Surface Area to Volume Ratio The surface area

Surface Area to Volume Ratio • The surface area to volume ratio refers to the ratio of the cell’s total surface area in relation to its volume. • Maximizing surface area to volume ratios is important so that the transport systems in cells can run efficiently

Surface- to- Volume Ratio Importance • A. Cells can only be so small. (There has to be enough room (volume) to hold things and to perform work inside a cell. ) • B. Cells can only be so large. (Larger means more traffic going in both directions across the cell membrane) • C. A cell must be large enough to contain DNA, Ribosomes, and some cytoplasm. They can only be so big because we have to be able to move enough “Food” into and “waste” out of a cell efficiently. If it is too large the cell becomes inefficient at moving these things so it divides to get back to a smaller state.

Surface Area to Volume Ratio • Reasons for keeping cell sizes small • Decreases distances that substances have to travel … increasing the rate of diffusion.

Human Systems • Cardiovascular system (alveoli in the lungs and capillaries that surround them aid in the diffusion of O 2 and CO 2 in and out of the blood)

Plant Systems • Structures in plants are also designed to maximize surface area to volume ratios for their specific functions. • Examples: • Leaf thickness and shape

Plant Systems • Root structures

Surface Area to Volume relationship

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 cm 3 4 cm 3 1 cm 3 Dead: nutrients can’t get to all parts of the cell. Surface Area = but still Alive! Nutrients make it to The. Better, 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. = (4 cm)(6 sides) S. A. = (2 cm)(6 sides) S. A. = (1 cm)(1 cm)(6 sides) = 96 cm 2 x 1 cube = 96 cm 2 = 24 cm 2 x 8 cubes = 192 cm 2 = 6 cm 2 x 64 cubes = 384 cm 2 Volume = (base) (width) (height) V = (4 cm)(4 cm) = 64 cm 3 x 1 cube = 64 cm 3 V = (2 cm)(2 cm) = 8 cm 3 x 8 cubes = 64 cm 3 V = (1 cm)(1 cm) = 1 cm 3 x 64 cubes = 64 cm 3

• 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?