CSIM 1.33 Bacterial Shapes Size and Structures

Question 1

What are the domains that make up prokaryotes?

Answer 1

• Bacteria

* Archaea

Question 2

What are the types of microorganism?

Answer 2

• Viruses
  
  • Bacteria
  • Protozoa
  • Algae
  • Fungi

Question 3

Outline the features specific to a eukaryotic cell.

Answer 3

• Cell membrane
  
  • Nucleus with membrane
  • DNA exclusively in this nucleus
  • Mitochondria
  • Capable of differentiation

Question 4

Outline the features specific to a prokaryotic cell.

Answer 4

• Cell membrane with a cell wall
  
  • No nuclear membrane
  • No mitochondria
  • Contains plasmids

Question 5

How are bacteria classified?

Answer 5

• Based on structural phenotype

* Based on molecular activity and content

Question 6

What are the basic shapes of bacteria?

Answer 6

• Bacillus (rod)
  
  • Coccus
  • Coccobacilli (elongated spheres)
  • Diplococcus
  • Streptococcus (chain)
  • Staphylococcus (cluster)
  • Tetrads (4 cocci in a square)
  • Sarcinae (cubic configuration of 8 cocci)
  • Fibrio (bent rods)
  • Spirillum (flexible spiral)
  • Spirochete (rigid spiral)

IMG 79

Question 7

How is structural phenotype determined?

Answer 7

• Shape
  
  • Staining different colours
  • Genetic makeup
  • Survival tests (with particular medicines)

Question 8

What are the two types of stain?

Answer 8

Direct stain
• Stain is basic
• Colour of dye is positively charged
• Bacteria have a negative charge and so the colour enters

Indirect stain
• Stain is acidic
• Colour of dye is negatively charged
• Bacteria have a negative charge and so the colour leaves

IMG 80 & 82

Question 9

Describe gram negative and gram positive bacteria

Answer 9

Gram positive
• 1 cell membrane, inside of the cell wall
• Thicker peptidoglycan cell wall

Gram negative
• 2 cell membranes, one inside and one outside of the cell wall
• Thinner peptidoglycan cell wall

Question 10

How can you differentiate gram positive and gram negative bacteria?

Answer 10

Gram stain test
• Add crystal violet which stains all cells
• Add iodine which binds to crystal violet and traps it in the cell
• Add alcohol which acts as a de-colourant
• This removes all dye which is not attached to the cell (‘washes it off’)
• Gram positive bacteria entrap the CV-I complex in its multilayered thick cell wall, so it is not washed away
• Gram negative bacteria have their CV-I washed away
• Safranin is added to counterstain the gram negative bacteria

Gram positive bacteria are purple
Gram negative bacteria are pink

IMG 81

Question 11

What is heat fixation?

Answer 11

Process by which organisms are killed and attached to a slide so that they cannot replicate or be washed away

Question 12

What shape is Neisseria meningitidis?

Answer 12

Diplococcus

Question 13

Which shape/association is Neisseria gonhoeae?

Answer 13

Diplococcus

Question 14

Which bacteria is mostly responsible for tooth decay?

Answer 14

Streptococcus mutans