# BIOL398-01/S11:Class Journal Week3

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### Alondra Vega's Journal Entry

- The purpose of this assignment was to know how to write and understand differential equations. Also, how matlab works with differential equations. The simulation allows us to understand how an ordinary differential equation works and how it applies to modeling different areas of biology.
- The part of this assignment that came easily to me was working with the simulation. It was easy since we did not have to write the actual program.
- The part of this assignment that came most difficult was writing the ordinary differential equations. I was using the example from class, but it was hard to know when we needed to subtract the concentrations and when it was needed to be added, or even included.
- What I still do not understand is the writing of a differential equation. Specifically, what I mentioned in number 3. I feel that I wrote the differential equations in the wrong order, as in I subtracted a number when it was supposed to be added. Also, in the first reaction I only wrote one rate of change equation and I was wondering if I needed one for the elements A and B. I did not write any, but am I supposed to have d[A]/dt = -k
_{1}[A][B]? The same equation would be d[B]/dt. I just was not sure to include them, since the reaction is only going in one direction. It makes sense that they would have an equation, since they are also changing over time. I am just not sure. - The relationship between homeostasis and equilibrium is that homeostasis focuses on having a stable internal environment, which also means to be in equilibrium.

Alondra Vega 12:53, 30 January 2011 (EST)