Microscopy Principle And Application

Transmission Electron Microscopy (TEM) is a powerful technique used to examine cellular structures. Negative-Staining involves adding a contrasting agent to the sample, which creates a dark background and enhances the visibility of the cellular structures. Shadow Casting involves coating the sample with a thin layer of metal, creating a shadow effect that helps visualize the surface features. Ultrathin Sectioning involves cutting the sample into extremely thin slices, allowing for detailed examination of the internal structures. Freeze-Etching involves freezing the sample and then removing the ice to reveal the surface structures. Therefore, all of these techniques are used in TEM for examining cellular structure.

Electron microscopy requires the specimen to be thin and dry in order for the electrons to pass through it easily. The image is obtained on a phosphorescent screen because the electrons that pass through the specimen interact with the screen, producing a visible image. Additionally, the electron beam must pass through an evacuated chamber to prevent the electrons from scattering or interacting with air molecules, which could distort the image. Therefore, all three statements are true for electron microscopy.

Negative staining is a technique used in microscopy to examine structures that are difficult to visualize using other staining methods. In negative staining, the background is stained, while the structure of interest remains unstained. This technique is particularly useful for visualizing virus particles, protein molecules, and bacterial flagella, as it allows for better contrast and resolution of these structures against the stained background. Therefore, the correct answer is d) virus particles, protein molecules, and bacterial flagella.

Electron microscopes use electron beams and magnetic fields to magnify and visualize specimens. Electron beams are used to illuminate the sample, and the interaction between the electrons and the sample produces signals that are then detected and used to create an image. Magnetic fields are used to control the path of the electron beam and focus it onto the sample. This combination of electron beams and magnetic fields allows for much higher resolution and magnification compared to light microscopes, which use light waves.

The resolving power of a microscope is determined by both the wavelength of light used and the numerical aperture of the lens system. The wavelength of light affects the ability of the microscope to distinguish between two closely spaced objects, with shorter wavelengths allowing for higher resolution. The numerical aperture of the lens system determines the amount of light that can enter the microscope and also affects the resolution. Therefore, both factors contribute to the resolving power of a microscope.

The minimum distance for the eye to focus any object is 25 cm. This is known as the near point or the closest point at which the eye can focus without straining. Beyond this distance, the eye's lens needs to adjust in order to focus on objects that are farther away.

In phase contrast microscopy, the rate at which light enters through objects is inversely proportional to their refractive indices. This means that objects with higher refractive indices will allow less light to pass through them, while objects with lower refractive indices will allow more light to pass through them. This is because the phase contrast technique enhances the visibility of transparent and unstained specimens by exploiting the differences in refractive index between the specimen and the surrounding medium.

Electron microscopes use a beam of electrons instead of light to magnify objects, allowing for much higher magnification than traditional light microscopes. The correct answer, a) 400,000X, suggests that an electron microscope can achieve a maximum magnification of 400,000 times. This high level of magnification enables scientists to study extremely small structures and details at the nanoscale level.

In a scanning electron microscope (SEM), the magnified image of the specimen is obtained on a cathode ray tube (CRT). The CRT is a display device that uses a beam of electrons to create an image on a fluorescent screen. In an SEM, the electron beam scans the specimen surface, and the interactions between the beam and the specimen produce signals that are then used to form an image on the CRT. This allows for the visualization and analysis of the specimen at high magnification and resolution.

The oil immersion objective lens has an NA (Numerical Aperture) value of 0.65. The NA value represents the ability of the lens to gather and resolve light. A higher NA value indicates a greater ability to gather and resolve light, while a lower NA value indicates a lower ability. In the case of the oil immersion objective lens, an NA value of 0.65 suggests that it has a moderate ability to gather and resolve light.