Active motion of particles in aqueous solution may lead to interesting 
collective phenomena such as pattern formation or macroscopic fluid flows. I 
will discuss two examples where this can be observed. First, I will present 
lattice Boltzmann simulations of a microscopic model for cytoplasmic
streaming in algal cells. Here, myosin motors entrain the surrounding fluid by 
walking along actin filaments while dragging vesicles or other organelles. I 
will pay particular attention to how the high speeds observed in experiments can 
be achieved by assuming a layer of lower viscosity at the outer wall of the 
simulated compartment. The second example is a system of sedimenting 
self-propelled particles with the additional property of bottom-heaviness, which 
results in a tendency of particles to swim upwards. I will give analytical 
results for the dilute limit and numerical results for the interacting case 
where particles form vortices and columns.