SALIVA TEST
Introduction This is a practical lesson using saliva to learn digestive enzyme activity. We can check the existence of reducing sugars clearly by Benedict’s reaction after salivary enzyme decomposes starch to maltose or glucose very swiftly. Using students’ own saliva, they can feel chemical reactions proceeding constantly in their body.
During the experiment students must check function of saliva under the following condition. After that students can summarize general properties of salivary enzyme through applying their known theories on enzyme. Experimental conditions 1. At room temperature (in Ghana from 25 to 30 degrees Celsius) and in neutral solution. 2. After keep on heating the enzyme solution above 75 degrees Celsius for more than 15 seconds. 3. Under temperature near freezing temperature. 4. Under presence of strong acid. 5. Under presence of strong base.
Note l The saliva test must be conducted in strict order. Lecturers must stress to the students repeatedly. Students must also prepare a control test tube. l Students must not touch other person’s saliva in order to avoid transmission of some diseases. l Please use starch glue made of ordinary flour as enzyme substance. Lecturers must check the glue whether it does not have any reducing sugars in advance using Benedict’s reaction or Fehling’s reaction. l Heat enzyme solution above 80 degrees Celsius in hot water bath for more than three minutes in order to denature the enzyme irreversibly (condition 2). l For condition 3; the enzyme solution and substance solutions must be stored near freezing point before the experiment. Before Benedict’s reaction, the enzyme must be denatured by trichloroacetic acid. We can omit this condition at junior high schools because of such complex procedure. l The strong base such as sodium hydroxide we use under condition 5 erodes skin and cornea. Lecturers must prepare buckets of clean water in case of accidents. l As we use assorted chemicals and glassware, lecturers must paste labels on containers and droppers.
SALIVA TEST
1. Objectives Learn property of enzyme reaction under various conditions through decomposition of starch by salivary amylases/ptyalin.
2. Materials and tools (for 1 group) 5 test tubes (13mm diameter), a test tube stand (rack), a permanent marker, 4mm diameter plastic straws, cotton wool, an improvised beaker, a 250ml glass beaker, a retort stand, a funnel holder, a fire clay triangle, a spirit burner, a clamp, a clamp holder, a laboratory thermometer, tweezers (forceps), 10ml measuring cylinder, a glass rod, a Petri dish, diluted sodium hydroxide (NaOH) aqueous, diluted hydrochloric acid (HCl), blue litmus paper, red litmus paper, potassium iodine aqueous, Benedict’s solution, tap water, methanol and human saliva
3. Note “Preparation of Benedict’s solution” 1) Put 400ml of hot distilled water (battery water is also available) in a 1000 ml beaker. 2) Add 87g of tri-sodium citrate. 3) Add 50g of sodium carbonate anhydrous. 4) Dissolve the mixture perfectly. 5) After dissolving it, filter the liquid using the funnel and filter paper. 6) Add distilled water to the filtrate and make a volume of 425ml (solution A). 7) Dissolve 8.7g copper II sulphate in 50ml distilled water (solution B). 8) Add solution B to solution A and add some distilled water to make the volume of the solution 500ml (Benedict’s solution).
Checking the reducing sugar Put about 1ml of solution, which you want to check, in a test tube. Add about 0.5 ml Benedict’s solution in the test tube. Put it in hot water bath for at least two minutes and observe the colour of the liquid. If the liquid stays blue, there is no reducing sugar in liquid, if it changes to a rather dirty yellow-green colour, there is a small amount of reducing sugar, if you see an orange or reddish brown precipitate, there is a lot of reducing sugar.
4. Method Collecting human saliva Wash your mouth and then put about 1cm diameter cotton wool ball in your mouth, wait about 30 seconds for absorption of saliva into the cotton. Collect all of your group mates’ cotton wool in the improvised beaker and add approximately 10ml tap water. From this point this diluted saliva solution is called enzyme solution.
Preparation of enzyme substance (starch glue) Put about 1g starch powder in a 250ml beaker. Add approximately 100ml tap water in the beaker. Heat the beaker with the burner and keep stirring the liquid constantly until the liquid becomes transparent. After it becomes transparent, stop the fire and leave the beaker out at room temperature to cool.
Enzyme reaction under different conditions 1) Set 5 test tubes in the test tube stand. 2) Write test tube name near the rim of each test tube (test tube A to test tube E) 3) Assemble a hot water bath set up and prepare boiling water. 4) Add the following liquids which are indicated in the illustration to designated test tubes. Follow the arrows which show the order of the procedure. When you add starch glue, collect the liquid at teacher’s table. If you use 13mm diameter test tube, 1ml is equivalent to 0.8cm deep. When you add HCl, NaOH and Benedict’s solution, use 4mm diameter plastic straws. 0.5ml is equivalent to 4cm water column in the straw.
SALIVA TEST ASSIGNMENT
1. Fill in the blank columns to summarize what happened or did not happen in the test tubes.
2. Summarize the property of salivary enzyme which was clarified in today’s experiment.
Sample answers
SALIVA TEST ASSIGNMENT 1. Fill in the blank columns to summarize what happened or did not happen in the test tubes.
2. Summarize the property of salivary enzyme which was clarified in today’s experiment. Salivary enzyme decomposes starch to reducing sugar at room temperature (by test tube B). Heating above 80 degrees Celsius denatures the enzyme irreversibly (by test tube C). Under existence of strong acid or strong base the enzyme is inactivated (by test tube D and E).
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