Eukaryotes: Classification, Reproduction, and Distribution

1. Chapter 12, Part A Characterizing and Classifying Eukaryotes

2. Eukaryotes • Four major groups • Protozoa • Fungi • Algae • Water Molds and Slime Molds • Include both human pathogens and organisms vital for human life

3. 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

4. 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

5. Cytokinesis (Cytoplasmic Division) • Typically occurs simultaneously with telophase of mitosis • In some algae and fungi, may be postponed or not occur at all • Results in multinucleated cells called coenocytes

6. Cytokinesis (Cytoplasmic Division) Figure 12.2a

7. Cytokinesis (Cytoplasmic Division) Figure 12.2b

8. Cytokinesis (Cytoplasmic Division) Figure 12.2c

9. Classification of Eukaryotic Organisms Figure 12.4

10. 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

11. 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

12. 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 • Variety in number and kinds of mitochondria • Some have contractile vacuoles • All produce trophozoites; some produce cysts

13. Contractile Vacuole Figure 12.5

14. 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

15. 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

16. Fungi • Chemoheterotrophic • Have cell walls typically composed of chitin • Lack chlorophyll; do not perform photosynthesis • Related to animals

17. 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

18. Fungal Morphology Figure 12.14a

19. Fungal Morphology Figure 12.14b

20. Fungal Morphology Figure 12.14c

21. Fungal Morphology Figure 12.15

22. Nutrition of Fungi • Acquire nutrients by absorption • Most are saprobes • Some trap and kill microscopic soil-dwelling nematodes • Haustoria allow some to derive nutrients from living plants and animals • Most are aerobic; some are anaerobic; many yeasts are facultative anaerobes

23. Reproduction of Fungi • All have some means of asexual reproduction involving mitosis and cytokinesis • Most also reproduce sexually

24. Asexual Spores of Molds Figure 12.17a

25. Asexual Spores of Molds Figure 12.17c

26. Subgroups Within the Fungi • Division Zygomycota • Division Ascomycota • Division Basidiomycota • Deuteromycetes

27. Division Zygomycota Figure 12.19

28. Division Ascomycota Figure 12.21

29. Division Basidiomycota Figure 12.23

30. Deuteromycetes • Contains heterogeneous collection of fungi who sexual stages are unknown

31. 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

32. 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

33. 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)

34. 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

35. Classification of Various Algae Table 12.4

36. Red Algae Figure 12.27

37. Diatom Figure 12.28

38. Brown Algae Figure 12.29

39. 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