Protists Protistans and Life cycles Protists are generally

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.

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

Plant-like Protists (Algae) 6 phyla 1. Euglenas (Euglenophyta) Some are autotrophs when sunny and heterotrophs when dark. Unicellular, found mostly in fresh water. Some have a flagella Plantlike Protists (Algae) 6 phyla s Red spot shields the photoreceptor 2. Diatoms (Chrysophyta) Examples in the lab. Fig 23. 16 c in text book Diatoms make 20% to 25% of global organic carbon fixation. Cyclotella stelligera

3. Dinoflagellates (Pyrrophyta) 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 Protoperidinium steinii Ulva on the sea shore

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

Life cycle of Chlamydomonas A thick-walled resistant zygote develops. Zygote (crosssection) Diploid Stage Nuclear Fusion Meiosis and Germination Haploid Stage Haploid cell ( - strain) Haploid cell (+ strain) Cytoplasmic Fusion – Mainly when nitrogen levels are low and light is of a certain quality and intensity, the cells develop into gametes. ASEXUAL REPRODUCTION More spores are produced. + Gametes of different mating types meet isogamy Mitosis occurs. Whether the resulting cells develop into spores or gametes depends on environmental conditions. SEXUAL REPRODUCTION: More spores are produced. + – Page 389 Fig 23. 22

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

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

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

What’s the function of sexual reproduction? 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 Don’t tell me that’s all there is to sex! enables specialization in: Sure … it does just fine for Chlamydomonas and Ulva (a) Ensuring fertilization (b) Producing and distributing successful progeny In some plant types producing and distributing large numbers is achieved by spores

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.

5. Red Algae (Rhodophyta) 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. Porphyra species 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

Life cycle of Porphyra sporophyte (2 n) zygote How does this life cycle differ from that of Ulva? Diploid Stage Fertilization Haploid Stage Meiosis germinating spore (n) male gametes female gametes gametophyte (n) 10 cm Diploid thallus and haploid thallus have different morphology, size and habitat and + gametes are different in size and morphology Fig 23. 19 Page 386

Animal-like Protists (Protozoa) - 4 phyla 1. Sarcodines (Sarcodina) Food is surrounded by pseudopods and stored in a food vacuole Amoeba 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. Image by Arturo Gonzalez, CINVESTAV, Mexico

3. Ciliates (Ciliophora) These protists move by beating cilia that also help it capture food. Paramecium is an example 4. Apicomplexa (Sporozoa) Parasites! 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. Oocysts: mosquito midgut Plasmodium - malaria Sporozoites Merozoite: in a red blood cell

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)

Slime moulds have structural adaptations and life cycles that enhance their ecological role as decomposers 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. Slime moulds have structural adaptations Clive Shirley http: //www. hiddenforest. co. nz/slime/intro. htm

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. Characteristics of Dictyostelium Up to 100, 000 cells Subsequent processes signal each other depend on cell-cell by releasing a communication chemo-attractant and aggregate to form a mound. Dictyostelium Many molecular and cellular processes of communication appear to have remained unchanged throughout evolution. A model organism for bio-medical research.

1 Stalked, spore-producing structure releases spores. MITOTIC CELL DIVISION MATURE FRUITING BODY CULMINATION 2 Spores give rise to free-living amoebas that feed, grow, and reproduce by AGGREGATION mitotic cell division. 3 When food gets scarce, the amoebas stream together to form an aggregate that crawls like a slug. MIGRATING SLUG STAGE either or The life cycle of a cellular slime mold, Dictyostelium But what’s wrong with this life cycle? 4 The slug may start developing at once into a sporebearing structure, or it may migrate elsewhere first. Fig. 23. 3, p. 375

1 Stalked, spore-producing structure releases spores. MITOTIC CELL DIVISION MATURE FRUITING BODY CULMINATION 2 Spores give rise to free-living amoebas that feed, grow, and reproduce by AGGREGATION mitotic cell division. 3 When food gets scarce, the amoebas stream together to form an aggregate that crawls like a slug. MIGRATING SLUG STAGE either or 4 The slug may start developing at once into a sporebearing structure, or it may migrate elsewhere first. Fig. 23. 3, p. 375

Protists are not plants – but they follow the same 5 principles in their own ways 1. Plants accumulate matter and make growth 2. Plant growth is an organized process following rules of anatomy, morphology and physiology Many protists show distinctive physiological adaptations – though some have distinct morphology 3. Plants actively maintain their heat and water balance Protists live in water, or in damp environments and tend to actively 4. Plants have a life cycle with reproduction and dispersal Life cycles are adapted to suit ecological conditions 5. Evolution is a constant process Many protists are specialists – adapted to very distinctive environments For unicellular organisms growth (cell division) asexual reproduction avoid dry (+/or low nutrient) conditions