Agar Diffusion Rate Calculator
Calculate the rate of diffusion for biology experiments (e.g., agar cubes in HCl or NaOH) and determine Surface Area to Volume ratios.
Calculation Results
How to Calculate Rate of Diffusion in Agar
Understanding the rate of diffusion is a fundamental concept in biology, particularly when studying cell size limitations. This calculator helps analyze the results of standard laboratory experiments where agar blocks (often containing phenolphthalein) are submerged in solutions like hydrochloric acid (HCl) or sodium hydroxide (NaOH).
The Diffusion Rate Formula
To calculate the basic rate of diffusion, you simply divide the distance the substance has traveled into the agar by the time it took to travel that distance.
Example: If the acid turned the agar clear to a depth of 2mm after 10 minutes, the calculation would be:
- Distance: 2 mm
- Time: 10 min
- Rate: 2 / 10 = 0.2 mm/min
Surface Area to Volume Ratio (SA:V)
In biology labs, this experiment is often used to demonstrate why cells are microscopic. The efficiency of diffusion depends heavily on the Surface Area to Volume ratio.
- Surface Area (Cube): Height × Width × Number of Sides (6)
- Volume (Cube): Height × Width × Depth
As a cell (or agar cube) grows larger, its volume increases much faster than its surface area. This results in a lower SA:V ratio, making diffusion less efficient at transporting nutrients to the center of the cell.
Calculating Percent Volume Diffused
To find out how much of the total cube was reached by the diffusion, we calculate the volume of the inner "undiffused" cube and subtract it from the total volume.
Formula: % Diffused = ((Total Volume - Inner Volume) / Total Volume) × 100
Where the Inner Cube side length = Total Side – (2 × Distance Diffused).
Factors Affecting Diffusion Rate in Agar
- Concentration Gradient: A higher concentration difference between the solution and the agar increases the rate.
- Temperature: Higher temperatures increase the kinetic energy of particles, speeding up diffusion.
- Density of Agar: A higher percentage of agar creates a denser matrix, potentially slowing down particle movement.
- Molecular Weight: Heavier molecules diffuse more slowly than lighter ones.