Final answer:
Cells remain small because the efficient transfer of substances across the cell surface is crucial for life processes and becomes increasingly difficult as cell size grows. Not all materials can flow through the nuclear pore due to a size limit of approximately 10-26 nanometers, preventing larger molecular structures from passing unless properly signaled or disassembled.
Step-by-step explanation:
The reason not all content can simply float through the nuclear pore is due to its size limit. The nuclear envelope, which surrounds the nucleus, contains pores that control the passage of ions, molecules, and RNA between the nucleoplasm and cytoplasm. The typical pore diameter is about 10 nanometers and can open up to as much as 26 nanometers in response to specific signals. This size restriction prevents complete ribosomes, which are larger than the nuclear pore when fully assembled, from passing through unless they are first disassembled into their subunits. Cells remain tiny and multiply rather than getting bigger because the ability of a cell to efficiently pass substances across its surface is critical for carrying out life processes and becomes limited as cell size increases.