‘What cells can do’ examines varied examples of cell specialisms that allow an organism to protect itself and respond to its environment. Firstly, it considers cells at the surface — epidermis in plants, exoskeletons in insects, and skin in animals. Blood is formed from a collection of various cell types, which are continuously produced from a small number of stem cells. White blood cells are specialist defensive cells that have evolved to protect multicellular organisms from attack by bacteria, viruses, and parasites. Cells working together and how the nervous system functions are explained. Over time, all cells accumulate multiple genetic changes to their DNA sequence. The mutations, adaptations, and evolutionary modifications of cellular change are also described.