A Transmission electron microscopy (TEM) micrographs of the four airborne microalgae and the two waterborne microalgae used as controls. These cells were sampled in the early stationary phase. Note the differences in the cell wall thickness among these strains. B The correlation between the UV-B stress survival rates and the cell wall thickness of the six microalgal strains (r = 0.99, p < 0.0001, analyzed using the StatView Correlation Coefficient method). The cell wall thickness of each strain was measured based on the TEM images (n = 10, mean ± SE).