Compared with small cells, large cells have more trouble doing what?

Larger cells have slower diffusion rates.

This is because the ratio of;

surface area of a cell : volume of a cell

Decreases with size, as volume increases exponentially with respect to surface area.

We might consider that;

Surface area = X²,

Volume = X³

As X increases, X² : X³ decreases.

So large cells have more trouble with diffusion.