Gram-Positive Bacteria Quiz

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Questions and Answers

What is the defining characteristic of gram-positive bacteria in the Gram stain test?

  • They retain the crystal violet stain (correct)
  • They have an outer membrane that degrades
  • They retain the safranin counterstain
  • They have a thinner peptidoglycan layer

What causes gram-negative bacteria to appear pink in the Gram stain test?

  • Their peptidoglycan layer is much thinner
  • They have a thicker cell wall
  • The alcohol used in the decolorization step (correct)
  • They retain the crystal violet stain

What component of gram-positive bacteria's cell wall retains the crystal violet stain?

  • Bacterial outer membrane
  • Peptidoglycan layer (correct)
  • Inner cell membrane
  • Cytoplasmic membrane

What happens to the crystal violet stain in gram-negative bacteria during the Gram stain test?

<p>It is degraded by the alcohol (B)</p> Signup and view all the answers

What distinguishes the cell wall structure of gram-negative bacteria from gram-positive bacteria?

<p>Presence of an outer membrane (A)</p> Signup and view all the answers

What enabled Robert Hooke to distinguish and name cells for the first time?

<p>The thick cell walls of cork (B)</p> Signup and view all the answers

What is the main difference between the plant cell wall and the extracellular matrix produced by animal cells?

<p>Plant cell walls are generally thicker, stronger, and more rigid (B)</p> Signup and view all the answers

What happens to the ability of plant cells as a result of evolving relatively rigid walls?

<p>They forfeited the ability to crawl about and adopted a sedentary life-style (A)</p> Signup and view all the answers

What is the origin of all cell walls in plants?

<p>Dividing cells, as the cell plate forms during cytokinesis (B)</p> Signup and view all the answers

What is the defining characteristic of the plant cell wall?

<p>It encloses each cell in a plant (C)</p> Signup and view all the answers

Flashcards

Gram-positive bacteria in Gram stain

Gram-positive bacteria retain the crystal violet stain due to their thick peptidoglycan layer, which traps the dye.

Gram-negative bacteria in Gram stain

Gram-negative bacteria lose the crystal violet stain during decolorization because their thin peptidoglycan cannot hold the dye.

Role of Alcohol in Gram Stain

The alcohol used in the Gram stain test decolorizes gram-negative bacteria by degrading their thin peptidoglycan layer, allowing the dye to be washed away.

Peptidoglycan in Gram-positive Bacteria

The thick peptidoglycan layer in gram-positive bacteria, present as a mesh-like structure, traps the crystal violet dye, making them appear purple.

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Structure of Gram-negative Bacteria

Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane, which distinguishes them from gram-positive bacteria.

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Robert Hooke's discovery

Robert Hooke used a microscope to observe the cell walls of cork, which were thick and rigid, allowing him to distinguish and name cells.

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Plant Cell Wall Composition

Plant cell walls are primarily composed of cellulose, hemicellulose, and pectin, providing structural support and rigidity.

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Evolution of Plant Cell Walls

Plant cells evolved rigid cell walls, limiting their mobility and promoting a sedentary lifestyle. This allowed for more complex structures to develop.

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Origin of Plant Cell Walls

All plant cell walls originate from the cell plate, a structure formed during cytokinesis (cell division), which eventually develops into a cell wall.

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Defining characteristic of plant cell wall

The defining characteristic of a plant cell wall is its rigid structure, which encloses each individual plant cell and provides mechanical support.

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Study Notes

Gram Stain Test

  • The defining characteristic of gram-positive bacteria in the Gram stain test is the retention of the crystal violet stain.
  • Gram-negative bacteria appear pink in the Gram stain test due to the decolorization of crystal violet by ethanol.
  • The peptidoglycan layer in gram-positive bacteria's cell wall retains the crystal violet stain.
  • In gram-negative bacteria, the crystal violet stain is washed out by ethanol during the Gram stain test.

Cell Walls

  • The cell wall structure of gram-negative bacteria is distinguished from gram-positive bacteria by the presence of a thinner peptidoglycan layer and an outer membrane.
  • Robert Hooke was able to distinguish and name cells for the first time using a light microscope.
  • The main difference between the plant cell wall and the extracellular matrix produced by animal cells is that the plant cell wall is rigid and composed of cellulose, whereas the extracellular matrix is flexible and composed of various proteins and carbohydrates.
  • The evolution of relatively rigid walls in plant cells resulted in a loss of ability to move and change shape.
  • All cell walls in plants originate from the embryonic cell layer.
  • The defining characteristic of the plant cell wall is its rigidity, which is provided by the cellulose fibrils.

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