Protists (Protistans) and Life cycles

1. Protists(Protistans) and Life cycles Protists are generally unicellular, but sometimes multicellular species. Most live in water, or places that have a watery film. Protists are all eukaryotic, their DNA is enclosed in a nucleus inside the cell unlike bacteria, which, whilst unicellular, are prokaryotic and have no nucleus to enclose their DNA. Some protists are heterotrophs, some are autotrophs and a few species are both! Protists are usually grouped into three subcategories: plant-like protists, animal-like protists , and fungus-like protists.

2. A Basic Life Cycle Structure Mitosis Spores n Gametes (?) Meiosis Fusion (syngamy) Zygote 2n Mitosis HAPLOID DIPLOID Is this what humans do? No, I don’t think so.

3. Plant-like Protists (Algae) 6 phyla Plant-like Protists (Algae) 6 phyla s shields the photoreceptor Red spot Cyclotella stelligera 1. Euglenas (Euglenophyta) Some are autotrophs when sunny and heterotrophs when dark. Unicellular, found mostly in fresh water. Some have a flagella 2. Diatoms (Chrysophyta) Examples in the lab. Fig 23.16c in text book Diatoms make 20% to 25% of global organic carbon fixation.

4. 3. Dinoflagellates (Pyrrophyta) Protoperidinium steinii Ulva on the sea shore Ocean dwelling, unicellular, covered by stiff plates, two flagella, bioluminescent (biochemical reaction to oxygen). Fig 23.17 of text book. 4. Green Algae (Chlorophyta) Mostly unicellular, but some form colonies, and a few are multicellular. Live in fresh water, salt water, and a few live on land. Fig 23.21 of text book

5. Chlamydomonas Dormant Chlorella nivalis Flagella are ~10 microns long. Generation time is ~5 hours The red “resting” stage

6. Life cycle of Chlamydomonas A thick-walled resistant zygote develops. Zygote (cross-section) More spores are produced. More spores are produced. + – + Gametes of different mating types meet – Diploid Stage Nuclear Fusion Meiosis and Germination Haploid Stage Haploid cell (- strain) Haploid cell (+ strain) Mitosis occurs. Whether the resulting cells develop into spores or gametes depends on environmental conditions. SEXUAL REPRODUCTION: Mainly when nitrogen levels are low and light is of a certain quality and intensity, the cells develop into gametes. Cytoplasmic Fusion ASEXUAL REPRODUCTION isogamy Page 389 Fig 23.22

7. What is different about the Chlamydomonas life cycle compared to the basic life cycle? One difference two important features and Prizes! Prizes! Prizes! Prizes!

8. Important life cycle features of Chlamydomonas Mitosis Spores n Gametes (?) Mitosis HAPLOID Meiosis Fusion (syngamy) DIPLOID Zygote 2n Mitosis “Sexual” reproduction induced by environmental conditions + and - gametes look the same In Chlamydomonas the diploid phase is a “resting” stage – no mitosis of the diploid phase

9. The life cycle of Ulva How does this suit Ulva’s niche? Important Feature Both the spores and the zygote develop into a multicellular thallus

10. What’s the function of sexual reproduction? Don’t tell me that’s all there is to sex! Sure … it does just fine for Chlamydomonas and Ulva Sexual reproduction introduces variations in the details of traits among offspring. This variation is the FEEDSTOCK of natural selection • Differentiation of the sexes is a characteristic that enables specialization in: • Ensuring fertilization • (b) Producing and distributing successful progeny In some plant types producing and distributing large numbers is achieved by spores

11. Alternation of Generations The occurrence within the life cycle of an organism of two or more distinct forms (generations), which differ from each other in appearance, habit, and method of reproduction. The phenomenon occurs in some protists, certain lower animals (e.g. parasitic flatworms), and in plants. The malaria parasite (Plasmodium), for example, has a complex life cycle involving the alternation of sexually and asexually reproducing generations.  In plants the generation with sexual reproduction is called the gametophyte and the asexual generation is the sporophyte, either of which may dominate the life cycle, and there is also alternation of the haploid and diploid states.

12. 5. Red Algae (Rhodophyta) Porphyraspecies The pigment phycoerythrin reflects red light and absorbs blue. Blue light penetrates water to a greater depth than light of longer wavelengths and so these pigments allow red algae to photosynthesize and live at somewhat greater depths than most other "algae".Fig 23.18 of text book. 6. Brown Algae (Phaeophyta) Large leaf-like structures called blades and frequently air-filled sacs called air bladders and root-like structure called a holdfast. Not closely related to land plants. Cells contain pigments such as chlorophyll c and fucoxanthin. They also lack plasmodesmata and starch production.Fig 23.20 of text book. Alginic acid: used in toothpastes, soaps, ice cream, tinned meats, fabric printing. It forms a stable viscous gel in water, and is as a binder, stabilizer, emulsifier, or moulding agent. Ascophyllum nodosum

13. Life cycle of Porphyra Diploid thallus and haploid thallus have different morphology, size and habitat gametes and + are different in size and morphology 10 cm How does this life cycle differ from that of Ulva? sporophyte (2n) zygote Diploid Stage Fertilization Meiosis Haploid Stage germinating spore (n) male gametes female gametes gametophyte (n) Fig 23.19 Page 386

14. Animal-like Protists (Protozoa) - 4 phyla Amoeba Image by Arturo Gonzalez, CINVESTAV, Mexico 1. Sarcodines (Sarcodina) Food is surrounded by pseudopods and stored in a food vacuole 2. Flagellates (Mastigophora) Parasite causing gasteroenteritis. Giardia lamblia trophozoites, are released from cysts by contact with stomach acids and attach to the epithelium of the small intestine. Scanning electron microscope photograph. 

15. 3. Ciliates (Ciliophora) 4. Apicomplexa (Sporozoa) Parasites! Plasmodium - malaria Oocysts: mosquito midgut Sporozoites Merozoite: in a red blood cell These protists move by beating cilia that also help it capture food.Paramecium is an example Named for a complex of organelles located at the apex of the cell used to break through tissues and cells of the host. Sexual and asexual stages and often need two or more hosts to complete life cycle.

16. Fungus-like Protists 1. Water Molds & Mildews (Oomycota) Saprolegnia mixta- Saprophytes and parasites. "Oomycota" means "egg fungi," and refers to the large round oogonia, or structures containing the female gametes, (picture)

17. Slime moulds have structural adaptations Slime moulds have structural adaptations and life cycles that enhance their ecological role as decomposers http://www.hiddenforest.co.nz/slime/intro.htm Clive Shirley 2 - Plasmodial slime moulds or true slime moulds, are a large single-celled mass with thousands of nuclei called a plasmodium formed when individual flagellated cells swarm together and fuse into one large bag of cytoplasm with many diploid nuclei.

18. Characteristics of Dictyostelium 3 - Cellular slime moulds spend most of their lives as separate single-celled amoeboid protists, but upon the release of a chemical signal, individual cells aggregate into a great swarm, known as a pseudoplasmodia and eventually muticellular slugs. Dictyostelium Up to 100,000 cells signal each other by releasing a chemo-attractant and aggregate to form a mound. Subsequent processes depend on cell-cell communication Many molecular and cellular processes of communication appear to have remained unchanged throughout evolution. A model organism for bio-medical research.

19. The life cycle of a cellular slime mold, Dictyostelium 1 Stalked, spore-producing structure releases spores. Fig. 23.3, p. 375 MITOTIC CELL DIVISION 2 Spores give rise to free-living amoebas that feed, grow, and reproduce by mitotic cell division. MATURE FRUITING BODY AGGREGATION CULMINATION But what’s wrong with this life cycle? 3 When food gets scarce, the amoebas stream together to form an aggregate that crawls like a slug. 4 The slug may start developing at once into a spore-bearing structure, or it may migrate elsewhere first. either or MIGRATING SLUG STAGE

20. 1 Stalked, spore-producing structure releases spores. MITOTIC CELL DIVISION 2 Spores give rise to free-living amoebas that feed, grow, and reproduce by mitotic cell division. MATURE FRUITING BODY AGGREGATION CULMINATION 3 When food gets scarce, the amoebas stream together to form an aggregate that crawls like a slug. 4 The slug may start developing at once into a spore-bearing structure, or it may migrate elsewhere first. either or MIGRATING SLUG STAGE Fig. 23.3, p. 375

21. Protists are not plants – but they follow the same 5 principles in their own ways Protists live in water, or in damp environments and tend to actively avoid dry (+/or low nutrient) conditions For unicellular organisms growth (cell division) asexual reproduction Many protists show distinctive physiological adaptations – though some have distinct morphology Life cycles are adapted to suit ecological conditions Many protists are specialists – adapted to very distinctive environments