2.1a Cell Theory: Limitations on cell size

25/08/2012 § Leave a comment

A cell’s surface area-to-volume ratio

As mentioned in my previous blog, one of the six functions of life is Metabolism, which, in a cell, are chemical reactions that release energy for the cell to accomplish multiple tasks. The rate of the reactions that occur within the cell (also known as the metabolic rate of the cell) is proportional to the volume of the cell.

This makes complete sense because know that all substances that are used for chemical reactions must pass through the plasma membrane, as does all the waste that the cell produces. The plasma membrane’s surface area is a large factor in the rate at which these substances and waste move into and out of the cell.

Linking the two together, the surface area of the cell is also directly related to the volume of the cell. If the cell’s volume is too large and the surface area too small, then the metabolic rate of the cell will be overwhelming for the cell to handle. With a ratio that is too small and imbalanced, substances and waste will struggle to enter and leave the cell at safe rates. The same goes for the production and loss of heat. A ratio that is too small won’t allow the cell to release heat fast enough and the cell could overheat.

Biology and Graphs

In a nutshell, graphs, in biology, are used to explain and visually display the relationship between two variables. The x-axis is used to represent the independent variable and the y-axis represents the variable that is affected by the independent variable.

DATA-BASED QUESTIONS

1. the surface area (µm^2) for each cell type is as follows:

  • Streptococcus pneumoniae = 3.141
  • white blood cells = 314.16
  • egg cell = 31415.93

2. the volume (µm^3) for each cell type is as follows:

  • Streptococcus pneumoniae = 0.5235
  • white blood cells = 523.6
  • egg cell = 523598.7

3. the surface area-to-volume ratio for each cell type is as follows:

  • Streptococcus pneumoniae = 6
  • white blood cells = 0.6
  • egg cell = 0.06

4. When the diameter of a cell increases, the surface area-to-volume ratio of the sphere decreases, as seen in the gradually increasing diameter (and gradually decreasing ratio) from the SP bacterium to the white blood cell to the egg cell.

5. …

a) The advantages of the SP bacterium in its small size is that it can do more  chemical reactions and accomplish more of its metabolic work. This makes it easier and perhaps faster for them to infect a human’s system, which is in its nature.

b) While the egg cell doesn’t need to do much until it is required to start producing offspring for the organism, white blood cells are like the soldiers of the body that need to do more for the organism. The egg cell can make it with a small surface area-to-volume ratio because it does not need to do as many chemical reactions as the white blood cells have to do (the little warriors of the human organism).

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