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2021-05-14

Why is the slide not heat fixed before negative staining?

Why is the slide not heat fixed before negative staining?

Negative stain is used when viewing bacteria by wet mount or hanging drop slide to view bacterial motility. Heat fixation is not used in negative staining because the goal of the experiment is to view bacteria that has not been distorted by harsh staining or heat fixing. Heat fixing shrinks cells!

Why do we fix the slide before staining?

The purpose of making a smear is to fix the bacteria onto the slide and to prevent the sample from being lost during a staining procedure.

Why do the slides have to be heat fixed before staining What do you think would happen if the slides were not heat fixed and then stained?

1. If you don’t completely air dry your slide, you will end up boiling your microorganisms when heat-fixing. If you don’t kill the bacteria during heat-fixation, their ability to accept stains is reduced and you will not see anything under the microscope.

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Why did the slides need to be heat fixed during the direct stain?

**3) Why are smears heat-fixed prior to being used in a direct stain? so that organisms are killed, adhere better to the slide, and take up dye more easily, used in direct staining. In a negative stain negative charges repulse each other causing the background to be stained, leaving the bacteria unstained.

What is the purpose of the negative stain?

Purpose: Negative stains are used to view cell morphology and arrangement of microorganisms and selected because of the minimal damage and distortion of the bacterial structures. Acidic stains such as Nigrosin are used in the staining process.

What is an example of a negative stain?

Some suitable negative stains include ammonium molybdate, uranyl acetate, uranyl formate, phosphotungstic acid, osmium tetroxide, osmium ferricyanide and auroglucothionate. These have been chosen because they scatter electrons strongly and also adsorb to biological matter well.

Is Nigrosin a negative stain?

We use nigrosin as our negative stain. Nigrosin is an acidic stain. This means that the stain readily gives up a hydrogen ion and becomes negatively charged. Since the surface of most bacterial cells is negatively charged, the cell surface repels the stain.

What is the difference between a simple stain and a negative stain?

In a simple staining technique, a positively charged stain colors the negatively charged cells, making them stand out against the light background. In a negative staining technique, a negatively charged stain colors the background, leaving the cells light colored and unstained.

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What happens if you leave a stain on a bacterial smear too long?

What are some consequences of leaving a stain on a bacterial smear too long (over-staining)? Consequences of over-staining are that the cell wall may be broken up or completely destroyed which would result in a loss of morphological characteristics of the bacterial cell.

Is basic dye a negative stain?

Acidic/Basic Dyes The most widely used histological stains differentiate between the acidic and basic components of cells and tissues. Basic dyes have a net positive charge and bind to components of cells and tissues that are negatively charged.

Does staining kill cells?

Since fixation and staining would kill the cells, darkfield microscopy is typically used for observing live specimens and viewing their movements. However, other approaches can also be used. For example, the cells can be thickened with silver particles (in tissue sections) and observed using a light microscope.

Does negative staining kill cells?

Principle of Negative Staining The acidic stain, with its negatively charged chromogen, will not penetrate the cells because of the negative charge on the surface of bacteria. Therefore, the unstained cells are easily discernible against the colored background. The practical application of negative staining is twofold.

What are the disadvantages of staining cells?

The disadvantages of histology and histological staining include: Preparation of the slides using the paraffin technique can be time-consuming; frozen slides are faster to prepare, but this can affect the resolution, especially when using light microscopy.

Can you see bacteria without staining?

Even with a microscope, bacteria cannot be seen easily unless they are stained. The largest bacteria, such as Bacillus megaterium, can also be seen at 400X. Most other bacteria require 1000X magnification. Algae and protozoa are best viewed in a wet mount without staining.

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What can you see at 1000x magnification?

0.180mm

What is the minimum magnification needed to clearly view bacteria?

400x magnification

Who used the microscope to view bacteria?

Anton van Leeuwenhoek

At what magnification can you see cells?

400x

What shape do viruses assume?

Shapes of viruses are predominantly of two kinds: rods, or filaments, so called because of the linear array of the nucleic acid and the protein subunits; and spheres, which are actually 20-sided (icosahedral) polygons. Most plant viruses are small and are either filaments or polygons, as are many bacterial viruses.

What are the 3 basic shapes of viruses?

Viral ShapesThere are three basic types of viral shapes: helical viruses have capsomeres that spiral around the nucleic acid, forming a tube-like structure; polyhedral viruses are roughly spherical, with a shape similar to a geodesic dome; and complex viruses have capsids of many different shapes.

How much bigger is a bacteria than a virus?

Size. Bacteria are giants when compared to viruses. The smallest bacteria are about 0.4 micron (one millionth of a meter) in diameter while viruses range in size from 0.02 to 0.25 micron. This makes most viruses submicroscopic, unable to be seen in an ordinary light microscope.

Why are viruses considered non living?

Viruses are not made out of cells, they can’t keep themselves in a stable state, they don’t grow, and they can’t make their own energy. Even though they definitely replicate and adapt to their environment, viruses are more like androids than real living organisms.