General PLTW Document
Activity #1: TasteThe tongue is the primary organ involved in taste. It is covered with papillae, or small projections located at the edges and tip of the tongue. In this lab you will investigate 4 distinct tastes: sweet, salty, sour, and bitter. Each taste is elicited by a specific group of substances. Sweetness is evoked by sugar, saltiness by a number of inorganic ions, sourness by acids, and bitterness by alkaloids.Bitterness is the most easily detected of the tastes and is probably a safety mechanism. Most poisons are bitter alkaloids; the taste buds are located at the back of the tongue and may help trigger involuntary vomiting in case of poison ingestion.The distribution of the different taste buds over the tongue is not even. The activity below will allow you to map this distribution based on your ability to taste sweet, salty, sour, and bitter on different regions of your tongue.To complete this activity, each student will need:4 cotton-tipped applicators4 cupsAccess to the 4 taste solutionsRinse waterBefore beginning this activity, remove gum or other food material from your mouth and rinse your mouth with water. If possible, rinse your mouth with water between tastes.ProcedurePour a small amount of one of the taste solutions into the cup so as to cover the bottom.Have the subject sit with mouth open and tongue extended.The observer will dip a clean cotton-tipped applicator into the liquid and drain the excess solution from the applicator by pressing the tip onto the side of the dish.One partner will then touch the applicator to their partner’s tongue in one of the regions outlined on the map. That partner will indicate with a (+) or (-) symbol if he or she was able to detect the taste. Be sure to rinse with water before testing the next area. This process is repeated for one taste in all 7 regions of the tongue shown on the map.Discard the swab and any solution remaining in the cup. Save or dispose of the cup as instructed by your teacher.Have the subject rinse his or her mouth with water. At the same time, prepare a cup containing a different test solution. Test all seven areas of the tongue with the second solution and record the results.Have the subject rinse with water again before moving on to the next solution. Repeat the taste test experiment for the two remaining solutions.Exchange roles and take turns mapping the 4 different tastes.Follow your teacher’s instructions to dispose of the applicators and cups.Answer the questions about this activity on the Student Response Sheet.Activity #2: SmellThe sense of smell is much more complex than the sense of taste. Smell is also much more sensitive and will work over long distances. The smell receptors are located in a pair of patches of mucous membranes located inside the nose or nasal cavity. Each receptor is about 1 ? square centimeters and is colored with a yellow pigment. Gaseous order molecules dissolve in the mucous layer and bind to the membranes of the receptor cells. These nerve cells carry impulses to the olfactory bulb, which lies under the frontal lobe of the brain.In time, sensitivity to continuous odors may diminish or even become nonexistent, while the response to other odors is unimpaired. This phenomenon is known as olfactory fatigue.To complete this activity, each student will need:Cotton swabs2 Erlenmeyer flasksProtective eyewearRe-sealable plastic bagTimerAccess to a vial of oil of cloves and a vial of oil of peppermint ProcedurePlace a cotton swab in an Erlenmeyer flask vertically so that the head of the swab is above the rim of the container.Place the flask and swab on a level surface approximately 30 centimeters (1 foot) away from and just below the nose of the test subject.Have the test subject close his or her left nostril by pressing on it with the left index finger.Place two drops of clove oil on the head of the cotton swab.Have the data recorder start the timer. At the same time, have the subject gently waft the odor toward his or her nose, gently fanning with your hand and inhaling through the right nostril, then exhaling through the mouth.Have the subject continue to sniff the odor and exhale through the mouth at a normal rate until the smell is no longer detectable or has greatly diminished. At this point, the data recorder marks the elapsed time on the student response sheet for the subject.Place the used swab in the re-sealable plastic bag. Seal the bag completely.Repeat the procedure using the peppermint oil, and record the results on the Student Response Sheet.Switch roles and repeat the process for everyone in the group.Leave the swabs in the re-sealable bag and return all the other materials to their original location.Answer the questions about this activity on the Student Response Sheet.Activity #3: HearingThe human ear is divided into three regions: the external, middle and inner ear. As the outer ear funnels sound to the ear canal, the tympanic membrane or ear drum vibrates at the same frequency as the sound waves which contact it. Beyond the tympanic membrane lies the middle ear which contains a chain of the three smallest bones in your body. These bones are called the auditory ossicles and include the malleus (hammer), the incus (anvil), and the stapes (stirrup). The ossicles transmit sound vibrations to the inner ear. The part of the inner ear concerned with sound reception is the cochlea, a snail shell shaped organ filled with fluid and lined with hair cells. The vibrations from the sound waves cause the hair cells to bend, triggering a nerve impulse which travels through the acoustic nerve to the brain.Because the cochlea is embedded in a bony cavity, vibrations transmitted through the skull can trigger the cells in the cochlea to elicit a sensation of sound. This is why a tuning fork placed against any portion of the skull can be heard even when both ears are plugged. This phenomenon is called bone conduction and will also be tested in this activity.To complete this activity, each student will need:Tuning forkMetric ruler and meter stickProcedurePart A: Auditory AcuityNote: During this activity, care must be taken to strike the tuning fork with equal force each time and to move the fork away from the subject at the same speed.Instruct the subject to close his or her eyes and plug one ear with a finger.Strike the prongs of the tuning fork against the edge of a table to set the fork in motion. Grip the tuning fork by the handle, and be careful not to touch the prongs while the fork is vibrating.Immediately place the tuning fork close to the subject’s open ear, and then move the tuning fork outward, away from the ear in a straight line, until the subject can no longer hear the sound. The recorder should note the distance at which this occurs in the Student Resource Sheet.Repeat the experiment with the subject’s other ear and compare the distances.Part B: Bone ConductionInstruct the subject to plug both ears with his or her fingers.The observer strikes the tuning fork and places the end of the handle against the top of the subject’s head.The sound will be heard only while the base of the tuning fork contacts the skull. Remove the tuning fork and then replace it to verify that the sound is perceived only through bone conduction.Strike the tuning fork and place the base against the subject’s left or right temple. Ask the subject whether the sound appears to be louder, the same, or quieter on the side touched. Record the results on the Student Response Sheet and exchange roles.Activity #4: Touch SensationActivity #4: Touch SensationSkin SensesHave you ever noticed that small children pick up and put everything in their mouths? This is how they explore the world around them. The tongue and fingertips have the highest concentration of touch receptors and will therefore send the most information to the brain to be interpreted. Your skin contains several types of receptors. These include touch, pain, heat, and cold receptors and vary throughout the body.Light Touch: Meissner’s corpuscles are nerve endings in the skin that are responsible for detecting the sensation of light touch. These are most prevalent in the fingertips and on the tongue.Deep Touch: Pacinian corpuscles are nerve fibers surrounded by thin coverings of connective tissue; they respond to pressure on the skin.To complete this activity, each student will need:Grid stamp and inkpad (shared)Paintbrush bristlesMetal pinProcedurePart A: Light TouchInk the grid stamp. Stamp the back of the subject’s hand (if it is not already stamped).Place the subject’s hand palm-down on the desk. Instruct the subject to close his or her eyes and say “Yes” upon feeling a touch on the area being tested.The observer lightly touches a grid area of their choice with a bristle and waits for a response.If no response is given, proceed to touch another grid area.If the subject does sense the touch, the recorder fills in the corresponding location on the grid in the Student Response Sheet. Then the observer touches the next grid area.Continue testing the grid according to your teacher’s instructions. Record all data on the Student Response Sheet.Repeat the test at two more locations, the palm and forearm. Again, record all positive pare the results for the three areas and answer the questions on the Student Response Sheet.Answer the questions on the Student Response Sheet.Part B: Deep Touch (Pressure)Follow the instructions in the “Light Touch” experiment above using the same grids but this time testing for deep touch (pressure) responses. Instead of a bristle, use the head (not the point!) of a pin. Instruct the test subject to say “Yes” upon feeling a touch, on the area being tested.Perform the test on the back of the hand, the palm, and the forearm. Record all positive responses by filling in the corresponding grids in the Student Response Sheet for the pare the data from the three areas and answer the questions on the Student Response Sheet.Exchange roles and repeat the process for each member of your group.Activity #5: Two-Point DiscriminationActivity #6: Two-point ThresholdThe touch sensors in the skin are located unevenly throughout the surface of the body. To determine the relative density of the touch sensors in any area of the body a two-point threshold can be used. For two stimuli to be felt as two distinct sensations they must each activate a separate touch sensor, with one sensor in between them.To complete this activity, each student will need:Carolina? two-point discriminatorProcedurePlace the test subject’s hand palm-up and motionless on the desk. Instruct the test subject to close his or her eyes and to say “One” or “Two” depending upon the number of points of contact felt on the area being tested.Start with the two point discriminator closed, with the pointer at 0 mm. Begin the experiment by touching the subject’s fingertip. The subject should keep his or her eyes closed and should feel only one point.Create a 1- or 2-mm gap between the points of the probe by moving the indicator to the 1-mm or 2-mm mark. Touch the subject’s fingertip with the discriminator points again.Repeat this process, increasing the distance between points 1 or 2 mm each time, until the test subject reports feeling two separate points. This minimum distance is the two-point threshold. Record this data in millimeters on the Student Response Sheet under “Fingertip/Trial 1.”Repeat the test for the following parts of the body: the back of the neck, the mid-calf, and the palm of the hand. Record each of these results in the “Trial 1” column on the table.Conduct two additional trials at each location. Record the two-point threshold values in the appropriate rows and columns of the table in the Student Response Sheet.Exchange roles and repeat the process until everyone in the group has been tested.Determine the average two-point threshold value for each location and answer the questions on the Student Response Sheet. ................
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