Question

In: Biology

1. Which of the following refers to a cellular arrangement of bacterial cells? a. rods b....

1. Which of the following refers to a cellular arrangement of bacterial cells?

a. rods

b. coccus

c. palisades

d. morphology

2. A coccus that divides along two planes of symmetry would produce which arrangement?

a. diplococcus

b. tetrad

c. coccobacillus

d. streptococcus

3. Bacteria that display significant differences in shape, even within the same species, are said to be

a. streptococcal.

b. flexible.

c. pleomorphic.

d. pathogenic.

4. The primary point of staining bacterial cells is to increase the contrast between the cells and the background.

a. true

b. false

5. A staining technique that results in light organisms against a darkened background is a

a. Gram stain.

b. simple stain.

c. positive stain.

d. negative stain.

6. Which staining technique would provide the most accurate size of a bacterial cell?

a. negative stain

b. Gram stain

c. simple stain

d. All staining techniques would give equivalent results.

7. When preparing a bacterial smear growing on a Petri dish for staining you would

a. use a loop to transfer an entire colony to the slide.

b. use a needle to transfer a small amount of growth to the slide.

c. use a needle to transfer a small amount of growth to a loop of water on the slide.

d. use a loop to transfer a large quantity of growth to a drop of water on the slide.

8. Which of the following is a differential stain?

a. simple stain

b. Gram stain

9. Microorganisms are commonly found in soil, surfaces, and dust, but not on living surfaces like skin.

a. true

b. false

c. negative stain

d. All are differential stains.

10. The mordant in a Gram stain is

a. crystal violet.

b. Gram’s iodine.

c. ethanol.

d. water

11. If you correctly stain a mixture of Gram-positive rods and Gram-positive cocci, you would expect to see

a. purple rods and pink cocci.

b. pink rods and purple cocci.

c. purple rods and purple cocci.

d. pink rods and pink cocci.

12. Draw and label the three most common bacterial shapes.

13. Draw and label cocci growing as diplococci, tetrads, streptococci, and staphylococci.

Solutions

Expert Solution

1, option-c- palisade

Palisade is the cellular arrangment seen in some bacteria during cell division where they are lined up side by side. Ex-Corynebacterium diptheriae

Rods and cocci are different shapes of bacteria.

2,option-b- tetrad

Tetrad (four cell) is the arrangement seen when  a coccus divides along two planes of symmetry.

Diplococcus- pair of cells that divide in single plane

coccobacillus-

Streptococci- Chain of cells resulted due to division at single plane many times

Coccobacillus is the shape of bacteria which resembles both cocci and a bacilli.

3, option-c- pleomorphic

Pleomorphic are cells which can change shapes or its size due to changes in environment.

4, True

Bacteria is colourless and the background of slide is also colourless. SO staining is done to increase the contrast between the cells and the background.

5, d- Negative staining

In negative staining, the background is stained dark whereas the bacteria is left uncoloured. It reveals the shape, size and arrangemet of bacteria which cannot be stained by using other dyes. Nigrosin or Indian Ink is used for negative staining

6,-a- Negative staining

In negative staining, the stain doesnt alter anything in the bacterial cell. It doesnt cause shrinkage like other stains. SO this gives accurate cell structure, shape and size.

7, c- use a needle  to transfer a small amount of growth to a loop of water on the slide.

SInce the culture to be taken from a petri dish is dry, it is important that we transfer the bacteria to a loop of water and spread it well. And it is also important to take minimal amount of bacteria from petri plate so that we can visualise it better.

8, Gram stain

Differential stain is the staining method where we use more than one stain. In Gram staing, we use- Primary stain-Crystal violet and Counterstain- Safranin.

9, false

Microorganisms are found in every habitats- air, water, skin, soil, surfaces, etc

10, Grams iodine is the mordant in Grams staining.

It fixes the Crystal violet dye complex inside the bacteria so that it doesnt get washed off easily.

11, option-c- purple rods and purple cocci

Gram positive bacteria results in purple colour due to Crystal violet whereas Gram negative bacteria looks pink in colour due to safranin.


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