Glucose is a sugar used as an important source of energy in plants, prokaryotes and eukaryotes via processes such as respiration and fermentation. In plants, algae, and cyanobacteria, the energy of light is synthesized into the storage form of sugars such as glucose. More specifically, in a downstream process known as the Calvin cycle, carbon dioxide is incorporated into organic carbon compounds, like ribulose bisphosphate. Using ATP and NADPH from upstream light-dependent reactions, the resulting compounds are then reduced and removed to form further carbohydrates, such as glucose. In animals, through the process of glycolysis followed by the citric acid cycle, glucose is broken down to water and CO2, resulting in energy from ATP formation. Glucose is often stored as a polymer such as glycogen. In humans, glucose is commonly measured in blood samples. Bloodstream levels of glucose are normally under tight regulation, however, high levels measured in fasting individuals may indicate prediabetes or diabetes. Blood Glucose Range Animal (mg/dL) ( mM) Human 79-110 4.4-6.1 Cow 42-75 3.7-6.6 Sheep 44-81 3.9-7.2 Goat 48-76 4.2-6.7 Cat 61-124 5.4-11.0 Dog 62-108 5.5-9.5 Horse 62-114 5.5-10.1 Pig 66-116 5.8-10.3 Rabbit 75-155 6.6-13.7 Llama 90-140 8.0-12.4 Mountain Goat 26-181 2.3-16.0 Beluga Whale 94-115 8.3-10.2 White Rhinoceros 28-140 2.5-12.4 Harp Seal 88-218 7.8-19.3 Hooded Seal 135-283 11.9-25.0 Table 1. Range of blood glucose levels in common animals (Ref. 1).