Q. What do you mean by Primary Metabolites ?
As the name indicates, primary metabolites are molecules involved in vital metabolic pathways. They are of universal occurrence and not very significant in chemotaxonomy. However, these molecules become useful as chemotaxonomic features when the quantity of such molecules varies considerably between taxa. For example, the sugar containing carbohydrate 'sedoheptulose' is stored in large quantities as a reserve food in the genus Sedum. Thus members of this genus can be easily identified by the presence of this primary metabolite. Interestingly, sedoheptulose diphosphate is a part of the photosynthetic carbon cycle and in a majority of the plants sedoheptulose does not accumulate at all. In the same way, the 22 amino acids are of universal occurrence. They serve as the building blocks of proteins. They can provide useful macromolecular data for chemotaxonomy. The amino acid sequence of different proteins can be investigated and the degree of similarity is presumably proportional to the degree of genetic relationship. However, only a few out of about 3 lakh species of angiosperms have been analysed for amino acid sequences. For example, the amino acid data on wheat and barley confirms the relationship of these genera as-suggested by classical taxonomists.