Define The process of respiration.​

It is the oxidation of food substances to release energy for metabolic activities

Explanation:

it is a biochemical process which involves the breaking down of food substances by the cell with or without oxygen for metabolic activities

it has one origin of replication, but it proceeds in two directions - d)

answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;