electron microscopes can view only dead cells becouse?????????

Answer 1

Tardigrades have been reported to survive being photographed in a scanning EM

http://www.earthlife.net/inverts/tardigrada.html

Answer 2

You have to prepare the samples so that they can be loaded into the SEM (scanning electron microscope). Since the SEM requires a vacuum to operate, any water remaining would evaporate and contaminate the chamber. If you put live cells in there, the boiling water would make a mess in the chamber. (Remember that water boils in a vacuum at room temp.) Since these are million dollar tools, nobody wants to make a mess in them. The cells are killed in the preparation process. They have to be dehydrated and then usually coated with a very thin layer of gold to keep from charging up and distorting the image.

Answer 3

The samples have to be viewed in a vacuum, as the molecules that make up air would scatter the electrons. This means that the samples need to be specially prepared by sometimes lengthy and difficult techniques to withstand the environment inside an electron microscope. Therefore, the answer is D.

Answer 4

The process of preparing cells for electron microscopes kills the cells. the process includes:

cryofixation: freezing the specimen extremely rapidly, to really really cold temperatures (like -200C), so that the water freezes but does not form ice crystals, because it froze too quickly. This preserves living things in the overall condition it was in previously, but kills the cell.

fixation: adding preservatives to the specimen
Dehydration: removing water and replaces it with ethanol or some other solvent.

other processes include cutting up the specimen, staining it, and coating it with ions or metals