Tip:
Highlight text to annotate it
X
Today's topic is the digestive system
In the first part, we will examine ptyalin effects.
- Students hold 40 cm3 of water in their mouth.
- They wait for about 5 minutes.
- Then they empty their mouth into the beaker.
- We put the starch into the test tube.
And add a few drops of Lugol's solution.
- The solution turns navy, nearly black.
- But when we pour the solution into the beaker with ptyalin, it gets decolorized.
- The molecules of starch are split by ptyalin enzyme into malt sugar, which is the final product of ptyalin digestion.
- We will observe the conversion of the starch into the maltose.
- Students chew a piece of bread properly for 5 minutes.
During the chewing, they experience a sweet taste in their mouth.
- Students write down the time of the first presence of the sweet taste
- Then the chewed bread is placed into a beaker for further experiments.
Demonstration of ptyalin digestion.
- Crumbled bread and water are put into one of the test tubes.
- Chewed bread and water are put into the second one.
-We add Lugol's solution and shake.
- Nothing happened In the first test tube.
- In the second one, with effect of ptyalin, contained in the saliva, the starch from bread transformed into dextrin .
Dextrin with iodine turn pink.
- The proof of the maltose with the use of Fehling's solution
We dilute chewed bread with water.
Fehling's solution is added into the test tube, after being prepared from Fehling I and Fehling II.
We heat up the mixture.
First, yellow coloration appears, then it turns orange.
Simple saccharides reduce cupric sulfate to red cuprous oxide.
In the second part, we will prove some components of eatables.
Is milk sweet?
We pour milk into the beaker.
We add 5 drops of acetic acid.
We heat the mixture up and filter it.
We add Fehling's solution into the test tube.
Then it is heated up and we watch colouring of the mixture.
Biuret's reaction
Mixture of egg white and water is prepared.
We add sodium hydroxide and cupric sulfate into the test tube.
The reactionary mixture changes its colour.
Proteins react with cupric ionts and the mixture turns blue-violet.
Xanthoprotein reaction
We heat up a mixture of egg white with 45% nitric acid.
We observe emergence of a yellow coloration.
Characteristics of proteins. Will the denaturation occur?
We add alkohol to the proteins. Proteins curdle.
Then diluted hydrochloric acid is added to the proteins. There is a noticeable change of pH. Denaturation occurs again.
We add lead(II) nitrate. Lead is a heavy metal. Denaturation takes place.
Now, solution of copper(II) sulfate. Denaturation occurs.
Now, solution of copper(II) sulfate. Denaturation occurs.
We try heating up the proteins. They do curdle.
translation Zuzana Stuchlíková timing Antonín Šmíd