How Big Can a Cell Get? Practical Discussion

Questions on How Big Can a Cell Get? Practical:

From the data, what can you conclude about the relationship between surface area:volume ratio and the rate of diffusion of the liquid?
As the surface area:volume ratio decreases (surface area-volume fraction), the rate of diffusion of the liquid decreases.

What is the size of the largest single cell organism? Explain why there is a cap on the maximum size of a living cell.
The largest single cell organism is a type of xenophyophore (a type of protozoa related to amoebas) measure 10cm across. They were discovered at depths of 10.6km deep in the Mariana Trench.
The ratio of cell volume to cell surface affects the maximum size of a cell. If the cell is too big, it will take too long for diffusion to take place and for necessary molecules to be transported from the cytoplasm through the cellulose cell membrane to the environment and vice versa. This can be proved by the results of the experiment. As the surface area:volume ratio of the agar block decreases, the rate of diffusion of the liquid decreases.

How does the concept of surface area to volume ratio be applied to the multi cellular organism and the specialisation of cells? Name some examples in our body that support your reasoning.
If a multi cellular organism is made up of solely cells clumped together, the cells in the middle would not be able to gain access to necessary molecules and diffusion would not take place, so they would die. The surface area would not be enough for the organism to survive. For it to survive, it would need to have a channel cutting through the mass of cells, like a tube, for necessary molecules and nutrients to reach the cells in the middle, allowing diffusion of these molecules to take place. The surface area of the cells mass exposed to the molecules would increase, increasing the rate of diffusion. Another way would be to develop a circulatory system, where specialised cells could pass the necessary molecules to other cells.
An example of this would be red blood cells. Red blood cells have a large surface area to volume ratio to allow rapid diffusion of oxygen, so that they can supply oxygen to other parts of our body, forming part of the circulatory system. Another example would be lung cells which are flatter, so they have a larger surface area:volume ratio. The rate of diffusion of oxygen as we breathe in would be faster so more oxygen can be taken in by the cells.