Food is stored in the structure labelled

Explanation

Food is stored in the pyrenoids, which are subcellular parts of the chloroplasts in the cells of the spirogyra. Spirogyra is a photosynthetic autotroph, meaning it makes its own food using energy from sunlight. The chloroplasts in spirogyra cells contain chlorophyll, which absorbs energy from sunlight to synthesize glucose. Excess glucose is then converted to starch and stored in the pyrenoids.

The part labelled IV is the pyrenoid.