Bacteria Identification Under a Microscope

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Questions and Answers

What is the shape of the bacteria in the first row?

Irregular

Rod-shaped

Spherical (correct)

Squiggle-shaped

Why are the bacteria in the third row viewed using dark field microscopy?

Because they are Gram-positive

Because they are motile

Because they do not stain the same way as other bacteria (correct)

Because they are too small to be seen with a light microscope

What is the term for a single bacterium with a spherical shape?

Coccus (correct)

Cocci

Spirillum

Bacillus

What is the appearance of the bacteria in the second row?

Rod-shaped Signup and view all the answers

Why are the bacteria in the first row purple in color?

Because of the type of dye used Signup and view all the answers

What is the term for multiple bacteria with a spherical shape?

Cocci Signup and view all the answers

Why is it necessary to view the bacteria in the third row using a different method?

Because they do not stain the same way as other bacteria Signup and view all the answers

What is the shape of the bacteria in the third row?

Squiggle-shaped Signup and view all the answers

What is the term used to describe a single rod-shaped bacterium?

Bacillus Signup and view all the answers

What is the purpose of the Gram stain in studying bacteria?

To differentiate between Gram positive and Gram negative bacteria Signup and view all the answers

What is the characteristic of the cell wall in Gram positive bacteria?

Thick and composed of peptidoglycan Signup and view all the answers

What is the function of the lipopolysaccharide layer in Gram negative bacteria?

To maintain the cell's outer membrane structure Signup and view all the answers

What is the term used to describe a single spiral-shaped bacterium?

Spirochete Signup and view all the answers

What is the main difference between the cell walls of Gram positive and Gram negative bacteria?

Peptidoglycan layer thickness Signup and view all the answers

What is the purpose of the capsule layer in bacterial cells?

To protect the cell from environmental stress Signup and view all the answers

What is the term used to describe the combination of sugar chains and peptides in bacterial cell walls?

Peptidoglycan Signup and view all the answers

What is the main component of the outer membrane in Gram negative bacteria?

Lipopolysaccharide layer Signup and view all the answers

What is the term used to describe the staining result of Gram positive bacteria?

Purple Signup and view all the answers

What is the layer above the plasma membrane in a bacterium?

Capsule Signup and view all the answers

What is the name of the space between the plasma membrane and the peptidoglycan layer?

Periplasmic space Signup and view all the answers

What is the reason why Gram negative bacteria stain pink?

Because they have a thin peptidoglycan layer Signup and view all the answers

What is the purpose of the Gram stain?

To determine the cell wall structure of bacteria Signup and view all the answers

What is the characteristic of the peptidoglycan layer in Gram positive bacteria?

It is thick Signup and view all the answers

What is the name of the substance used to restain Gram negative bacteria?

Safranin Signup and view all the answers

What is the location of the polysaccharides in a bacterium?

At the top of the cell wall Signup and view all the answers

What is the term for the region next to the plasma membrane?

Periplasmic Signup and view all the answers

Study Notes

Bacteria Shapes

Bacteria can have different shapes, including:
- Coccus (singular) or Cocci (plural): spherical shape
- Bacillus (singular) or Bacilli (plural): rod-shaped
- Spirochete (singular) or Spirilla (plural): spiral-shaped

Gram Staining

The Gram stain is a special stain used to distinguish between bacteria
It stains the outside of the bacteria
If the stain is retained, the bacteria is Gram positive and appears purple
If the stain is washed off and restained with Safranin, the bacteria is Gram negative and appears pink

Gram Positive Bacteria

Have a thick peptidoglycan layer in their cell wall
The peptidoglycan layer is made up of long chains of sugars (glycan) connected by proteins (peptide)
This layer is responsible for retaining the Gram stain, making the bacteria appear purple
Gram positive bacteria also have a plasma membrane and a capsule or slime layer

Gram Negative Bacteria

Have a thin peptidoglycan layer in their cell wall
The thin peptidoglycan layer is washed off by the Gram stain, making the bacteria appear pink after restaining with Safranin
Gram negative bacteria have an outer membrane, a lipopolysaccharide (LPS) layer, and a capsule or slime layer
The LPS layer is composed of lipids and polysaccharides

Cell Wall Structure

Gram positive bacteria have a thick peptidoglycan layer, a plasma membrane, and a capsule or slime layer
Gram negative bacteria have a thin peptidoglycan layer, an outer membrane, an LPS layer, and a capsule or slime layer

Key Differences

Gram positive bacteria have a thick peptidoglycan layer, while Gram negative bacteria have a thin peptidoglycan layer
Gram positive bacteria retain the Gram stain, while Gram negative bacteria are washed off and restained with Safranin
The cell wall structure of Gram positive and Gram negative bacteria differs significantly