Which component is added in excess to media used to detect the fermentation of lactose?

• A. Peptone
• B. Glucose
• C. Sodium chloride
• D. Lactose

Answer: (D)

Verified step by step guidance

1. Understand the purpose of the media used to detect lactose fermentation: it is designed to identify whether an organism can ferment lactose by producing acid or gas.
2. Recognize that to test for fermentation of a specific sugar, that sugar must be present in the medium in sufficient quantity to serve as the substrate for fermentation.
3. Identify that lactose is the sugar of interest in this test, so lactose must be added in excess to ensure that if the organism can ferment it, the reaction will be detectable.
4. Note that other components like peptone, glucose, or sodium chloride serve different roles (nutrient source, osmotic balance) but are not the primary fermentable sugar in this test.
5. Conclude that the component added in excess to detect lactose fermentation is lactose itself, as it is the fermentable carbohydrate whose metabolism is being tested.