Cation-exchange chromatography is used when the molecule of interest is positively charged, the stationary phase is negatively charged and positively charged molecules are loaded to be attracted to it. So, the amino acids with negative charge will elute the first. Glutamate, leucin, arginine is the order of elution because of their pI values ~3, ~6 ~10.
Mutualism is relationship that is beneficial to both organisms involved. The relationship between a plant and a bacterium called a mutualism because both of them help each other. Bacteria are involved in increasing the fertility of the soil by fixing atmospheric nitrogen and thus provide plant with nitrogen. In return, the bacteria make their homes in what usually become nitrogen "nodules" along plant roots. The plant gets food, the bacteria gets shelter, everybody wins.
I believe it is natural selection. Natural selection is when over a period of time, traits that are formed to help the organism survive, are passed to the next generation. For example, if there were two types of rabbits. One had black fur and the other was white. They both lived in the artic. The black furred rabbits are mostly eaten by predators because their black fur is easily seen against the ice and snow. Over a period of time, the black furred rabbit would die out. The next generation would mostly have white fur to help them survive.
