what accounts for the differences between black tube containing yeast with no substrate and tube containing 5% sodium lactate or ethanol?
To understand the differences between the black tube containing yeast with no substrate and the tube containing 5% sodium lactate or ethanol, we need to consider the role of substrates in yeast metabolism. Yeast is a type of microorganism that can undergo fermentation to produce energy. During fermentation, yeasts convert sugars or other substrates into alcohol (ethanol) and carbon dioxide.
The black tube containing yeast with no substrate serves as a control, where there is no external supply of sugar or substrate for the yeast to metabolize. In this case, the yeast may undergo a process called anaerobic respiration or fermentation using the sugar reserves already present within it. However, without an external substrate, the yeast's metabolic activity may be limited, and it may produce less carbon dioxide and ethanol.
On the other hand, the tube containing 5% sodium lactate or ethanol provides an external supply of substrates that the yeast can metabolize. Sodium lactate is a salt derived from lactic acid, and ethanol is a type of alcohol. Both of these substances can serve as substrates for yeast fermentation. By adding sodium lactate or ethanol to the tube, we are providing the yeast with an abundant supply of substrates for metabolism.
As a result, the yeast in the tube with 5% sodium lactate or ethanol will have more favorable conditions for fermentation. This means that the yeast will be able to generate more energy, resulting in increased production of carbon dioxide and ethanol. The increased metabolic activity with an external substrate like sodium lactate or ethanol will likely result in a more noticeable color change, such as a darker appearance, in the tube.
In summary, the presence of an external substrate like sodium lactate or ethanol in the tube enhances the metabolic activity of the yeast, leading to increased production of carbon dioxide and ethanol, which may manifest as changes in color and fermentation byproducts.