Q.40 Cyanophyceae in general are
- Autotrophs
- Heterotrophs
- Obligate photoautotrophs
- Obligate heterotrophs
Cyanophyceae (blue-green algae or cyanobacteria) are generally autotrophs. They perform oxygenic photosynthesis using chlorophyll-a, fixing CO₂ into organic compounds.
Question Analysis
Cyanophyceae represent prokaryotic algae classified under Cyanophyta. The question tests their primary nutritional mode, with “in general” indicating the predominant autotrophic nature despite rare exceptions.
Option Breakdown
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Autotrophs: Correct. They synthesize food via photosynthesis with pigments like chlorophyll-a, phycocyanin in thylakoids. Capable of photomixotrophy in some strains, but fundamentally autotrophic.
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Heterotrophs: Incorrect. They do not primarily rely on external organic carbon; such growth is secondary or lab-induced in specific mutants.
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Obligate photoautotrophs: Partially true for many strains requiring light and CO₂ exclusively, but not all—some exhibit flexible heterotrophy, so not strictly “obligate.”
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Obligate heterotrophs: False. No Cyanophyceae depend solely on organic carbon without photosynthetic ability.
Correct Answer: Autotrophs.
Cyanophyceae in general are autotrophs, harnessing light for CO₂ fixation in diverse aquatic/terrestrial habitats. This photosynthetic prowess defines their ecological role in nitrogen fixation and primary production.
Nutrition Modes
They possess thylakoids for oxygenic photosynthesis but show metabolic flexibility—photomixotrophy with glucose/glycerol in strains like Synechocystis PCC 6803. True heterotrophy remains rare.
Option Applies to Cyanophyceae? Notes Autotrophs Yes Primary mode, chlorophyll-based Heterotrophs No (rarely) Lab conditions only Obligate photoautotrophs Partially Many strains, not universal Obligate heterotrophs No Contradicts photosynthetic nature Exam Relevance
For NEET/CSIR, recognize autotrophs as the general classification despite exceptions. Their prokaryotic simplicity (no nucleus, 70S ribosomes) reinforces this. Key for algal classification questions.
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