30 lines
3.0 KiB
Markdown
30 lines
3.0 KiB
Markdown
[[Cell Structure and Function]]
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Surface area-to-volume ratio (SA:V) controls how well a cell exchanges materials and energy with its environment. Smaller cells have higher SA:V, so more efficient. As things get bigger, cells require more adaptations to remain fast.
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# Summary
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* Higher SA:V means more efficient exchange.
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* Volume grows faster than SA as a cell gets bigger, so SA:V decreases.
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* Folds and projections like microvilli and root hairs increase SA without adding much V.
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* Lower SA:V in larger bodies slows heat exchange and is linked to lower metabolic rate.
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Plasma membrane SA must be large enough to exchange stuff fast enough for cell needs.
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SA:V doesn't only affect size, but also shape. Sphere isn't all that efficient for SA:V.
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- _Sphere:_ SA = 4πr², V = (4/3)πr³
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- _Cube:_ SA = 6s², V = s³
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- _Cylinder:_ SA = 2πrh + 2πr², V = πr²h
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- _Rectangular Solid:_ SA = 2(lw + lh + wh), V = lwh
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Because SA:V impacts thermal energy transfer, larger organisms lose heat slower than smaller organisms proportionally.
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| Term | Definition |
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| ---------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
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| heat exchange | The transfer of thermal energy between an organism's body and the surrounding environment; rate decreases as organism size increases. |
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| membrane folds | Infoldings of the cell membrane that increase surface area to facilitate more efficient material exchange in complex cells. |
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| metabolic rate | The rate at which an organism uses energy; typically higher per unit body mass in smaller organisms than in larger organisms. |
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| nutrient exchange | The process by which cells obtain necessary nutrients from the environment. |
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| plasma membrane | The selectively permeable membrane that surrounds the cell, composed of phospholipids, proteins, and other molecules that regulate what enters and exits the cell. |
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| surface area-to-volume ratio | The relationship between the total surface area and the total volume of a cell or organism; affects the efficiency of material exchange with the environment. |
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| thermal energy exchange | The transfer of heat energy between an organism and its environment. |
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| waste products | Byproducts of cellular metabolism that must be eliminated from cells or organisms. | |