Greenwood press
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book-20600
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area (cm 2 ) volume (cm 3 ) ratio of volume to area 1 6 1 1/6 ≈ 0.17 3 54 27 27/54 ≈ 0.5 10 600 1,000 1,000/600 ≈ 1.67 50 15,000 125,000 125,000/15,000 ≈ 8.33 80 38,400 512,000 512,000/38,400 ≈ 13.33 100 60,000 1,000,000 1,000,000/60,000 ≈ 16.67 Ratio of volume to area for different cubes. 134 SURFACE AREA An animal loses heat through external surface area. The energy needed for basic metabolism is roughly proportional to the volume of the animal. An animal that has a large volume with respect to its surface area will have an easier time maintaining its metabolism. A large animal will have a lower heart rate and food requirements that are a fraction of its weight. An animal that has a small volume compared with surface area will have to work hard to replace the heat lost. We can expect small animals to have rapid heartbeats and daily food requirements that may be multiples of the animals’ weight. A polar bear is compact: Its large bulk means that it will have a large volume-to-area ratio. A hummingbird has a volume-to-surface-area ratio close to 0.5. It loses heat rapidly and hence must have a rapid heartbeat and relatively large food intake to maintain its metabolism. Perhaps that is one of the reasons that there are no hummingbirds in the Arctic. Of course, animals aren’t cubes. A human being is not packaged like a polar bear. We have hands that are very useful, but in winter they provide more surface area proportional to the volume they contain, so the wise person will wear mit- tens instead of gloves to reduce the heat loss. The volume-to-surface-area ratio is a factor at the microscopic level. Cells cannot benefit from larger volume-to-surface-area ratios. Since energy must come through the cell membrane, small ratios are an advantage. The compensation made by plant cells is that larger plant cells maintain less of a spherical shape (more cylindrical), while small plant cells are close to spherical. With a less spher- ical shape, the larger cells maintain an advantageous volume-to-surface-area ratio. online sources for further exploration Camping (wearing gloves) Figuring out how many rolls of wall covering you need Lead paint concentrations Medicinal tablet surface area Minimum surface area of a can Painting Soap bubbles Size effects on airplane lift Theory of flight Download 1.81 Mb. Do'stlaringiz bilan baham: |
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