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Published byWilliam Keith Modified over 3 years ago

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What does the city do with wastes?What does the city do with wastes? How does a city get new nutrients?How does a city get new nutrients?

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How Big is Too Big? All living organisms are made up of cells. Cells are really small. Why? Why cant a human be made of just one big cell instead?

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All cells diffuse nutrients and wastes in and out at a constant rate. Basically, the more surface area (aka cell membrane), the more nutrients and wastes a cell can exchange. Using the formulas for volume and surface area, we can make a ratio to compare the two.

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Surface Area to Volume Assignment Follow along for two examples then complete the rest of the assignment using the formulas provided. Ratio: SA / V

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If we were to watch nutrients being absorbed at a constant rate in 3 different size cubes, the nutrients could reach the entire cytoplasm of smaller cells because, for their volume, they had a much larger surface area. Dead: nutrients cant get to all parts of the cell. Better, but still dead. Alive! Nutrients make it to all parts of the cell. 4cm 3 1 cm 3 2 cm 3 Surface Area =(base) (height) added up for all sides S.A.= (4cm)(4cm)(6 sides) = 96 cm 2 x 1 cube = 96 cm 2 S.A.= (2cm)(2cm)(6 sides) = 24 cm 2 x 8 cubes = 192 cm 2 S.A.= (1 cm)(1cm)(6sides) = 6 cm 2 x 64 cubes = 384 cm 2 Volume = (base) (width) (height) V = (4cm)(4cm)(4cm) = 64cm 3 x 1 cube = 64cm 3 V = (2cm)(2cm)(2cm) = 8cm 3 x 8 cubes = 64 cm 3 Surface Area to Volume Ratio V = (1cm)(1cm)(1cm) = 1cm 3 x 64 cubes = 64 cm 3 The smaller the cell, the larger the SA / V ratio, and the easier it is for diffusion to reach all parts of the cell

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Shape also affects surface area to volume ratio. 16 7.11 Skinnier, flatter cells large SA / V ratios. Cells with projections, like microvilli, have large SA / V ratios.

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In order for an organism to be large, it must be multi cellular. Which of the equal volumes below has the greatest SA / V Ratio and is therefore most likely to survive?

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Distribution systems, such as your circulatory system deliver nutrients to and remove waste from each cell. Diffusion is sufficient because of each cells large SA / V ratio.

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