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Why is a specimen smaller than 200 nm not visible with a light microscope?

Anything smaller than 200 nm cannot interact with visible light.

What happens to the light rays when they hit the specimen?

They are reflected, refracted, or absorbed by the specimen.

What is the role of the ocular lens?

To recreate the image in the viewer's eye

What is meant by light rays being divergent?

It is spreading out

In a typical brightfield microscope (seen in the animation), at which point does magnification begin?

The objective lens

In which type of microscopy do the specimens appear to be three-dimensional (3-D), allowing their external features to be viewed best?

Scanning electron microscopy (SEM)

While staining a mixed culture of Gram-positive and Gram-negative bacteria, switching the order of steps 2 and 3 would result in

all bacteria appearing pink

Which structural feature of Gram-positive bacteria enhances their ability to retain the crystal violet dye?

a thick peptidoglycan layer

What would you anticipate seeing if you accidentally switched crystal violet and safranin while performing a Gram stain?

All bacteria would appear purple

What would you expect to see if you forgot to perform step 2 of the Gram stain procedure?

All bacteria would appear pink.

What is the purpose of safranin in the Gram stain technique?

It is a counterstain, which turns gram-negative bacteria pink.

What is the total magnification of a chloroplast viewed with a 10x ocular lens and a 45x objective lens?


Assume you stain Bacillus by applying malachite green with heat and then counterstaining with safranin. Through the microscope, the green structures are


Bacterial smears are fixed before staining to

kill the bacteria and affix the cells to the slide.

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