Oxygen crosses into the cell primarily by the process of diffusion. Oxygen molecules move from an area of higher concentration in the blood within capillaries to an area of lower concentration inside the cells, allowing oxygen to diffuse through the cell membranes into the cytoplasm where it is used for metabolism.
Detailed Process of Oxygen Entry into Cells
- Oxygen enters the body through inhalation, reaching tiny air sacs in the lungs called alveoli where gas exchange occurs. Oxygen diffuses across the thin alveolar and capillary walls into the bloodstream.
- In the blood, oxygen binds to hemoglobin in red blood cells and is transported through the arteries to tissues.
- At the tissue level, oxygen concentration in the blood is higher than in the body's cells, so oxygen moves by diffusion from the blood through the capillary walls and into the interstitial fluid, then across the cell membrane into the cell.
- This diffusion follows the concentration gradient, meaning oxygen moves naturally from an area of high concentration (blood) to low concentration (cell interior).
- Inside the cell, oxygen is used in mitochondria for cellular respiration, producing energy and generating carbon dioxide as a waste product, which then diffuses out of the cell in the opposite direction.
