Gas exchange in humans question

I have two questions to do with gas exchange in humans im just wondering if someone could help me figure out the answer?


Question 1) The air you breathe in contains about 20% oxygen and only about 0.04% carbon dioxide. The air your breathe out contains around 16% oxygen and 4% carbon dioxide. What happens in the lungs to bring about these changes? (I'm not sure what happens in the LUNGS, I know that cells use oxygen from the inhaled air to release energy and give out carbon dioxide as a byproduct but is that the answer)

Question 2) Sometimes people injured in an accident such as a car crash suffer from a pneumothorax. This is an injury where the chest wall is punctured allowing air to enter the pleural cavity. A patient was brought into A and E suffering from a pneumothorax on the left side of his chest. His left lungs had collapsed but he was able to breath normally with his right lung.

a) Explain why the pneumothorax caused the left lung to collapse [2 marks]

b) Explain why the right lung was not affected [2 marks]

c) If a patients lung is injured or infected a surgeon used to sometimes 'rest' it by performing an operation called an artificial pneumothorax. What do you think might be involved in this operation? [2 marks]

(I have no idea how to answer this one)

No point answering them for you, but I can give you the clues to help you answer them for yourself

Q1 - this is about movement of these two gases within the alveolus. So how does CO2 move from the blood to the lungs to be expired and how does oxygen move out of the inspired air into the blood?

Q2a - look at a diagram of pleural pressures, transmural pressures and the role of the interpleural space and fluid. What keeps the lung inflated under normal conditions? Can you see why equalising the pressure between the lung and the atmosphere (which is what happens with a PT) results in the lung collapsing.

Q2b - again, have a look at the anatomy of the lungs with respect to the pleura.

For Q1 would it be something like - The oxygen we breathe in goes from the lungs through to the alveoli to the blood, the oxygen is then picked up by our red blood cells. This is then called oxygenated blood. The oxygenated blood is then pumped around the body to the cells in our tissues. The cells in our tissues then use the oxygen making our blood become deoxygenated, the cells in our tissue produce a waste gas called carbon dioxide. The carbon dioxide is then moved from our blood into our lungs. The increase in carbon dioxide is the waste product of gas exchange. ?

Good - getting there but not quite.

Why does the oxygen move from the inspired air in the lungs to the blood? What 'force' is driving it? Why doesn't it just stay in the lungs?

Similarly, why does the CO2 move out of the blood into the alveolar air to be expired? Again, what 'force' is driving it?

This is the key to full marks on this question. No problems if you genuinely can't work it out, but I want to give you a chance to arrive at the answer yourself.

errrr I really can't think of what it will be, I looked through my notes and can't find anything useful

Ohhh, I remember learning about this now! So could I write something like = The oxygen we breathe in goes from the lungs through to the alveoli. The inspired alveolar air is a higher concentration than that of the deoxygenated blood in the alveolar capillaries. The oxygen then moves down its concentration gradient from the lungs to the blood, the oxygen is then picked up by our red blood cells. This is then called oxygenated blood. The oxygenated blood is then pumped around the body to the cells in our tissues. The cells in our tissues then use the oxygen making our blood become deoxygenated. This then creates a waste product called carbon dioxide. The concentration of CO2 in the alveolar-capillary blood is higher than that of the alveolar air. The CO2 moves down its concentration gradient from the blood to the lungs. The increase in carbon dioxide is the waste product of gas exchange. ?

You didn't quote me, so I didn't know you'd replied

That's much, much better. But you still need to mention diffusion. Give me a shout if you need any more help by quoting this post.

Oh sorry I forgot to quote, for mentioning diffusion what sort of thing would I need to write? Could I put something like "This is called diffusion as the gas particles are moving from a high concentration to a low concentration" ?

For diffusion you need to get across the idea of random movement of particles from an area of high concentration to low concentration. Again, for bonus marks you could relate structure to function and say how the respiratory membrane is adapted to maximise diffusion rate.

I bang on about structure relating to function a lot. That's because it's a central theme in biology.

Overall, you've got a good answer there

Thankyou so much for your help!

Thankyou so much for your help!

You're welcome

It was good to see someone get help and arrive to their final answer as a joint effort.

Good luck OP with future questions, it sounds like you’ll be fine come exam time with that kind of answer.

I absolutely threads like this. This is what TSR is about for me. That and being unnecessarily brusque in the other fora

No point answering them for you, but I can give you the clues to help you answer them for yourself

Q1 - this is about movement of these two gases within the alveolus. So how does CO2 move from the blood to the lungs to be expired and how does oxygen move out of the inspired air into the blood?

Q2a - look at a diagram of pleural pressures, transmural pressures and the role of the interpleural space and fluid. What keeps the lung inflated under normal conditions? Can you see why equalising the pressure between the lung and the atmosphere (which is what happens with a PT) results in the lung collapsing.

Q2b - again, have a look at the anatomy of the lungs with respect to the pleura.

Hi, just wondering I did Question 2) and looked at some diagrams of the pressures I got this answer. Would these be correct?

a) The patient suffering from a pneumothorax had it on the left side of their chest meaning the air was only able to enter the pleural cavity on the left side. The pleural cavity is the potential space between the visceral and parietal pleura. Negative pressure is created in the pleural space as the thoracic cage enlarges. The negative pressure is lost as fluid collects in the pleural space which makes the lung unable to expand fully.

b) The right lung was not affected as the air only entered the left pleural cavity. Each lung has its own pleural cavity which is separated by the mediastinum.

c) I think that the operation involves adding more air or nitrogen into the pleural cavity to force the lung to collapse so that it can repair itself.

Just before I comment on these answers, what level is this? GCSE/A level? I should really have asked you this earlier