Origin Of Life: Issues

Trophic Method

Contemporary carbon-based organisms can be categorised according to the way in which they obtain the molecules required for the synthesis of their organic molecules. The two categories are as follows:- Organisms can also be categorised according to their energy sources as follows:- Different combinations of carbon and energy source give rise to four kinds of metabolism: photoautotrophy, chemoautotrophy, photoheterotrophy and chemoheterotrophy.

It is generally assumed that these categorisations are also relevant in relation to discussion of the trophic method of the first organisms. This does however require a modification to the definition of heterotrophy when used in the context of the origin of life; if the first organisms were heterotrophs then they clearly could not have been dependent on autotrophic organisms as contemporary heterotrophs are. Thus, primordial heterotrophs are regarded as organisms that used preformed organic molecules synthesised by non-life chemical processes.

The organisms envisaged by Oparin and Haldane were primordial heterotrophs, dependent on chemical building blocks synthesised in the prebiotic soup; the ability of organisms to synthesise such relatively complex nutrients came as a later evolutionary development.

By contrast, an alternative view is that the first organisms were autotrophic, and so not dependent on the abiotic synthesis of complex nutrients.