Exchange Surfaces Summary

Exchange Surfaces Summary

Exchange Surfaces

Tiny organisms, like bacteria, can rely solely on diffusion to get all the nutrients they need to survive.

Multicellular organisms cannot rely on diffusion alone, they require these specialised surfaces.

Multiple Choice

Which of these are reasons why humans need specialised exchange surfaces?

• they have a large SA:vol

• their metablism is too high to rely on diffusion alone

• we have lots of cells

Surface Area to Volume Ratio

Bacteria can rely on diffusion alone to get all of the nutrients that they need to survive as they have a large surface area to volume ratio.

Multicellular organisms cannot rely on diffusion as they have a small surface area to volume ratio.

Calculating SA:vol

• SA / vol

• vol / vol

• 
  

  
  

• If we look at the middle example...

• SA / vol = 24 / 8 = 3

• vol / vol = 8 / 8 = 1

• SA:vol = 3:1

Multiple Choice

If an object has a SA of 42 cm² and a volume of 7 cm³, what would the SA:vol be?

• 7

• 6

• 5

• 4

YT video :)

Multiple Choice

From the video you just watched: what would happen to cells in your feet if humans had to rely on diffusion to get oxygen?

• they would shrink

• they would grow

• they would die

Open Ended

From the video you just watched: name an example of a specialised exchange surface

Multiple Choice

From the video you just watched: how far is the distance between the alveoli and the blood capillaries?

• 2 cells thick

• 3 cells thick

• 1 cell thick

• 4 cells thick

Multiple Select

From the video you just watched: what are two factors that the video mentioned at the end, which increase the rate of diffusion?

• short diffusion distance

• small SA:vol

• increased surface area

• maintaining a low to high concentration gradient

The villi in the small intestines is a specialised exchange surface. Explain how it is well adapted for the diffusion of nutrients. (6)

The small intestines (SI) are highly folded and include villi which both increase the surface area of the SI.

The lining of the villi are only one cell thick which decreases the diffusion distance.

The rich blood capillary network maintains a steep diffusion gradient by removing nutrients and transporting them around the body as they are absorbed.

The increased surface area, reduced diffusion distance and maintaining a concentration gradient all increase the rate of diffusion.