Download Wear safety goggles and plastic gloves when handling

Biology A
Cells and Energy
Unit 4 Lesson 4
Name: Robert Gordon
Class: Biology
Date: 10/23/12
The Effect of Cell Size on Material Transport
Directions:
Question: How does cell size affect the rate of diffusion of materials into a cell?
Background information
Cells are so small that their existence went unnoticed until the microscope was
invented. The microscope allowed scientists to examine the cellular make up of living
organisms for the first time. A question that arises is: why are cells so small? Is there a
factor that limits the size of a cell? In this lab, you will investigate the possibility that
diffusion of nutrients into the cell may be a limiting factor on cell size.
In this lab, you will work with raw potato cut into cubes as a working model of a cell.
You will cut the potato into cubes of pre-determined size and then place the cubes in a
dish containing an iodine solution. Iodine is a stain that reacts with starch molecules to
make a black product. As iodine diffuses into the potato, it will produce a visible black
stain. After incubating all “cells” in iodine solution for the same time period, you will
slice open each “cell” to determine how far the iodine diffused. By comparing the
distance that the iodine diffuses into each size “cell” that you make, you will be able to
draw conclusions about whether the rate of material transport may be one of the
limiting factors on cell size.
Materials:
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Safety
2 raw potatoes
Knife
Metric ruler
Iodine solution
250-mL beaker
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Tweezers
Paper towels
Cutting board
Potato peeler
Wear safety goggles and plastic gloves when handling iodine solutions. Rinse off any
solution that spills on your skin or clothing. Use caution when handling the knife to
cut potato cubes. Alert your teacher if you accidentally cut yourself. Wash your
hands thoroughly with soap and warm water before leaving the lab.
©2012 Connections Education LLC. All rights reserved.
Biology A
Cells and Energy
Unit 4 Lesson 4
Pre-Lab work
1. Design an Experiment: What is the independent variable in this experiment (i.e., the variable
that you manipulate)?
the size of the potato
2. Measure: How will you determine the size of your “cells”?
by measuring the amount of iodide that diffused through the center of the potato
3. Control Variables: Why will you incubate all “cells” in the same iodine solution for the same
length of time?
so each cell will have the same amount of time to diffused the iodine
Procedure
1. Put on your safety goggles. Carefully remove the skin from the raw potatoes with the potato
peeler. Then cut four potato cubes out of the bodies of the potatoes. Each cube should have
the same length, width, and height. For the first cube, make each side equal to 0.5 cm. For
the second cube, make each side equal to 1.0 cm. For the third cube, make each side equal
to 2.0 cm. For the fourth cube, make each side equal to 3.0 cm.
2. Put on your plastic gloves. Pour the iodine solution into the beaker so that the liquid height
will cover the largest cube.
3. Carefully place each potato cube into the iodine solution.
4. Start a timer to allow the potato cubes to incubate undisturbed for 5 minutes. While the
cubes incubate, calculate the surface area, volume, and surface area to volume ratio for
each cube. Enter the values into the data table. At the end of 5 minutes, remove the potato
cubes from the iodine solution.
5. At the end of 5 minutes, remove the potato cubes from the iodine solution.
6. Place the cubes on the cutting board and slice each down the center. Measure the distance
that the iodine diffused into each “cell.”
7. Record your observations in the data table.
©2012 Connections Education LLC. All rights reserved.
Biology A
Cells and Energy
Unit 4 Lesson 4
Gather Data
Cell
Length of
one side
Data Table
Volume
Surface Area to
volume ratio
Surface
area
Distance iodine traveled
1
0.5
1.5
0.25
13.5 cm2
0.1
2
1.0
6
1
216 cm2
0.1
3
2.0
25
8
3750 cm2
0.2
4
3.0
54
27
17496 cm2
0.1
Analyze and Conclude
Using the information you have gathered answer the following questions.
1. Compare and Contrast: Summarize your observations of the distance traveled by the iodine in
the four cells.
for all four cells the amount of iodine diffused was the same.
2. Analyze Results: Did the cell size affect the extent of diffusion of iodine into the cells?
no the cell size did'nt change
3. Infer: Do the cells have the same surface area to volume ration? How might the surface area to
volume ratio affect the ability of a cell to take in and use nutrients from its environment?
no. and from doing this experiment i don't think the affect will change because when the cell
was diffusing the iodine all the cells had the same result
4. Apply Concepts: Which cell would be able to supply itself most efficiently with nutrients
diffusing in from the outside—a large cell or a small cell? Why?
a small cell because the small cell might diffuse more faster than the larger cell
©2012 Connections Education LLC. All rights reserved.