Answer:
Glucose
Step-by-step explanation:
Glucose is the most essential carbohydrate that acts as a fuel for human cells.
The have a considerably small size, therefore they are allowed by cell memebrane to pass easily into the cell.
Also glucose has high solubility in water due to which it is easy for glucose to travel with in cell.
When glucose molecule is metabolised as a part of the process of respiration, the following exothermic chemical reaction occurs -
C6H12O6 + 6O2 --> 6CO2 + 6H2O