1. Define:
· Resolution – ability to distinguish two separate points as two separate points
· Magnification - The process of enlarging the size of something, as an optical image. Something that has been magnified; an enlarged representation, image, or model. The ratio of the size of an image to the size of an object.
· Transmission – the passage of light through a specimen
· Absorption – the retention of light as it passes through a specimen
· Refraction – the bending of light as it passes through a specimen
2. Describe the following types of microscopes used in microbiology:
· Brightfield – the condenser focuses light on the entire field of vision, best used with stained cells
· Darkfield – and opaque disc in the condenser keeps light from entering the objective lens directly and only allows light reflected by the specimen to enter the objective lens. The specimen appears light against a dark background. Good for cells that either can’t be stained by ordinary methods or are distorted by staining.
· Phase-contrast – uses a condenser that focuses light waves that pass directly through the specimen without being altered and light waves that are diffracted (scattered) by structures in the specimen on a diffraction plate in the objective lens. The light waves are brought together to form the image. Waves that are in phase are bright, those that are out of phase are darker. Allows examination of internal structures of a living cell and requires no staining.
· Differential interference contrast – similar to phase contrast but uses two beams of light split into several wavelengths. Provides color and three dimensional resolution, requires no staining.
· Fluorescence – fluorescent stains are used to identify specific structures or antigens, when excited by uv or near uv light the stains fluoresce (emit light of a characteristic longer wavelength).
· Confocal – uses fluorescence and multiple scans in one plane. By scanning in successive planes and using a computer to generate the images three dimensional images can be constructed.
· Electron – a beam of electrons is used instead of light. Allows much greater resolution.
3. List and describe the following techniques: We’ll do 3-8 in lab.
· smear preparation
· aseptic transfer
4. List two differential staining procedures and describe each.
5. List three special staining procedures and describe each.
6. Give the gram stain procedure in the correct order and explain the function of each step.
7. Know the function of the reagents in the Gram stain procedure.
8. Be able interpret a gram stain.