Textbook Question
Which of the following terms best describes stiff, spiral-shaped prokaryotic cells?
a. Cocci
b. Bacilli
c. Spirilla
d. Spirochetes
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7. Prokaryotic Cell Structures & Functions
Bacterial Cell Morphology & Arrangements
1:25 minutesProblem 1
Textbook Question
Label the shapes of these prokaryotic cells.
a. ___________ <IMAGE>
b. ___________ <IMAGE>
c. ___________ <IMAGE>
d. ___________ <IMAGE>
e. ___________ <IMAGE> stiff
f. ___________ <IMAGE> flexible
g. ___________ <IMAGE>
Verified step by step guidance1
Step 1: Understand the common shapes of prokaryotic cells. The main shapes include cocci (spherical), bacilli (rod-shaped), spirilla (spiral-shaped with rigid structure), spirochetes (spiral-shaped but flexible), vibrio (comma-shaped), and filamentous forms.
Step 2: For each image, observe the overall shape of the cell. Determine if the cell is spherical, rod-like, spiral, comma-shaped, or filamentous. Pay attention to whether the spiral shape is rigid or flexible, as this distinguishes spirilla from spirochetes.
Step 3: Match the observed shape to the correct term. For example, if the cell is round, label it as 'coccus'; if rod-shaped, label it as 'bacillus'; if spiral and stiff, label it as 'spirillum'; if spiral and flexible, label it as 'spirochete'; if comma-shaped, label it as 'vibrio'.
Step 4: For any filamentous or unusual shapes, consider if the cells form chains or filaments, which can be characteristic of certain bacteria like filamentous cyanobacteria or actinomycetes.
Step 5: Write down the appropriate shape name next to each image based on your observations and the definitions of prokaryotic cell shapes.
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Video duration:
1mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Prokaryotic Cell Shapes
Prokaryotic cells exhibit distinct shapes that help in their identification and classification. The main shapes include cocci (spherical), bacilli (rod-shaped), and spirilla (spiral-shaped). Recognizing these shapes is fundamental for understanding bacterial morphology and its implications in microbiology.
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Cell Wall Structure and Rigidity
The rigidity or flexibility of prokaryotic cells is influenced by their cell wall composition. Gram-positive bacteria have thick peptidoglycan layers providing stiffness, while Gram-negative bacteria have thinner walls and an outer membrane, often resulting in more flexible shapes. This structural difference affects cell shape and staining properties.
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Motility and Shape Variations in Prokaryotes
Some prokaryotes have flexible shapes, such as spirochetes, which enable motility through twisting motions. The flexibility or stiffness of the cell shape relates to their ecological roles and movement mechanisms. Understanding these variations aids in identifying bacteria and their functional adaptations.
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