NAME ______ DIFFUSION in JELLO CELLS Bigger Isn T Always Better INTRODUCTION Diffusion

NAME ______

DIFFUSION IN “JELLO CELLS” Bigger isn’t always better

INTRODUCTION Diffusion and osmosis are among the most commonly studied topics in biology. Virtually all living cells are, to varying degrees, dependent on these processes. This activity will enable students to explore the relationship between diffusion and cell size by experimenting with model “cells.”

Gelatin containing red cabbage juice will be cut into appropriate sizes. Red cabbage contains a colored pigment that is sensitive to changes in pH. In acidic conditions it will turn pink. In basic conditions it will appear blue.

Surface area VOLUME SA/Volume (cm2) (cm3) Ratio L X W X 6 L X W X H

1cm X 1cm X 1cm

2cm X 2cm X 2cm

3 cm X 3 cm X 3 cm

Which “Jello cell” had the LARGEST SA/Volume ratio? ______

Which “Jello cell” had the SMALLEST SA/Volume ratio? ______

As the size of a cell INCREASES, what happens to its Surface area/volume (SA/Vol) ratio?

It INCREASES It DECREASES It STAYS THE SAME

MAKE A HYPOTHESIS: Use what you know about SA/Vol ratios and cell size. If you place the blocks into a solution of vinegar, in which block would the solution diffuse throughout the entire cube the fastest?

______

PROCEDURE: 1. Cut Jello cubes into correct sizes. 2. Place your gelatin cubes in container filled with vinegar (a weak acid). 3. Time for 20 minutes then remove cubes from vinegar. 4. Slice open down the middle of the cube. 5. Measure the thickness of the stripe. How far did the vinegar move into cube? (Look for color change) 6. Fill in the following chart.

Calculate the % diffusion in each of the three cubes.

BIG OUTSIDE CUBE = TOTAL VOLUME LITTLE INSIDE CUBE = VOLUME DIFFUSION DIDN’T REACH

BIG OUTSIDE CUBE – LITTLE INSIDE CUBE = VOLUME REACHED BY DIFFUSION

Width of Big cube volume – % Diffusion= JELLO purple Big Cube Volume Little Purple Cube Little cube volume Volume reached by CELL square L X W X H Volume = Volume reached by ___diffusion___ (cm) L X W X H diffusion Big Cube Volume 1cm X 1cm X 1 cm

2cm X 2cm X 2 cm

3cm X 3cm X 3 cm

ANALYSIS and CONCLUSION:

1. Surface area in the “Jello cell” corresponds to which part in a real cell?

2. Volume in the “Jello cell” corresponds to which part in a real cell?

3. Which model of a cell showed the highest % diffusion? WHY?

COMPARE THE FOLLOWING “JELLO CELLS”

SURFACE AREA VOLUME SA/Volume RATIO CHANGE TO A L X W X H COMMON DENOMINATOR 2cm X 2cm X 2cm L X W X 6

1cm X 1cm X 8 cm (L x W) X 2 + (L X W) X 4 L X W X H

Which “Jello cell” had the LARGEST SA/Volume ratio? ______

Which “Jello cell” had the SMALLEST SA/Volume ratio? ______

How does the Volume of the two cells compare?

How does the surface area of the two cells compare?

In which of these “Jello cells” do you think molecules moving by diffusion will reach the center the fastest? EXPLAIN WHY.

What is the connection between SMALL SURFACE AREA/VOLUME RATIOS and MITOSIS?

THINK ABOUT IT: USE YOUR COMPUTER AND RESEARCH SOME PICTURES OF DIFFERENT SHAPES OF BODY CELLS. IF YOU WANTED TO HAVE A CELL WITH A LARGE SURFACE AREA TO VOLUME RATIO, WHAT SHAPE WOULD IT BE? WHAT MODIFICATIONS MIGHT IT HAVE TO INCREASE SURFACE AREA? DESIGN A CELL THAT WOULD HAVE A GREATER SURFACE AREA TO VOLUME RATIO THAN A CUBE OR A SPHERE. DRAW A PICTURE OF ITS SHAPE BELOW.