Gas Exchange

Gas Exchange

  • Gas exchange is the process where oxygen (O2) and carbon dioxide (CO2) move between organisms and their environment.

  • This process involves diffusion of gases where they move from an area of higher concentration to an area of lower concentration.

  • Gas exchange takes place at a respiratory surface — a boundary where oxygen in the air or water meets the body’s circulating blood.

In Humans

  • In humans, the main respiratory surface is the alveoli in the lungs.

  • When we breathe in, oxygen in the air fills the alveoli.

  • Oxygen then diffuses across the alveolar walls into the surrounding capillaries, where it binds to haemoglobin in red blood cells.

  • At the same time, carbon dioxide in deoxygenated blood diffuses into the alveoli to be breathed out.

In Plants

  • In plants, gas exchange happens in tiny pores in leaves called stomata.

  • Carbon dioxide from the air diffuses through the stomata into the plant during photosynthesis.

  • Oxygen produced during photosynthesis diffuses out of the plant through the stomata.

  • At night, when photosynthesis isn’t happening, oxygen is used by the plant in respiration, and excess carbon dioxide diffuses out through the stomata.

In Fish

  • In fish, gas exchange occurs in their gills.

  • Oxygen dissolved in water diffuses into gill capillaries, while carbon dioxide in the blood diffuses out into the water.

Factors Affecting Gas Exchange

  • Temperature: Higher temperatures increase the rate of gas exchange as the gases have more energy and move more quickly.

  • Surface area: An increased surface area of the respiratory organ allows for more gas exchange to occur simultaneously.

  • Concentration gradient: A large difference in the concentration of gases inside and outside the respiratory organ can cause gases to diffuse more quickly.

  • Moisture: Many respiratory surfaces need to be moist for gases to dissolve and diffuse across them.