In 2011 I wrote about a research project I went on in France to investigate how invertebrates can show the level of water pollution in rivers and streams (click here). While I was there, I quickly picked up on the huge diversity of life in rivers, far beyond what we would expect. While searching through one kick sample, I came across a twig which moved and then a little Caddisfly larva emerged – I was fascinated!
Back in the very beginnings of my scientific education, I was taught the ‘MRS GREN’ code of life (movement, respiration, sensitivity, growth, reproduction, excretion and nutrition). Although quite rudimentary, this was a perfectly satisfactory way of distinguishing between things that were living, and things that were not.
The S in MRS GREN, sensitivity, stands for the ability of all living things to detect changes in their environment. To do this we use our senses, a characteristic dating back to virtually the beginning of life. Even simple, single celled organisms can sense their environment and respond to it.