Ilikerevising
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- Describe how the effectiveness of exchange surfaces are increased.
- Use ideas about surface area to volume ratio to describe why
multicellular organisms need exchange surfaces
- Link ideas about diffusion to explain how the adaptations of exchange
surfaces increase their effectiveness.
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macpatgh-Sheldon
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I see you are still awake - let me try and help you with this Q!

Watch this space - give me 10-15 min

M
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macpatgh-Sheldon
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- Describe how the effectiveness of exchange surfaces are increased.
- Use ideas about surface area to volume ratio to describe why
multicellular organisms need exchange surfaces
- Link ideas about diffusion to explain how the adaptations of exchange
surfaces increase their effectiveness.


As living things get bigger [as they have done with evolution], their bodies have many more and more cells and tissues that are far from the outside environment - in single-celled [= unicellular] organisms like bacteria or amoeba, the ratio of surface area for exchange of food and waste, oxygen, etc to volume is high. This is not so in higher organisms, so they have evolved specialized structures for exchange of materials with the outside.

Diffusion is quicker when there is a large difference in concentration of substance as diffusion is the movement of a substance from high to low concentration areas. In lungs, breathing produces a high conc-n of oxygen [in the alveoli] so this gas diffuses into the blood in the capillaries where O2 conc-n is low.

Also diffusion is quicker when the distance the substance has to travel is very small - in lungs O2 only has to cross a single layer of cells of the alveolar wall and a single layer of the capillary wall, both of which are v thin.

Large surface area helps and is very important in nature - examples:-

In intestine: villi and microvilli to absorb digested food.
In blood: millions of tiny doughnut-shaped red cells to carry O2.
In roots of flowering plants, thousands of thin long root hairs to absorb water and minerals
In plants, thousands of flat leaves to absorb sunlight and to exchange gases
In gills of fish, lamellae and gill plates to absorb O2.

etc etc

I hope this helps! Do you have an exam t-rrow? - best of luck!

M
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Ilikerevising
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(Original post by macpatelgh)
- Describe how the effectiveness of exchange surfaces are increased.
- Use ideas about surface area to volume ratio to describe why
multicellular organisms need exchange surfaces
- Link ideas about diffusion to explain how the adaptations of exchange
surfaces increase their effectiveness.

As living things get bigger [as they have done with evolution], their bodies have many more and more cells and tissues that are far from the outside environment - in single-celled [= unicellular] organisms like bacteria or amoeba, the ratio of surface area for exchange of food and waste, oxygen, etc to volume is high. This is not so in higher organisms, so they have evolved specialized structures for exchange of materials with the outside.

Diffusion is quicker when there is a large difference in concentration of substance as diffusion is the movement of a substance from high to low concentration areas. In lungs, breathing produces a high conc-n of oxygen [in the alveoli] so this gas diffuses into the blood in the capillaries where O2 conc-n is low.

Also diffusion is quicker when the distance the substance has to travel is very small - in lungs O2 only has to cross a single layer of cells of the alveolar wall and a single layer of the capillary wall, both of which are v thin.

Large surface area helps and is very important in nature - examples:-

In intestine: villi and microvilli to absorb digested food.
In blood: millions of tiny doughnut-shaped red cells to carry O2.
In roots of flowering plants, thousands of thin long root hairs to absorb water and minerals
In plants, thousands of flat leaves to absorb sunlight and to exchange gases
In gills of fish, lamellae and gill plates to absorb O2.

etc etc

I hope this helps! Do you have an exam t-rrow? - best of luck!

M

thank you so much

but could you seperate them so i know which goes with which cos i dont know when ur paragraphs finish... ty
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macpatgh-Sheldon
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- Describe how the effectiveness of exchange surfaces are increased.

Diffusion is quicker when there is a large difference in concentration of substance as diffusion is the movement of a substance from high to low concentration areas. In lungs, breathing produces a high conc-n of oxygen [in the alveoli] so this gas diffuses into the blood in the capillaries where O2 conc-n is low.

Also diffusion is quicker when the distance the substance has to travel is very small - in lungs O2 only has to cross a single layer of cells of the alveolar wall and a single layer of the capillary wall, both of which are v thin.

X --------------------------------------------------- O ------------------------------------------------- X

Use ideas about surface area to volume ratio to describe why
multicellular organisms need exchange surfaces

As living things get bigger [as they have done with evolution], their bodies have many more and more cells and tissues that are far from the outside environment - in single-celled [= unicellular] organisms like bacteria or amoeba, the ratio of surface area for exchange of food and waste, oxygen, etc to volume is high. This is not so in higher organisms, so they have evolved specialized structures for exchange of materials with the outside. SO DIFFUSION ALONE IS NOT GOOD ENOUGH NOW [in higher organisms] AS CELLS IN THE MIDDLE OF THE ORGANISM ARE TOO FAR FROM OUTSIDE.

X ---------------------------------------------------- O ---------------------------------------------------- X

Link ideas about diffusion to explain how the adaptations of exchange
surfaces increase their effectiveness.

Large surface area helps and is very important in nature - examples:-

In intestine: villi and microvilli to absorb digested food.
In blood: millions of tiny doughnut-shaped red cells to carry O2.
In roots of flowering plants, thousands of thin long root hairs to absorb water and minerals
In plants, thousands of flat leaves to absorb sunlight and to exchange gases
In gills of fish, lamellae and gill plates to absorb O2.

( NB: there is some overlap between 1st part and 3rd part)
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macpatgh-Sheldon
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(Original post by Ilikerevising)
thank you so much

but could you seperate them so i know which goes with which cos i dont know when ur paragraphs finish... ty
Ilikerevising


Done for you - see above!
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