Question

Given the correct order of the procedures listed below, to prepare a specimen for microscopic examination.
A. Embedding, rehydration, dehydration, mounting, fixation, staining, sectioning.
B. Embedding, dehydration, rehydration, mounting, fixation, staining, sectioning.
C. Fixation, dehydration, embedding, sectioning, staining, mounting, rehydration.
D. Fixation, dehydration, embedding, sectioning, rehydration, staining, mounting.

Answer 1

Light microscopy is the most widely used biological technique used to study microscopic entities in the biological world. To study a biological sample with this technique, it has to undergo some preparatory procedures beforehand.

Complete answer:
-The entire procedure consists of the following steps:
1. Fixation: It is the process in which the biological sample is treated with either heat or a chemical or freeze-drying, to terminate any ongoing biochemical reaction, providing mechanical strength and stability.
2. Dehydration: It is done to remove the water from fixed tissue to prepare the tissue for embedding in a non-aqueous media.
3. Embedding: This process is carried out to provide mechanical strength and stability to the biological tissue so that it can sustain invasive processes like sectioning.
4. Sectioning: In this, the tissue is cut to an appropriate size.
5. Rehydration: Since most staining solutions are aqueous, the wax is dissolved and the sample is rehydrated so that it takes up the stain.
6. Staining: It is done to stain the entities to be observed by enhancing the contrast and it depends on their morphology and membrane permeability of the organelle/cell to be observed.
7. Mounting: This usually involves the situation of the tissue on the glass slide of the microscope for observation and analysis.

Therefore, the correct answer is (D) Fixation, dehydration, embedding, sectioning, rehydration, staining, mounting.

Note: - Some biological samples do not need sectioning and embedding. Such samples are called smears and are usually a thin layer of tissue, spread out evenly on the microscope slide. For example, to analyze RBCs, the sample is diluted a hundred folds and then smeared across the slide in order to visualize and study them using light microscopy.
- Stains are of different types depending upon the nature of its constituents. There are acidic stains, basic stains, negative stains, etc.