# Diffusion in Agar Cubes

Below is a timelapse video of our Agar cube in the sodium hydroxide solution

This is the process of our lab:

Our Agar cubes cut into their sizes

Our Agar cubes in the sodium hydroxide solution, immediately after placed in the solution.

Our Agar cubes once removed from the solution, and cut open.

In terms of maximizing diffusion, what was the most effective size cube that you tested?

The agar cubes were placed in the sodium hydroxide solution for 10 minutes, and when taken out all three sizes were pink. However, when cut open, it was clear that the smallest cube (1cm by 1cm) was the most effective. It was completely pink throughout the cube whereas the other two were not soaked pink completely. The picture above shows the cut open cubes, and shows the pink one is completely soaked through.

Why was that size most effective at maximizing diffusion?  What are the important factors that affect how materials diffuse into cells or tissues?

The smallest cube was the most effective because of the surface area to volume ratio. The small cube had the greatest surface area to volume ratio, meaning that once the sodium hydroxide solution had covered the surface area, there was less volume for it to soak into.

Some other factors that can affect how materials diffuse into cells or tissues are concentration, temperature, type of material/thickness and pressure. In this lab, surface area to volume ratio that caused the cube to have the most effective diffusion, however all of these factors could have an effect.

If a large surface area is helpful to cells, why do cells not grow to be very large?

A large surface area is helpful because it allows things such as energy and waste to travel in and out of a cell. However, a larger surface area has a smaller SA to V ratio. This means that less materials can enter the cell as even though the surface area is large the volume is smaller. A smaller cell, in the end, allows the cell to contain more inside of it creating a more efficient diffusion process.

You have three cubes, A, B, and C.  They have surface to volume ratios of 3:1, 5:2, and 4:1 respectively.  Which of these cubes is going to be the most effective at maximizing diffusion, how do you know this?

The most effective cube for maximizing diffusion would be Cube C (4:1 ratio). This is because the Surface Area to Volume ratio is greater, meaning the diffusion is maximized. I know this because when your surface area grows, the volume decreases. The 4:1 ratio allows the largest surface area and volume of the cubes A, B and C. This relates to our lab as the smaller agar cube is the cube with the greater surface area to volume ratio, while the largest agar cube has a smaller surface area to volume ratio. This proves that the 4:1 would be the most effective.

How does your body adapt surface area-to-volume ratios to help exchange gases?

Your body can adapt surface area-to-volume ratios to help exchange gases in a few ways. Membranes can have folds like the majority of organelles in a cell do. When our cells get too big, they will divide creating two cells; this maintains the large surface area to volume ratio. Lastly, some cells can be long and thin to help exchange gases. Small cells maximize the diffusion process, but it also can help in movement of materials in and out of parts of the body.

Why can’t certain cells, like bacteria, get to be the size of a small fish?

When a cell has a large surface area to volume ratio, it can grow rapidly to become ‘the size of a small fish.’ However, with cells such as bacteria, although it starts to grow large initially  it looses it’s efficiency for how it functions. This causes the cell to divide, making it small again and causing the cell to regain its large surface area to volume ratio. This process means these types of cell won’t grow to the size of a small fish as the cell can not survive that large.

What are the advantages of large organisms being multi cellular?

Large organisms being multi cellular’s largest advantage is that it has a higher rate of diffusion. This is important as there are lots of functions that need to happen with multi cellulars specialized systems and cells. Some examples of this are gas exchanges and materials being moved from our systems.  It also allows an increase in the rate of diffusion. The large number of specific and specialized cells working together successfully is the result of multi-cellular organisms.