Topic 6.4 Gas Exchange Topic 6: Human Health and Physiology

Definitions Breathing – inhaling and exhaling Ventilation – The muscle movements that bring about the movement of air into and out of the lungs. Gas Exchange – the exchange of oxygen (in) and carbon dioxide (out).

More on Gas exchange Air in lungs  oxygen in blood CO 2 in blood  air in lungs Happens in alveoli O 2  water around cells Alveoli cells  capillary cell Capillary cell  erythrocyte Erythrocyte takes O 2 away to maintain diffusion gradient

Maintaining concentration gradients Oxygen –Blood always moves Carbon dioxide –Air in lungs is always replaced Watch this animation.animation

Cellular respiration Cell respiration is the release of energy from large organic molecules such as glucose that happens in every cell in living organisms. It is a chemical reaction – not a physical action. Gas exchange, ventilation and respiration are all dependent on each other.

Why do we need a ventilation system? Remember the work on surface area to volume ratio from topic 2? Is bigger better for diffusion?

2.1.6 Surface area: Volume ratio As organisms get bigger both their volume and surface area get bigger However the increase is not by the same amount.

2.1.6 Surface area: Volume ratio Each side is 1cm long Volume = Surface area = Each side is 2cm long Volume = Surface area = Volume x 8 Surface area x ?Surface area x 4

2.1.6 Surface area: Volume ratio Consequences for organisms: All organisms need to exchange substances with surroundings by diffusion and osmosis –e.g. ?? They can only do this through their surface – why? The amount of exchange needed depends on the organism’s volume –But the rate of exchange depends on what?

2.1.6 Surface area: Volume ratio Therefore, diffusion/osmosis decreases as the organism gets bigger. Trying to balance the rate of exchange and the needs of the organism becomes a deciding factor in the size of the organism. So the ability to meet the requirements of a cell depends on the Surface area : Volume ratio

2.1.6 Surface area: Volume ratio Each side is 1cm long Volume = Surface area = Ratio = Each side is 2cm long Volume = Surface area = Ratio =

2.1.6 Surface area: Volume ratio The bigger the organism, the smaller the surface area to volume ratio. So the less surface area there is (for diffusion) for every unit of volume.

Why do we need a ventilation system? If oxygen can’t diffuse in through the surface of an organism then it needs to develop a different method to maintain concentration gradients for gas exchange. This is why we need a ventilation system.

Features of alveoli that adapt them for gas exchange In groups discuss what you remember from IGCSE. You should have come up with the following ideas: –Large surface area –Thin walls (short distance for diffusion) –Moist (so gases dissolve before diffusing) –Good blood supply (to maintain the concentration gradient)

6.4.4 Ventilation System Homework: Draw a diagram of the ventilation system including the following parts: trachea, lungs, bronchi, bronchioles and alveoli. The alveoli should be drawn as an inset at a higher magnification. DO NOT JUST PRINT IT OUT FROM THE INTERNET!!! DRAW IT!!!

Ventilation Ventilation – The muscle movements that bring about the movement of air into and out of the lungs.

Diaphragm contracts and gets ____________ Intercostal muscles contract. Ribs move out and ______ Volume _____________ Pressure ____________ Air enters the lungs Inhalation

Diaphragm _______ and returns to its dome shape Intercostal muscles ______. Ribs move ___ and ______ Volume _____________ Pressure ____________ Air _____ the lungs Exhalation

Lung volumes Tidal volume – the amount of air breathed in or out of the lungs. This is about 500cm 3 Inspiratory reserve volume – extra lung volume available if you breathe in as much as you can. This is about 3000cm 3 Expiratory reserve volume – extra lung volume available if you breathe in as much as you can. This is about 1100cm 3

Lung volumes Vital capacity – this is the TV + IRV + ERV or the useable lung capacity. It is about 4500cm 3 Residual air – this is the amount of air that needs to stay in your lungs to stop them collapsing. It is about 1200cm 3

Lung capacity practical Look at the instructions for how to use the lung volume kit. Try to measure your own lung volume Plan an investigation into a factor that could affect vital capacity. Due in next Wednesday.