Final answer:
The core genome of a bacterial species contains genes found in every member, responsible for essential functions such as replication, transcription, translation, and vital for central metabolism.
Step-by-step explanation:
Within a bacterial species, the core genome refers to the collection of genes that are found in every member of that species. These genes are responsible for the essential functions necessary for the survival of the bacteria, such as replication, transcription, and translation. Hence, the correct answer to your question is that the core genome is (b) found in every member of the species, and it is also (a) responsible for 'core' functions including replication, transcription, and translation. Additionally, it could be considered (d) important for central metabolism since those core functions are vital for the bacteria's metabolic processes.
Now, contrasting with the core genome, there is also a concept of 'pan-genome,' which includes all the genes present across different strains and members of the species, including those genes not found in every individual, reflecting genetic diversity and adaptation. The operons, or groups of genes regulated together found in prokaryotes like bacteria, also contribute to the complexity and variability of the bacterial genome which can influence the bacteria's capabilities and behavior, such as antibiotic resistance spread through the exchange of plasmids.