Question

1)A recent expedition to the planet Bizard led to the discovery of a microorganism that cannot destained with crystal violet, malachite green, or safranin. However, cell can be stained with the anionic dye nkgrosine. which of the following statements can BEST account for this observation?

a)the membrane have a net negative charge and repel the cationic dyes

b)the cells have a capsule

c)the cell wall contain mycolipids

d) the membrane have a positive charge and repel cationic dye

2) you have been trying to characterize one of your unknown organisms. You perform the urease test and observe that the tube was bright pink. Based on the other biochemical test you perform, this results was not expected. Which of of the following statements might explain your observations?

a) The test was contaminated with organism that is negative for the test

b)you failed to incubate the test at 37 degree Celsius

c)the test was contaminated with an organism that is positive for the test

d) yo failed to inoculate the test

Answer 1

Answer 1:
Option d) - the membrane have a positive charge and repel cationic dye.

If the cell can be stained with anionic dye which carries a negative charge, then cell membrane must have a positive charge. The positive charge of membrane will repel the positively charged cationic dyes, because similar charges repel and opposite charges attract.

Answer 2:
Option c) - the test was contaminated with an organism that is positive for the test

Development of pink colour is a positive reaction for urease test. If urease test came positive when it was not expected to do so, then the culture has got contaminated with another organism that gives urease test positive.