Final answer:
The option that does not describe a role of the normal microbiota in the intestine is the production of oxygen to kill anaerobic pathogens; microbiota help maintain health by lowering pH, flushing microbes, and occupying space to prevent pathogen growth.
Step-by-step explanation:
Among the options provided, the one that does NOT describe how normal microbiota of the intestine helps prevent infection is "It generates large quantities of oxygen that kill anaerobic pathogens." The role of normal microbiota is multifaceted, including the production of acids that lower the pH to inhibit the growth of harmful organisms, speeding up the process by which microbes are flushed from the digestive tract, and consuming food and occupying space to outcompete potential pathogens.
However, they do not generate oxygen as a means of defending against anaerobic pathogens. The body's defense mechanisms are also aided by formed elements in the blood, such as red blood cells, white blood cells, and platelets, which help in supplying tissues with oxygen, providing nutrients, removing metabolic waste, and defending against pathogens and foreign substances.