The size of a single cell can range from a mycoplasma, which is considered the smallest cell, to a giant skeletal muscle fiber or ostrich egg.
Assume that Escherichia coli cells, human hepatic cells, and epidermal cells of an onion scale are cylinders with approximate lengths of 1 micrometer, 20 micrometers, and 100 micrometers, respectively, and the length to diameter ratio is equal 5 to 1. Plant cells are usually much larger.
Also assume that the transport activity of the plasma membrane is proportional to its surface area, and the metabolic capacity of the cell is proportional to its volume.
True or false?
Q16.1. Escherichia coli has the lowest surface area (S) to volume (V) ratio (S/V) amongst the mentioned cells.
Q16.2. The S/V ratio of human hepatic cells, compared to onion epidermal cells, differs by 5 fold.
Q16.3. A relatively low S/V ratio demands a relatively high plasma membrane density of active transport proteins for the maintenance of constant metabolism level inside the cytoplasm.
Q16.4. To maintain relatively high cytoplasmic metabolic activity, plant cells usually have large metabolically passive vacuoles and active cytoplasmic streaming.
Q16.5. More spherical cells usually sustain a higher metabolic activity than long or flat cells with the same volume.
Question reproduced from IBO 2023, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF