The Importance of Being The Right Size.

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The Importance of Being The Right Size

'The higher organisms are not larger than the lower because they are more complicated.

They are more complicated because they are larger.'

Hyung-woo (Shane) Cho

L6GW

Most people will be most likely to believe that the higher organisms, such as, animals, are larger because they are more complicated. However, actually, the higher organisms are complicated because they are larger. In other words, they have to be complicated in order to be large. Then why do they have to be complicated? And why do they want to get bigger?

Simply, the higher organisms are more complicated because they need more organisms and support from their body itself, to keep their large sized body. All the living things have their own features to adapt their living habitats. Complicated mechanisms and large sized body are included in these features as well. The feature that is linked with the size of a living organism is surface area and the gas exchange. To get the energy to continue their lives organisms need to do respiration. Gaseous exchange is necessary for this, for respiration oxygen is taken into their body, and carbon dioxide are released out to the atmosphere. There are some other gases that are also need to be exchanged, for example, water and urea (waste). Gas exchange normally occurs by a process called diffusion, and the important properties of gas exchanging surface are :

As seen on the points on the right, large surface area takes very important part in the gas exchange. The amount of gas an organism needs to exchange is largely proportional to its volume (the bulk of respiring cells), but the amount of exchange that can occur is proportional to the surface area over which diffusion takes place.

Every organism varies considerably in size. For example, the size of amoeba (protozoa) and is 10µm, whereas the size of blue whale (animal) is 30m, which is 30 million µm. We are able to recognize that

blue whale is 3 million times bigger than amoeba.

(Obviously the volume will vary much more.)

Surface Area

6cm²

24cm²

54cm²

Volume

cm³

8cm³

27cm³

SA : V

6 : 1

3 :1

2 : 1

In the table showing surface area : volume ratios, the surface area and volume increases as the linear dimension increases. However, surface area is much smaller compared to the volume. As you can see from this, small objects have a large surface area compared to their volume, meaning that the small size of one cellular organism such as amoeba will have a large surface area over which gas exchange may take place. Therefore smaller organisms are able to respire more efficiently through their surfaces. Normally, the large animals such as human and animals have got specialized mechanism or organ system that is suitable for respiration and transport. For example, the humans ventilate to gain all the O2 required, which enters the lungs by defusing across a thin permeable moist membrane into capillaries to supply oxygen all around the body by heart.
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Just big sized body will not be very effective without the support from specialized features for the size and habitats. It might feel a bit strange, but we are about to find out if an imaginary character in a movie called 'King-Kong' could be existed in real life.

King-Kong is about ten times bigger than normal gorilla in size. For this data and comparison, we will assume that density of 1g/cm³, and the linear dimension of a normal gorilla to be 200cm. (Therefore 2000cm for King-Kong).

Volume

Mass in grams

Mass in kilograms
...

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