Answer:
This is to ensure accurate recording and interpretations of the observed results without Carbohydrate.
To ensure that the observed results was due to the expected investigating factor, and not due to any external factor.
Step-by-step explanation:
The basal media without carbohydrate is the negative control setup. since there is no carbohydrate their will be no bacterial growth .Therefore the activities of the bacteria can be fully observed . However the basal media with carbohydrate have full growth since CHO is available as nutrient; ,asexual reproduction will occur and growth takes palce. Thus the control(without CHO) and the actual experiment can be compared for accuracy. Therefore the basal media without CHO. acted as active negative control for results analysis and interpretation.
In addition the two growth media should be inoculated. Thus any observable changes can be attributed to bacterial growth, and not due to any external factors.This justify reasons for the answers above.