Week 3 - Day 2

What are protists?

• diverse group of eukaryotic organisms, mostly single-celled, live in many environments

• NOT plants, animals, or fungi, but share some characteristics with each group

• No longer considered kingdom because some protists more closely related to plants, fungi, or animals than other protists! (all are diff)

  • paraphyletic group, not a true kingdom

What are key cellular features of protists?

• Have a nucleus and membrane-bound organelles (eukaryotes)

• Possess a well-developed cytoskeleton

• Can have asymmetric shapes

• Able to change shape over time

What are some examples of protists?

Protists make up much of diversity of eukaryotes.

• Organisms in most eukaryotic lineages are protists

• Amoeba, Paramecium, Euglena, Diatoms, Dinoflagellates

Why are protists important for eukaryotic diversity?

• Make up a large portion of eukaryotic diversity

• Most eukaryotic lineages are protists

• Include many evolutionary groups (e.g., SAR clade, Excavata, Archaeplastida, Unikonta)

Why do Protists Matter?

• Make up much of eukaryotic diversity

• Form the base of aquatic food chains

• Produce much of the world’s oxygen

• Some cause disease

• Help scientists understand the evolution of complex life

What gave rise to the diversity of protists?

• Ancient origins

• Endosymbiotic events (mitochondria, plastids)

• Adaptation to many environments

• Multiple nutritional strategies

• Rapid evolution in single-celled organisms

Why and how do protists show structural and functional diversity? (physical features wise)

• because they evolved early and adapted to diverse environments.

  • Protists vary widely in cell structure shape, and complexity and cell coverings

What unique structural feature do some protists have?

• Some unicellular protists have unique organelles not found in most other eukaryotic cells.

• Some dinoflagellate protists have eye-like organelle called an ocelloid

  • Functions like a lens + retina

What contributes to the functional diversity of protists? (how they live and behave)

• Protists evolved early and adapted to many environments

• Show diversity in:

  • Modes of nutrition

  • Reproduction

  • Ecological roles

• Can resemble:

  • Animal-like, plant-like, or fungus-like forms

How are protists nutritionally diverse?

• Photoautotrophs → photosynthesis (chloroplasts)

• Heterotrophs → absorb or ingest food

• Mixotrophs → combine both strategies

• Some are parasites with specialized nutrient uptake

• → Protists are the most nutritionally diverse eukaryotes

What is endosymbiosis and why is it important in eukaryotic evolution?

• Endosymbiosis = process by which one organism lives inside another

• Evidence shows of protist diversity has origins in endosymbiosis

• Led to origin of key eukaryotic organelles and enabled protists to acquire new metabolic abilities.

Origin of Eukaryotic Cells

• Ancestral prokaryotes formed symbiotic relationship when host cell engulfed aerobic bacterium.

• Instead of being digested, bacterium evolved into mitochondrion (from aerobic bacteria) + Chloroplasts (from photosynthetic bacteria)

• Gave early protists efficient aerobic respiration, allowing larger, more complex cells to evolve + gain new metabolic abilities

• Significance: Marks origin of eukaryotes, including all protists

What are the four major supergroups of eukaryotes?

Understanding of evolutionary relationships among protist groups changes rapidly!

Current hypothesis divides all eukaryotes (including protists) into four

supergroups

1. Excavata

2. SAR clade (Stramenopiles, Alveolates, Rhizarians)

3. Archaeplastida

4. Unikonta

• → All eukaryotes (including protists) are grouped into these lineages

What is the first supergroup?

Excavata

• Includes: Parabasalids, Diplomonads, Euglenozoans

• Often have a feeding groove

• Some are parasites

• Example:

  • Giardia intestinalis → causes intestinal infections

What is the second supergroup?

SAR

• Major eukaryotic supergroup

• Includes three clades:

  • Stramenopila

  • Alveolata

  • Rhizaria

• Examples:

  • Diatoms (photosynthetic stramenopiles)

  • Rhizarians (amoebas with threadlike pseudopodia, e.g., Globigerina)

What is Stramenopila?

the S in SAR

• Stramenopiles include some of most important

  photosynthetic organisms on Earth.

  • Most have “hairy” flagellum paired with “smooth” flagellum.

  • Diatoms, oomycetes, and brown algae are three important

  groups.

What is Alveolates?

• have membrane-enclosed sacs (alveoli) just under plasma membrane.

• Three clades are dinoflagellates, apicomplexans, and ciliates.

What are Dinoflagellates?

• sub category of Alveolates

• major components marine and freshwater phytoplankton.

• Major primary producers/key in nutrient cycling

• Important symbionts in coral reefs

• Have two flagella housed in grooves of armor-like cellulose plates that surround cell

• Beating spiral flagella causes dinoflagellates to spin as they move through water

What are apicomplexans?

• another subunit of alveolates

• Nearly all apicomplexans parasites of animals

• Spread through host as infectious cells called sporozoites

• Apex (cell end) contains complex of organelles specialized forpenetrating host cells and tissues

What are ciliates?

• last subunit of alveolates

• named for use of cilia to move around and feed on bacteria or other protists.

  • Cilia may completely cover cell surface or be clustered in few rows or tufts.

  • Well developed organelles

  • Two nuclei

  • 9+2 filament pattern

What are the two types of nuclei in ciliates and their functions?

• tiny Micronucleus:

  • Small

  • Genetic/reproductive role

  • Can be diploid or haploid

• large Macronucleus:

  • Large

  • Controls cell functions (metabolism, growth)

  • Contains multiple copies of genome

• Each cell has one or more of each type