Final answer:
Inside a yeast cell, selection favors mitochondria that respire (option 2), as they are more efficient in energy production compared to those that ferment or have larger genomes. The ability to utilize oxygen via aerobic respiration provides a significant advantage for the survival and energy needs of the cell.
Step-by-step explanation:
Selection in Yeast Cell Mitochondria
At the level of mitochondria inside of a yeast cell, selection favors mitochondria that respire. Yeast cells are eukaryotic organisms that contain mitochondria, which are large, complex organelles where aerobic cellular respiration takes place. Through the endosymbiotic theory, we understand that mitochondria were once free-living aerobic prokaryotes engulfed by an ancestral eukaryotic cell. This event empowered the host cell with the ability to utilize oxygen to release energy from nutrients. Since yeast cells can perform both fermentation and aerobic respiration, in environments with oxygen, the mitochondria capable of respiration are more advantageous due to their efficiency in energy production compared to fermentation. Fermentation is an anaerobic process that yeasts can use to generate energy but is less efficient than aerobic respiration.
It is important to note that while mitochondria have their own genome, the size of the genome does not necessarily confer a selective advantage. Similarly, parasitic mitochondria would be selected against, as they would be deleterious to the survival of the cell. Thus, the selection within a yeast cell at the mitochondrial level is not for larger genomes or parasitic behavior, but for the functionality that supports the cell's survival and energy needs, which is most effectively met through mitochondria capable of cellular respiration in the presence of oxygen.