Questions: Eukaryotic Cells

Question 1

Which feature most fundamentally distinguishes eukaryotic cells from prokaryotic cells?

• A. Eukaryotic cells are always larger
• B. Eukaryotic cells have a membrane-bound nucleus
• C. Eukaryotic cells have ribosomes
• D. Eukaryotic cells have a cell wall

Answer: (B)

The defining feature of eukaryotes is the membrane-bound nucleus that houses the cell's DNA. Size tends to differ, but is not the defining criterion — some eukaryotes are small and some prokaryotes are large. Both domains have ribosomes (though structurally different). Cell walls are present in some eukaryotes (plants, fungi) but absent in others (animals), and are common in prokaryotes.

Question 2

Most eukaryotic cells contain a nucleus, mitochondria, and the same full complement of organelles.

• T. True
• F. False

Answer: False

Eukaryotic cells show considerable diversity. Mature human red blood cells, for example, eject their nucleus and mitochondria during differentiation. Plant cells have chloroplasts and a central vacuole that animal cells lack, while animal cells have centrioles that most plant cells do not. The shared feature is the potential for compartmentalization, not an identical organelle inventory.

Question 3

What advantage does compartmentalization provide to eukaryotic cells that prokaryotic cells lack?

Model answer: Compartmentalization allows eukaryotic cells to maintain distinct chemical environments for different reactions simultaneously. For example, the acidic pH needed for lysosomal digestion, the reducing environment of the mitochondrial matrix, and the process of transcription in the nucleus can all occur at the same time without interfering with each other. This enables far greater metabolic complexity and specialization than is possible in the undivided cytoplasm of a prokaryote.

Prokaryotes carry out all reactions in a single cytoplasmic compartment, which limits the range of conditions any one reaction can have. Membrane-bound organelles allow eukaryotes to tune each compartment independently — pH, ion concentrations, enzyme sets — and run incompatible reactions in parallel. This is directly related to eukaryotes' greater size and functional complexity.