Hello people! Today, lets take a tour deep down into our digestive system! Let us follow a broccoli on a one way trip to the toilet.
We begin in the mouth, where we can see two rows of teeth, a tongue, and lots of this sticky and slippery stuff known as saliva. Now, we can see the broccoli getting chewed on by the teeth into smaller chunks, and the saliva, which contains amylase, which helps to break down the food and soften it so as to make it easier to swallow.
Now, we move on to the esophagus. Nothing special here. The esophagus is lined with muscle, so as move food down efficiently. Its walls are lined with saliva and mucus, so as to allow it to have a slippery surface so that food would not get stuck. The broccoli is observed to slide down easily.
Then, we have the stomach. Now the stomach is a muscle, and it churns every now and then to help digest food. Additionally, proteases and hydrochloric acid is added to turn the broccoli, into a pile of foul smelling, weird colored, soupy substance.
In the small intestine , three types of substances are digested. Proteins and peptides, Lipids, and Carbohydrates. They get broken down in amino acids, fatty acids and glycerols, and simple sugars respectively. Now the digested food is able to diffuse through the walls of the digestive system. We observe the broccoli to be one watery blob now.
Finally, we have the large intestine, where water is drawn from the undigested food into the body. Food is then passed out as brown masses out of the anus.
There we have it! A quick "run" through the digestive system!
Viking... No Visking Tubing!
Now today, I would like to talk about this object which is known as a visking tubing.
Now, what is interesting about this little tube is that it has a semi permeable membrane; which means that it only allows certain things to pass through. Technically, it is made from cellophane, which is the crinkly object that keeps your candy away from ants. The tubing is only permeable to glucose, however for other substances such as starch and protein, it is impossible for them to pass through as their particles are too large to diffuse through the visking tube. Due to the properties of the visking tubing, it is also used as a dialysis bag to help those patients diagnosed with kidney failure etc.
Here is an experiment we can try:
Source:
http://www.practicalbiology.org/areas/advanced/exchange-of-materials/digestion-and-absorption/evaluating-visking-tubing-as-a-model-for-a-gut,49,EXP.html
Length of Visking tubing, knotted at one end, 15 cm, 1 per group
Syringe barrel, sawn off, 1 (see note 1 and diagram)
10 cm3 syringe, 6
Beaker of soluble starch, 250 cm3 (see note 2)
Beaker of glucose solution, 100 g dm-3 (10%) or more, 250 cm3
For each group of students:
Boiling tube, 1
Elastic band, 1
Iodine solution, in a dropper bottle (see note 3)
Benedict’s (qualitative) reagent (see note 4)
Starch suspension, 5 cm3
Glucose solution, 5 cm3
Teat pipette, 2
White dimple or spotting tile
Test tube, 4
Beaker, 100 cm3, 1
Kettle (to provide boiling water for a water bath)
2 Starch suspension – make fresh. Make a cream of 5 g soluble starch in cold water. Pour into 500 cm3 of boiling water and stir well. Boil until you have a clear solution.
3 Iodine solution (Refer to Hazcard 54B and Recipe card 39). A 0.01 M solution is suitable for starch testing. Make this by 10-fold dilution of 0.1 M solution. Once made, the solution is a low hazard but may stain skin or clothing if spilled.
4 Benedict’s (qualitative) reagent (refer to Recipe card 8). No hazard warning is required on the bottle as the concentrations of each of the constituents are low. Take care making up the reagent as sodium carbonate is an irritant to the eyes and copper(II) sulfate(VI) is harmful if swallowed. See Hazcards 27C and 95A.
5 Glucose solution – 10% or more.
Preparation
a Soak the Visking tubing in water.
b Fasten the knotted length of Visking tubing to the sawn-off syringe barrel (see note 1) with an elastic band as shown in the diagram.
c Set out the beakers of starch and glucose, each with 3 x 10 cm3 syringes.
Investigation
d Set up a boiling tube and four test tubes in a rack.
e Set out a dimple tile, with dropper bottles of iodine solution and Benedict’s reagent in your work area.
f Collect a model gut made of Visking tubing.
g Use syringes to put 5 cm3 of starch suspension and 5 cm3 of glucose solution into your model gut.
h Rinse the outside of the Visking tubing under the tap then suspend it in the boiling tube.
i Use a teat pipette to remove about 1 cm3 of the “gut” contents. Put one drop on the dimple tile, and the rest in a test tube. Then put the teat pipette back into the Visking tubing.
j With a second pipette, put water into the boiling tube until its level is the same as the gut contents.
k Start a stopclock.
l Immediately use the second teat pipette to remove about 1 cm3 of the water. Put one drop on the dimple tile, and the rest in a test tube. Then put the teat pipette back in the water outside the Visking tubing.
m Test the drops of liquid in the dimple tile by adding one drop of iodine solution from the dropper bottle. If they turn blue-black, the liquid contains starch.
n Test the liquids in the test tubes by adding an equal volume of Benedict’s reagent and then place the test tubes in a beaker of boiling water for 2 to 3 minutes. If they turn orange (or greeny-yellow), the liquid contains glucose.
o After 15 minutes, sample the liquids inside and outside the tubing again. Ensure that you have a fresh sample by squeezing the pipette a couple of times to expel the remnants of any earlier sample and to mix the liquids well before sampling.
p Test a drop of each liquid with iodine solution and 1 cm3 with Benedict’s reagent as in m and n.
It can be hard for students to visualise the unseen molecules and tiny holes in this experiment. You could introduce additional models, such as chicken wire (or the net bags you buy oranges in) to represent the membrane, single poppet beads to represent glucose and chains of poppet beads to represent starch.
Health and safety checked, September 2008
Now, what is interesting about this little tube is that it has a semi permeable membrane; which means that it only allows certain things to pass through. Technically, it is made from cellophane, which is the crinkly object that keeps your candy away from ants. The tubing is only permeable to glucose, however for other substances such as starch and protein, it is impossible for them to pass through as their particles are too large to diffuse through the visking tube. Due to the properties of the visking tubing, it is also used as a dialysis bag to help those patients diagnosed with kidney failure etc.
Here is an experiment we can try:
Source:
http://www.practicalbiology.org/areas/advanced/exchange-of-materials/digestion-and-absorption/evaluating-visking-tubing-as-a-model-for-a-gut,49,EXP.html
Evaluating Visking tubing as a model for a gut
Introduction
Set up a length of Visking tubing and fill with a mixture of starch and glucose. Suspend in a boiling tube of water for a period of time. Periodically test the water outside the Visking tubing for the presence of starch and glucose. Establish that the Visking is permeable to glucose but not to starch. Compare the properties of Visking with the properties and function of the gut of a multicellular organism.Lesson Organisation
This activity prepares students for the investigation of the effect of amylase on starch and gives them an opportunity to practise handling Visking tubing in this way. It could be run as a demonstration, with selected students removing and testing samples, or as a class practical. Instructions below are for a class practical.Apparatus And Chemicals
For the class – set up by technician/ teacher:Length of Visking tubing, knotted at one end, 15 cm, 1 per group
Syringe barrel, sawn off, 1 (see note 1 and diagram)
10 cm3 syringe, 6
Beaker of soluble starch, 250 cm3 (see note 2)
Beaker of glucose solution, 100 g dm-3 (10%) or more, 250 cm3
For each group of students:
Boiling tube, 1
Elastic band, 1
Iodine solution, in a dropper bottle (see note 3)
Benedict’s (qualitative) reagent (see note 4)
Starch suspension, 5 cm3
Glucose solution, 5 cm3
Teat pipette, 2
White dimple or spotting tile
Test tube, 4
Beaker, 100 cm3, 1
Kettle (to provide boiling water for a water bath)
Technical Notes
1 The end of an old syringe makes a convenient support for the Visking tubing.2 Starch suspension – make fresh. Make a cream of 5 g soluble starch in cold water. Pour into 500 cm3 of boiling water and stir well. Boil until you have a clear solution.
3 Iodine solution (Refer to Hazcard 54B and Recipe card 39). A 0.01 M solution is suitable for starch testing. Make this by 10-fold dilution of 0.1 M solution. Once made, the solution is a low hazard but may stain skin or clothing if spilled.
4 Benedict’s (qualitative) reagent (refer to Recipe card 8). No hazard warning is required on the bottle as the concentrations of each of the constituents are low. Take care making up the reagent as sodium carbonate is an irritant to the eyes and copper(II) sulfate(VI) is harmful if swallowed. See Hazcards 27C and 95A.
5 Glucose solution – 10% or more.
Ethical issues
There are no ethical issues associated with this procedure.Procedure
SAFETY: Wear eye protection when handling the chemicals.Preparation
a Soak the Visking tubing in water.
b Fasten the knotted length of Visking tubing to the sawn-off syringe barrel (see note 1) with an elastic band as shown in the diagram.
c Set out the beakers of starch and glucose, each with 3 x 10 cm3 syringes.
Investigation
d Set up a boiling tube and four test tubes in a rack.
e Set out a dimple tile, with dropper bottles of iodine solution and Benedict’s reagent in your work area.
f Collect a model gut made of Visking tubing.
g Use syringes to put 5 cm3 of starch suspension and 5 cm3 of glucose solution into your model gut.
h Rinse the outside of the Visking tubing under the tap then suspend it in the boiling tube.
i Use a teat pipette to remove about 1 cm3 of the “gut” contents. Put one drop on the dimple tile, and the rest in a test tube. Then put the teat pipette back into the Visking tubing.
j With a second pipette, put water into the boiling tube until its level is the same as the gut contents.
k Start a stopclock.
l Immediately use the second teat pipette to remove about 1 cm3 of the water. Put one drop on the dimple tile, and the rest in a test tube. Then put the teat pipette back in the water outside the Visking tubing.
m Test the drops of liquid in the dimple tile by adding one drop of iodine solution from the dropper bottle. If they turn blue-black, the liquid contains starch.
n Test the liquids in the test tubes by adding an equal volume of Benedict’s reagent and then place the test tubes in a beaker of boiling water for 2 to 3 minutes. If they turn orange (or greeny-yellow), the liquid contains glucose.
o After 15 minutes, sample the liquids inside and outside the tubing again. Ensure that you have a fresh sample by squeezing the pipette a couple of times to expel the remnants of any earlier sample and to mix the liquids well before sampling.
p Test a drop of each liquid with iodine solution and 1 cm3 with Benedict’s reagent as in m and n.
Teaching Notes
This diagram shows starch and sugar molecules and the holes in Visking tubing.It can be hard for students to visualise the unseen molecules and tiny holes in this experiment. You could introduce additional models, such as chicken wire (or the net bags you buy oranges in) to represent the membrane, single poppet beads to represent glucose and chains of poppet beads to represent starch.
Health and safety checked, September 2008
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