micro lab exam

Oil immersion

light scatters because the lens gets tiny, so immersion oil preserves resolving power/clarity by matching glass refractive index

Bright field vs. dark field

Bright field forms a dark image on a bright background; dark field uses a dark stop so only light reflecting off the specimen enters, making it great for unstained, living organisms and spirochetes

Parfocal

The microscope stays mostly in focus when you switch objectives

Simple staining

one dye, use bacterial smear to evenly spread out bacteria, do heat fixation then crystal violet used (binds to negatively charged molecules like nucleic acids and proteins allowing us to see the cell better)

Negative stain

only the background is dyed, cell is not because there's a repulsion between the negatively charged stain and the negatively charged cell surface

types: nigrosin, India Ink, Eosin Blue, Congo Red

Gram staining

differential, aseptically transfer loopful to slide, heat fix, stain with crystal violet (leave for 30s) (+&- are purple), rinse with water, use mordant iodine (leave for 1 min) (+&- are purple), rinse with water, decolorizer-ethanol drop by drop (leave for 30s) (+ purple, - clear), rinse, counter stain-safranin (leave for 1min) (+ purple, - pink because of safranin). rod are pink and cocci are purple