BIOL102 Lecture 5 Notes

Alveolates

have membrane-enclosed sacs (alveoli) just under the plasma membrane

includes: Dinoflagellates, Apicomplexans, and Ciliates

Phylum Dinoflagellata

two flagella extend from perpendicular grooves

each cell is reinforced by cellulose plates

abundant components of both marine and freshwater phytoplankton

diverse group of aquatic phototrophs, mixotrophs, heterotrophs

toxic "red tides" are caused by dinoflagellate blooms (Pfiesteria)

Peridinium - mutualistic symbiont of coral reefs

Phylum Apicomplexa

mostly parasites of animals; some cause serious human diseases

spread through their host as infectious cells called sporozoites

the apex of a sporozoite contains a complex of organelles specialized for penetrating host cells and tissues

life cycles have sexual and asexual stages and require 2+ hosts

Plasmodium vivax - causes malaria and carried by female Anopheles mosquito

apicoplast

non-photosynthetic plastid for fatty acid synthesis in apicomplexans

Plasmodium

apicomplexan parasite that causes malaria

requires both mosquitos and humans to complete its life cycle

~200 million people in the tropics are infected; 600k die each year from malaria

two-host life cycle of Plasmodium

1. infected Anopheles mosquito bites a human, injecting Plasmodium sporozoites in its saliva

2. Sporozoites enter the person's liver cells. After several days, they divide many times and become merozoites, which use their apical complex to penetrate RBCs

3. Merozoites divide asexually inside the RBCs, after 48-72 hours many merozoites break out of the RBCS, causing periodic chills and fever. Some merozoites infect new RBCs

4. Some merozoites form gametocytes

5.Another Anopheles mosquito bites the infected person and picks up Plasmodium gametocytes along with blood

6. Gametes form from gametocytes; fertilization occurs in their GI tract, and zygote forms (only diploid stage in the life cycle)

Phylum Ciliophora

large varied group of protists, named for their use of cilia to move and feed

most are predators of bacteria/other protists

oral groove leads to mouth-like buccal cavity

contractile vacuoles- for storage and release of excess water

two nuclei: macro and micronuclei

macronucleus- polyploid nucleus for most cell functioning

micronucleus- diploid nucleus for reproduction

genetic variation from conjugation (two individuals exchange haploid micronuclei) usually occurs by binary fission

Life cycle of Paramecium

1. Two compatible cells align side by side and partially fuse

2. Meiosis of micronuclei produces four haploid micronuclei in each cell

3. Three micronuclei in each cell disintegrate, the remaining micronucleus in each cell divide by mitosis

4. The cells swap one micronuclei

5. The cells separatea

6. Micronuclei fuse, forming a diploid micronucleus

7. Three rounds of mitosis without cytokinesis produce eight micronuclei

8. The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei

9. Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of four daughter cells

Rhizarians

many are amoebas (protists that move and feed by pseudopodia - extensions of the cell surface)

have threadlike pseudopodia

include: Radiolarians, Forams, and Cercozoans

Phylum Radiolaria

mostly marine protists, have delicate symmetrical internal skeletons generally made of silica

pseudopodia reinforced by microtubules radiate from the central body of radiolarians

cytoplasm covering the microtubules engulf prey that become attached to the pseudopodia

Phylum Foraminifera

named for their porous shells (tests)

pseudopodia extend through the pores in the test and are used for swimming, test formation, and feeding

some are nourished by the photosynthetic activity of symbiotic algae living within their tests

found in both freshwater and marine forms

Phylum Cercozoa

large group of amoeboid and flagellated protists with threadlike pseudopodia

common in marine, freshwater, and soil ecosystems

most are heterotrophs, including parasites and predators

Paulinella chromatophora is a cercozoan autotroph with a unique photosynthetic structure called a chromatophore

evolved from a diff. cyanobacterium than the plastids of other photosynthetic eukaryotes

Archaeplastida

the supergroup that includes red algae, green algae, and plants

Phyla Rhodophyta (red algae), Chlorophyta (green algae)

Phylum Rhodophyta

red algae

red pigment called phycoerythrin, masks green of chlorophyll

color varies from greenish-red in shallow water to dark red or almost black in deep water

multicellular, the largest are seaweeds

most abundant large algae in coastal waters of the tropics

glucose stored as Floridean starch

cell walls of agar

uses: agar plates, nori

Phylum Chlorophyta

green algae

grass-green chloroplasts

paraphyletic group

unicellular and multicellular

glucose stored as starch

sexual and asexual reproductive stages

cell walls of cellulose

most live in freshwater, many are in marine, or damp soil

some reproduce through alteration of generations

closest living ancestors to plants

Zygnema, Ulva, Caulerpa

Life cycle of Chlamydomonas

1. Mature cells are haploid and contain a single cup-shaped chloroplast

2. In response to a shortage of nutrients, drying of the pond, or some other stress, cells develop into gametes

3. Gametes of opposite mating types pair off and cling together. Fusion of the gametes (syngamy) forms a diploid zygote

4. The zygote secretes a durable coat that protects the cell against harsh conditions

5. After a dormant period, meiosis produces four haploid individuals (two of each mating type) that emerge from the coat and develop into mature cells

6. When a mature cell reproduces asexually, it resorbs its flagella and then undergoes two rounds of mitosis, forming four cells

Unikonta

supergroup that includes animals, fungi, and some protists

amoebas and opisthokonts (animals,fungi,related protists)

Phyla Gymnamoeba, Entamoeba, Myxogastrida, Dictyostelida

Phylum Gymnamoeba

naked and shelled free-living amoebas

broad pseudopodia for movement and feeding

feed by phagocytosis

large nucleus

numerous food vacuoles

Amoeba proteus

Phylum Entamoeba

parasitic amoebas

pseudopodia for movement and feeding

feed by phagocytosis

Entamoeba histolytica - causes amebic dysentery through contaminated drinking water, food or utensils (third leading cause of death by a parasite)

slime molds (mycetozoans)

spore-producing fruiting bodies

include two lineages: plasmodial and cellular slime molds

Phylum Myxogastrida

many species of plasmodial slime molds are bright orange or yellow

form a unicellular feeding mass called a plasmodium (not the malaria one)

undivided by plasma membranes and contains many diploid nuclei

Physarum polycephalum

Life cycle of a plasmodial slime mold

1. Feeding stage is a multinucleate plasmodium that lives on organic refuse

2. The plasmodium takes a weblike form

3. The plasmodium erects stalked fruiting bodies (sporangia) when conditions become harsh

4. Within the bulbous tips of the sporangia, meiosis produces haploid spores

5. The resistant spores disperse through the air to new locations and germinate, becoming active haploid cells when conditions are favorable

6. Cells are either amoeboid or flagellated; the two readily convert from one to the other

7. The cells unite in like pairs, forming diploid zygotes

Phylum Dictyostelida

cellular slime mold form multicellular aggregates in which cells are separated by their membranes

cells feed individually but can aggregate to migrate and form a fruiting body

aggregation migrates as a slug

sorocarp- reproductive sporangium

Dictyostelium discoideum - experimental model for studying the evolution of multicellularity

terrestrial and heterotrophic