A student carries out an experiment to investigate the factors affecting the rate of diffusion.
In our experiment:
- She prepares three agar jelly cubes: one with sides of 4.5 cm4.5\text{ cm}4.5 cm, one with sides of 3.0 cm3.0\text{ cm}3.0 cm, and one with sides of 1.5 cm1.5\text{ cm}1.5 cm.
- She covers each cube in a solution of colored dye for 5 minutes.
- She then cuts the cubes to observe how far the dye has diffused.
The diagram shows a cross-section through the largest cube after 5 minutes.
Describe what is meant by the term diffusion.
Using the dimensions shown in the diagram, calculate the depth of dye penetration into the large cube in millimeters (mm\text{mm}mm).
Describe the expected cross-section of the smallest cube (1.5 cm1.5\text{ cm}1.5 cm) after 5 minutes, including the dimensions of any dyed and undyed regions.
The student then carries out a second experiment, but this time she leaves the cubes in the dye for 10 minutes. Describe the results you would expect to see in the cross-section of the largest cube after 10 minutes.
Other factors may affect the rate of diffusion of the dye. Identify two factors that the student should keep constant in her investigation, and explain how an increase in each factor would affect the rate of diffusion.
Explain how the results of the student's investigation support the idea that large organisms need a circulation system.