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Eukrayotic cells are large, have a nucleus, contain membrane-bound organelles, and use a cytoskeleton The nucleus is the synapomorphy that unifies eukaryotes Endosymbiotic theory mitochondria arose from proteobacteria, and chloroplasts arose from cyanobacteria It is possible that the first eukaryotic cell was formed by an archaeal cell engulfing a bacterium Page 2
BIOLOGY - CLUTCH Secondary endosymbiosis organism engulfs photosynthetic eukaryotic cell, and retains chloroplast as an organelle Primary endosymbiosis explains the origin of chloroplasts in the Plantae lineage Secondary endosymbiosis accounts for the origin of chloroplasts in other eukaryotic lineages Protists encapsulate eukaryotes that do not belong to the clades Fungi, Animalia, and Plantae Protists are a group of convenience, and are not a monophyletic, but a paraphyletic group As a group, they have some shared features, but many protist species display unique characteristics Most protists are unicellular, but some are colonial or multicellular (brown algae, red algae, and slime molds) - Multicellularity arose independently in multiple eukaryotic lineages Most protists undergo asexual reproduction, which includes mitosis and cell division - Sexual reproduction was a major evolutionary development Many protists undergo some form of sexual reproduction Page 3
BIOLOGY - CLUTCH Protists as a group don t have unifying features, but some features are shared by many protists Multinucleated eukaryotic cells that contain more than one nucleus Many protists have cell walls, or shells, that serve as hard protective outer layers Flagella and cilia are used by many protists for locomotion Amoeboid movement common locomotion in eukaryotic cells, cytoplasmic protrusions form pseudopodia Many protists are predators, and consume their prey by phagocytosis, others use photosynthesis to obtain nutrients Phagocytosis form of ingestive feeding, pseudopodia surround prey and absorb it into the cell Decomposers absorb nutrients directly across the cell membrane via transport proteins Page 4
Alteration of generations life cycle in which both the haploid and diploid stages are multicellular Gametophyte haploid, multicellular stage of life cycle that produces gametes Sporophyte diploid, multicellular stage of life cycle that produces spores by meiosis - Spore unit of asexual reproduction, generally haploid and unicellular Heteromorphic sporophyte and gametophyte are structurally different Isomorphic sporophyte and gametophyte appear the same Page 5
Haploid dominant life cycle life cycle in which the zygote formed by the fusion of gametes is the only diploid phase Zygote undergoes meiosis producing haploid cells that reproduce asexually, or can form gametes via mitosis Diploid dominant life cycle life cycle in which the only haploid cells are the gametes formed by a mature cell via meiosis Zygote will form mature cell that can reproduce asexually via mitosis Unlike haploid dominant life cycle, the mature cells undergo meiosis, rather than the zygote Page 6
Excavata major subgroup of unicellular eukaryotes, many species lack mitochondria, most reproduce asexually Diplomonads lack mitochondria, contain reduced mitochondria lacking electron transport, anaerobic metabolism - Cells have 2 equal nuclei, and use flagella for locomotion - Many species are parasites, including Giardia intestinalis Parabasalids lack mitochondria, use flagella and undulate membrane to move, many species parasitic Euglenozoans earliest cells to contain mitochondria - Kinetoplastids large mitochondria, Tripanosoma causes sleeping sickness transmitted by tsete fly - Euglenids contain chloroplasts, some are photosynthetic and heterotrophic (mixotrophs) Archaeplastida (Plantae) major monophyletic group of eukaryotes that includes red and green algae, and land plants These organisms originate from protist that engulfed cyanobacterium via endosymbiosis Red algae mostly multicellular, some cells contain multiple nuclei, many reproduce via alteration of generations - Phycoerythrin photosynthetic pigment masks green from chlorophyll, red intensity correlates with depth Green algae structurally similar to land plants, similar composition of photosynthetic pigments - Charophytes algae most similar to land plants - Chlorophytes many unicellular and multicellular species, and have haploid dominant life cycle Page 7
BIOLOGY - CLUTCH SAR clade monophyletic supergroup that contains many photosynthetic organisms, and water molds Stramenopila and alveolates contain chloroplasts that likely originate from secondary endosymbiosis Stramenopila mostly photosynthetic algae, both unicellular and multicellular, contain flagella with hair-like projections Many species exhibit diploid dominant life cycles Diatoms unicellular, photosynthetic organisms encased in protective silicone dioxide covering - Responsible for much of Earth s photosynthesis, can have a significant effect on atmospheric carbon Golden algae contain yellow and brown carotenoids, some species are mixotrophs, most are unicellular Brown algae contain brown carotenoids, contain gas filled chambers in photosynthetic regions to float up - Reproduce via alteration of generations, both hetero- and isomorphic Alveolata have membrane-enclosed sacs (alveoli) right under plasma membrane Dinoflagellates mostly unicellular, aquatic organisms, enclosed by two cellulose plates - Have two flagella, one that projects outward, and another that runs around the groove in the plating - Roughly half are heterotrophic, and half phototrophic, though many of these are actually mixotrophic - Most have chromosomes that lack histones, and attach directly to the nuclear envelope (dinokaryon) Page 8
Apicomplexans all known species are parasitic, mostly to animals, cells lack cilia and flagella - Contain modified plastids (apicoplastid), likely from red algae - Life cycles involve sexual and asexual reproduction, and sometimes moving between species - Malaria caused by Plasmodium reproduces asexually and forms gametocytes in humans - Zygote formation and production of sporozoites occurs in mosquitos Page 9
Ciliates covered in cilia, use for movement and feeding, mostly by preying on bacteria - Diploid micronucleus only used for reproduction, polyploidy macronucleus used for transcription - Reproduce asexually by binary fission, and sexually through via their micronuclei Page 10
BIOLOGY - CLUTCH Rhizarians mostly unicellular amoebas that use pseudopodia Radiolarians contain internal silica skeletons, pseudopodia projections used for feeding on microorganisms Forams CaCO3 shells with holes through which pseudopodia emerge, some cells contain multiple nuclei Cercozoans amoeba and flagellated protists that feed with thin pseudopods Opisthokonta group of eukaryotes that includes fungi and animals Amoebozoa amoebas with lobe and tube shaped pseudopodia Amoeba simply refers to an organism that changes its shape by extending and retracting pseudopodia Plasmoidal slime mold massive continuous cells containing thousands of nuclei, forms fruiting bodies Cellular slime mold slime mold that forms aggregates of cells to form fruiting bodies Page 11