LAB: CELL SIZE & DIFFUSION1-cut 3 cubes in agar—calculate SA & vol for each cube2-place 3 cubes in beaker w/NAOH

DO NOT touch NAOH—MUST wear goggles!!3-stir gently—turn cubes gently—10 minutes4-remove cubes—place on paper towel—blot dry5-dry for 5 minutes—cut each cube in ½ w/ruler6-look at pink—measure on each cube7-record--DRAW each cube

1cm2cm 3cm

PROBLEM

-Why are cells so small?-Why do cells stop growing after reaching a certain size?-What causes cells to stop growing and divide?

RESULTS

L x W x #sides

L x W x H SA:VOL

54

.000001

1

8

27

24

6

.0006

2:1

3:1

6:1

600:1 na

3

3

3

QUALITATIVE DATA

SHADE in the cross section of each of the 3 cubes showing the relative amount of material diffused into each cube.

1cm2cm 3cm

SCIENTIFIC METHOD

INDEPENDENT VARIABLE:-size of cell (SA:vol)

DEPENDENT VARIABLE:-% of cell diffused

CONSTANTS:-time, type of cell, NaOH solution

CONCLUSION: summarization-As cube size increases the SA:VOL decreases -Diffusion rate is the same regardless of cube size-Smaller cells have a higher % of the cell “diffused”

QUESTIONS

1-What evidence is there that NaOH diffused into the cube? -dark pink border 2-What evidence is there that the RATE of diffusion is about the same for each cube?-WIDTH of dark pink is SAME for all cubes

-distance diffused

QUESTIONS

4- Which cube has the greatest surface area……the 3 cm cube or the 1 cm cube? -3cm cube 5- Which has the greater surface area in proportion to its volume? -1cm cube 6:1

QUESTIONS

 6-What predictions can you make about the efficiency of each cube/cell model based on the information above?-smaller cube is more efficient -nutrients/waste don’t need to diffuse as far 7-What happens to the surface area-to-volume ratio of cubes as they increase in size?-SA:VOL decreases as cube size increases

QUESTIONS 8-Most cells and microorganisms measure less than .01 cm on a side. What is the relationship between RATE of diffusion and cell size?-RATE: how long it takes to diffuse

-is SAME for all cells -greater % of cell is diffused if smaller 

 9-Explain why large organisms (like yourself) have developed from MORE cells rather than LARGER cells.-smaller cells are more efficient-gain nutrients and remove waste more easily through entire cell-cells have different functions (nerve, skin, heart…) 

CHALLENGE QUESTION

How could you increase the surface area of a cell without changing the size of the cell?

-change the shape-poke holes with straw-make scallops on edges w/straw

Esophagus cells