The physics experienced by microorganisms is non-intuitive to us. Aspects that bear no importance at large scales, such as viscosity, molecular diffusion, Brownian movement and kinematic reversibility, have a profound impact in all aspects of planktonic life, from nutrient dynamics to individual interactions. The consequences for the ecology and evolution of microorganisms are transcending. I will review the peculiarities of low Reynolds numbers physics and their implications to nutrient uptake and motility, and illustrate them with examples from our research on the function of microbial shape. The incorporation of these concepts, along with new developments in numerical modelling, microfluidics and single-cell analyses, are leading us to a qualitative leap in our mechanistic understanding of how individual behaviour affects the entire planktonic system.