How does starting the y-axis at 300 affect the graph? Remember that no matter what number you start labeling an axis at, you have to go up by the same amount for each subsequent tick mark!

Not sure if this applies to biology, but I’m using more statistics for this.

Basically, when you change the y-axis to 300, you are able to exaggerate the patterns on the graph. From afar, or starting the y-axis at 0, a person cannot easily identify the increases and decreases of CO2. However, with a y-axis at 300, you see these changes much more easily, so you can make accurate inferences and conclusions regarding the graph.

Hope this helps