Which occurs as part of gas exchange?
oxygen is exhaled
carbon dioxide is inhaled
carbon dioxide diffuses from the trachea to blood in capillaries
oxygen diffuses from alveolar sacs to blood in capillaries

oxygen diffuses from alveolar sacs to blood in capillaries

Cellular respiration is a metabolic process that occurs in all organisms. In humans the process of respiration is highly complex. The respiratory system in humans involves a set of organs that allows an individual to breathe and exchange gases (oxygen and carbon dioxide) throughout the body. In humans the respiratory system includes organs like nasal passage (nose), larynx, trachea, bronchial tubes, alveoli and lungs.

The lungs are the main organs which provides a platform for gas exchange occurring in a body. The oxygenated air when enters the lungs, passes into tube like structures called as alveolar sacs. The blood inside the alveolar sacs passes into the fine blood vessel network called as capillaries. The capillaries provide a surface when the carbon dioxide present in the blood gets replaced with the oxygen. The carbon dioxide exhaled out from the body and the oxygen is transported to the all the body organs and cells.

i think the answer is composed of atoms