Why do living organisms need carbon ?

Oxygen helps the body's cells function normally. The cycle of carbon dioxide and oxygen on Earth is dependent on plants and animals. Plants provide the oxygen that animals and other living things need to survive. Animals and other living things provide the carbon dioxide that plants need to make their own food.

Explanation:

Plants obtain carbon from the atmosphere in the form of carbon dioxide which they need for photosynthesis they convert inorganic carbon into organic carbon in the form of sugar and starch which they add to their tissues.

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