Solution: The surface area of a sphere is $ 4\pi r^2 $. For the pollen grain, this is $ 4\pi r^2 $. The surface area of a hemisphere includes the curved surface ($ 2\pi (3r)^2 $) and the flat circular base ($ \pi (3r)^2 $), so total surface area is $ 2\pi (9r^2) + \pi (9r^2) = 18\pi r^2 + 9\pi r^2 = 27\pi r^2 $. The ratio is: - Portal da Acústica