Chapter 12,

Characterizing and Classifying Eukaryotes

Eukaryotes

" Four major groups

" Protozoa

" Fungi

" Algae

" Walter Molds and Slime Molds

" Include both human pathogens and organisms vital for human life

Reproduction in Eukaryotes

" More complicated than that in prokaryotes

" Eukaryotic DNA packaged with histones as chromosomes in the nucleus

" Have variety of methods of asexual reproduction (budding, fragmentation, spore formation, and schizogony)

" Many reproduce sexually by forming gametes and zygotes

" Algae, fungi, and some protozoa reproduce sexually and asexually

Nuclear Division

" Nucleus has one or two complete copies of genome

" Single copy – haploid (most fungi, many algae, some protozoa)

" Two copies – diploid (remaining fungi, algae, and protozoa)

" Two types

" Mitosis

" Meiosis

Mitosis

" Begins after cell has duplicated its DNA; cell partitions replicated DNA equally between two nuclei

" Maintains ploidy of parent nucleus

Meiosis

" Nuclear division involving partitioning of chromatids into four nuclei

" Diploid nuclei use meiosis to produce haploid daughter nuclei for sexual reproduction

Schizogony

Classification of Eukaryotic Organisms

Protozoa

" Diverse group defined by three characteristics

" Eukaryotic

" Unicellular

" Lack a cell wall

" With exception of apicomplexans, they are also motile by means of cilia, flagella, and/or pseudopodia

Distribution of Protozoa

" Require moist environments

" Most live worldwide in ponds, streams, lakes, and oceans; critical members of plankton

" Some live in moist soil, beach sand, and decaying organic matter

" Very few are pathogens, but are major causes of disease.

Morphology of Protozoa

" Characterized by great morphologic diversity

" Some have two nuclei

" Macronucleus contains many copies of genome – controls metabolism, growth, and sexual reproduction

" Micronucleus – involved in genetic recombination, sexual reproduction, and regeneration of macronuclei

" All produce trophozoites; some produce cysts

Nutrition of Protozoa

" Most are chemoheterotrophic

" Obtain nutrients by phagocytizing bacteria, decaying organic matter, other protozoa, or the tissues of host

" Few absorb nutrients from surrounding water

" Dinoflagellates and euglenoids are photoautrophic

Reproduction in Protozoa

" Most reproduce asexually only (binary fission or schizogony)

" Few also have sexual reproduction

" Some become gametocytes that fuse to form diploid zygote

" Some utilize a process called conjugation

Fungi

" Chemoheterotrophic

" Have cell walls typically composed of chitin

" Lack chlorophyll; do not perform photosynthesis

" Related to animals genomically, but cell wall is major difference.

Significance of Fungi

" Decompose dead organisms and recycle their nutrients

" Form beneficial associations with roots of vascular plants that help plant absorb water and minerals

" Used for food, in religions ceremonies, and in manufacture of foods and beverages

" Produce antibiotics

" Important research tools

" 30% cause diseases of plants, animals, and humans

" Can spoil fruit, pickles, jams, and jellies

Nutrition of Fungi

" Acquire nutrients by absorption

" Most are saprobes

" Some trap and kill microscopic soil-dwelling nematodes

" Most are aerobic; some are anaerobic; many yeasts are facultative anaerobes

Reproduction of Fungi

" All have some means of asexual reproduction involving mitosis and cytokinesis

" Most also reproduce sexually

Budding and Asexual Spore Formation

" Yeasts bud in manner similar to prokaryotic budding

" Pseudohypha – series of buds that remain attached to one another and to parent cell

" Filamentous fungi produce lightweight spores that differ in mode of development

Lichens

" Partnerships between fungi and photosynthetic microbes (green algae or cyanobacteria)

" Abundant throughout the world, particularly in pristine habitats

" Grow on soil, rocks, leaves, tree bark, other lichens, and even on backs of tortoises; almost every habitat

" Occur in three basic shapes – crusts, foliose, fruticose

" Important in creation of soil from rocks

" Eaten by many animals

Algae

" Simple, eukaryotic, phototrophic organisms that carry out oxygenic photosynthesis using chlorophyll a

" Have sexual reproductive structures; every cell becomes a gamete

" Differ widely in distribution, morphology, reproduction, and biochemical traits

Distribution and Morphology of Algae

" Most are aquatic, living in the photic zone of fresh, brackish, and salt water

" Have accessory photosynthetic pigments that trap energy of light and pass it to chlorophyll a

" Unicellular, colonial, or have simple multicellular bodies (thalli)

Reproduction in Algae

" Asexual reproduction in unicellular algae involves mitosis followed by cytokinesis

" Unicellular algae that reproduce sexually form zygotes from individual gametes; zygote undergoes meiosis

" Multicellular algae reproduce asexually by fragmentation

" Many multicellular algae reproduce sexually with alternation of generations

Water Molds

" Differ from fungi in the following ways

" Have tubular cristae in their mitochondria

" Cell walls of cellulose instead of chitin

" Spores have two flagella – one whiplike and one tinsel-like

" Have true diploid thalli

Water Molds

" decompose dead material

" recycle nutrients into the environment

" pathogens of crops

" cause of Irish potato famine

Slime Molds

" Differ from fungi in two main ways

" Lack cell walls

" Nutrition is phagocytic rather than absorptive

" Two groups – plasmodial (acellular) and cellular slime molds

Parasitic Helminths and Vectors

" Parasitic worms have microscopic infective and diagnostic stages – usually eggs or larvae

" Vectors are animals such as ticks, lice, and mosquitoes that carry and transmit microscopic pathogens

MORE TO COME IN CHAP 23!