OCR Biology F211 Exam - Tues 11&#x27;th January 2011

Original post by The Smeezington

How would you answer the follwing

list four ways in which the structure of a dicotyledonous leaf is adapted for gas exchange?

i dont they will ask for four ways a leaf is adapted for GAS EXCHANGE. is there even four ways it is adapted?

Reply 182

Original post by The Smeezington

How would you answer the follwing

list four ways in which the structure of a dicotyledonous leaf is adapted for gas exchange?

1. transparent upper epidermis-lets light through
2. palisade layer underneath-consists of thin. long and tightly packed cells containing lots of cholorplast & chlorophyll
3. loosely packed spongy mesophyll layer- has many air spaces 2 allow circulation of gases
4.lower epidermis has pores called stomata-allow gases 2 be exchanged between leaf and outside air.
5. stomata have TWO GUARD CELLS that can swell 2 open the pore, when the guard cells are not turgid then stoma closes
6. leaf vein system-contains xylem & phloem tissues 2 transport water in2 leaf and assimilates to other part.

Reply 183

Original post by pastpaper-guy

i dont they will ask for four ways a leaf is adapted for GAS EXCHANGE. is there even four ways it is adapted?

lol yeah there are plenty of points :biggrin:

Reply 184

hellosarah

Original post by anonymous_angel_16

I don't think you can ever be ready for a test but this one I am seriously not ready for!
Just had a panic attack feeling I don't know anything!
I blame my maths exam - I was concentrating on that :frown:

but yh, hope i do well. Good luck! and judging from your posts, I really don't think you'll get an E - you'll do a lot better

yeaahhh that was copied from my notes.
But seriously, tomorrow better run smooothly or i will kick up a fuss with OCR.
GOOD LUCK FOR TOMORROW !! :biggrin:

Reply 185

Right guys im struggling with HOW TO ANSWER something.. I fully understand the concept but I cringe when I see this question 'cos i get the wording wrong.. its quite simple..

Something like why a multi cellular organism needs a transport/circulatory system?

Why a multi cellular organism needs specialised exchange surface?

I mean HOW do you answer this and whats the difference? Please anyone? :smile:

Reply 186

Original post by 786girl

lol yeah there are plenty of points :biggrin:

daymm. better revise that bit then lol

Reply 187

Jhyzone

13

Original post by Rosi M

Right guys im struggling with HOW TO ANSWER something.. I fully understand the concept but I cringe when I see this question 'cos i get the wording wrong.. its quite simple..

Something like why a multi cellular organism needs a transport/circulatory system?

Why a multi cellular organism needs specialised exchange surface?

I mean HOW do you answer this and whats the difference? Please anyone? :smile:

have you consulted the mark scheme for the answers? :biggrin:

Reply 188

Original post by Rosi M

Right guys im struggling with HOW TO ANSWER something.. I fully understand the concept but I cringe when I see this question 'cos i get the wording wrong.. its quite simple..

Something like why a multi cellular organism needs a transport/circulatory system?

Why a multi cellular organism needs specialised exchange surface?

I mean HOW do you answer this and whats the difference? Please anyone? :smile:

a multicellular organism requires alot of oxygen to be able to respire. diffusion alone is insufficient for the needs of the organism so has a gas exchange transport system which would supply sufficient oxygen to the cells.
some organisms have a large surface area to volume ratio meaning diffusion will not get to all parts of the organism, thus requiring a transport system.

closed ciculatory systems are something else. that just means the blood is in vessels.

Reply 189

Tabers

15

Original post by The Smeezington

Why is there always so little on the heart when it's the area i'm best at.

Might be the year then. I never used to be able to do the heart and the cardiac cycle and couldn't for the first time however now I can do the cardiac cycle. But if there was, I wouldn't want there to be anything about electrocardiograms as I can never remember what each of the letters is.

Reply 190

Original post by Rosi M

Right guys im struggling with HOW TO ANSWER something.. I fully understand the concept but I cringe when I see this question 'cos i get the wording wrong.. its quite simple..

Something like why a multi cellular organism needs a transport/circulatory system?

Why a multi cellular organism needs specialised exchange surface?

I mean HOW do you answer this and whats the difference? Please anyone? :smile:

Why a multi cellular organism needs specialised exchange surface?

well, because;
-they need 2 remove waste products eg co2 (in animals) o2 (in plants) urea etc
-single celled need it coz they can exchange gases, nutrients &wastes across their outer surfaces-they have a LARGE SA;V

larger organisms need it bcoz they need it for oxygen for respiration. they cannot supply enough through their skin surface as theyhave a SMALL SA;V.
a special surface area 4 exchange gives a greater area so more o2 can be absorbed and more co2 can be removed.

Reply 191

Original post by pastpaper-guy

a multicellular organism requires alot of oxygen to be able to respire. diffusion alone is insufficient for the needs of the organism so has a gas exchange transport system which would supply sufficient oxygen to the cells.
some organisms have a large surface area to volume ratio meaning diffusion will not get to all parts of the organism, thus requiring a transport system.

closed ciculatory systems are something else. that just means the blood is in vessels.

Right thanks for that :biggrin:

So basically large SA:V, more oxygen/nutrients needed, diffusion not enough to meet needs so gas exchange system. ok :smile:

Reply 192

giraffegiraffe

10

Original post by pastpaper-guy

daymm. better revise that bit then lol

haha me too, didnt realise we had to learn it! thankfully its kindof straightforward

Original post by Rosi M

Right guys im struggling with HOW TO ANSWER something.. I fully understand the concept but I cringe when I see this question 'cos i get the wording wrong.. its quite simple..

Something like why a multi cellular organism needs a transport/circulatory system?

Why a multi cellular organism needs specialised exchange surface?

I mean HOW do you answer this and whats the difference? Please anyone? :smile:

i think its pretty much the same concept for both,
large organisms have a small SA:vol so direct diffusion from environment to cells to supply the organism with the nutrients etc it needs and remove the waste products at the rate it needs to maintain a safe level, is not feasible/inefficient compared to smaller organisms (for which gases etc can simply diffuse directly through their plasma membranes). also multicellular organisms are a larger size therefore some cells are too deep inside and not exposed to the environment directly for diffusion in this way. plus active organisms have a higher demand for O2 and to remove CO2 (high respiration rate) and so need a specialised exchange surface/transport system.

i think its basically to do with diffusion being too slow to supply needs regarding SA:Vol, size, and activity levels. but i know exactly what you mean about losing marks so easily for the right answer but just not the exact specific words they want :frown:

edit... Sorry didnt realise replies had already come in! :colondollar:

(edited 13 years ago)

Reply 193

fahimak

hey can anyone xplain transpiration 2 me....i still dont get it :frown:

Reply 194

Original post by Jhyzone

have you consulted the mark scheme for the answers? :biggrin:

I am now

Reply 195

Original post by giraffegiraffe

haha me too, didnt realise we had to learn it! thankfully its kindof straightforward

i think its pretty much the same concept for both,
large organisms have a small SA:vol so direct diffusion from environment to cells to supply the organism with the nutrients etc it needs and remove the waste products at the rate it needs to maintain a safe level, is not feasible/inefficient compared to smaller organisms (for which gases etc can simply diffuse directly through their plasma membranes). also multicellular organisms are a larger size therefore some cells are too deep inside and not exposed to the environment directly for diffusion in this way. plus active organisms have a higher demand for O2 and to remove CO2 (high respiration rate) and so need a specialised exchange surface/transport system.

i think its basically to do with diffusion being too slow to supply needs regarding SA:Vol, size, and activity levels. but i know exactly what you mean about losing marks so easily for the right answer but just not the exact specific words they want :frown:

Thanks

Yeah I know.. I've literally memorised mark schemes for translocation/transpiration etc. They are unbelievably fussy!

Original post by 786girl

Why a multi cellular organism needs specialised exchange surface?

well, because;
-they need 2 remove waste products eg co2 (in animals) o2 (in plants) urea etc
-single celled need it coz they can exchange gases, nutrients &wastes across their outer surfaces-they have a LARGE SA;V

larger organisms need it bcoz they need it for oxygen for respiration. they cannot supply enough through their skin surface as theyhave a SMALL SA;V.
a special surface area 4 exchange gives a greater area so more o2 can be absorbed and more co2 can be removed.

Thanks for that :biggrin:

xx

Reply 196

rasklatz

my arse hurts after all this revision.

Reply 197

Original post by rasklatz

my arse hurts after all this revision.

lol revise in bed then.

Reply 198