In which of the following species is the biomass of an individual the smallest?

Analyze the question: Biomass is the total mass of living organic matter in an organism. We need to find which organism is the smallest, since an individual of that species will have the least biomass.

Concept: Compare the organisms by size and body complexity:

• Tilapia sp: a freshwater fish, a vertebrate that can weigh hundreds of grams to a few kilograms.
• Agama sp: the rainbow lizard, a vertebrate that weighs tens of grams.
• Bufo sp: the toad, a vertebrate that weighs tens of grams.
• Spirogyra sp: a filamentous green alga. Each individual is a thin, microscopic filament of cells, so its mass is tiny compared with the vertebrates.

Solution:

1. Tilapia, Agama and Bufo are all multicellular vertebrates with bones, muscles and organs, so they have a large body mass.
2. Spirogyra is a simple, thread-like alga (visible as slimy green strands in ponds). A single filament weighs only a tiny fraction of a gram.
3. So Spirogyra has the smallest biomass per individual.

Answer: D. Spirogyra sp

Tip: For biomass-size questions, rank the organisms: large vertebrates > small vertebrates > invertebrates > algae/microorganisms. Also note that the spelling in the question ("Spirogvra") is just a typo for Spirogyra.