The two processes of the carbon cycle are photosynthesis and cellular respiration. In photosynthesis carbon from carbon dioxide is fixed into carbohydrates. In cellular respiration, carbohydrates are...
Nitrogen fixing bacteria, often called Rhizobia (singular Rhizobium), are a key component of the nitrogen cycle. Atmospheric nitrogen is useless to living organisms, but often binds to hydrogen...
If by off road cycling, you mean mountain biking, the reason is primarily for the fact that mtn cleats get clotted with dirt and other junk when riding whereas you rarely clip out when on a road...