OCR AS Biology (F211) - Jan 2013.

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Original post by HeyMickey6

What is the resolutions for the different types of microscopes ?

LIGHT MICROSCOPE: 200nm --> 0.2um
election microscope: 0.2nm --> 0.002um

Reply 982

kad7422

the questions 'describe and explain how water is moved up the xylem' and 'describe and explain how transpiration contributes to the mechanism of water transport up the stem' both have come up on previous papers and have the same type of answer. Is this likely to come up again this time because I have nightmares about this,really hope it doesn't come up :frown:

Reply 983

Raine6

Cud someone please answer these for me xxx I'm so scared xxx

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Reply 984

Original post by Raine6

Cud someone please answer these for me xxx I'm so scared xxx

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The first is that the blood plasma moves out of the capillary wall into tissue and becomes tissue fluid, the second.. I'm working on :biggrin:

Reply 985

Original post by kad7422

the questions 'describe and explain how water is moved up the xylem' and 'describe and explain how transpiration contributes to the mechanism of water transport up the stem' both have come up on previous papers and have the same type of answer. Is this likely to come up again this time because I have nightmares about this,really hope it doesn't come up :frown:

Email me @ [email protected] and I will explain both in detail, if you want? :smile:

Reply 986

phaseshift

12

Original post by Tom_hess

So they can cut off an extra bit before they put the sample in the soil, this is because due to mass flow, air moves up the stem as well as water, and this will kill the leaf. So if he or she can get the most stem as possible, then they can cut a tad off, to get rid of the 'oxygen bubble' they can guarantee survival of that sample! I think :redface:

Yes and no. The main reason is the presence of meristematic cells at the base of the leaf, hence new growth can continue unhindered.

Reply 987

explain why multi-organisms need a exchange surface and uni-cellular organisms do not. (3marks)

explain why mammals need a transport system.(3marks)

I always seem to confuse the two. Any help?

Reply 988

Original post by Raine6

Cud someone please answer these for me xxx I'm so scared xxx

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The second is that there is less volume of blood pushing against it, as the blood moves away from the heart, it branches off into different arteries, this increased distance decreases the volume as it branches off into different areas.. That's the gist of the answer, I'll try to find the specifics, or you can just look at the mark scheme!

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Reply 989

kad7422

Original post by Tom_hess

Email me @ [email protected] and I will explain both in detail, if you want? :smile:

omg yes please u are too kind :smile:

the email is on its way... :smile:

Reply 990

Shadow_Amber

Original post by Tom_hess

What kind of questions could they ask on
Arteriole->Venuole stuff
Lymph and tissue fluid
Plasma Membrane(probably something to do with glycoproteins/lipids and cell communication/adhesion etc..)

Reply 991

phaseshift

12

Original post by noor momo

explain why multi-organisms need a exchange surface and uni-cellular organisms do not. (3marks)

explain why mammals need a transport system.(3marks)

I always seem to confuse the two. Any help?

Well, a mammal (us) is a multi-cellular organism and yes, we need some kind of transport system.

Why? Think about the poor hepatocytes or cells within your hypothalamus, how would they attain oxygen to respire? Certainly not through diffusion as the process is far too slow, not to mention oxygen stealing cells nabbing it on the way in. :wink:

(edited 11 years ago)

Reply 992

Original post by noor momo

explain why multi-organisms need a exchange surface and uni-cellular organisms do not. (3marks)

explain why mammals need a transport system.(3marks)

I always seem to confuse the two. Any help?

The first, you have to quote about single called organisms, eg, they have a large sa:v, therefore they can get the nutrients, eg. Oxygen by simple diffusion, whereas we need blah blah low sa:v, the second one I think just needs you to state that we have a low surface area to volume ratio, therefore can't get the nutrients we need for survival, and get rid of some things, eg. CO2...

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Reply 993

HeyMickey6

What is Mass Flow and where does it occur ?

Reply 994

phaseshift

12

Original post by HeyMickey6

What is Mass Flow and where does it occur ?

"Mass Flow" as a process is self explanatory, an example being water transportation in the xylem vessels of plants through the combined processes of turgor, adhesion and cohesive forces.

You could also talk about blood circulation as that is technically an example of mass flow. Oh, and the transport of assimilates in the phloem of plants too!

Reply 995

Original post by HarryMWilliams

Well, a mammal (us) is a multi-cellular organism and yes, we need some kind of transport system.

Why? Think about the poor hepatocytes or cells within your hypothalamus, how would they attain oxygen to respire? Certainly not through diffusion as the process is far too slow, not to mention oxygen stealing cells nabbing it on the way in. :wink:

Thank you very much :hugs:

Reply 996

Beni24

2

what is an ateriole and venule?

Reply 997

Original post by Tom_hess

The first, you have to quote about single called organisms, eg, they have a large sa:v, therefore they can get the nutrients, eg. Oxygen by simple diffusion, whereas we need blah blah low sa:v, the second one I think just needs you to state that we have a low surface area to volume ratio, therefore can't get the nutrients we need for survival, and get rid of some things, eg. CO2...

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This kinda made things more clear, thank you :h:

Reply 998

Original post by HeyMickey6

What is Mass Flow and where does it occur ?

So mass flow is the movement of water up a xylem,
There are three ways that this occurs and they are all passive except the first!
Root pressure-
Active as you will see
The movement of minerals, eg K+ ions, into the root makes a very low psi value in the root, due to this, lots of water moves into the root. This increases the water pressure in the root so that it is above the water pressure in the xylem, because of this, water moves into the xylem down a pressure gradient and moves up the xylem likewise, until it gets to the leaves! It is active because it couldn't work without the active transport of K+ ions into the root!
Transpiration Pull-
Due to cohesion, the attraction between water molecules, as water moves out of the plant by transpiration, water moves into the xylem and up the xylem by transpiration pull! A good way of remembering this is that imagine you have a hollow tube and a chain that fits in the tube. Each link of the chain is holding onto the next link and so on.. If you pull the chain out of the top of the tube, the chain will move up the tube, because it is attached! This is due to the cohesion-tension theory, which is about the water molecules being attracted to each other when in long, thin lines!
Finally, capillary action-
This is due to Adhesion! Adhesion is where the water molecules are attracted to the sides of the xylem, and this only works because the xylem are so thin! The forces of attraction(somehow, I don't know and we don't need to know) pull the water up the xylem.

Just remember mass flow is the movement of water up the xylem, not into or out of, just up, remember the key words, transpiration pull & cohesion. Capillary action & adhesion and root pressure!
When answering these questions, also give note to the psi values and the pressures! :smile:

Sent from my iPhone

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Reply 999