What can occur if blood flow in an artery is blocked or greatly restricted?

Will someone me with this.. specialized cells which perform a particular function form: tissues organs or organism

The carbon cycle is best defined as a process in which a. carbon changes from inorganic forms to organic forms and back b. carbon is changed into other elements such as oxygen or nitrogen c. carbon is continually created from the sun’s energy by plants d. carbon is consumed and regenerated from other elements such as oxygen and nitrogen

Which nucleotide component contains nitrogen