Find the incorrect match

The correct option representing the incorrect match is Spirogyra – motile gametes.

Let's evaluate each of the given pairs to understand why this match is incorrect:
1. Nostoc – water blooms: Nostoc is a genus of filamentous cyanobacteria (blue-green algae). In nutrient-rich water bodies, these organisms can multiply rapidly to form dense visible accumulations known as water blooms. Therefore, this is a correct match.
2. Basidiomycetes – puffballs: Basidiomycetes is a class of fungi commonly referred to as club fungi. Puffballs are a well-known group of fungi that produce their spores inside a spherical fruiting body and belong to this class. Therefore, this is a correct match.
3. Sargassum – Chlorophyll: Sargassum is a genus of brown algae (Phaeophyceae). Since they are photosynthetic organisms, they contain chlorophyll pigments (specifically chlorophyll a and c) to trap light energy, along with brown accessory pigments like fucoxanthin. Therefore, this is a correct match.
4. Spirogyra – motile gametes: Spirogyra is a filamentous green alga. Sexual reproduction in Spirogyra occurs via conjugation, where the fusing gametes are morphologically similar (isogamous) but are characteristically non-flagellated and non-motile. The transfer of the male gamitic content occurs through a conjugation tube without the aid of flagella. Thus, pairing Spirogyra with motile gametes is incorrect.