Biology 11–12 · Year 11

Visking tubing as a model of a partially permeable membrane and a gut wall

Module 1: Cells as the Basis of Life (Cell Function); also Module 2 (Nutrient and Gas Requirements)

PracticalMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

The idea

Small molecules such as glucose diffuse through a partially permeable membrane while large molecules such as starch do not, which is why digestion must break food down before absorption.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

Boiling water bath: scalds
Benedict's reagent contains copper sulfate and is an irritant
Iodine stains skin and may irritate eyes

Controls

Use test-tube holders and eye protection
Point test tubes away from people when heating
Rinse splashes at once

Note

Benedict's reagent and iodine: consult RiskAssess (https://www.riskassess.com.au/) and the NSW Department of Education Chemical Safety in Schools package (https://education.nsw.gov.au/content/dam/main-education/asset-management/chemical-safety/1._Section_1_-_General_information_for_all_staff.pdf).

What you need

Visking (dialysis) tubing, 15 cm lengths, soaked in water, 1 per group
Starch suspension 1 percent, 5 mL; glucose solution 1 percent, 5 mL (the source uses 5 cm3 of each inside the tubing)
Boiling tube or 100 mL beaker of distilled water; syringe barrel or elastic band to support the tubing
Iodine solution in a dropper bottle; Benedict's reagent, 20 mL; water bath at boiling, test tubes, 6
Stop clock; pipettes

How to do it

Knot one end of the soaked tubing, fill it with 5 mL starch suspension and 5 mL glucose solution, rinse the outside with water and suspend it in a tube of distilled water so the levels match.
At the start, test a sample of the outside water with iodine and with Benedict's reagent (heat for 2 to 3 minutes in the boiling water bath) and record the colours.
After 15 minutes, test the outside water again with both reagents; also test a drop from inside the tubing.
Record which substances have crossed the membrane and which have not, and relate this to molecular size.

What you should see

At the start the outside water stays orange-brown with iodine and blue with Benedict's reagent. After 15 minutes the outside water still gives no starch reaction with iodine but turns green, yellow or orange-red with Benedict's reagent, showing that glucose has crossed and starch has not; the inside still turns blue-black with iodine. The learner knows it worked when the outside water is negative for starch and positive for reducing sugar.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

The membrane lets substances through according to whether they are useful; it discriminates by size and charge only.
Glucose stops crossing once some is outside; net diffusion continues until concentrations equalise.
Starch is absorbed by the gut as starch; it must first be digested to sugars.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Biology Stage 6 Syllabus (2017), current: Year 11 taught to the end of 2026 and Year 12 to Term 3 2027BIO11-8 BIO11-9 BIO11/12-3
Biology 11–12 Syllabus (2025), Year 11 focus area Cells as the basis of life; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11-01
Biology 11–12 Syllabus (2025), Year 11 focus area Cells to systems; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11-02
Biology 11–12 Syllabus (2025), Year 11 Working scientifically; new syllabus not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027BI-11WS-03
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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