Determinants of small cell size: which factors may account for why cells are typically small?

Introduction / Context:
Cell size is constrained by physical transport limits and biosynthetic capacity. Understanding why most cells are microscopic integrates physics (diffusion), geometry (surface area to volume), and molecular biology (gene expression throughput).

Given Data / Assumptions:

• Substances move within cells largely by diffusion over micrometer scales.
• Cell exchange with the environment scales with surface area; metabolic demand scales with volume.
• Eukaryotic cells rely on transcription/processing/export of mRNAs from the nucleus, which can bottleneck protein production.

Concept / Approach:
Small size shortens diffusion distances, enabling rapid metabolite and signaling flux. A high surface area/volume (SA/V) ratio improves nutrient uptake and waste removal per unit cytoplasm. In eukaryotes, the nucleus imposes throughput limits on mRNA synthesis and export, linking gene expression to cytoplasmic volume.

Step-by-Step Solution:

Verification / Alternative check:
Examples: giant cells (skeletal muscle) circumvent limits via multinucleation; microvilli increase SA/V in absorptive epithelia; prokaryotes lack a nucleus and rely even more on diffusion constraints.

Why Other Options Are Wrong:
Picking any single factor understates the multifactorial nature of size constraints.

Common Pitfalls:
Thinking only SA/V matters; overlooking diffusion time scaling and biosynthetic throughput from the nucleus.

Final Answer:
All of the above