Q6. Proteins are used for structural integrity inside and outside of animal cells, but carbohydrates are not. a. TRUE b. FALSE Q7. A deficit in oxygen supply would cause levels of NAD+ to… a. become elevated b. remain unchanged c. become reduced Solution Q6. a. TRUE Carbohydrates are mostly energy source for cells, Q7. A deficit in oxygen supply would cause levels of NAD+ to… c. become reduced Under anaerobic conditions NADH accumulates since there is no oxygen to oxidize NAD+..