Starch Hydrolysis

Summary

The lab experiment investigates starch hydrolysis by bacteria, focusing on the production of an exoenzyme called diastasis. Starch agar plates streaked with two bacterial samples were incubated and then tested with iodine, a starch indicator. A clear zone around one bacterium indicates starch hydrolysis due to diastasis, as the iodine does not turn dark, whereas the other shows no hydrolysis with a brown coloration. This visual differentiation highlights the presence or absence of the enzyme's activity in breaking down starch into glucose.

Takeaways

• 🧪 The lab is conducting a test on starch hydrolysis to determine if a bacterium can produce an exoenzyme called diastasis.
• 🌿 The bacteria are streaked on a starch agar plate and incubated to observe their effect on starch.
• 💧 Iodine is used as an indicator to test for the presence of starch; it turns a dark color when it binds with starch.
• 🔍 A clear zone around bacterial growth indicates starch has been hydrolyzed by the exoenzyme diastasis, as there is no longer any starch to react with the iodine.
• 📦 The iodine is added to the Petri plate just enough to cover the surface of the agar to avoid excess spillage.
• ⏱ After adding iodine, the plate is left for about 30 seconds to a minute to allow for the reaction to occur.
• 🚫 Care must be taken not to tip or pick up the plate to prevent the liquid iodine from spilling.
• 🗑 Excess iodine is poured into a disposal container to maintain safety and cleanliness in the lab.
• 🔬 A white background is used to enhance visibility of the clear zone, making it easier to assess the results of the hydrolysis.
• 📈 The results show that the bacterium on the left did not hydrolyze starch as the agar turned brown, while the one on the right did, indicated by a clear zone.
• 🔍 The presence or absence of a clear zone is the key observation for determining whether starch has been hydrolyzed by the bacterium.

Q & A

What is the purpose of the starch hydrolysis test in the lab?

The purpose of the starch hydrolysis test is to determine whether a bacterium can produce an exoenzyme called diastasis that can break down starch into glucose.

What is the role of diastasis in this experiment?

Diastasis is an exoenzyme that, if produced by the bacterium, can hydrolyze starch into glucose.

What type of medium was used for the bacteria in the experiment?

A starch agar plate was used for the bacteria in the experiment.

How were the bacteria applied to the starch agar plate?

The bacteria were applied to the starch agar plate by making single streaks using an auger.

What is the function of iodine in the starch hydrolysis test?

Iodine is used as a starch indicator in the test. It reacts with starch, turning it a dark brown to black color, which indicates the presence of unhydrolyzed starch.

What does a clear zone around bacterial growth indicate after iodine is added?

A clear zone around bacterial growth indicates that the starch has been hydrolyzed by the exoenzyme diastasis, as there is no longer any starch to react with the iodine.

How long should iodine be left on the plate after being added?

Iodine should be left on the plate for about 30 seconds to a minute to allow for the reaction with the starch.

Why is it important to be careful with the iodine after it has been added to the plate?

It is important to be careful with the iodine because it is a liquid and can run off the plate if it is tipped or picked up, potentially staining clothes or skin.

What was the method used to remove excess iodine from the plate?

The excess iodine was poured into a disposal container to prevent it from running off the plate.

How can the results of the starch hydrolysis test be more easily observed?

The results can be more easily observed by placing a white background behind the plate, which helps to contrast the clear zone against the dark iodine-stained agar.

What was the outcome for the two organisms tested in the script?

The organism on the left did not hydrolyze the starch, as indicated by the brown color where the starch reacted with iodine. The organism on the right produced a clear zone, indicating that it hydrolyzed the starch.