#82 Inspired and expired air, blood pH and breath rate

* inspired air: air we breath in

* expired air: air we breath out

The composition of inspired and expired air 

Testing for CO₂ 

To investigate the differences in composition between inspired and expired air, we use limewater because it change colour when the gas is bubbled through, from colourless to milky. 

  

There is more CO₂ present in expired air ---> it makes limewater change colour more quickly (than inspired air).

 Limewater test. 

Effects of physical activity on breathing

* tidal volume: amount of air during normal, relaxed breathing

  vital capacity; maximum amount of air breathed in or out in one breath

During normal breathing:

- depth (tidal volume) : ≈ 0.5ℓ

- rate: 12 breaths/ minute

During exercise:

- depth: ≈ 5ℓ (depending on age, sex, size & fitness of person)

- rate: over 20 breaths/ minute

The total lung volume is greater than vital capacity (some air always remains in the lungs). If not, alveoli walls would stick together, the lung would collapse.

Link between physical  activity and rate and depth of breathing

• when you run, muscles in your legs use up a lot of energy.  
• cells in the muscles need a lot of O₂ very quickly.
• they combine O₂ + glucose as fast as they can, to release energy for muscle construction ---> a lot of O₂ is needed
• you breath deeper and faster to get more O₂ into your blood.
• your heart beast faster to get O₂ to the leg muscles as quickly as possible.
• a limit is reached - the heart and the lung can not supply O₂ to the muscles any faster.
• some extra energy (not much) is produced by anaerobic respiration: some glucose is broken down without combing with O_2:

Glucose ---> lactic acid + energy.

• CO2 and lactic acid concentration in tissue and in the blood ↑ ---> blood pH ↓
• Brain sens the change ---> nerve impulses sent to the diaphragm and the intercostal muscles, stimulating them to contract harder and more often ---> faster and deeper breathing. 

Try this

a) The composition of the air inside the lungs changes during breathing.

i) State three differences between inspired and expired air.           [3 marks]

ii) Gaseous exchange in the alveoli causes some of the changes to the inspired air. Describe three features of the alveoli which assist gaseous exchange.  [3 marks]

b) i) State what is meant by anaerobic respiration [2 marks]

    ii)Where does anaerobic respiration occur in human? [1mark]

Answer

a) i) Inspired air contains more O₂, less CO₂, and less water vapor then expired           air.

  ii) Three features from:

- the wall of the alveolus is one cell thick (or very thin)

- there is a moist surface to the alveoli

- there are large number of alveoli

- the air in the alveoli is constantly being replaced.

b) i) The release of energy by cells without the use of oxygen.

    ii) In muscle cells.