The Size Of An Organism

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AC 2.1
1) When the size of an organism increases its surface area also increases.
2) When the size of an organism increases its volume also increases.
3) As the size of an organism increases both its surface area and volume increase however the surface area to volume ratio decreases. This is because the volume increases at a greater rate than the surface area. Organisms with a smaller surface area to volume ratio can exchange substance more easily compared with bigger organisms, which require more specialised systems. Having a large surface are to volume ratio enables the organism to heat up more quickly however they do not retain the heat compared with organisms with a small surface area.
4) Bacteria and Amoeba
Small organisms such as
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Bacteria have adapted to digest large micro nutrients by secreting enzymes that break down micro nutrients, for example the enzymes break down proteins into amino acids so that they can be absorbed into the cell.
Amoebas are larger than bacteria and are approximately 100µm in diameter but still have a relatively large surface area to volume ratio. Amoebas, unlike bacteria, do not secrete enzymes externally to digest food, instead they extend their cytoplasm and around the nutrients and then break it down within the cell. Figure 1 shows the nutrition of an amoeba. Figure 1
Microorganisms can heat up quickly but cannot retain heat well compared with larger organisms. This is because they have large surface area to volume ratio, so heat escapes easily.
Flies
Larger organisms have adapted to overcome limitations what occur in more simpler organisms, by developing more complex systems to exchange substances and retain heat. Multicellular organisms rely on many different cells that are specialised to perform different tasks, however they all work together in order for the organism to function. When cells are produced they have the potential to specialise as any type of cell for example a nerve cell or tissue cell depending on the requirements of the organism. This process is called cell differentiation and enables organisms to have more complex systems.
A housefly 's surface area to volume ratio is too big to diffuse oxygen
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