Hi Lia,
On the procedure page of this project:
https://www.sciencebuddies.org/science- ... #procedure
which uses the Cybow test strips, the numbers above the colored boxes are the percent glucose in the solution and the numbers below are the equivalent amounts of glucose in milligrams (mg) per deciliter (dL or one tenth of a liter or 100 milliliters). When a person tests their blood for glucose, the result is given in mg/dL.
Sucrose is a molecule that contains TWO sugars--glucose and fructose. The invertase enzyme breaks the chemical bond that holds the two sugars together so the glucose is free and you can measure it with the test strips.
Testing the food before invertase treatment will tell you how much free glucose it has, if any, then after reacting it with invertase you measure glucose again and the difference between this reading and the first one is the amount of sucrose in the food. To determine the % concentration of sucrose in the food just use the formula given in the procedure:
Using the data you collected, you can determine the sucrose concentration in each of the foods you tested.
Look at the graph you made in the "Testing Invertase Activity" section. At the linear time point, what was the glucose concentration? If you multiply the glucose concentration at the linear time point by the original sucrose concentration (10%), this will tell you what percentage of the total sucrose was converted to glucose at this time point. We will call this value "Percentage of sucrose converted." You can see this equation written out in Equation 1.
For example, if at the linear time point the 10% sucrose solution had a reading of 1% glucose, then this means that 10% of the total sucrose (10% multiplied by 1%) had been converted to glucose.
Original sucrose concentration × Glucose concentration at linear time point = Percent of sucrose converted
Look at the data you collected in the "Testing the Foods for Glucose Concentration Before and After Adding Invertase" section. To determine the original sucrose concentration of each of your food samples, use Equation 1 and divide the percentage of sucrose converted (which you just determined) by the glucose concentration at the linear time point.
For example, if at the linear time point a food had a 2.5% glucose reading, and we calculated that the percentage of sucrose converted is 20%, then we could calculate that the original sucrose concentration of this food was 8% (20% divided by 2.5%).
Does this answer your question? If not, tell us what you don't understand and we will try to explain it better.
Sybee