Cell Envelope and Its Modifications
Every bacterial cell is wrapped in a layered boundary called the cell envelope. This quiz tests your grasp of its three concentric layers — the glycocalyx, the cell wall and the plasma membrane — and the surface structures that project beyond them.
- Gram positive versus Gram negative wall architecture
- Slime layer versus capsule forms of the glycocalyx
- Peptidoglycan, osmotic protection and cell shape
- Selectively permeable fluid mosaic membrane
- Mesosomes and chromatophores as membrane modifications
- Flagella, pili and fimbriae and their roles
Work through all fifteen questions carefully — each explanation reinforces the underlying concept.
Q1. Which sequence correctly lists the three layers of the prokaryotic cell envelope from outermost to innermost?
The envelope is described as three concentric layers: the glycocalyx outermost, the cell wall beneath it, and the plasma membrane innermost.
Q2. In Gram positive bacteria, which feature of the envelope explains why the primary dye complex is retained after staining?
Gram positive bacteria have a thick wall that retains the primary dye complex, whereas the arrangement in Gram negative cells differs.
Q3. The bacterial cell wall is built from peptidoglycan. Which description best matches this material?
The lesson states that the bacterial wall is built from peptidoglycan, a meshwork of sugar chains cross-linked by short peptides.
Q4. A glycocalyx that appears as a loose, poorly organised covering is best described as which of the following?
The glycocalyx may appear as a loose slime layer or as a more organised capsule; the loose form is the slime layer.
Q5. Which statement about the glycocalyx is supported by the lesson?
The glycocalyx is described as a covering of carbohydrate-rich material, and its composition varies with species.
Q6. What is the principal mechanical role of the bacterial cell wall?
The wall is a rigid structure that gives the cell its shape and protects it from osmotic rupture.
Q7. The plasma membrane of a prokaryote is described as selectively permeable. What does this mean in practice?
The plasma membrane is the selectively permeable barrier separating cytoplasm from the exterior, admitting nutrients selectively.
Q8. According to the lesson, what determines what enters and leaves the bacterial cell?
The lesson states that the proteins embedded in the plasma membrane determine what enters and leaves the cell.
Q9. Mesosomes are best described as which of the following?
Mesosomes are internal membrane modifications derived from the plasma membrane, discussed alongside chromatophores.
Q10. Chromatophores are membrane modifications characteristically associated with which group of organisms?
The lesson specifically links chromatophores with cyanobacteria as internal membrane modifications.
Q11. Which surface structure is responsible for giving a bacterium motility?
The lesson states that the surface structures extending beyond the envelope give the cell motility and the ability to attach; motility is provided by the flagellum.
Q12. Pili are described in the lesson as which kind of structure?
Pili are described as elongated tubular structures projecting from the bacterial surface.
Q13. What is the primary function associated with fimbriae?
Fimbriae are surface appendages associated with attachment, allowing the bacterium to cling to surfaces.
Q14. The glycocalyx is important in deciding whether a bacterium can cling to a surface or form a biofilm. Which property of the glycocalyx underlies this?
The lesson notes that the glycocalyx decides whether a bacterium can cling to a surface or form a biofilm, reflecting its carbohydrate-rich covering.
Q15. The Gram stain is described as a readout of envelope chemistry. Which pair of structural features is said to separate the two Gram classes?
The lesson states that the relative thickness of the wall and the presence or absence of an additional outer membrane separate the two Gram classes.