This microbe is photosynthetic, but in the absence of light it can use organic compounds as an energy source. Its carbon source is an organic compound. The appropriate classification for this organism would be .

The correct answer is- photoheterotroph

Explanation:

Photoheterotroph are the organisms that gain the energy from the sunlight but carbon dioxide is not their source of carbon and rather than carbon dioxide they use organic compound as their source of carbon.  

Some examples of heterotrophic organisms are purple non-sulfur bacteria, green non-sulfur bacteria. Some of the sap-sucking insects are also considered as photoheterotrophs because they supplement their energy supply with the sunlight. So as the microbe is photosynthetic nut use organic compound for carbon source therefore it is a photoheterotroph.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.