Stomach contents/ Identifying Organic Compounds

 Introduction:  The most common organic compounds found in living organisms are lipids, carbohydrates, proteins, and nucleic acids.  Common foods, which often consist of plant materials or substances derived from animals, are also combinations of these organic compounds.  Substances called indicators or reagents can be used to test for the presence of organic compounds.  In this investigation you will use several indicators to test for the presence of lipids, carbohydrates, proteins, vitamin C and salts.

 

 Materials:

 

Spot Plate  *must be washed with soap and water and dried before you leave this station after collecting data.

 beaker of stomach contents (contains a pipette)

disposable test tubes (in box) *these should be thrown into the lab waste as soon as you are finished with the testing.

test tube rack

test tube clamp

Piece of brown paper bag  (in box)

Hot plate

100 ml beaker w/ 50 ml water

1% Benedict's solution

1% Biuret solution

1% Lugol's iodine solution

1% DPIP

1 beaker of Stomach Contents Nutrient Determination

1 beaker of Stomach Contents Consistency Determination

 

Lipid test  using brown paper bag

1. Place 2 drops of stomach contents  nutrient determination beaker onto a piece of brown paper bag.

2. Gently rub it around with your finger.

3. Let it dry completely. (you might need to place this into your notebook and look at it tomorrow)

4.  Hold the piece of brown paper bag up to the light.  Observe any translucence (can you see light through it?)

5.  Record the results

 

Protein test:

1. Place 3 drops of the stomach contents  nutrient determination beaker  into the #1 spot plate well 

2.  Add 3 drops of Biuret solution. 

3. Observe any color change

4.  Record the results

 

  Starch test:

1.  Place 3 drops of the stomach contents  nutrient determination beaker into well  #2.

2.  Add 1 drop of Lugol's iodine solution.

3.  Observe any color change

4.  Record the results

 

Poison (Vitamin C in this case) *note vitamin C is not a poison!!! To avoid using real poisons we are "simulating" a poison.

1.  Place 3 drops of the stomach contents  nutrient determination beaker into well #3

2.  Add 1 drop of DPIP

3.  If the blue colored DPIP disappears when it hits the stomach contents, then poison (vitamin C) is present.

Record results.

4.  Continue to add 1 drop of DPIP at a time until a color change DOES NOT occur.  KEEP AN ACCURATE ACCOUNT OF THE NUMBER OF DROPS OF DPIP USED AS THAT WILL CORRESPOND TO THE AMOUNT OF POISON (vitamin C) in solution.  *1 drop DPIP = .5 cc of poison

5.  Record results

 

Glucose test:  *to be done in a disposable test tube

1. Place .5 ml of the stomach contents  nutrient determination beaker into a disposable test tube

2. Add 5 drops of Benedict's solution. 

3. Place a small piece of parafilm over the end and gently invert it one time.

4.  Place the tube in the 100 ml  beaker of steaming water for 2 minutes.

5.  Use test tube clamps to remove hot test tubes. 

6.  Observe any color change

7.  Record the results

 

pH test:

1.   Place 3 drops of the stomach contents  nutrient determination beaker into well #4

2.  Use a piece of pH paper to determine the pH.

3.  Record.

 

Part II: Stomach Contents

1. Use the beaker marked Stomach Contents Consistency to determine the relative consistency of the stomach contents based on the following scale:

+ = the contents has large chunks of undigested food some of which are identifiable (ie. pieces of apple, orange, meat)

++ = the contents has few chunks of undigested food none of which are easily identifiable.

+++ = the contents has no chunks of undigested food, the consistency is that of chyme.

 

Clean up

Clean up Procedure:

WASH and DRY the spot plate.  Throw the disposable test tube and the used pH paper in the lab waste.  Remove the hot water bath beaker from the hot plate.  Unplug the hot plate and place wrapped cord on the table top.