Featured in PASCO’s Advanced Biology through Inquiry Teacher Guide

Advanced Biology through Inquiry Teacher Guide

(PS-2852)

This manual features 22 challenging, standards-based, inquiry lab activities for AP, IB, and honors programs.

Diffusion

Lab Summary

Students use a pH sensor to investigate the diffusion of hydrogen ions through a semipermeable membrane, comparing the rates of diffusion for two solutions that differ in their acidity.

Theory

Students investigate the diffusion of ions through a semipermeable membrane using apple cider vinegar and a pH sensor. The vinegar is added to a dialysis bag to represent the intracellular solution of a model cell. Distilled water in a beaker represents extracellular fluid and students monitor the pH of the water over time to measure the rate of diffusion out of the model cell.

The color of the apple cider vinegar provides evidence of the semipermeable nature of the membrane; hydrogen ions easily diffuse through the membrane while pigments molecules do not. Student-designed experiments that test factors affecting the rate of diffusion can be accomplished with minimal materials and within the time frame of a single class period.

NOTE: Since hydrogen ions form bonds with water molecules, students are actually determining the rate of diffusion of hydronium ions: H3O+(aq).

Method

Diffusion within biological systems is affected by several factors. The most notable is the concentration gradient across a membrane. A large concentration gradient across the membrane speeds up diffusion. Other factors affecting diffusion rates within biological systems include temperature, distance between solute and membrane, surface area-to-volume ratios, and solute size. All these factors can be manipulated in student-centered investigations.

Sensors / Equipment Used:

PASPORT Conductivity Sensor

(PS-2116A)

Utilizes platinum probes for greater range and improved accuracy in high & low concentrations.

PASPORT pH Sensor

(PS-2102)

Has a wide measurement range of 0 to 14 pH. Has a resolution of 0.01 pH. For use with PASPORT Interfaces.

The Associated Bundle:

Advanced Biology Standard Sensor Bundle

(PS-2851)

Contains an EcoChamber, a Metabolism Chamber and all the probeware needed to perform the activities in the Advanced Biology through Inquiry lab manual.

Interface Required

This experiment may require software and an interface for data collection.