IB 2021 MAY BIOLOGY IA – GRADE 7

Investigating the effect of adding sodium chloride (salt) on the yeast respiration rate

Research Question : To what extent does changing the amount of sodium chloride (0g,2g,4g,6g,8g,10g) affect the yeast respiration rate measured by the volume of CO2 gas produced (ml) in 10 minutes?

Background :

Yeast is a single-celled, living organism classified under the kingdom Fungus. To sustain life, it needs energy which is obtained through both aerobic and anaerobic respiration by taking in monosaccharide sugar glucose from its surrounding environment via facilitated diffusion. Once the glucose enters the cytoplasm of the cell, glycolysis occurs that causes the six-carbon molecule glucose to get broken down into two pyruvate molecules with a net release of two ATP molecules (Allot 382). In the process, NAD+ is reduced to NADH+H+ and all of these occur in absence of oxygen. When there is not enough oxygen, yeast continues to thrive via alcoholic fermentation. After glycolysis, pyruvate gets converted into acetaldehyde and carbon dioxide gas with the help of an enzyme pyruvate decarboxylase(Bank). Acetaldehyde then accepts hydrogen from NADH which is stimulated by another enzyme called alcohol dehydrogenase (Bank). The final product is ethanol and carbon dioxide. The net product of NAD+ allows glycolysis to continue thus consistently producing ATP in the process. Fermentation, unlike aerobic respiration does not involve the Kreb’s cycle and the electron transport chain and therefore less energy is produced in absence of oxygen (Allot 124)…