​Glucose

Glucose enters most cells by facilitated diffusion. There seem to be a limiting number of glucose-transporting proteins. The rapid breakdown of glucose in the cell (a process known as glycolysis) maintains the concentration gradient.

​Cellulose

​Cellulose is the main substance in the walls of plant cells, helping plants to remain stiff and upright. Humans cannot digest cellulose, but it is important in the diet as fibre. Fibre assists your digestive system – keeping food moving through the gut and pushing waste out of the body.