What are the membranous extensions containing pigments in certain cyanobacteria referred to as?

Chromatophores

The correct answer is Option (3)-  Chromatophores

The membranous extensions containing pigments in certain cyanobacteria are referred to as chromatophores. Chromatophores, specialized compartments within cyanobacteria's cytoplasm, house essential photosynthetic pigments like chlorophyll a, carotenes, and xanthophylls, vital for conducting photosynthesis.

Heterocysts, distinct cells in cyanobacteria, fulfill the role of nitrogen fixation under aerobic conditions. These specialized cells develop when fixed nitrogen (NH⁺₄ or NO₃) becomes scarce.

Pneumatophores are specific root structures that emerge above the water surface, aiding in the aeration necessary for root respiration in hydrophytic trees, particularly in various mangrove species.