Visking Tubing Practical (AQA A Level Biology): Revision Note

Exam code: 7402

Lára Marie McIvor

Written by: Lára Marie McIvor

Reviewed by: Naomi Holyoak

Updated on

Visking tubing models

  • Visking tubing can be used to model the process of absorption that occurs in the small intestine

    • Visking tubing, or dialysis tubing, is a non-living, partially permeable membrane made from cellulose

  • Pores in the tubing are small enough to prevent the passage of large molecules, e.g. starch, but allow smaller molecules, e.g. glucose, to pass through by diffusion

Beaker with Visking tubing containing starch and amylase solution, submerged in distilled water, ends tied with threads, diagram labels present.
Visking tubing can be used to model the process of absorption in the small intestine.

Method

  • The procedure used to model digestion and absorption using Visking tubing is as follows:

    1. Cut a section of Visking tubing and tie one end

    2. Fill tubing with a starch and amylase mixture

    3. Suspend the tubing in a beaker of water for a set period of time

    4. Take samples from the liquid outside the tubing at regular intervals and test for the presence of starch and glucose

  • The results should show that glucose is present outside the tubing, while starch is absent

    • Starch molecules are too large to pass through the pores in the tubing

    • The amylase inside the tubing digests and breaks down starch into glucose molecules, which are small enough to diffuse into the surrounding liquid

  • The rate of absorption/diffusion can be investigated quantitatively by taking a series of samples over a period of time and measuring the concentration of glucose with the use of colorimetry

Visking tubing and temperature / pH

  • The Visking tubing model described above can also be used to investigate the effect of other factors on digestion and absorption, e.g.

    • pH: multiple visking tubes can be set up, containing solutions of starch and amylase kept at different pH levels using buffer solutions

    • temperature: multiple visking tubes can be set up in water baths at different temperatures

Visking tubing as a model

  • While both Visking tubing and the intestinal lining are partially permeable, the Visking tubing model has several limitations, e.g.:

    • Visking tubing does not contain biological membranes, or any features of membranes, e.g. channel proteins

    • active transport cannot occur across Visking tubing due to a lack of carrier proteins and energy from respiration

    • the surface area of Visking tubing is less than that of intestinal epithelium due to the absence of villi

    • the distilled water does not flow like blood, and so does not maintain the concentration gradient

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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology, Psychology & Sociology Subject Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

Naomi Holyoak

Reviewer: Naomi Holyoak

Expertise: Biology Content Creator

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.