Q.23 Lichens are
- Autotrophs
- Heterotrophs
- Biotrophs
- Phagotrophs
Lichens are classified as autotrophs because their algal or cyanobacterial component performs photosynthesis to produce food, sustaining the symbiotic partnership despite the fungal component’s heterotrophic nature.
Option Breakdown
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Autotrophs: Correct. Lichens rely on photosynthesis by their algal photobiont (phycobiont) to fix carbon and generate organic compounds, making the organism self-sustaining like plants.
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Heterotrophs: Incorrect. While the fungal mycobiont absorbs nutrients externally, the overall lichen functions autotrophically due to the photosynthetic partner.
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Biotrophs: Incorrect. Biotrophs (biotrophic organisms) derive nutrients from living hosts parasitically or mutualistically without killing them; lichens are self-feeding via symbiosis, not host-dependent.
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Phagotrophs: Incorrect. Phagotrophs engulf solid food particles (e.g., amoebae); lichens absorb dissolved nutrients and photosynthesize, lacking phagocytosis.
Introduction
Lichens are autotrophs that thrive in harsh environments through a unique symbiotic association between fungi and photosynthetic algae or cyanobacteria. Understanding why lichens are autotrophs—rather than heterotrophs, biotrophs, or phagotrophs—is key for biology students tackling MCQs on organism nutrition. This guide breaks down each term with examples for exam success.What Are Lichens?
Lichens form stable mutualistic partnerships where fungi (mycobiont) provide protection, water, and minerals, while algae or cyanobacteria (photobiont) perform photosynthesis as autotrophs. This makes lichens pioneer species in barren habitats, acting as primary producers.
They colonize rocks, trees, and soil globally, indicating air quality due to pollution sensitivity.
Why Lichens Are Autotrophs
The algal component uses sunlight to convert CO₂ and water into glucose via photosynthesis, supplying energy to the fungus. Thus, lichens are autotrophs at the organism level, independent of external organic food.
Unlike true heterotrophs, they form the base of food chains, eaten by herbivores like reindeer.
Nutrition Type Definition Applies to Lichens? Reason Autotrophs Self-feed via photosynthesis or chemosynthesis Yes Algal photobiont produces food Heterotrophs Depend on external organic matter No Fungus relies on algae, but overall self-sustaining Biotrophs Live on living hosts for nutrients No Not parasitic; symbiotic self-feeders Phagotrophs Engulf solid particles No Absorb nutrients, no engulfing Exam Tips for Lichens MCQs
For questions like “Lichens are:”, always recall the autotrophic role of photobionts. Common errors include confusing them with fungi alone (heterotrophs). Practice with past papers to master symbiotic nutrition.
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