Biology hw help!! Watch

Mej
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I wasn't sure where to put this....im kind of new to tsr!!

Anyway i've got a past paper question for hw and dont how to write it.....i've answered the first part which the answer is the alveolus, part B then asks " describe the process by which gases are exchanged at the alveolus"

By the way this is the new ocr syllabus AS Biology and the this module is transport and exchange....I know the answer to the question is just i need a smaller answer that is worth 3 marks and i don't know how to shorten it into a sentence or to......and i have a maths test to revise for!!

I know i should do it myslf but if anyone here knows the answer and maybe come across it plz help....i'll be very greatful. THanks
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.SK.
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I'd suggest the concise exam answer you require would be along the lines of:

"Gas diffuses across the moist (1 mark) surface of the alveolus. The rich vascular supply (1 mark) and single cell epithelium (1 mark) aids efficient diffusion, utilising a steep concentration gradient."

If you want to be sure, chuck in something to do with large surface area, or surfactant proteins on the inner membrane.



EDIT: Re-read your post. If the question specifically asks "gases" (the plural) you may also want to write about 2 way gradient, high p02 to low p02 one way, high pCO2 to high pCO2 the other.
But for 3 marks, the above answer should be fine.
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HOLDTIGHTME
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Diffusion Gradient?

High conc. CO2 in vessels so moves into alveolus.
High conc. O2 in alveolus so moves into blood vessels.

Something like that simplified.
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Banana_Pancake
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well, if you bulletpoint all the main points and then select the most relevant 3, that should help.
stuff like: co2 diffuses from the atmosphere to the capillaries across the alveolar epithelium (one cell thick) whilst o2 diffuses back out of the alveolus to the atmosphere. you could also mention shizzle like haemoglobin releasing the o2 molecules, and state how the alveolus is adapted to it's function (one cell thick, moist, copious blood supply, large surface area - to speed up diffusion rate).

hope that helps, but knowing the question in it's entirety would have made it easier to address you more specifically.
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Mej
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Thank you sooo much!!

Just one more question...part c "Explain why mammals have large numbers of alveolus in their lungs" (2 mks)...Unlike the last question i asked i have no ide what the answer to this is!! Please help
THanks
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Sanjetti
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(Original post by Mej)
Thank you sooo much!!

Just one more question...part c "Explain why mammals have large numbers of alveolus in their lungs" (2 mks)...Unlike the last question i asked i have no ide what the answer to this is!! Please help
THanks
Large Number of alveolus provides large surface area for gas exchange (1 mark)
Ensures that oxygen diffuses more rapidly into the blood, and carbon dioxide out of the blood into the alveoli (1 mark), thereby maintaining the concentration gradient for gas exchange (1 mark)
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Sanjetti
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(Original post by .SK.)
I'd suggest the concise exam answer you require would be along the lines of:

"Gas diffuses across the moist (1 mark) surface of the alveolus. The rich vascular supply (1 mark) and single cell epithelium (1 mark) aids efficient diffusion, utilising a steep concentration gradient."

If you want to be sure, chuck in something to do with large surface area, or surfactant proteins on the inner membrane.



EDIT: Re-read your post. If the question specifically asks "gases" (the plural) you may also want to write about 2 way gradient, high p02 to low p02 one way, high pCO2 to high pCO2 the other.
But for 3 marks, the above answer should be fine.
Umm not sure about this answer .SK., you're talking more about adaptations than how the gases actually DIFFUSE (your edit covers it though!) etc. Oh and btw being moist does NOT help with gas exchange! :p:
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Mej
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Thanx a lot!!
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Sanjetti
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(Original post by Mej)
Thanx a lot!!
No problem! Be careful though, I'm not a walking talking mark scheme :P: Those points might well not be exactly the same as in the real mark scheme, but learning the general principles coupled with the mark schemes will put you in very good stead.
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.SK.
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(Original post by Sanjetti)
Umm not sure about this answer .SK., you're talking more about adaptations than how the gases actually DIFFUSE (your edit covers it though!) etc. Oh and btw being moist does NOT help with gas exchange! :p:
He said he knew all the material, and wanted it written more concisely, thats what I was trying to do for him. I'm pretty sure my answer will get you full marks in the exam.
And sorry, a moist inner membrane does facilitate gas diffusion. Do a bit of research.
www.google.com perhaps.
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red.ninja13
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1 cell thick epi... = short diffusion pathway, always worth 1 mark!
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Sanjetti
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(Original post by .SK.)
He said he knew all the material, and wanted it written more concisely, thats what I was trying to do for him. I'm pretty sure my answer will get you full marks in the exam.
And sorry, a moist inner membrane does facilitate gas diffusion. Do a bit of research.
www.google.com perhaps.
No you misunderstand me. The layer of liquid itself would inhibit diffusion to an extent (partly because its another layer on top of the epithelial cells). The reason why it facilitates diffusion is because it keeps the epithelial cells alive, hence allowing more efficient diffusion. I'm not sure if you meant this, but I felt like you were saying the moist lining itself facilitated gas diffusion.

And I just realised the OP was doing OCR! I did AQA B, so maybe I've been tuned to think differently hehe
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.SK.
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(Original post by Sanjetti)
No you misunderstand me. The layer of liquid itself would inhibit diffusion to an extent (partly because its another layer on top of the epithelial cells). The reason why it facilitates diffusion is because it keeps the epithelial cells alive, hence allowing more efficient diffusion. I'm not sure if you meant this, but I felt like you were saying the moist lining itself facilitated gas diffusion.

And I just realised the OP was doing OCR! I did AQA B, so maybe I've been tuned to think differently hehe
. . .but, it does facilitate diffusion in its own right.
Layer of moisture allows the gas to dissolve an thus diffuse at a more rapid rate than it otherwise would, i.e. if it was just gaseous, and had to go through epithelial cell lining.
Its nothing to do with keeping the epithelial cells alive. The only thing close to what you propose is the surfactant protein that reduces the surface water tension so that the alveoli do not collapse.

Did you actually do A-Level Biology? How did you end up doing?
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Sanjetti
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(Original post by .SK.)
. . .but, it does facilitate diffusion in its own right.
Layer of moisture allows the gas to dissolve an thus diffuse at a more rapid rate than it otherwise would, i.e. if it was just gaseous, and had to go through epithelial cell lining.
Its nothing to do with keeping the epithelial cells alive. The only thing close to what you propose is the surfactant protein that reduces the surface water tension so that the alveoli do not collapse.

Did you actually do A-Level Biology? How did you end up doing?
Umm ok...what's this about how I ended up doing. We're having a discussion, it's not the end of the world if one of us is wrong.

Well OK, maybe I'm wrong I dont know. Maybe I misheard what the teacher was saying. I just finished my AS biology and started the A2 this year, so I haven't really come across in too much detail.

Just a question, how are the epithelial cells kept alive without surrounding interstitial fluid (surfactants apart)?
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Sanjetti
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(Original post by .SK.)
. . .but, it does facilitate diffusion in its own right.
Layer of moisture allows the gas to dissolve an thus diffuse at a more rapid rate than it otherwise would, i.e. if it was just gaseous, and had to go through epithelial cell lining.
Its nothing to do with keeping the epithelial cells alive. The only thing close to what you propose is the surfactant protein that reduces the surface water tension so that the alveoli do not collapse.

Did you actually do A-Level Biology? How did you end up doing?
Oh btw, I just checked with the head of the biology department at my school, and he agrees.

Two things: i) Being moist (as an adaptation for gas exchange) has been taken out of most GCSE and A-level syllabuses because its not an adaptation. It's a CONSEQUENCE of water being drawn out by osmosis from the cells in alveoli (because its only a cell layer thick)
ii) A layer of water actually reduces rate of diffusion of gases

edit: I guess this isn't too important anyway, the OP has probably handed in her paper already :p:
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.SK.
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Meh, we've been taught two different things
I'm interested, I can't find anything to back up what your saying, but I'm sure your Bio teacher isn't just making stuff up.

Being a consequence and an adaption isn't mutually exclusive. All adaptions are consequences of, if nothing else, selection.
I agree that in generall diffusion is gas > diffusion through liquid, but for the purposes of becomming a solute in the capillary after passing 2 p.p.membranes, being already in solution would be an advantage.
Also, afaik, the moisture of the inner alveolar surface and the tissue fluid are seperate i.e. the moisture's presence does not keep the epithelial cells alive, and vice versa, its absence would not kill them.

I'll get my tutor to clear it up soon, shall report back here if I remember

Edit: and sorry for having a go, wasn't fully sober when I made that reply, was just about to go out. Ignore it
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Sanjetti
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(Original post by .SK.)
Meh, we've been taught two different things
I'm interested, I can't find anything to back up what your saying, but I'm sure your Bio teacher isn't just making stuff up.

Being a consequence and an adaption isn't mutually exclusive. All adaptions are consequences of, if nothing else, selection.
I agree that in generall diffusion is gas > diffusion through liquid, but for the purposes of becomming a solute in the capillary after passing 2 p.p.membranes, being already in solution would be an advantage.
Also, afaik, the moisture of the inner alveolar surface and the tissue fluid are seperate i.e. the moisture's presence does not keep the epithelial cells alive, and vice versa, its absence would not kill them.

I'll get my tutor to clear it up soon, shall report back here if I remember

Edit: and sorry for having a go, wasn't fully sober when I made that reply, was just about to go out. Ignore it
Ye, no problem at all mate!

Yeah I am interested...I asked 4 biology teachers that question, and two said it did facilitate diffusion and 2 said it didn't. I'd be interested in what your tutor says as well, it seems to be quite an interesting thing.

And what you're saying about consequesnces and being an adaptation is correct. All I'm saying is that the exam boards have taken it out of the syllabus because the moist surface strictly isnt an evolutionary adaptation as such (just a question of terminology-exam boards eh? :p:) since the moisture was not intentiona, so to speak. BUT it still facilitates diffusion (assuming you're right of course), so it still helps with gas exchange, but unwittingly...a bit confused atm actually

Ah, gotcha about the intersitial fluid and inner alveolar suface.
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Click101xox
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I'm new to this but I have a question!

' state one way inhaled and exhaled a differ apart from in their gas composition'
it's a one mark question!!!!x
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