Final answer:
Under an electron microscope, a pollen tetrad appears as four attached structures with detailed textures on their surface. Lily pollen grains are bean-shaped and about 50µm long, and contain cells for fertilization. The high resolution provided by electron microscopy reveals the detailed structures of these tiny biological entities.
Step-by-step explanation:
A pollen tetrad viewed under the microscope typically appears as a group of four closely attached spherical structures, resulting from the division of a microspore mother cell by meiosis. When observed using an electron microscope, which allows for much higher resolution than a light microscope, a pollen tetrad can be seen in greater detail due to the shorter wavelengths of electrons. For instance, an electron microscope image from the Dartmouth College Electron Microscope Facility shows various shapes and sizes of pollen grains, which can range from spiky spheres to bean-shaped structures, with significant detail on their surface textures. The bean-shaped grains of lily (Lilium auratum) pollen are about 50µm long and, like other pollen forms, have an outer layer (exine) and an inner layer (intine), and contain the cells necessary for fertilization, including the generative cell and pollen tube cell.
During the development process within the anther, pollen matures and is released when the pollen sac walls split open. This evolutionary adaptation facilitates the transport of pollen to the female gametophyte, enabling fertilization and the creation of a diploid zygote.