Question

Microcystis aeruginosa is a species of cyanobacteria. What CANNOT be true of this species?

A. It can produce toxins harmful to aquatic life.
B. It forms colonies called "blooms" on the water's surface.
C. It is a nitrogen-fixing bacterium.
D. It is commonly found in freshwater ecosystems.

Answer 1

The incorrect statement about Microcystis aeruginosa is that it is a nitrogen-fixing bacterium, as it does not form heterocysts required for nitrogen fixation.

Step-by-step explanation:

The student has asked which statement cannot be true of the cyanobacterium Microcystis aeruginosa. Given the information provided, option C, 'It is a nitrogen-fixing bacterium', cannot be true for Microcystis aeruginosa. While some cyanobacteria have the ability to fix nitrogen, this capacity is associated with the presence of specialized cells called heterocysts.

Microcystis aeruginosa does not form heterocysts, therefore it does not fix nitrogen. On the other hand, statements A, B, and D can indeed be true about Microcystis aeruginosa. This species can produce toxins that are harmful to aquatic life and even humans, it forms blooms on water surfaces especially in warm temperatures, and it is commonly found in freshwater ecosystems.