Anatomy and Physiology 12

Cell Size Lab

Data Table

**Can be used as reference for real-life pictures and explanations below**

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

After the 10 minutes of various-sized agar cubes being in the sodium hydroxide solution, we were able to cut open the three cubes, largest being 3cm by 3cm, then 2cm by 2cm, and finally 1cm by 1cm. As we opened the cubes it was clear that the smallest cube would be the most effective at diffusion as it was fully pink. The other two cubes showed distinct areas of white agar still as it was not as effective maximizing diffusion. This is shown below in the photo.

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 most effective as it had the greatest surface area to volume ratio. This means that the solution can spread around the cube and “enter”/diffuse with a greater surface area, and then as the cube has a smaller volume, the solution can then diffuse throughout it and effect more or it’s “insides”. Furthermore, concentration, temperature, type of material/thickness, pressure, and of course surface area to volume ratio are all factors affecting diffusion. All of these can cause a higher or slower reaction rate which inevitably either increases or minimizes the effectiveness of diffusion. The factor we saw in the lab was how diffusion through a cell happens at various sizes; therefore, volume and surface area. Below is a photo of how the cubes looked after being taken out of the solution showing the initial factor of SA to V without being cut into.

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

Surface area is highly helpful to cells as this allows resources, waste, energy, and more in and out of cells through the cell membrane. Thus, as there are so many processes happening within cells you might wonder why a cell might not want to be large and accommodate all these processes. This is shown through the results we acquired today, a larger size creates a smaller SA to V ratio which means less materials and wastes etc. can enter or exit the less making the cell less efficient and not as useful. In the end, a small size creates a larger SA to V ratio meaning the cell is more efficient with diffusion and all the processes can occur and function better.

 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 is cube C (4:1 ratio being the largest like the 6:1 ratio as shown above with the photos and explanation). This means the SA to V is greater allowing diffusion to be maximized. You can think of it like this: You have a reaction happening which needs reactants. but also releases fumes (consider this as “waste”). As you increase this reaction you need more reactants, but the fumes exiting also increase; however, the container this is all happening in doesn’t change, meaning adding more reactants and taking out more waste isn’t possible. The reason the container doesn’t change is to mimic the idea of volume increasing exponentially, but surface area not being able to. In the end, a “smaller” reaction in this container allows for it to be a lot more efficient with needing its resources and its removal of wastes. This finally showcases how our lab shows the need for smaller cells and smaller cells are the ones with greater SA to V ratios, while larger cells have smaller SA to V ratios; therefore, cube C, 4:1 ratio.

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

This is done by a variety of ways, such as having folds in membranes like most of the organelles in cells as well as the intestines. Also, when our cells get too large, they will divide to continue to maintain this large SA to V ratio. Additionally, some cells are long and thin like our nerve cells to maximize diffusion and help exchange gases. Finally, one big factor is how there are small cells that maximize this diffusion factor, but there are also other features/structures that help in the movement of materials in and out such as our lungs or circulatory system, specifically in our bodies.

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

This is because as bacteria has a large SA to V ratio initially and starts to grow to become the “size of a fish”, it starts loosing it’s efficiency on how it can function; therefore, the cell will divide to regain this large SA to V ratio allowing for it to maximize diffusion and it’s efficiency. In the end, this process repeats which means the cell will never grow to become a large size as that doesn’t allow the cell to “survive” and “live” well.

What are the advantages of large organisms being multicellular?

The greatest advantage is that large multicellular organisms have a higher rate of diffusion which is necessary as there are a lot of functions needed to be performed with their specialized systems and cells. This includes gas exchange, materials being moved in and out of the circulatory system, and more for example. Multicellular organisms being large also allow for some specific features that increase the rate of diffusion and movement of resources and wastes. In the end, multicellular organisms create a large number of specialized cells and systems working all together to function well.

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