Chapter 28 Protists

Ancestors to modern protists, plants, animals and fungi. Oldest known are 2.1 billion years old (acritarchs). – Most DIVERSE eukaryotes – Most are unicellular – Most use cellular respiration – Fall into 3 nutritional groups: ingestive (animal like), absorptive (fungus like) and photosynthetic (plant like) – Most are motile with cilia or flagella – Vary in reproductive/life cycles (some asexual, some sexual)

Evolution of Eukaryotic Cell SYMBIOSIS: mitochondria and chloroplasts were originally small prokaryotes in larger cells (serial endosymbiosis theory)

Phylogeny: Difficult to classify 1. Archaezoa: lack mitochondria – Question: Does their ancestry precede mitochondrial evolution??? – 3 subgroups: diplomonads, trichomonads, microsporidians

2. Euglenozoa: flagellates – Euglenoids: characterized by anterior pocket from which flagella emerge, mostly autotrophic – Kinetoplastids: single large mitochondrion and kinetoplast housing extranuclear DNA Ex. African tse tse fly: spreads Trypanosoma that causes African sleeping sickness.

3. Alveolata: small membrane bound cavities (alveoli) under cell surfaces. – Dinoflagellates: component of plankton found near the water surface, most are unicellular, perpendicular flagella causes spinning motion, episodes of population growth called blooms – cause red tides that may be toxic. (fish kill) – Apicomplexans: animal parasites. Ex. Plasmodium: causes malaria – Ciliates: uses cilia to move and feed, live along in fresh water. Cilia may cover all of cell or may be clustered. Two types of nuclei: 1 macronucleus that divides by binary fission and micronuclei that combine by SYNGAMY (union of two gametes) for genetic variation.

Misc protists: – Rhizopods (amoebas): pseudopodia – Actinopods (helizoans): axopodia – Foraminiferans: marine, porous shell – Plasmoidial slime molds – Cellular slime molds

Stramenophilia Photosynthetic autotrophs and hetertrophs – Diatoms: yellow and brown, glasslike silica walls, reproduce asexually, live in plankton – Golden algae: yellow and brown carotene and xanophyll, biflagellated, live in plankton – Oomycota: water molds – Brown algae: multicellular, marine, brown pigments SEAWEEDS: Thallus (Plantlike body), holdfast (rootlike), stipe (stemlike) and blades (leaflike) Alternation of generations: diploid sporophyte releases haploid spores that develop into gametophyte, produces gametes that unite to make zygote that turns into diploid sporophyte.

Rhodophyta Red Algae: no flagella, many different pigments, most abundant in tropical oceans, alternation of generations is common

Green Algae Green chloroplasts, common ancestor with plants, mostly freshwater Form “pond scum” Most produce sexually