Mechanical and Chemical Digestion Labs
Introduction:
Mechanical digestion is the breaking down of food into smaller pieces. This occurs when you
chew your food in your mouth, or when your stomach churns your food. These small pieces will
be mixed with digestive enzymes and moved through the alimentary canal.
Chemical digestion is when enzymes and other chemical substances break down small food
pieces into nutrients that can be used by the body’s cells.
Chemical digestion takes place in the mouth, stomach, and small intestine. The salivary glands,
liver, gall bladder, and the pancreas help with the chemical digestion. During mechanical
digestion, the teeth and tongue break down food and moisten it. The food will become a soft
round call called a bolus. The bolus will be swallowed and passed down the esophagus into the
stomach. Mechanical digestion continues in the stomach where the muscles churn and break
the bolus into smaller particles.
Chemical digestion also occurs in the stomach with the help of digestive enzymes. The
glandular cells in the stomach lining secrete enzymes or acids. Pepsin is an enzyme secreted by
these cells. Hydrochloric acid (HCl) is an acid secreted by stomach lining cells as well. It is to be
noted, these different chemicals are secreted by different types of cells that both happen to be
located in the lining of the stomach. Pepsin and acids are important in the digestion of proteins.
When this partially digested food leaves the stomach and enters the small intestine it will be
called chyme.
Key Terms: Digestion, mechanical digestion, chemical digestion, enzyme, protein, albumin, acid,
base, pH, macromolecule, molecule, Biuret reagent
Objective: Discover the effects of mechanical digestion and chemical digestion
Mechanical Digestion Lab
Materials (Per group)
 200 mL Beakers (3)
 100 mL H2O (to put in each beaker)
 Effervescent tablets (3)
 China marker
 Stopwatch
 Mortar
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Pestle
Thermometer
Goggles
Hot plate
Erlenmeyer Flask
Instructions
 Collect materials
 Add 100 mL of H20 to each beaker
 Number beakers 1, 2, 3, 4 using the china marker
 Heat 300 mL of H2O in an Erlenmeyer flask in the microwave for 1 minute
 Measure temperature with the thermometer, heat or let cool until the water reaches
100F (Note: 100F is roughly the temperature inside of the digestive organs)
 Carefully pour 100 mL into beakers 1, 2, & 3.
 Get stopwatch ready
 Add 1 solid effervescent tablet into beaker 1 and watch it dissolve: time it with a
stopwatch.
 Break a tablet in HALF.
 Drop both halves into beaker 2. Watch it dissolve: time it with a stopwatch.
 Break the third tablet into small pieces.
 Add the small pieces to the mortar
 Crush the pieces in the mortar with the pestle until you get a fine powder
 Add the powder to beaker 3. watch it dissolve: time it with a stopwatch.
Digestion Lab 1 Questions:
1. How long did the tablet in beaker 1 take to dissolve? ___________________
2. How long did the tablet in beaker 2 take to dissolve? ___________________
3. How long did the tablet in beaker 3 take to dissolve? ___________________
4. How does increasing surface area affect the time it takes for the tablets to dissolve?
5. If increasing the surface area of the tablet represented thoroughly chewing your food
during mechanical digestion, how would you describe its importance in total digestion?
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Chemical Digestion Lab
Materials
 Lab Coat
 Goggles
 Gloves
 Test Tube Rack
 Test Tubes (4)
 10 mL Graduated cylinders (4)
 200 mL Erlenmeyer flask (3)
 Pepsin Solution (pepsin dissolved in water)
 HCl Solution (diluted)
 Pepsin + HCL Solution
 Albumin (protein) powder (albumin is a protein found in egg whites)
 China marker
 ¼ Teaspoon (alternatively weigh out 1.25 g of powder using digital scale)
 Stoppers for test tubes (4)
 Water
 Vortexer (optional)
 Water bath
 Biuret Reagent (this solution is Caustic! It can burn your eyes and skin. Be careful and
keep PPE on at all times)
Instructions
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Number the test tubes P1, P2, P3, and P4 (where = protein digestion)
Place the test tubes in the test tube rack
Add 1/4 teaspoon of albumin powder to each tube
Add 5 mL of the pepsin solution to tube P1
Add stopper to P1, swirl the tube. You can vortex the tube, but do not shake the tubes.
Add 5 mL of the HCl solution to tube P2.
Add stopper to P2, swirl the tube.
Add 5 mL of the pepsin + HCl solution to tube P3.
Add stopper to P3, swirl the tube.
Add 5 mL of H2O to tube P4.
Add stopper to P4, swirl the tube.
Place al 4 test tubes into a water bath at 100F (38C)
Test tubes will remain in the hot water bath for 45 minutes. Set a timer.
After 45 minutes remove the tubes from the water bath and return them to the test
tube rack.
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Now, we will check each test tube for the presence of proteins. ** if proteins are
present in the solution, it means protein digestion did NOT take place.
The chemical indicator for this experiment is Biuret’s reagent.
Add 6 drops of Biurets reagent to EACH test tube.
If proteins are present, the tube will turn purple, alternately if protein digestion has
occurred the tube will turn pink.
Digestion Lab 2 Questions:
1. What color did each tube turn? What does that mean?
a. P1- _____________________________________________________________
b. P2- _____________________________________________________________
c. P3- _____________________________________________________________
d. P4- _____________________________________________________________
2. What is the reason for creating tube 4? What purpose does it serve?
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3. If proteins are NOT present, what does that mean occurred in the tube?
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4. What is a protein?
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5. What is an amino acid?
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6. How is this lab a good example of chemical digestion?
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