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Transcript
• What does the city do with wastes? • How does a city get new nutrients? • Just like a city, a cell needs to receive nutrients and remove wastes. • This is done through the cell membrane. • At what point, does it become too hard to transport materials in and out? In other words... How Big is Too Big? • All living organisms are made up of cells. • Cells are really small. Why? • Why can’t a human be made of just one big cell instead? • 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. Surface Area to Volume Assignment • Follow along for two examples then complete the rest of the assignment using the formulas provided. • Ratio: SA / V Surface Area to Volume Ratio • 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. 2 cm3 4cm3 1 cm3 Dead: nutrients can’t get to all parts of the cell. Surface Area = but still Alive! Nutrients make it to TheBetter, smaller the cell, dead. all parts of the cell. the larger the SA / V ratio, and the (base) (height) easieradded it isup for to reach fordiffusion all sides all parts of the cell S.A.= (4cm)(4cm)(6 sides) S.A.= (2cm)(2cm)(6 sides) S.A.= (1 cm)(1cm)(6sides) = 96 cm2 x 1 cube = 96 cm2 = 24 cm2 x 8 cubes = 192 cm2 = 6 cm2 x 64 cubes = 384 cm2 Volume = (base) (width) (height) V = (4cm)(4cm)(4cm) = 64cm3 x 1 cube = 64cm3 Surface Area Volume S.A. 96 1.5 V 64 V = (2cm)(2cm)(2cm) = 8cm3 x 8 cubes = 64 cm3 S . A. 192 3 V 64 V = (1cm)(1cm)(1cm) = 1cm3 x 64 cubes = 64 cm3 S . A. 384 6 V 64 • 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. • 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? • Distribution systems, such as your circulatory system deliver nutrients to and remove waste from each cell. • Diffusion is sufficient because of each cell’s large SA / V ratio.