Iodine Test for Polysaccharides 2.0

Summary

In this video, Drew Callup demonstrates the iodine test for identifying carbohydrates, focusing on the distinction between glycogen and starch. By adding iodine to various samples, including negative and positive controls, the test highlights how iodine reacts differently with each polysaccharide—producing a brownish-red color for glycogen and a blue-black color for starch. Drew also explains the chemical similarity but structural differences between glycogen (used by animals) and starch (used by plants) for energy storage. The video concludes with a preview of the next test, Barfoid's test, aimed at identifying monosaccharides versus disaccharides.

Takeaways

• 😀 The iodine test is used to identify polysaccharides like glycogen and starch.
• 😀 Iodine reacts differently with glycogen and starch, creating a brown radish color for glycogen and a blue-black color for starch.
• 😀 Both glycogen and starch are polysaccharides of glucose but differ structurally.
• 😀 Water serves as the negative control, while glycogen and starch are used as positive controls in the test.
• 😀 The iodine test helps distinguish between glycogen and starch based on their chemical and structural differences.
• 😀 Glycogen and starch are both used for energy storage, with glycogen being used by animals and starch by plants.
• 😀 The iodine test for polysaccharides builds on the previous carbohydrate identification test, the Benedict's test for simple sugars.
• 😀 This test helps identify which unknown samples are polysaccharides and which are not.
• 😀 The chemical structure of glycogen and starch is similar, but their functional use and structure in organisms differ.
• 😀 Future tests in the series will include Barfoid's test, which distinguishes between monosaccharides and disaccharides.

Q & A

What is the primary focus of the iodine test in this lab?

The iodine test is used to identify polysaccharides, specifically glycogen and starch, by observing their reaction with iodine.

What does iodine do when it reacts with glycogen?

When iodine reacts with the structure of glycogen, it produces a brownish-red color.

What color does iodine produce when it reacts with starch?

Iodine produces a blue-black color when it reacts with starch.

Why is there a difference in the iodine test results for glycogen and starch?

The difference in the color response is due to the structural differences between glycogen and starch, even though they are chemically similar.

How are starch and glycogen structurally different?

Starch is a polysaccharide found in plants, and glycogen is a polysaccharide used by animals for energy storage. Starch has a different branching structure compared to glycogen.

What is the significance of the iodine test's positive and negative controls?

The positive controls for glycogen and starch demonstrate the expected reactions, while the negative control (water) shows no reaction, allowing for a comparison to the unknown samples.

What types of organisms typically use starch and glycogen?

Plants typically use starch to store energy, while animals use glycogen for the same purpose.

What role do glycosidic bonds play in the structure of starch and glycogen?

Glycosidic bonds link glucose molecules together to form starch and glycogen, which are both polysaccharides used for energy storage.

What should you observe when testing the unknown samples in this iodine test?

You should compare the color reactions of the unknown samples to the positive and negative controls to determine whether they contain glycogen or starch.

What is the next test mentioned in the video after the iodine test?

The next test mentioned is the Barfoed's test, which is used to distinguish between monosaccharides and disaccharides.