Protists - Bio 111

Bio 111 - Chapter 28: Protists

Learning Objectives for this Topic

Definition of Protist:
  - The word "protist" refers to a diverse group of eukaryotic organisms that are not classified as animals, plants, or fungi. This kingdom is not considered a clade because:
    - There may not have been just one eukaryotic ancestor, and endosymbiosis likely occurred multiple times, resulting in a polyphyletic group.
    - Some descendants of early protists are not classified as protists, making the group paraphyletic.
Seven Supergroups of Eukaryotes: Identify and describe one group of protists in each supergroup:
  1. Discoba: Known for having distinctive feeding grooves.
  2. Land Plants and Relatives: Includes red algae and green algae.
  3. Alveolata: Characterized by sac-like membranes (alveoli).
  4. Stramenopila: Includes organisms with straw-like flagella.
  5. Rhizaria: Composed predominantly of amoeboid organisms with filose pseudopodia.
  6. Amoebozoa: Features amoebas that move using pseudopodia.
  7. Opisthokonta: Includes fungi and animal relatives, characterized by a single posterior flagellum in swimming cells.
Endosymbiont Theory: Summarize the evidence supporting the endosymbiont theory regarding the evolution of eukaryotes and their organelles:
- Eukaryotic cells and organelles (mitochondria, chloroplasts) originated through the engulfment of prokaryotic cells.
Evolutionary Advancements from Protists:
  - Protists exhibited significant biological advancements leading to increased complexity in eukaryotic life:
    - Sexual life cycles
    - Multicellularity
    - Development of complex organelles
    - Linear chromosomes, facilitating mitosis
Biology of Two Protists:
- Discuss details about the structure, ecology, and reproduction of two protists, ensuring at least one is non-pathogenic.

Protists: Diverse Eukaryotes

Protists are classified within the Eukaryotic domains:
- Domain Bacteria
- Domain Archaea

Classification of Protists

Classifications Include:
  - Ecological Role:
    - Photosynthetic species (algae)
    - Heterotrophs (protozoa)
    - Fungus-like organisms
    - Parasitic organisms
    - Mixotrophs combining characteristics of the above.
  - Habitat: Most commonly aquatic.
    - Plankton: Small swimming or floating unicellular organisms.
    - Periphyton: Attached organisms that produce multicellular bodies (e.g., seaweeds).
Motility Classification:
  - Microscopic protists display diverse locomotion:
    - Flagella
    - Cilia
    - Ameboid movement

Protist Defenses

Various defensive adaptations include:
  - Ejecting 'spears' when disturbed
  - Emitting light
  - Producing toxins
  - Having silica shells

Evolutionary Timeline (in millions of years ago)

3.8–3.5 bya: First prokaryotic cells appear.
3.5 bya: Fossils of primitive cyanobacteria.
1.8 bya: Eukaryotic cells first appear.
1.5 bya: Multicellular eukaryotic organisms first appear.

Features Developed by Protists

Sexual Reproduction:
  - Protists exhibit various reproductive strategies:
    - Asexual reproduction through repeated mitotic divisions in favorable conditions.
    - Cyst formation for survival in tough conditions.
    - Examples include the spread of Cryptosporidium through cysts.
Zygotic Life Cycle:
- Involves haploid cells developing into gametes (+ and − strains) and forming diploid zygotes that can survive in a cyst form.
Alternation of Generations:
  - Seen in multicellular seaweeds:
    - Haploid gametophyte produces gametes.
    - Diploid sporophyte produces spores via meiosis.
  - Example of Laminaria, a kelp, adapting its life cycle to environmental conditions.

Parasitic Protist Life Cycle

Some protists require multiple hosts for their life cycles:
  - Example: Malarial parasite Plasmodium alternates between humans and Anopheles mosquitoes, with specific stages occurring in each host:
    - Sporozoites enter human blood via mosquito bites.
    - Merozoites form in the liver and infect red blood cells, reproducing and causing symptoms like chills and fever.
    - Some merozoites form gametocytes, which are taken up by another mosquito, continuing the cycle.

Classification and Characteristics of Protist Supergroups

Discoba:
- Contains organisms that are often parasitic, including Trichomonas vaginalis and Giardia.
- Features a feeding groove and modified mitochondria.
Land Plants and Relatives:
- Includes red and green algae, with common ancestry linked by plastid evolution.
Supergroup Alveolata:
  - Characterized by membranous sacs (alveoli) and includes:
    - Ciliophora ( ciliates)
    - Apicomplexa (important parasites like Plasmodium)
    - Dinozoa (dinoflagellates, some capable of photosynthesis).
Stramenopila:
- Organisms possess straw-like flagellar hairs, includes algae and diatoms.
Rhizaria:
- Comprises amoeboid organisms that utilize filose pseudopodia for movement.
Amoebozoa:
- Contains a variety of amoebae including Dictyostelium discoideum, notable for aggregating into multicellular forms during stress.
Opisthokonta:
- Encompasses animals and fungi, characterized by a single posterior flagellum on swimming cells.

Endosymbiotic Theory Evidence

Process:
  - An archaeon capable of invaginating its plasma membrane formed the nuclear envelope.
  - This invagination allowed for engulfing bacteria, leading to the establishment of endosymbiotic relationships, resulting in:
    - Formation of mitochondria or an independent endosymbiotic event for these organelles.
    - A subsequent endosymbiotic event involving cyanobacteria leading to chloroplasts.
Key Evidence:   - Mitochondria and chloroplasts share similarities with prokaryotic cells:
    - Their ribosomes resemble prokaryotic ribosomes more than eukaryotic ones.
    - Both organelles transcribe and translate their own DNA.
    - Their division processes are similar to some prokaryotic divisions.
Horizontal Gene Transfer: Occurred from endosymbionts to host nuclei, greatly contributing to the complexity of eukaryotic cells.