Sejaphala M.D.
Student No. 62399543
Unique Number: 770819
Introductory Microbiology
MIB2601
Assignment 02
Due Date: 13 April 2018
QUESTION 1
1. Bacteria is stained using a primary stain called crystal violet and then fixed with a mordant which in most cases is iodine. While some bacteria have the ability to retain the primary stain, others discolor when exposed to the acetone and alcohol (95%). Hence, the Gram stain divides bacteria into two groups- these bacteria are grouped according to their differential staining properties. One group is Gram positive bacteria and the other group is Gram negative bacteria. The Gram positive bacteria have cell walls with thick layer of protein-sugar and low content of lipids. During the decolorization …show more content…
The cellular structure of these group of bacteria is the opposite of the cellular structure of Gram positive bacteria. Even though the cell wall of Gram negative bacteria also takes up the crystal violet-iodine complex, it gets washed off because of the lipids on the outer layer. During the decolorization step bacteria is exposed to alcohol (95%), dissolving the lipids inside the cell walls allowing the crystal violet-iodine stain to escape from the cells leaving them colorless. And then when stained with safranin, they absorb the stain and change their color to pink. Hence the other sample is pink under a …show more content…
The time taken for a population of bacteria to double is called generation time. When a bacteria population is placed on an environment that favors growth, they follow a characteristic pattern whereby they increase in number then later the numbers decrease. This can be plotted as a growth curve with the number of cells present over a period of time. The growth curve is represented by the lag phase which shows a significant increase in number of microbes, exponential growth phase where the population is continuously doubling, stationary phase showing the equal number of new cells and dying cells and death phase whereby unfavorable leads to a decrease in the number of living
Student No. 62399543
Unique Number: 770819
Introductory Microbiology
MIB2601
Assignment 02
Due Date: 13 April 2018
QUESTION 1
1. Bacteria is stained using a primary stain called crystal violet and then fixed with a mordant which in most cases is iodine. While some bacteria have the ability to retain the primary stain, others discolor when exposed to the acetone and alcohol (95%). Hence, the Gram stain divides bacteria into two groups- these bacteria are grouped according to their differential staining properties. One group is Gram positive bacteria and the other group is Gram negative bacteria. The Gram positive bacteria have cell walls with thick layer of protein-sugar and low content of lipids. During the decolorization …show more content…
The cellular structure of these group of bacteria is the opposite of the cellular structure of Gram positive bacteria. Even though the cell wall of Gram negative bacteria also takes up the crystal violet-iodine complex, it gets washed off because of the lipids on the outer layer. During the decolorization step bacteria is exposed to alcohol (95%), dissolving the lipids inside the cell walls allowing the crystal violet-iodine stain to escape from the cells leaving them colorless. And then when stained with safranin, they absorb the stain and change their color to pink. Hence the other sample is pink under a …show more content…
The time taken for a population of bacteria to double is called generation time. When a bacteria population is placed on an environment that favors growth, they follow a characteristic pattern whereby they increase in number then later the numbers decrease. This can be plotted as a growth curve with the number of cells present over a period of time. The growth curve is represented by the lag phase which shows a significant increase in number of microbes, exponential growth phase where the population is continuously doubling, stationary phase showing the equal number of new cells and dying cells and death phase whereby unfavorable leads to a decrease in the number of living