Dinoflagellates: Structure & Red Tides — NEET Biology
📚 Practice ConceptThese organisms are mostly marine and photosynthetic. They appear yellow, green, brown, blue or red depending on the main pigments present in their cells. The cell wall has stiff cellulose plates on the outer surface. Most of them have two flagella: one lies longitudinally and the other transversely in a furrow between the wall plates. Very often, red dinoflagellates (Example: Gonyaulax) undergo such rapid multiplication that they make the sea appear red (red tides). Toxins released by such large numbers may even kill other marine animals such as fishes.
Which of the following statements about dinoflagellates are NOT correct? S1: Dinoflagellates are primarily marine and photosynthetic, exhibiting various colors depending on the pigments present. S2: Their cell walls are characterized by two thin overlapping siliceous shells that fit together like a soapbox. S3: They typically possess two flagella; one is longitudinal and the other is transverse, lying in a furrow between the wall plates. S4: Red dinoflagellates, such as Gonyaulax, often undergo rapid multiplication, causing 'red tides' and releasing toxins that can kill marine animals. S5: Dinoflagellates are primarily multicellular organisms that are found mostly in freshwater environments.
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Correct answer: B — S2 and S5 are not correct
This question tests the specific characteristics of dinoflagellates, including structural features, habitat, and ecological impact, identifying incorrect information. S1: Correct. Dinoflagellates are mostly marine and photosynthetic, and they appear yellow, green, brown, blue or red depending on their main pigments. S2: Incorrect. The description of 'two thin overlapping siliceous shells that fit together like a soapbox' applies to diatoms (Chrysophytes), not dinoflagellates. Dinoflagellates have stiff cellulose plates on their outer surface. S3: Correct. Dinoflagellates typically have two flagella: one longitudinal and the other transverse in a furrow between the wall plates. S4: Correct. Red dinoflagellates like Gonyaulax multiply rapidly to cause 'red tides', releasing toxins that can kill marine animals. S5: Incorrect. Dinoflagellates are single-celled eukaryotes (being protists) and are mostly marine, not multicellular or primarily freshwater. Therefore, statements S2 and S5 are NOT correct.
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