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Difficulty: Very hardKingdom Protista: Protozoa and Unicellular Algae

Four unicellular protists (P, Q, R, and S) were isolated and observed for specific cellular structures, nutritional habits, and reproductive characteristics:

- Organism P: Possesses a flexible proteinaceous pellicle, a photoreceptive stigma (eyespot), and synthesizes paramylon starch during daylight while absorbing dissolved organic nutrients in prolonged darkness.
- Organism Q: Exhibits nuclear dualism with a polyploid macronucleus and a diploid micronucleus, utilizing cilia arranged in longitudinal rows for propulsion.
- Organism R: Lacks locomotory organelles and contractile vacuoles in its mature stage, producing microgametocytes and schizonts during its life cycle inside a vertebrate host.
- Organism S: Features a rigid cellulose cell wall, two equal anterior flagella, and a single cup-shaped chloroplast containing a pyrenoid for starch synthesis.

Which of the following correctly identifies organisms P, Q, R, and S respectively?

  1. P: Euglena, Q: Paramecium, R: Plasmodium, S: ChlamydomonasAnswer
  2. B
    P: Chlamydomonas, Q: Paramecium, R: Amoeba, S: Euglena
  3. C
    P: Euglena, Q: Plasmodium, R: Paramecium, S: Chlamydomonas
  4. D
    P: Amoeba, Q: Euglena, R: Plasmodium, S: Paramecium

Answer

P is Euglena, Q is Paramecium, R is Plasmodium, and S is Chlamydomonas.
The combination correctly matches all four diagnostic profiles: Euglena possesses a protein pellicle, eyespot, and paramylon synthesis under mixotrophic conditions; Paramecium exhibits ciliary propulsion and nuclear dimorphism (macronucleus and micronucleus); Plasmodium is an endoparasite reproducing by schizogony without a contractile vacuole; Chlamydomonas is a unicellular alga with a cellulose cell wall, twin anterior flagella, and a cup-shaped chloroplast with a pyrenoid.

Step-by-Step Solution

1
Analyze Organism P characteristics
Organism P has a flexible pellicle (no rigid wall), a stigma (eyespot) for phototaxis, mixotrophic nutrition (photosynthesis forming paramylon starch in light, saprozoic in dark). This specifically defines Euglena.
Euglena is unique among flagellated protists in storing carbohydrate as paramylon and lacking a rigid cellulose wall.
2
Analyze Organism Q characteristics
Organism Q shows nuclear dualism (macronucleus for vegetative functions and micronucleus for sexual conjugation) along with cilia. This uniquely identifies Paramecium (Ciliophora).
Ciliates like Paramecium are characterized by nuclear dimorphism and rows of cilia.
3
Analyze Organism R characteristics
Organism R has no locomotory structures or contractile vacuoles in mature stages and undergoes schizogony within a host. This defines the parasitic apicomplexan Plasmodium.
Parasitic protozoa residing in isotonic host blood fluids do not require osmoregulatory contractile vacuoles and move via gliding or passive transport rather than active flagella/cilia in adult forms.
4
Analyze Organism S characteristics
Organism S has a true cellulose cell wall, two equal anterior flagella, and a single cup-shaped chloroplast with a pyrenoid. This defines Chlamydomonas (unicellular green alga).
Chlamydomonas represents a classic unicellular photosynthetic chlorophyte.

Key Concept

Diagnostic features, locomotory mechanisms, organelle functions, and nutritional modes across major protistan lineages (Euglenophyta, Ciliophora, Apicomplexa, and Chlorophyta).
Estimated Time:1m 30s
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Topics

Kingdom Protista: Protozoa and Unicellular Algae

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