1Which type of microscopy uses only diffracted light rays fr

1.Which type of microscopy uses only diffracted light rays from the specimen to contribute to the visible image? As a result, how does the image appear?

A. darkfield, image seen only after staining
B. brightfield, images are dark after staining
C. phase-contrast, images light on dark background
D. phase-contrast, images have significant contrast
E. darkfield, image light on dark background

2.If your countable plate has 60 colonies on it and the dilution factor of the plated sample is 10^-4, What is the cfu/ml of the original sample?

A. 60 x 10^5 cfu/ml
B. 6.0 x 10^4 cfu/ml
C. 6 X 10^5 cfu/ml
D. 100 cfu/ml
E. 6000

Solution

1. Microscope is an optical instrument used for viewing very small objects. The phase contrast microscopy took advantage of direct and diffracted light to increase the quality and definition of transparent objects. Nowadays, two types of phase contrast microscopes are available: Positive phase contrast and negative phase contrast. Positive phase contrast reveals medium to grey images on a light background while negative phase contrast does an opposite thing i.e the specimen appears lighter with dark background. Option C is the correct answer.

2. Colony forming units (cfu/ml) is the measure of viable bacterial or fungal cells. Cfu/ml can be calculated as follows:

cfu/ml= (Number of colonies X dilution factor) / Volume of culture plate

The number of colonies is 60 and dilution factor is 10^-4 . So, to calculate the cfu/ml, volume of culture plate is 1 ml.

cfu/ml = (60 X 10^-4)

= 6 X. 10^-3

Note: Your question has value of dilution factor in 10^-4 , and answers provided by you does not have a correct answer matching this question. kindly, check your options.