Microscopic Techniques

Step 1: Understanding the Concept:
The question asks about the specific equipment needed to visualize microbial cells, such as bacteria, which are microscopic.

Step 2: Detailed Explanation:
Microbial cells are typically only a few micrometers (µm) in size. To see them clearly, a high level of magnification is required.
Option (3) is the most precise and correct answer. Option (1) is correct but less specific. Option (2) is incorrect. Option (4) is contradictory as 1,000X is high magnification, not low.

Step 3: Final Answer:
For the examination of microbial cells, we require the use of a high-power microscope at a magnification of about 1,000 X.

Step 1: Understanding the Concept:
The question asks which property of a microscope was most fundamentally improved by switching from using photons (light) to electrons as the illumination source.

Step 2: Detailed Explanation:
The ability of a microscope to distinguish between two closely spaced points is known as its resolving power or resolution. This ability is fundamentally limited by the wavelength of the illumination used. The relationship is described by the Abbe diffraction limit, which states that the minimum resolvable distance (d) is proportional to the wavelength ( ). Electrons have a much shorter de Broglie wavelength than photons of visible light. By switching from light to electrons, the wavelength ( ) of the illumination source was reduced by several orders of magnitude. This dramatically decreased the minimum resolvable distance (d), thereby significantly increasing the microscope's ability to see fine details. This ability is called resolving power.
While magnification was also increased, the improvement in magnification is only useful if the resolving power is high enough to make the magnified details clear. The primary, limiting factor that was overcome was resolution. Resolving power is the direct measure of this ability.

Step 3: Final Answer:
The change of source of illumination from light to electrons significantly improved the resolving power of the microscope.

Step 1: Understanding the Concept:
The question asks to identify the type of microscopy for which the negative staining technique is primarily used.

Step 2: Detailed Explanation:
Negative staining is a sample preparation technique where a specimen is suspended in a solution of an electron-dense material, such as uranyl acetate or phosphotungstic acid. When dried, the heavy metal stain forms a dark background around the much lighter, unstained specimen. This creates a high-contrast image that reveals the size and surface morphology of very small objects like viruses, bacteria, or macromolecules. Because this technique relies on the differential scattering of electrons passing through the stained background versus the unstained sample, it is a method used for Transmission Electron Microscopy (TEM).

Step 3: Final Answer:
The negative staining method is generally used in TEM (Transmission Electron Microscopy).