Surface Area: Volume Ratio Flashcards

3.3.1

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1
Q

Why is a large surface area required for the exchange of substances?

A

For efficient exchange to occur, a large surface area is needed since the exchange takes place over the surface.

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2
Q

Describe the surface area: volume ratio of single celled organisms?

A

Large SA:V ratio so exchange can occur over the outer surface

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3
Q

Why don’t larger multicellular organisms exchange over their body surface?

A
  • the larger the organism the smaller the SA:V ratio
  • need for waterproofing (if living on land)
  • diffusion is much to slow (ficks law)
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4
Q

What is the solution for SA:V ratio getting smaller as the organism gets bigger?

A

Have specialised exchange surfaces with very large SAs eg. Lungs, Gills, Tracheal system

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5
Q

What is the solution for the need to waterproofing terrestrial organisms?

A

Have specialised exchange surfaces that are tucked away within the body to reduce water loss. This means the outer skin can become waterproof.

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6
Q

What is the solution to the problem that diffusion is too slow over long distances?

A

A transport system, a system of open tubes to carry air to every cell

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7
Q

What are the features of a specialised exchange surface?

A
  • large surface area
  • very thin (short diffusion distance)
  • maintains a diffusion gradient
  • selectively permeable
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8
Q

What’s the relationship with metabolic rate and SA:V ratio?

A

The greater the metabolic rate, the greater the quantities of the substances that need to be exchanged. Therefore they require an exchange surface with a larger surface area and a transport system to meet the requirements of the organism.

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