LABORATORY 4: Exercise 3 Answers

Is the reducing sugar present before or after yeast fermentation?

The sugar (glucose) was present before fermentation (see strong positive of tube 4). Some sugar is still present after fermentation as indicated by the week positive of tube 5.

What happened to the sugar?

The yeast consumed the glucose in fermentation to produce alcohol, carbon dioxide and ATP (see overview of fermentation)

What is the purpose of each tube?

• Tube 1 - 3 ml Benedicts and 1 ml Water - Control
• Tube 2 - 3 ml Benedicts and 1 ml 1% Glucose- Positive Control
• Tube 3 - 3 ml Benedicts and 1 ml 1% Sucrose- Negative control
• Tube 4 - 3 ml Benedicts and 1 ml Yeast Culture Before Fermentation - Experimental
• Tube 5 - 3 ml Benedicts and 1 ml Yeast Culture After Fermentation- Experimental

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