Fig. 2: Nutrient transport by diffusion versus cilia-driven feeding currents.
From: Flow physics of nutrient transport drives functional design of ciliates
A–C In small bacterial cells, both intracellular transport and transport to the cell surface are limited by diffusion. A When a large number of molecule-specific receptors (medium gray) are randomly but uniformly distributed over the cell surface (light gray), the nutrient uptake is nearly maximal; equivalent to that of a fully-absorbing cell1. B Clustering receptors over a fraction of the cell surface reduces diffusive flux. C Concentration (colormap) and diffusive flux (white arrows) when only half the cell surface is absorbent. D–G In ciliates, intracellular transport relies on cytoskeletal molecular motors; extracellular transport is driven by the coordinated activity of cilia (dark gray) covering (D) Ac = 90% and E Ac = 20% of the outer cell surface; nutrient uptake over a fraction Af = 10% of the cell surface (medium gray). Flow streamlines (blue lines) and speed (colormap) for (F) swimming (shown in lab and cell frame) and (G) fixed cells. H Cell design space (Ac, Af) describes the fractions of the cell surface dedicated, respectively, to the mouth and cilia coverage.
