Survey of Protists: The Algae (Vocabulary Flashcards)
Protists: Overview and Algae
Domain Eukarya includes kingdoms Fungi, Animalia, Plantae, plus diverse groups collectively termed protists.
Protists are eukaryotes that lack distinguishing characteristics of Fungi, Animalia, or Plantae.
Most protists live in moist habitats and range from microscopic to multicellular organisms (e.g., brown alga, kelp).
Modern phylogenetic analyses show protists are not a well-defined, monophyletic group; they likely share ancestry with fungi, plants, and animals.
Protist phyla are organized into several eukaryotic supergroups, each with distinctive features; some supergroups link protists to plants, others to animals and fungi.
Protists are often categorized by ecological roles into algae, protozoa, and fungus-like protists.
This exercise focuses on algae; protozoa and slime molds are addressed in a subsequent exercise.
Algae (Latin: seaweeds) comprise about 10 phyla of protists that are predominantly photosynthetic.
Algae are not a monophyletic group; they are polyphyletic and have multiple ancestral origins.
Why algae matter (economic and ecological importance)
Removing algae would drastically reduce global oxygen production and major food sources for ecosystems.
Algae harbor thousands of irreplaceable species with diverse chemicals of potential pharmaceutical value.
Absence of algae would lead to rapid extinction of many invertebrates and collapse of ecosystems.
Algae have thrived for roughly 1.5 imes 10^9 years.
Key features of algae
Photosynthetic, eukaryotic organisms commonly lacking multicellular sex organs.
Major grouping by pigment composition, energy storage products, and cell walls, which influence color (green, brown, red, etc.).
The diversity of algal body types includes unicellular, colonial, filamentous, and multicellular forms.
Plastids and pigments determine not only color but also ecological niche and phylogeny.
Algae: energy storage and pigments (summary cues)
Energy storage products and pigments vary by phylum and color (green, brown, red algae).
Pigments influence light absorption and photosynthetic strategy in different habitats.
Common storage products include starch, laminarin, mannitol, lipids, and modified starches.
Eukaryotic supergroups and example phyla (from Table 25.1)
Excavata: Jakobida; Euglenozoa (Euglenida) – e.g., euglenoids; distinctive feeding grooves or flagellar organization.
Archaeplastida: Glaucophyta; Rhodophyta (red algae); Chlorophyta (green algae) – primary plastids; plant-like lineages.
Alveolata: Dinozoa (dinoflagellates); Ciliophora (ciliates); Apicomplexa (apicomplexans).
Stramenopila (also called Ochrophyta in some contexts): Bacillariophyta (diatoms); Phaeophyta (brown algae); and related groups with secondary/tertiary plastids.
Rhizaria: Radiolaria; Foraminifera.
Amoebozoa: Dictyostelia (slime molds); Rhizopoda (amoebas).
Opisthokonta: Choanomonada (choanoflagellates).
Note: Within these supergroups, kingdoms Plantae, Animalia, and Fungi are placed as examples of larger lineages; many protists are placed within these supergroups rather than a single kingdom.
Common algal body plans (Figure-guided overview)
Unicellular: single, unattached cells; may be motile (e.g., Chlamydomonas).
Colonial: groups of cells that adhere loosely or form colonies (e.g., Pediastrum).
Filamentous: chains of cells attached end-to-end (unbranched or branched).
Multicellular: differentiated cells and tissues; interdependence among cell types.
Examples pictured include Chlamydomonas (unicellular with flagella), Pediastrum (colony), Desmidium (filamentous), Cladophora (branched filamentous), and Acetabularia (seaweed-like macroalga).
Major algal phyla by pigment and organization (Table 25.2 cues)
Chlorophyta (Green Algae): unicellular and multicellular forms; pigments include Chl a and Chl b; storage as starch; cell walls cellulose.
Phaeophyta (Brown Algae): filamentous and multicellular; pigments include fucoxanthin; storage as laminarin.
Rhodophyta (Red Algae): mostly multicellular; pigments include phycoerythrin and phycocyanin; storage as laminarin; modified starch: floridean starch.
Bacillariophyta (Diatoms): unicellular; pigments include chlorophyll c; fucoxanthin; storage as lipids and chrysolaminarin.
Euglenida (Euglenoids): unicellular; chlorophyll b; storage as paramylon and lipids.
Other representatives by pigment and organization are summarized in Table 25.2.
Green Algae: Phylum Chlorophyta
The most diverse and familiar group of algae in freshwater; some genera inhabit saltwater.
Despite the name, green algae are not plants, but share many characteristics with land plants (e.g., Chlorophyll a and b, starch as storage, cellulose in cell walls).
Green algae are potential ancestors of land plants.
Representative features:
Chlorophyll a and Chlorophyll b
Starch as the primary storage carbohydrate
Cell walls composed of cellulose
Unicellular green alga: Chlamydomonas (example)
A motile, unicellular alga found in soil, lakes, and ditches.
Likely the simplest green alga in structure and reproduction.
Egg-shaped cells contain a large chloroplast and a pyrenoid involved in starch production and storage.
Life cycle is dominated by haploid cells; reproduction is often asexual via mitosis.
When environmental conditions become unfavorable, sexual reproduction can occur.
Life cycle and reproduction: Chlamydomonas
Asexual reproduction: mitosis producing identical copies; vegetative cells can also act as gametes.
Sexual reproduction (response to unfavorable conditions): mitosis produces vegetative cells that can act as gametes; gametes fuse (syngamy) to form a diploid zygote.
Zygote forms a thick, resistant wall and becomes a zygospore; when conditions improve, the zygospore undergoes meiosis to produce haploid individuals.
In Chlamydomonas, gametes from two strains are typically isogamous (similar in shape/appearance). Gametes are denoted as + and -; fusion yields a diploid zygote.
Terminology:
Syngamy: pairing and fusion of morphologically similar haploid gametes to form a diploid zygote (analogous to fertilization but refers to similar gametes).
Zygospore: resting diploid zygote with a resistant surface; undergoes meiosis to yield haploid spores.
Typical life cycle diagram reference: Chlamydomonas life cycle shows haploid vegetative cells, asexual mitosis, formation of isogametes, zygote via syngamy, and meiosis back to haploid progeny.
Key question prompts from lab: under what environmental conditions would a zygote not undergo meiosis immediately? Are spores haploid or diploid? Which portions of the life cycle are haploid vs. diploid? How does the stigma (in related contexts) assist survival? (Contextual prompts for understanding.)
Filamentous Green Algae: Spirogyra and Cladophora
Spirogyra and Cladophora are common filamentous green algae.
Spirogyra typically inhabits running streams of cool freshwater and secretes mucilage, giving it a slippery feel.
Cladophora forms branched filaments and is common in streams; it has a coarser texture.
Spirogyra reproduction is sexual via a process called conjugation; Cladophora is described by its branched morphology and filamentous organization.
Spirogyra: conjugation (sexual reproduction in green algae)
Opposite mating-type filaments lie side-by-side and extend projections that touch, forming conjugation tubes.
The separating wall dissolves, allowing cellular contents to move through the conjugation tube; the migrating contents are non-flagellated isogametes (the “+” and “−” strains).
Fusion of gametes produces a zygote, which develops a thick wall and becomes a zygospore.
The zygospore is a resting stage; under favorable conditions, it undergoes meiosis to form haploid cells that can divide to form a new filament.
In the lab, it is suggested to examine both living Spirogyra undergoing conjugation and prepared slides to locate conjugation tubes, gametes, and zygotes.
Important terms:
Isogamete: gametes with identical morphology; in Spirogyra, conjugation involves isogamous gametes.
Zygospore: diploid resting spore formed after gamete fusion.
Syngamy (in a broader sense): pairing and fusion of similar haploid gametes to form a diploid zygote; in Spirogyra, it leads to zygospore formation.
Cladophora: branched, multinucleate filamentous alga
Filaments are branched and can be quite large; cells may be multinucleate.
Habitat and organization: attaches to nearshore surfaces; grows in streams and other moist habitats.
Life cycle concepts and terminology to know
Haploid (n) vs. Diploid (2n): haploid cells carry a single set of chromosomes; diploid cells carry two sets.
Mitosis: asexual reproduction generating genetically identical diploid (2n) or haploid (n) cells, depending on the organism’s ploidy at the time.
Meiosis: reduction division producing haploid cells from diploid parents; in algae, meiosis often follows zygospore formation to restore haploidy.
Zygospore: diploid resting stage formed after syngamy/conjugation; resistant wall aids survival in adverse conditions.
Spores: reproductive cells capable of developing into an adult without fusion; in Chlamydomonas, meiosis yields haploid spores from the zygospore.
Planktonic vs attached protists; morphological diversity (Figure 25.2 cues)
Planktonic protists: often single-celled with flagella (e.g., Chlamydomonas).
Colonial forms (e.g., Pediastrum) form lacy star-shaped colonies to aid buoyancy.
Filamentous forms (e.g., Desmidium) occur as twisted rows of cells.
Branched filamentous forms (e.g., Cladophora) may be visible with the naked eye.
Seaweed-like single-celled green algae (Acetabularia) can be relatively large.
These body types reflect habitat adaptation and ecological roles in aquatic systems.
Scale cues from Fig. 25.2 (illustrative sizes): 15 mm, 0.2 mm, 32 μm, 25 μm.
Procedure highlights (lab-oriented observations)
Procedure 25.1: Observe Chlamydomonas
Observe living Chlamydomonas cells in water under a microscope; note movement and basic morphology.
If needed, review microscope technique and lab videos on the lab website.
Observe a fixed/ prepared slide for additional features.
Procedure 25.2: Observe syngamy in Chlamydomonas
Place drops of + and − gametes side-by-side on a slide without mixing.
Under low magnification, mix the two drops to observe clumping of isogametes and eventual pairing.
Switch to high magnification to observe paired cells and clumping dynamics.
Answer accompanying questions about zygote formation, meiosis timing, and haploid/diploid portions of the life cycle.
Procedure 25.3: Examine Spirogyra and Cladophora
Examine living Spirogyra and prepared slides to observe conjugation structures (conjugation tubes, gametes, zygotes).
Observe prepared slides of Cladophora for filamentous architecture.
Connecting to broader themes
Phylogeny and classification challenges: protists occupy multiple supergroups; algae are polyphyletic, highlighting the complexity of grouping by function (photosynthesis) rather than strict ancestry.
Ecological significance: algae are foundational in aquatic ecosystems, contributing to photosynthetic oxygen production and forming the base of many food webs.
Evolutionary relevance: Green algae (Chlorophyta) share several traits with land plants, suggesting they are plausible ancestors and share common pathways (e.g., Chlorophylls a and b, starch storage, cellulose walls).
Practical and ethical implications: understanding algal diversity informs ecological management, conservation, and biotechnological applications (pharmaceuticals, biofuels, etc.).
Quick-reference definitions and terms
Protist: a eukaryote that is not a fungus, plant, or animal.
Algae: photosynthetic protists; many are aquatic and come in unicellular, colonial, filamentous, and multicellular forms.
Green Algae (Chlorophyta): primarily photosynthetic, chlorophylls a and b, starch storage, cellulose cell walls.
Isogamy: gametes that are morphologically similar;
Syngamy: fusion of similar haploid gametes to form a diploid zygote.
Zygospore: thick-walled resting diploid zygote that can produce haploid offspring via meiosis.
Conjugation: sexual process in filamentous algae like Spirogyra where adjacent filaments exchange genetic material without natural gamete fertilization.
Cytology terms: mitosis (asexual reproduction), meiosis (gamete formation), haploid (n), diploid (2n).
Numerical and structural cues mentioned in the text
Algae have thrived for roughly 1.5 imes 10^9 years.
Figure references and scales: Fig. 25.2 provides scale cues such as 15 mm, 0.2 mm, 32 μm, 25 μm for various algae illustrations.
Chlamydomonas cells are unicellular and typically less than 100 ext{ μm} long.
The Chlamydomonas life cycle diagram emphasizes the dichotomy of haploid mitotic cycles and diploid zygote formation through syngamy, followed by meiosis to yield haploid spores.
Spirogyra conjugation involves isogametes that migrate through conjugation tubes to form a diploid zygospore; zygospore undergoes meiosis to yield haploid filaments.
Cladophora describes colonial, multinucleate, branched filaments (a morphological cue for comparative anatomy within green algae).
Summary takeaway
Algae are a diverse, ecologically foundational group of photosynthetic protists with a range of body plans and life cycles, exemplified by green algae such as Chlamydomonas, Spirogyra, and Cladophora.
Their study combines morphology, reproductive strategies (asexual vs sexual cycles), and phylogenetic context (supergroups and pigment profiles) to understand their roles in past and present ecosystems.
The alternation of generations and life-cycle transitions (haploid/diploid phases, zygospore formation, meiosis, and spore production) illustrate how algae balance growth and survival under environmental fluctuations.