Question

How do you prepare tissue for electron microscopy without using fixatives?

A) Freeze it gradually over a few hours.
B) Freeze it rapidly.
C) Subject it to a vacuum rapidly.
D) Heat it to dry it rapidly.
E) Coat it quickly in heavy metal.

Answer 1

To prepare tissue for electron microscopy without using fixatives, one should rapidly freeze the sample, a process called cryofixation, followed by cryoultramicrotomy and coating with heavy metal to improve conductivity and contrast. The correct option is B.

Step-by-step explanation:

In the context of electron microscopy, preparing tissue samples without using fixatives typically involves rapid freezing, a technique known as cryofixation. This method preserves cellular structures by minimizing ice crystal formation that can disrupt and damage cellular components.

The tissue sample is frozen rapidly, often by plunging it into a cryogen like liquid nitrogen or a slush of liquid nitrogen and ethane. After freezing, the sample can be fractured or sectioned at low temperatures, a process known as cryoultramicrotomy.

The sections are then usually coated with a heavy metal, such as platinum, to render them conductive and to improve contrast when observed under the electron microscope.

This method circumvents the need for traditional fixatives that chemically stabilize the tissues but might cause artifacts or alter fine structures. Rapid freezing maintains the specimen's hydration state and its biological context more closely than the traditional methods of chemical fixation and staining. The correct option is B.