Eukaryotic cells: select the statement that is NOT true of eukaryotes as a group
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ANucleus is bounded by nuclear membrane
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BChromosomes contain histones
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CChloroplasts and mitochondria contains 70S ribosomes
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DGas vacuoles are present
Answer
Correct Answer: Gas vacuoles are present
Explanation
Introduction / Context:Distinguishing features of eukaryotic cells include membrane-bound organelles and chromatin architecture. Test questions often probe knowledge of exceptions and organelle-specific traits.
Given Data / Assumptions:
- Eukaryotes possess a true nucleus with a double membrane.
- Eukaryotic chromatin includes histone proteins.
- Mitochondria and chloroplasts are of bacterial ancestry (endosymbiosis) and retain 70S ribosomes.
- Gas vacuoles are typical of some aquatic prokaryotes (e.g., cyanobacteria), not eukaryotes.
Concept / Approach:We identify the one statement that does not generally describe eukaryotes. Organellar ribosomes (70S) are a classic endosymbiotic hallmark within otherwise 80S cytosolic contexts. Gas vacuoles, used for buoyancy control, are a prokaryotic adaptation and rare to absent in eukaryotes.
Step-by-Step Solution:
Option A: True. Eukaryotes have a nucleus with nuclear envelope and pores.Option B: True. Histones package DNA into nucleosomes.Option C: True. Organelle ribosomes are 70S due to bacterial origin.Option D: Not a general feature of eukaryotes; gas vacuoles characterize many prokaryotic plankton.Verification / Alternative check:Review endosymbiotic theory and ribosome sedimentation coefficients: 80S (cytosol) vs 70S (organelles).
Why Other Options Are Wrong:They correctly describe standard eukaryotic traits and organelle specifics, so they are not the “not true” choice.
Common Pitfalls:Confusing organelle ribosomes (70S) with cytosolic ribosomes (80S); overlooking prokaryotic adaptations like gas vacuoles.
Final Answer:Gas vacuoles are present