and small micronuclei and are relatively complex cells. - The micronuclei function during conjugation, a sexual process that produces genetic variation. - Conjugation is separate from reproduction, which generally occurs by binary fission within the same species. ## Brown Algae - Brown algae are the largest and most complex algae. - All are multicellular, and most are marine. - Brown algae include many species commonly called "seaweeds". - The algal body is plantlike but lacks true roots, stems, and leaves. - The rootlike holdfast anchors the stemlike stipe, which in turn supports the leaflike blades. ## Golden Algae - Golden algae are named for their color, which results from their yellow and brown carotenoids. - The cells of golden algae are typically biflagellated, with both flagella near one end. - All golden algae are photosynthetic, and some are also heterotrophic. - Most are unicellular, but some are colonial. ## Stramenopiles - The clade Stramenopila includes several groups of heterotrophs as well as certain groups of algae. - Most have a "hairy" flagellum paired with a "smooth" flagellum. The image accompanying this text shows a Stramenopile with a hairy flagellum and a smooth flagellum. ## Alveolata - Members of the clade Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane. - The function of the alveoli is unknown. - Alveolata includes the dinoflagellates, apicomplexans, and ciliates. ## Chromalveolates - Some data suggest that the clade Chromalveolata is monophyletic and originated by a secondary endosymbiosis event. - The proposed endosymbiont is a red alga. - This clade is controversial and includes the alveolates and the stramenopiles. ## Kinetoplastids - Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast. - They include free-living consumers of prokaryotes in freshwater, marine, and moist terrestrial ecosystems. - This group includes *Trypanosoma*, which causes sleeping sickness in humans. - Frequent changes in the surface protein prevent the host from developing immunity like in *Plasmodium* (malarial parasite). ## Euglenids - Euglenids have one or two flagella that emerge from a pocket at one end of the cell. - Some species can be both autotrophic and heterotrophic (mixotrophic) and contain chloroplasts. The image accompanying this text shows an Euglena with its flagella, eyespot, and chloroplasts. ## Euglenozoans - Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites. - The main feature distinguishing them as a clade is a spiral or crystalline rod of unknown function inside their flagella. - This clade includes the kinetoplastids and euglenids. ## Diplomonads and Parabasalids - **Diplomonads**: - Have two nuclei. - *Giardia intestinalis*. - **Parabasalids**: - Have undulating membranes. - *Trichomonas vaginalis*. This slide includes two micrographs, labelled a and b, depicting a diplomonad and a parabasalid, respectively. The micrographs highlight features that are characteristic of these groups: two nuclei in the diplomonad and undulating membranes in the parabasalid.