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Heterocysts

Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025

Definition

Heterocysts are specialized nitrogen-fixing cells found in some filamentous cyanobacteria. They create an anaerobic environment necessary for the activity of the enzyme nitrogenase.

AP course connection

Topic 4.3: 4.3 Nonproteobacteria Gram-Negative Bacteria and Phototrophic Bacteria

Unit 4

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5 Must Know Facts For Your Next Test

  1. Heterocysts differentiate from vegetative cells when fixed nitrogen is scarce.
  2. They possess thick cell walls that limit oxygen diffusion, protecting nitrogenase from oxygen.
  3. Photosynthesis does not occur in heterocysts; instead, they rely on neighboring vegetative cells for carbohydrates.
  4. Heterocysts are interconnected with other cells through microplasmodesmata, allowing nutrient exchange.
  5. The differentiation process of heterocysts is regulated by several genes, including hetR and patS.

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