The correct choice is (a) Aerobic
Easy explanation: The Crabtree effect describes the phenomenon whereby the yeast, Saccharomyces cerevisiae, produces ethanol (alcohol) in aerobic conditions and high external glucose concentrations rather than producing biomass via the tricarboxylic acid (TCA) cycle, the usual process occurring aerobically in most yeasts e.g. Kluyveromyces spp. Increasing concentrations of glucose accelerates glycolysis (the breakdown of glucose) which results in the production of appreciable amounts of ATP through substrate-level phosphorylation. This reduces the need of oxidative phosphorylation done by the TCA cycle via the electron transport chain and therefore decreases oxygen consumption.
