Is glycogen the most abundant carbohydrate in the biosphere?

No, glycogen is not the most abundant carbohydrate in the biOSphere. The most abundant carbohydrate is cellulose, which is a key component of plant cell walls and contributes significantly to the structure of plants. Cellulose is produced in vast quantities by plants and is a primary source of biomass in terrestrial ecosystems. Glycogen, while important for energy storage in animals and fungi, is present in much smaller amounts compared to cellulose.