Some examples from this set of practice questions
1.
Inventor of Gram staining
Answer: Hans christian Gram
2.
Which are the theories of Gram staining.
Answer: 4 theories 1. cell wall theory 2. lipid content theory 3. Magnesium ribonucleate theory 4. Cytoplasmic pH theory
3.
cell wall theory
Answer: cell wall of gram positive bacteria is 40 times thicker than that of gram negative bacteria, the dye-iodine complex thus gets retained.
4.
Lipid content theory
Answer: cell wall of gram -ve bac, contains additional membrane (outer membrane), which means it contains more lipids than gram +ve bac. alcohol or the acetone will dissolve the lipid creating pores through which the dye-iodine complex gets leaked out. in gram +ve alcohol/acetone dehydrates it, shrinks the cell wall and thus closes the pores.
5.
Magnesium ribonucleate theory
Answer: gram positive bac have a compound of Mg ribonuycleate and a basic protein - helps to retain the primary dye, gram -ve bac do not have this.
6.
Cytoplasmic theory
Answer: cytoplasm of gram positive is more acidic than gram negative, hence the dye binds with more affinity to gram +ve cells.
7.
which part of the bacteria gets stained
Answer: its the cytoplasm that gets stained and not the cell wall
8.
which bacteria cant be stained by gram staining
Answer: extremely slender bacteria 2. cells containing waxy substances which are impermeable to stain 3. minute intracellular bacteria like Chlamydia 4. cells organelles such as capsule, spore, flagella.
9.
positive control for gram stain
Answer: staphylococci
10.
negative control for gram staining- example
Answer: e coli, pus cells.
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