BACTERIA LABORATORY 2B EXERCISE 1: OBSERVING BACTERIA Cell wall characteristics
ID: 149914 • Letter: B
Question
BACTERIA LABORATORY 2B EXERCISE 1: OBSERVING BACTERIA Cell wall characteristics (shape and thickness) are typically used to identify and classify bacteria. Most bacteria exhibit one of three shapes: bacillus (short cylindrical rods), coecus (round spheres), or spirillum (spirals resembling corkscrews). From the organism's perspective, shape is important because it can influence the efficiency with which a bacterium absorbs nutrients, moves through its environment, and escapes predators. The thickness of the cell wall and its response to a procedure called Gram staining is also useful in idenification Cell walls of gram-positive bacteria have a thick peptidoglycan layer that retains a violet dye once it is applied. Consequently, gram-positive bacteria appear blue/purple when observed through a microscope. that does not retain the violet dye after rinsing so gram-negative However, cell walls of gram-negative bacteria have a much thinner peptidoglycan layer bacteria appear pink/red. Ascertaining erium is gram-positive (+) or gram-negative(-) is an important piece of evidence used by type of antibiotic to prescribe for a bacterial infection. diagnosticians to determine what SHAPES AND CELL WALL FEATURES View prepared (fxed and stained) slides of the bacteria, Bacillus, Staphylococcus, and Spirillum using the demonstration microscopes in the back of the room. To maximize resolution and clarity, an n was used to set up each demonstration. All you should need to do is view. Please do not move the stage or rotate the objectives. For each bacterium on display, draw and describe the cells that you observe in Figure 2B.1. Based on your observations, answer the questions that follow. Figure 2B.1 Various Types of Bacteria Bacteria sp. Cell Shape* Stain Color** PuT PIe Bacillus anthracis Spirillum volutans Staphylococcus aureus Spial pink Pur P1 Gram or Gram Drawing " rods, spheres, or spirals blue/purple or pink/red O kbhartney 2B-3
Explanation / Answer
Magnification of the microscope = power of objective lens x power of eyepiece = 10 x 100 = 1000x.
If individual cells are not visible at this magnification, that means the bacteria are very very small ( more than 1000 times smaller than the smallest object that can be seen by naked eye. The human eye can see a size of 0.1 millimeters. The bacterium will lie in the size range of 0.1 micrometers)
All the organisms of a species have the same characteristic features. Yes, all the bacteria within a species will have the same shape.
The bacterial cell wall maintains the shape of the bacteria. It is freely permeable. It keeps out large particles and prevents the bursting of the bacterial cell due to change in osmotic pressure.
It is made of peptidoglycan.
The cell wall in plant cells is made of cellulose and is also freely permeable. Peptidoglycan and cellulose are both polysaccharides.
The plant cell wall is much thicker and much less rigid than the bacterial cell wall.
No. Bacteria are prokaryotes and they do not have any organelles. They are primitive organisms which do not have membrane-bound bodies.
If we could look inside the cell, we would expect to find the genetic material (chromosomes, which lie in the cytoplasm as chromatin) and some ribosomes.
On the entry of water, the bacterial cell would become turgid but the cell wall prevents the entry of too much water and the subsequent bursting (lysis).
If anything such as penicillin would compromise the cell wall, water, and other large particles would be able to penetrate the cell, eventually causing its lysis.
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