Data Processing
Calculations for surface area of agar blocks:
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10mm × 10mm × 6 = 600mm2
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(5mm × 10mm × 4) + (10mm × 10mm × 2) = 400mm2
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(5mm × 10mm × 4) + (5mm × 5mm × 2) = 250mm2
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5mm × 5mm × 6 = 150mm2
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(2.5mm × 5mm × 4) + (5mm × 5mm) = 100mm2
Calculations for volume of each agar blocks:
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10mm × 10mm × 10mm = 1000mm3
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5mm × 10mm× 10mm = 500mm3
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5mm × 5mm × 10mm = 250mm3
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5mm × 5mm × 5mm = 125mm3
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2.5mm × 5mm × 5mm = 62.5mm3
Calculations for surface area to volume ratio:
- 600 : 1000
= 0.6 : 1.0
- 400 : 500
= 0.8 : 1.0
- 250 : 250
= 1.0 : 1.0
- 150 : 125
= 1.2 : 1.0
- 100 : 62.5
= 1.6 : 1.0
Example calculation for time taken for agar blocks to decolourise
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Data obtained from Table 1.2, agar block number 1.
Graph 1.1: Averaged time taken for agar blocks to decolourise
Conclusion
From the results obtained above, it is agreed that a larger agar block will result in longer time for the agar block to decolourise due to the smaller surface area to volume ratio. A smaller agar block will result in shorter time to decolourise due to the bigger surface area to volume ratio. As seen from Graph 1.1, the larger the surface area to volume ratio, the shorter time is needed for agar blocks to decolourise. This can be seen when an agar block with a 0.6 : 1.0 surface area to volume ratio needed 3332.20seconds to decolourise while agar block with 1.6 : 1.0 surface area to volume ratio only needed 1459.12 seconds to decolourise. These observations and results proves that the ratio of surface area : volume is a limiting factor in cell size.
Many important chemical reactions occur within the cell. Substances moves into the cell to be used as fuel for the reactions that occur within cell, collectively known as the cell metabolism. Products of these reactions (waste substances) need to be removed out of the cell in order for metabolism to continue. These two processes (substances moving in and out of cell) depend on the cell’s surface area to volume ratio.
This is due to the fact that the metabolic rate of the cell is directly proportional to the cell’s volume, hence the chemical activity per unit time. On the other hand, the rate at which substances move in and out of the cell depends on the cell surface area.
The chemical activity of a cell increase as the cell size increase, as more substances needs to be taken in and to be removed. As the cell increase in size, so will the volume and the surface area of the cell, but not to the same extent. As shown above, as cell gets bigger, the surface area to volume ratio gets smaller. This is proven when agar block 1 (the biggest agar block) had the smallest surface area to volume ratio ( 0.6 : 1.0 ) while agar block 5 ( the smallest agar block) had the biggest surface area to volume ratio ( 1.6 : 1.0 ).
If the surface area to volume ratio of a cell gets too small, substances will not be able to enter the cell fast enough to fuel reactions and waste products will start to accumulate within the cell as they are produced more rapidly than they are secreted.
Surface area to volume ratio is also important for heat production and heat loss. If the ratio is too small, the cell may overheat due to faster heat production from the processes of metabolism than they are lost over the cell’s surface.
The hypothesis above can be applied to animals (mammals) living in the cold regions of the earth. The Allen’s rule theory suggests that, mammals living in cold regions tend to be large in size. Though the cold weather, Antarctic mammals are still able to regulate the same internal body temperature. Their large figure helps them to conserve more energy due to the smaller surface area to volume ratio. This is also true for the opposite: animals that live in warmer climate will have a higher surface area to volume ratio to prevent overheating.
Evaluation
Table 1.4: Problems and effect of problem on the experiment and ways to improve it.
Bibliography
Allot, A. & Mindroff, D. (2007). Biology Course Companion .Great Britain:Bell and Bain Ltd.
