Respiratory surfaces
In humans
Gas exchange occurs in the alveoli which are found in the lungs.
When air is The action of breathing in., oxygen diffuses from the alveoli into the blood to be used for respiration by the body’s cells.
Carbon dioxide is a waste product made by the body’s cells during The chemical change that takes place inside living cells, which uses glucose and oxygen to release the energy that organisms need to live. Carbon dioxide is a by-product of respiration..
It The random movement of a substance from a region of high concentration to a region of low concentration from the blood into the alveoli and is The action of breathing out..
Adaptations of the alveoli:
- Large surface area - many alveoli are present in the lungs with a shape that further increases surface area.
- Thin walls - alveolar walls are one cell thick providing gases with a short diffusion distance.
- Moist walls - gases dissolve in the moisture helping them to pass across the gas exchange surface.
- Permeable walls - allow gases to pass through.
- Good blood supply - ensuring oxygen rich blood is taken away from the lungs and carbon dioxide rich blood is taken to the lungs.
- A large diffusion gradient - breathing ensures that the oxygen concentration in the alveoli is higher than in the capillaries so oxygen moves from the alveoli to the blood. Carbon dioxide diffuses in the opposite direction.
In plants
Gas exchange occurs in the The plant tissue in a leaf which has loosely packed cells and air spaces between them to allow gas exchange. cells that surround air spaces in the leaves.
Many spongy mesophyll cells are in contact with the air spaces, providing a large surface area for gas exchange to happen.
The spongy mesophyll cell membranes are also thin, moist and permeable, aiding gas exchange further.