The root hair cells in plant roots use active transport to absorb mineral ions such as nitrates from the soil- even though there are lower concentrations of minerals in the soil than there are within the root hair cell.
source: https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi81JS04WHbWlNcswE4KGiSAb3bgekuAkcU7fzkP4w_eGjPgQkCWESDUu1gB6aoZdegvvDjc7vel_rPIfCpPPAI-af-XBXcsEqvoSWHXZL704u1xwGNAjWfoV_g0BKpocQz2MhLGFhL4vtY/s400/gb110711_root_hair_apoplast_and_symplast.jpg
Root hair cells have a large surface area to speed up the process of osmosis. The cell sap in the vacuole is hypertonic (low concentration of water molecules), hence causing water to pass through the partially permeable cell membrane by osmosis. This results in a high concentration of water molecules and a lower concentration of cell sap containing sugars, organic acids and ions. The water will then osmosize into the next cell, travelling from a region of high concentration to a region of low concentration.
Small intestine villi cells
The small intestine villi cells use active transport alongside diffusion to maximise the absorption of glucose and other substances (eg minerals).
source: http://www.acbrown.com/neuro/Lectures/Mmbr/AVFigs/NrMmbr51.jpg
The villus is made up of many cells to increase the surface area and therefore the rate of diffusion. The microvillar membrane of the microvilli (found on surface of every cell in villus) is packed with enzymes to maximize the breakdown of complex nutrients into simple compounds.
