1. Advanced Biology Visualizing Cells

2. The Human Eye  Resolution – The minimum distance two points can be apart and still be distinguished as two separate points.

3.  If smaller than 100 micrometers, the light reflected strikes the same “detector” cell at the rear of the eye  Only when the objects are larger than 100 micrometers will the light from each strike different cells, allowing your eye to resolve them as two objects rather than one.

4. MEANING?  Anything smaller than 100 micrometers, your eye cannot determine what it is without help.

6. Light Microscopes  Bright-field: Light is simply transmitted through a specimen in culture, giving little contrast. Staining specimens improves contrast but requires that cells be fixed (not alive), which can cause distortion or alteration of components.

8.  Dark Field: Light is directed at an angle toward the specimen; a condenser lens transmits only light reflected off the specimen. The field is dark, and the specimen is light against the dark background.

10.  Phase-contrast: Components of the microscope bring light waves out of phase, which produces differences in contrast and brightness when the light waves recombine.

11.  The phase contrast microscope is widely used for examining such specimens as biological tissues.  It is a type of light microscopy that enhances contrasts of transparent and colorless objects by influencing the optical path of light.

12.  The phase contrast microscope uses the fact that the light passing trough a transparent part of the specimen travels slower and, due to this is shifted compared to the uninfluenced light. This difference in phase is not visible to the human eye. However, the change in phase can be increased to half a wavelength by a transparent phase- plate in the microscope and thereby causing a difference in brightness. This makes the transparent object shine out in contrast to its surroundings.

13.  The phase contrast microscope is a vital instrument in biological and medical research. When dealing with transparent and colorless components in a cell, dyeing is an alternative but at the same time stops all processes in it. The phase contrast microscope has made it possible to study living cells, and cell division is an example of a process that has been examined in detail with it. The phase contrast microscope was awarded with the Nobel Prize in Physics, 1953.

15.  Differential-interference contrast microscope: Out of phase light waves to produce differences in contrast are combined with two beams of light traveling close together, which create even more contrast, especially at the edges of structures.

17.  Fluorescence: A set of filters transmits only light that is emitted by fluorescently stained molecules or tissues.

19.  Confocal: Light from a laser is focused to a point and scanned across the specimen in two directions. Clear images of one plane of the specimen are produced,

20.  While other planes of the specimen are excluded and do not blur the image. Fluorescent dyes and false coloring enhances the image.

22. Electron Microscopes  Transmission Electron (TEM)  A beam of electrons is passed through the specimen. Electrons that pass through are used to form an image. Areas of specimen that scatter electrons appear dark. False coloring enhances the image.

25.  Scanning Electron (SEM)  An electron beam is scanned across the surface of the specimen, and electrons are knocked off the surface.

26.  Thus, the surface topography of the specimen determines the contrast and the content of the image. False coloring enhances the image.