Question

the clear zone seen after iodine is added in the starch test indicates: acid production starch hydrolysis (enzyme present) protein digestion no starch hydrolysis question 10 (bonus) (1 point) a kliglers iron agar tube shows a red slant and yellow butt. which of the following interpretations is correct? ferments glucose and lactose ferments all three sugars no sugar fermentation ferments glucose only

Explanation:

• Starch test: Iodine reacts with starch to form a blue - black complex. If there is a clear zone, it means starch has been broken down (hydrolyzed). This hydrolysis is usually catalyzed by an enzyme (amylase). Acid production is not directly related to the clear zone in the starch - iodine test. Protein digestion is tested with other methods (e.g., using biuret reagent). If there was no starch hydrolysis, the entire area would turn blue - black with iodine.
• Kligler’s Iron Agar (KIA) tube: The medium contains glucose and lactose. When only glucose is fermented, the organism first uses the small amount of glucose. In the butt (anaerobic environment), glucose fermentation produces acid (turns yellow). As the glucose is exhausted (since it is in a smaller amount), the organism starts to use peptones in the slant (aerobic environment). Peptone degradation produces alkaline products (turns red). If lactose was fermented (in addition to glucose), the slant would also be yellow (because lactose is in a larger amount and its fermentation would produce enough acid to keep the slant yellow). If no sugar fermentation occurred, both slant and butt would be red (from peptone degradation).

Answer:

• For the starch test: Starch hydrolysis (enzyme present)
• For the Kligler’s Iron Agar tube: Ferments glucose only