The proximal end of the ulna illustrates the relationship of form and function. The rounded trochlear notch articulates with the hourglass shape of the trochlea. This forms a joint that allows for .

 hinge like motion of the forearm

Explanation:

The trochlea is the rough hourglass shaped structure that can be found on the distal end of the humerus. The trochlea articulates with the trochlear notch of the ulna. This structure performs the function of the hinge joint in the forearm and allows the functions like movements of the circumduction, flexion and extension muscles. These movements does not take place in the antero-posterior side of the humerus.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.