What does SA : V mean?

'surface area : volume'   or   'surface area to volume ratio'.


This tells you how many times larger the surface area is than the volume.

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What is the relationship between an organism's size and its surface area to volume ratio?

The larger the organism, the lower the surface area to volume ratio will be.

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How does the surface area to volume ratio affect the transport of molecules?

The lower the surface area to volume ratio, the further the distance molecules need to travel to reach all parts of the organism.


Once the distance becomes too great, diffusion alone is not sufficient to transport molecules quickly enough.

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Why do larger organisms require specialised exchange surfaces?

Their small surface area to volume ratio means they cannot exchange all the substances they need across their body's surface.


Exchange surfaces provide a large extra surface area adapted specifically for exchanging substances. 

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Why do very small organisms not require specialised exchange surfaces?

The distance between their cells and the outside world is very small.


This means diffusion between their cells and the outside world happens quickly enough for them to get the substances they need to survive (e.g. oxygen).

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Why do larger organisms require mass transport systems?

Diffusion alone is not sufficient to quickly transport substances long distances.


Mass transport systems transport substances between the organism's specialised exchange surfaces, and their body's cells, which are usually very far apart (in terms of molecules and diffusion).

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How would you calculate the surface area of this cube?

  1. Find the area of a single face:

 5 x 5 = 25 cm2


  1. Multiply the area of a single face by the number of faces (a cube has 6 faces):

25 x 6 = 150 cm2


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How would you calculate the volume of this cube?

  1. Multiply the width, height, and depth together (which is exactly the same as cubing a side length):

5 x 5 x 5


or:


53

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