the lungs

• aveoli carry out gas exchange in the body
• the lungs contain millions of alveoli which are air filled spaces that allow for gas exchange surrounded by a network of blood capillaries ( gas exchange )
• the blood entering alveoli has returned from lungs so contains lots of CO2 and little oxygen.

  oxygen diffuses out of alveolus (high concentration) into the blood(low concentration).
• alveoli - CO2 diffuses into the alveoli and O2 diffuses out
• CO2 diffuses from the blood (high concentration) into the alveoli (low concentration) to be breathed out
• O2 diffuses from the alveoli (high concentration) into the blood (low concentration)
• inspiration is when we breathe in, expiration is when we breathe out.
• when blood reaches body cells oxygen is released from red blood cells (high concentration) and diffuses into body cells (low concentration)
• during exercise more energy is needed so there are higher levels of CO2 and lower levels of O2 in the blood