LAB: CELL SIZE & DIFFUSION 1-cut 3 cubes in agar—  calculate SA & vol for each cube 2-place 3 cubes in beaker w/NAOH  DO NOT touch NAOH—MUST wear goggles!! 3-stir gently—turn cubes gently—10 minutes 4-remove cubes—place on paper towel—blot dry 5-dry for 5 minutes—cut each cube in ½ w/ruler 6-look at pink—measure on each cube 7-record--DRAW each cube 1cm 2cm 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 #sidesL x W x H SA:VOL :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. 1cm 2cm 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