Focusing up and down on Spirogyra
The animation shows three sequential views of Spirogyra. The first view was obtained by focusing on the upper surface of the cell. The second view was focused on the center of the cell where the nucleus is clearly visible. The third view focused on the lower surface of the cell. Note that the chloroplasts (the stripes) in top view have an orientation opposite from that seen when observing the bottom surface. Once reaching the lower surface of the cell, the animation returns to the center view before starting again at the upper surface.