What type of microscope would a biologist use to study sub-cellular structures?

A biologist would use a Transmission Electron Microscope (TEM) to study sub-cellular structures. Here are the steps explaining why:

1. Sub-cellular structures, such as organelles, are extremely small and cannot be effectively observed with a standard light microscope, which has a limited resolution.

2. A Transmission Electron Microscope (TEM) uses a beam of electrons instead of light to magnify the specimen. This allows for a much higher resolution, up to 0.2 nanometers, and therefore, a much more detailed view of the specimen.

3. The specimen preparation for TEM involves dehydrating the specimen and embedding it in a resin. It is then cut into extremely thin slices, stained with heavy metals to deflect the electrons and create an image.

4. The electron beam passes through the specimen, and the deflected electrons are captured on a photographic plate or a screen, creating a detailed image of the specimen.

5. This high-resolution, detailed image allows biologists to study the intricate structures within cells, such as organelles, membranes, and even individual molecules.

So, to study sub-cellular structures in detail, a biologist would use a Transmission Electron Microscope.