1. A loop or needle is sterilized by inserting it to a Bunsen burner until it is

Question

1. A loop or needle is sterilized by inserting it to a Bunsen burner until it is red hot. This will a. coagulate any contaminating organisms that may be present b. incinerate any contaminating organisms that may be present c. activate any contaminating organisms that may be present d. all of the choices are true 2. With a pure culture, one is able to study a. the cultural characteristics of an individual organism b. the morphological characteristics of an individual organism c. the physiological characteristics of an individual organisnm d. all of the above 3. The use of a single stain to color a bacterial cell is commonly referred to as a special stain b. simple stain c. negative staind. pure stain 4. The phase contrast microscope is best suited for observing a. living organisms in an uncovered drop on a slide b. stained slides with cover glasses c. living organisms in hanging drop slide preparation d. living organisms on a slide with a cover glass

Explanation / Answer

Ans. #1. Correct option- B.

During incineration of inoculation loop the temperature rises upto around 8150C, thus turns the loop red hot. Such a high temperature BURNS/ incinerate all types of contaminating microbes present on the loop – thus, the loop is sterilized.

# The contaminating microbes are completely combusted into CO2 and H2O (a chemical process) and thus killed. Coagulation is sticking together of microbes, a physical process that need not necessarily kill them.

# It kills micorbes.

#2. Correct option- D.

# A pure culture consists of only type of microbe. To study any aspect of a microbe (or any other substance), there must be a pure culture of its where only the specified microbe but no other organisms are present.

# The cultural characteristics like optimum growth temperature, pH, growth rate in different culture media, physiological characteristics, etc. can be studied by inoculating and incubating the microbe in specified cultural conditions.

# The microbe can be stained and morphological characteristics can be studied.

#3. Correct option- B. simple stain. A simple staining method involves the use of a single type of stain that stains/color the bacterial cell. For example, staining the cells with safranin alone (but no other stain in addition) is also a simple staining.

# Special stains stain/color the cell appendages (like cilia, flagella, etc.) but NOT the cell itself.

# Negative stains stain the background but NOT the cell itself.

#4. Correct option- D.

The phase contrast microscope is used to study living cells. The sample is placed on a slide and covered with cove glass / cover slip.

https://www.nobelprize.org/educational/physics/microscopes/phase/preparation.html

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