1. Do Now: Calculate the volume of the shapes below: 8 cm 2 cm 1 cm 2 cm

2. V rp = LWH  The volume of a rectangular prism is length x width x height.  Both of the example prisms have a volume of 8 cm 3 8 cm 2 cm 1 cm 2 cm V = LWH = 8cm*1cm*1cm = 8cm 3 V = LWH = 2cm*2cm*2cm = 8cm 3

3. Surface Area  The surface area of a 3d object is the total area of all of it’s sides.  For an object with identical sides  SA = # sides * area of each side 2 cm # sides = 6 Area of 1 side = 4cm 2 Surface Area = 24cm 2

4. Surface Area to Volume Ratio  The surface area to volume ratio measures how much surface area an object has per unit of volume.  Surface Area to Volume Ratio = SA / V  What is the SA / V ratio of our example shapes? Surface Area = 24cm 2 Volume = 8 cm 3 SA / V = ??? 8 cm 1 cm

5. So What’s the Biology Connection?  Cells are 3d shapes.  The surface area of a cell determines how quickly nutrients can enter and wastes can leave.  The volume of a cell determines how much material it needs to take in or remove in order to survive.

6. Bigger Organisms Need More Food The more of an organism there is (volume), the more food it needs to eat and the more waste it produces. Since materials can only enter or exit through a surface however, that determines how fast transport can happen.

7. So Why Are Cells Small?  Complete the Surface Area, Volume, and Ratio columns on your lab data table.  What happens to the SA/V ratio as shapes get bigger?

8. About the experiment  Tomorrow, you will cut 3 cubes from a block of agar, a small, medium, and big version.  You will then place them in a solution that causes them to change color as it seeps into the cubes.  By measuring how far into each cube the color gets, you will see the effect of the SA/V ratio on how quickly a cell can get materials it needs

9. Tomorrow’s Calculations  Notice that your data table has 2 columns we have not yet completed.  “Distance” will measure the distance the color has moved into the cube from one edge Distance Traveled

10. Q: How far can you walk into a Cemetary?  A: Only halfway, because then you’re walking out  The point: if the cube completely changes color, distance traveled = ½ * diameter Distance Traveled

11. % Distance Traveled Calculation  The last calculation you will do is % distance traveled. This number represents what % of our model cells got the “nutrients” they needed.  To calculate it, divide the distance traveled by ½ of the diameter, then multiply by 100%  % dist. traveled = [dist traveled / (d * 0.5) ] x 100%

12. The importance of shape  Size affects SA / V ratio, but shape does too. 8 cm 2 cm 1 cm 2 cm

13. Little Parts = high SA/V ratio 2 cm SA / V = 3 SA / V = 6

14. Why are these cells small and have this funny shape?