These form about 1%part of protoplasm, they are comparatively simpler compounds of carbon, hydrogen and oxygen in the ratio 1:2:1 The ratio hydrogen to oxygen is thus these as water (H2O) .some carbohydrates may also have traces of nitrogen, sulphur, phosphorus etc.
Carbohydrates include all sugars and starches. Sugars are mostly sweet and simpler, water soluble compounds. Starches are tasteless and mostly insoluble complex compounds. The simplest carbohydrates are monosaccharide sugars. These have the empirical formula (CH2O) where n = 3 or more but only upto 7. Protoplasm usually contains pentose's and hexoses. The most common hexose sugars are mainly four isomers that is, fructose galactose and mannose. These have a common empirical formula C6H12O6 the different between them being only the arrangement of OH groups in their molecules. Of these, glucose (D-Glucose) is the most common and most abundant monosaccharide of nature. It is the chief source of chemical energy .i.e. the main fuel compound in protoplasm.