bio lab 4

Learning Objectives

  • Label the major structures of and differentiate between 4 different protists, including how they feed and move.

  • Explain the endosymbiont theory and its importance to evolution.

  • Demonstrate proper microscope use.

  • Construct a hypothesis on why protists are successful from an evolutionary point of view.

Key Words

  • Amoebozoans

  • Cilia

  • Ciliates

  • Diatoms

  • Endosymbiont Theory

  • Euglenozoans

  • Eukaryote

  • Flagella

  • Phytoplankton

  • Protist

  • Symbiosis

Introduction to Protists

Rise of Eukaryotes

  • Eukaryotes are organisms made up of cells that have a

    • Membrane-enclosed nucleus

    • Membrane-enclosed organelle

  • Eukaryotes can be:

    • Unicellular: organism is a single cell.

    • Multicellular: organism consists of many cells.

Historical Context

  • The oldest known eukaryote originates from a fossil approximately 1.8 billion years old.

  • This ancient organism had structures resembling some modern algae and was distinct from prokaryotes (archaea and bacteria).

  • This fossil marks the beginning of life's diversification on Earth.

Key Features of Eukaryotic Cells

  • Today, all eukaryotes exhibit 7 key features:

    • Origin of DNA replication enzymes: Archaeal

    • Origin of transcription enzymes: Archaeal

    • Origin of translation enzymes: Mostly Archaeal

    • Cell division apparatus: Mostly Archaeal

    • Endoplasmic reticulum: Archaeal and Bacterial

    • Mitochondrion: Bacterial

    • Metabolic genes: Mostly Bacterial

The Endosymbiont Theory

  • The prevailing theory explaining how eukaryotes acquired features from prokaryotes is known as endosymbiosis:

    • Definition: A symbiotic relationship where one organism (the symbiont) lives inside another (the host).

    • Hypothesis: An ancestral archaeal cell engulfed a smaller bacterial cell, leading to the development of organelles (mitochondria and plastids) essential for eukaryotic cells.

Evidence Supporting the Endosymbiont Theory

  • Homologous enzymes and transport systems in inner membranes of mitochondria and plastids resemble that of modern prokaryotes.

  • Mitochondria and plastids replicate similarly to prokaryotes and possess circular chromosomes akin to bacterial plasmids.

  • These organelles have the machinery to transcribe and translate their DNA independently, similar to prokaryotic cells.

  • Ribosomes in mitochondria and plastids resemble prokaryotic ribosomes more than eukaryotic cytoplasmic ribosomes.

Protists

Classification and Characteristics

  • Early eukaryotes were classified within the kingdom Protista as protists, which are largely unicellular eukaryotic organisms.

  • Protists are essential in the evolutionary development of modern complex organisms (fungi, plants, and animals).

Paraphyletic Nature of Protista

  • Traditional grouping of protists was based on similar morphology.

  • Advancements in molecular data revealed that Protista is paraphyletic, meaning it includes a common ancestor but excludes some descendants.

  • Due to this reclassification, Protista is no longer used in modern taxonomy, but the term "protist" persists informally.

Diversity of Protists

  • Estimated 200,000 extant species of protists.

  • Protists can be categorized into:

    • Animal-like (protozoans): Heterotrophic, feeding on bacteria and other protists.

    • Plant-like (phytoplankton): Autotrophic, producing food via photosynthesis, featuring chloroplasts.

Mixotrophic Protists

  • Some protists are mixotrophic, capable of photosynthesis and the capture of prey.

Phylogenetic Grouping of Protists

  • Four supergroups identified:

    1. Excavata

    2. SAR (Stramenopiles, Alveolates, Rhizaria)

    3. Archaeplastida

    4. Amoebozoa

  • Additional clade: Opisthokonta (including fungi and animals).

Supergroup Excavata

  • Characterized by

    • A groove on one side of the cell body.

  • Includes Euglenozoans:

    • Possess flagella, distinct from prokaryotic flagella.

  • Parabasalid Protists:

    • Symbiotic organisms (e.g., those in termite guts) that help break down wood, providing nutrients to the host in return for protection and food.

Supergroup SAR

  • Contains diverse protists, mainly plant-like.

  • Notable groups:

    • Diatoms: Photosynthetic and critical for oceanic primary production, contributing to 25% of Earth's oxygen. Diatoms have two interlocking valves.

    • Ciliates: Animal-like protists that predators of bacteria.

    • Dinoflagellates: Responsible for harmful algal blooms (red tide).

Supergroup Archaeplastida

  • Includes red and green algae:

    • They contribute to primary production in aquatic ecosystems.

    • Closely related to modern plants, believed to be ancestral to multicellular plants.

Supergroup Amoebozoa

  • Comprises many animal-like protists known as amoebas:

    • Use pseudopodia for movement and prey capture.

Complexity of Protist Organisms

  • Protists, despite being considered simple, exhibit vast diversity in shapes, forms of feeding, and reproduction.

  • Some exhibit colonial forms, with complex cellular functionalities surpassing those of specialized cells in higher organisms.

Lab Procedures

Microscope Use

  • Start with the lowest power objective.

  • Use coarse adjustment only on the lowest power.

  • Employ fine adjustment for higher power objectives only.

  • Once in focus at low power, do not move the stage down.

  • Clean and store the microscope appropriately after use.

Wet Mount Slide Preparation

  • Add one drop of specimen to the slide (liquid media from pond water).

  • For fast-moving protists, a slowing agent may be required.

Examining Protists in Lab

  • Observe and identify four different protist species.

  • Use a dichotomous key for identification based on physical characteristics.

Specific Protists to Observe:

  1. Spirogyra (prepared)

  2. Euglena (prepared)

  3. Paramecium (prepared)

  4. Amoeba (prepared)

  5. Pond water (various species) (wet mount)

Drawing and Documentation

Scientific Drawing Guidelines

  • Title with organism's name and include date and location of collection if applicable.

  • Indicate total magnification.

  • Focus on general shape, label structures without crossing lines, and draw to scale.

Detailed Descriptions of Selected Protists

Amoeba (Plural: Amoebas)

  • Characteristics:

    • Amorphous shape, relatively large.

    • Pseudopodia act as arms for movement and prey capture (engulfing prey into a food vacuole).

Paramecium (Plural: Paramecia)

  • Characteristics:

    • Ciliated protists belonging to the SAR supergroup.

    • Move using cilia, resembling tiny legs.

    • Feed by sweeping bacteria and algae into an oral groove.

    • Covered by a pellicle, visible in stained samples.

Euglena

  • Characteristics:

    • Small protist in Excavata with a flagellum for propulsion.

    • Autotrophic, possessing chloroplasts.

    • Senses light via a structure called the stigma to optimize photosynthesis.

Spirogyra spp.

  • Characteristics:

    • Colonial green algae in the Archaeplastida supergroup.

    • Filamentous strands resemble green hair, with distinguishable individual cells.

    • Each cell has a cell wall and spiral chloroplasts with pyrenoids for starch storage.