Difficulty: Intermediate | Prerequisites: Part 1 notes (Euglenozoans and Stramenopiles), basic understanding of parasitic life cycles
This is the second part of the microbial eukaryotes lab and covers three more supergroups: Alveolates (dinoflagellates, apicomplexans, ciliates), Rhizarians (radiolarians, foraminifera), and Algae (red and green). These organisms span an enormous range of ecological roles, from causing malaria to building coral reefs to being the closest living relatives of land plants. You should already be comfortable with the euglenozoan and stramenopile material from Part 1 before tackling this section. The sheer number of organisms here makes labelling practice essential.
Alveolates include armoured dinoflagellates (Ceratium), the malaria parasite Plasmodium, and ciliates like Paramecium with their elaborate internal structures. Rhizarians are amoeba-like protists with mineral skeletons (radiolarians in silica, forams in calcium carbonate), and their fossils are used to date rock layers. Red and green algae range from freshwater filaments to multicellular seaweeds, with green algae (charophytes) being the closest protist relatives of land plants.
Transverse groove (cingulum)
The horizontal groove encircling a dinoflagellate where one flagellum sits. Think of it as the "belt" around the middle of the cell.
Apical horn
The pointed projection at the top (anterior) end of Ceratium hirundinella.
Epitheca
The upper half of a dinoflagellate's cellulose armour, above the transverse groove.
Hypotheca
The lower half of a dinoflagellate's cellulose armour, below the transverse groove.
Apicomplexan
A parasitic protist in the Alveolata characterised by an apical complex of organelles used to penetrate host cells. In simple terms, these are obligate parasites, and Plasmodium (the malaria agent) is the most important example.
Ring stage (trophozoite)
The feeding stage of Plasmodium visible inside a red blood cell, so named because the parasite appears as a thin ring with a dark-staining dot of chromatin.
Gametocyte
The sexual stage of Plasmodium found in the blood. These are the forms picked up by mosquitoes to continue the life cycle.
Macronucleus
The large nucleus in ciliates such as Paramecium that controls day-to-day gene expression. Think of it as the working copy of the genome.
Micronucleus
The small nucleus in ciliates used for genetic exchange during conjugation. Think of it as the backup copy, reserved for sexual recombination.
Conjugation (in ciliates)
A form of sexual reproduction where two Paramecium cells join temporarily and exchange micronuclear material. No new offspring are produced; both cells simply gain new genetic combinations.
Pellicle
A flexible, protein-rich layer beneath the cell membrane in Paramecium that maintains cell shape.
Oral groove
A funnel-shaped depression on the surface of Paramecium that directs food particles towards the cytostome.
Cytostome (cell mouth)
The opening at the base of the oral groove where food enters the cell.
Cytopharynx (gullet)
The channel leading from the cytostome into the cell interior, where food vacuoles form.
Trichocyst
A bottle-shaped, thread-like organelle embedded in the pellicle of Paramecium, discharged as a defensive mechanism when stimulated (e.g. by acetic acid).
Radiolarian
A marine amoeboid protist in the Rhizaria with an intricate skeleton made of silica. Their fossils are used in biostratigraphy.
Foraminifera (foram)
A marine amoeboid protist with a chambered shell (test) made of calcium carbonate. In simple terms, forams build spiral or multi-chambered shells, and the number of chambers indicates relative age.
Test (in forams)
The shell of a foraminiferan, composed of calcium carbonate, divided into compartments called locules (chambers). Older organisms have more chambers.
Rhodophyta (red algae)
A group of mostly marine algae characterised by the accessory pigment phycoerythrin, which gives them their red colour.
Charophyte
A group of green algae considered the closest living relatives of land plants. Examples include Chara, Coleochaete, and Zygnema.
Chlorophyte
A group of green algae that includes Ulva (sea lettuce) and other forms, distinct from charophytes.
Oogonium
The female reproductive structure in Chara that contains the egg.
Antheridium
The male reproductive structure in Chara that produces sperm.
Conjugation tube (in Spirogyra)
A bridge formed between two adjacent filaments of Spirogyra during sexual reproduction, through which the contents of one cell migrate to form a zygote in the other.
All alveolates share membrane-bound sacs (alveoli) beneath the cell surface. Three major groups appear in this lab.
Viewed on a prepared slide
Key structures to identify:
Transverse groove – the horizontal groove where one flagellum sits, dividing the cell into two halves
Apical horn – the pointed projection at the top
Epitheca – the upper half of the cellulose plate armour
Hypotheca – the lower half
Dinoflagellates are important marine and freshwater plankton. Some cause harmful algal blooms (red tides). Others are symbiotic with corals (zooxanthellae).
Viewed under oil immersion in a blood smear
Key structures to identify:
Ring stage – the trophozoite feeding stage inside a red blood cell, appearing as a thin ring
Gametocyte – the sexual stage, crescent-shaped in P. falciparum, picked up by mosquitoes
All apicomplexans are obligate parasites. Plasmodium causes malaria and is transmitted by Anopheles mosquitoes.
The mosquito is the definitive host (where sexual reproduction occurs); the human is the intermediate host.
Prepared slide of conjugation: identify the macronucleus (large, controls gene expression) in paired cells
Wet mount with 1% acetic acid: observe trichocyst discharge (thread-like defensive structures ejected from the pellicle)
At-home assignment (detailed drawing): identify all of:
Pellicle – flexible outer layer
Cytopharynx (gullet) – channel from mouth to interior
Oral groove – surface funnel directing food
Cytostome (cell mouth) – opening where food enters
Contractile vacuole – osmoregulation
Food vacuole – digestion
Macronucleus – large, gene expression
Micronucleus – small, genetic exchange
Cilia – short, hair-like structures covering the surface, used for locomotion and feeding
Viewed on a prepared slide; sketch several different skeleton shapes
Radiolarians produce intricate silica (glass) skeletons with radial symmetry
They are marine planktonic organisms; their skeletons accumulate on the ocean floor as radiolarian ooze
The diversity of skeleton shapes (spherical, spiny, latticed) is a key visual identification feature
Viewed on a prepared slide; count the chambers (locules) in the test
Each chamber was added as the organism grew, so more chambers = older organism
The test is made of calcium carbonate (CaCO3), unlike radiolarian skeletons which are silica
Forams are critical biostratigraphic index fossils: oil companies hire paleontologists to identify fossilised forams in rock cores to determine the age of sedimentary layers and locate potential petroleum deposits
This is a real-world application worth remembering for exams
Batrachospermum
Freshwater red alga viewed as a wet mount
Has a beaded, branching filamentous appearance
Contains the accessory pigment phycoerythrin (though Batrachospermum often appears greenish or brownish rather than bright red)
Porphyra
A preserved marine specimen, commonly known as nori (sushi wrapper)
Leaf-like (sheet) morphology
Pigments: phycoerythrin, phycocyanin
Attachment: holdfast
Commercially harvested for food
Zygnema
Filamentous green alga viewed on a prepared slide
Each cell contains two stellate (star-shaped) chloroplasts, which is the identifying feature
Contains chlorophyll a and b
Coleochaete
A disc-shaped colonial green alga
Viewed on a prepared slide; identify chloroplasts and chlorophyll
Considered one of the closest relatives of land plants due to features like retention of the zygote on the parent
Chara
A large, complex charophyte that superficially resembles a plant
Viewed on a prepared slide; identify:
Oogonium – the female structure containing the egg
Antheridium – the male structure producing sperm
Egg – visible inside the oogonium
Chara is used as evidence for the plant-algae transition because it shares features with embryophytes (land plants)
Ulva (sea lettuce)
A chlorophyte with a broad, leaf-like thallus, two cells thick
Preserved specimen; bright green
Pigments: chlorophyll a and b
Attachment: holdfast
Spirogyra
Filamentous green alga viewed in both vegetative and conjugation forms
Vegetative form structures:
Single cell – each rectangular cell in the filament
Filaments – unbranched chains of cells
Cell wall – clearly visible boundaries
Chloroplast – one or more spiral (ribbon-shaped) chloroplasts per cell, which is the defining visual feature
Conjugation form structures:
Conjugation tube – a bridge connecting two adjacent filaments
Zygote – the result of fusion, often visible as a dark, rounded mass in one of the paired cells
Zygote nucleus – contained within the zygote
Chloroplast – still visible in the non-donor cells
Students often confuse the macronucleus and micronucleus. The macronucleus is large and runs day-to-day cell functions. The micronucleus is small and reserved for genetic exchange during conjugation.
Students sometimes think conjugation in Paramecium produces offspring. It does not. Both cells survive with new genetic material; no new cells are created.
Students mix up radiolarian and foram skeletons. Radiolarians = silica. Forams = calcium carbonate. The material matters for identification and for understanding which sediments they form.
Students assume all red algae look red. Some, like Batrachospermum, can appear green or brown depending on the balance of pigments.
⚠️ Be able to label all Paramecium structures from a diagram: pellicle, oral groove, cytostome, cytopharynx, contractile vacuole, food vacuole, macronucleus, micronucleus, cilia, trichocysts.
⚠️ Know the Plasmodium life cycle stages visible in a blood smear (ring stage vs gametocyte) and which host is definitive vs intermediate.
⚠️ Be ready to explain why oil companies search for fossilised forams (biostratigraphy, dating rock layers, locating petroleum).
⚠️ Identify the spiral chloroplast of Spirogyra and the stellate chloroplast of Zygnema as distinguishing features.
⚠️ Understand why green algae (charophytes) are considered the closest relatives of land plants.
⚠️ Know the difference between vegetative and conjugation forms of Spirogyra, and be able to label conjugation tubes and zygotes.
True or false: Conjugation in Paramecium produces new daughter cells. (False. Both parent cells survive with recombined genetic material.)
Fill in the blank: Foraminifera build their tests from ______, while radiolarians use ______. (Calcium carbonate; silica.)
True or false: The mosquito is the intermediate host in the Plasmodium life cycle. (False. The mosquito is the definitive host.)
Fill in the blank: The identifying feature of Zygnema is its two ______ chloroplasts per cell. (Stellate / star-shaped.)
True or false: Chara reproduces sexually using oogonia and antheridia. (True.)
Q: Explain why slime molds were once classified as fungi but are now classified as protists.
A: Slime molds were originally classified as fungi because they produce spore-bearing reproductive structures similar to those of fungi. They are now classified as protists (amoebozoans) because they exhibit an amoeboid, motile stage during their life cycle, a feature absent in true fungi.
Q: Why would oil companies hire paleontologists to search for fossilised forams? What information would they glean from such a discovery?
A: Fossilised forams are index fossils that help determine the age of rock layers. This is crucial for locating potential oil reserves: companies can infer the geological history of a region and identify sedimentary environments likely to contain oil deposits.
Q: What ecological niche is shared by green, red, and brown algae?
A: All three are primary producers in aquatic environments. They photosynthesize and form the base of the food chain in marine and freshwater ecosystems.
Q: Describe three modes of locomotion in microbial eukaryotes and give an example of each.
A: Flagella are long, whip-like structures used for movement (example: Euglena, Trypanosoma). Cilia are short, hair-like structures that move in coordinated waves (example: Paramecium). Pseudopodia are temporary extensions of the cell membrane used for movement and feeding (example: Amoeba proteus).
Q: What structures would you label on a Paramecium diagram, and what is the function of trichocysts?
A: Pellicle, oral groove, cytostome, cytopharynx, contractile vacuole, food vacuole, macronucleus, micronucleus, and cilia. Trichocysts are defensive organelles embedded in the pellicle; when stimulated (for example, by acetic acid), they discharge thread-like projections.
The Plasmodium life cycle connects to parasitology and public health topics you may encounter in microbiology or infectious disease courses. Foram biostratigraphy ties into geology and paleontology. The charophyte-to-land-plant transition is central to evolutionary biology and will likely reappear in any botany or plant biology unit. Ciliate nuclear dimorphism (macro- vs micronucleus) is a useful example for genetics discussions about the distinction between somatic function and germline inheritance.
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