Surface Area and Cell Size
Procedure 1 Investigation 2
Big Idea 2.A.3.b.1
• These are cells and tissues with specialized
functions. Think about their similarities in
shape, size, nutrient procurement. Discuss.
http://www.technion.ac.il/~mdcours
e/274203/slides/Digestive%20tract/
17-Intestinal%20villi%20JejunumA.jpg
http://www.cytochemistry.net/
cell-biology/actin.6.gif
http://iweb.tntech.edu/mcapr
io/roots.htm
2
Modeling Surface Area and Cell
Size
• Wear your safety eyewear
• Wear your apron or lab coat
• Wear your closed toe shoe
• The agar cubes are soaked in a 0.01% NaOH
solution.
• The agar cubes have been prepared with 1%
phenolphthalein, which is a pH indicator.
3
Acid or Base?
• Phenolphthalein Color Indicator
Color
pH
Acid or Base
Colorless
0-8.2
Acidic or slightly
Neutral
Pink to Red
8.2-12.0
Basic
4
You have been given, or will cut, 3
agar blocks.
•
•
•
•
These are models for your cells.
Measure the surface area of each “cell.”
Calculate the volume.
When the blocks are placed into a solution, which
block will the solution diffuse all the way through
fastest? Explain your prediction in your journal.
• Plan, get approval, & perform an experiment to test
your prediction. Have a prepared table and a plan for
calculations you will perform.
5
Check your work (formative)
• Did you record all your data appropriately?
• Did you measure using a metric ruler? Did you rinse
the ruler off after use?
• Did you calculate rate of diffusion for each cube in
cm/min?
• Did you graph this as a function of SA/Vol?
• Did you calculate the extent diffusion as a percent of
the total volume?
• Did you graph the extent diffusion against surface
area/volume?
6
Extent Diffusion as a percent of
total
•
•
•
•
Calculate the clear volume of the cube.
Calculate the total volume of the cube.
Subtract to get the pink volume.
Divide the pink volume by the total volume.
7
Percent
Diffused
Surface Area/Volume
8
Procedure 2:
Modeling Diffusion and Osmosis
• With your assigned partner work through
Procedure 2: Modeling Diffusion and Osmosis
through page S57.
• During your 30 minute wait time look at
osmosis in the red onion. (Continue ppt)
• Do not discard your solutions. We still need
them.
• As you get your data (Step 4: Percent change
in weight), record with the class.
9
Class Data
Procedure 2, Lab 4
Percent Change in Mass (final –Initial/Initial ) x 100
1M Sucrose
1MNaCl
1M Glucose
5% Albumin
Water
1M Sucrose
1M NaCl
1 M Glucose
5% Albumin
Water
10
Onion Osmosis
Using Image J
11
Before Starting…
• You need to have
– A microscope
– A red onion
– Something to cut with (scalpel or razor)
– A slide and cover slip
– Some 15% salt solution and a pipette
– A piece of paper towel
– A clear metric ruler
– Image J installed (free at NIH.gov)
• You need to know
– The diameter of the field of view of your microscope.
– Directions follow.
12
How to: Microscopic Measurement
Determine the diameter of your
“field of view.”
1. Begin with a clear ruler.
2. Place on the stage, visible under
the lowest magnification for your
microscope.
1 mm
3. Determine the diameter of the
field of view in mm.
4. 1mm=1000 Micrometers (μm)
13
How to: FOV under a higher power
lens
For a higher power, you need
to calculate the field of view.
Zoom in
Original
Original
New
Objective Objective FOV (μm)
New
FOV
4x
10x
4500
1800
4x
40x
4500
450
4x
100x
4500
180
• (Original Obj/New Obj) x Original FOV=New FOV
• FOV=Field of View
15
Onion Osmosis
Analysis with Image J
Cut a piece of outer pigmented
tissue
Make a wet mount
Add concentrated salt solution
Take a picture through the
microscope.
Save to computer.
Determining Percent Change in
Area
Find your file and
open it.
To get area and perimeter...
Select the straight line tool. Drag
across your field of view.
Under analyze: Set scale
Pixels are already there. Enter your
known distance.
Analyze: Set Measurements
Trace with the freehand tool
Go to analyze: Measure
Compare before and after
• Calculate
– Percent change in area
– Percent change in perimeter.
28
Assessment
• Excerpt from “The Rime of the Ancient Mariner” by Samuel
Taylor Coleridge. This is a poem about a sailor.
•
•
•
•
Water, water everywhere,
And all the boards did shrink;
Water, water, everywhere ,
Nor any drop to drink.
• Why did the boards of the ship shrink?
• Why couldn’t the mariner drink any of the water?
From BSCS Biology 9th ed
29
Brainstorm with your partner and
another pair.
• See page S58.
• Come up with questions to investigate.
• Share with the class.
30
Procedure 3
Observing Osmosis in Living Cells
31
• Design an experiment to determine the
relative molarity of several solutions. You
must use the principles of osmosis and
diffusion and a plant tissue. See Page S59.
32
Question
If we soak potato CELLS in sucrose which way
will water move?
Water always moves from a higher water
potential to a lower water potential.
Ψ = Ψ p + Ψs
Water Potential
Pressure
Potential
Solute Potential
Water always moves to a lower, more negative,
water potential.
Ψs= Solute Potential
Ψs
Solutes are always
negative
More solutes = more
negative
Which way will water
move?
What is happening
to the pressure
potential in cell?
Ψp= Pressure Potential
Usually Positive
Water Potential in the Potato Cells
 Revise your definition: Osmosis is the movement of
water molecules through a selectively permeable
membrane from a region of higher water potential
to an area of lower water potential
 Water always moves to a more negative water
potential.
Water Potential
• Ψ= Ψp + Ψs
• Where there is no % change in mass, the
solution in the beaker has the same water
potential as the potato cells.
Water Potential
at Equilibrium
Ψ of Solution in Beaker
= Ψ of Potato
Potato cells
=
(Ψ= Ψp + Ψs)
=
(Ψ= Ψp + Ψs)
Water Potential
Solution
(Ψ= Ψp + Ψs)
=
Potato Cells
(Ψ= Ψp + Ψs)
Pure water at atmospheric pressure has a water potential of zero.
Ψp= 0 (open beaker)
Ψ=Ψs + 0
=
Ψ=Ψs
=
Ψs
=
Ψ= Ψp + Ψs
Ψ= Ψp + Ψs
Ψ= Ψp + Ψs
• Going Further
41
Collect Temperature of liquid!
Potato Core ResultsPercent Change in Mass
Sucrose Trial1
Trial 2
Trial 3
Average
0.0 M
0.2 M
0.4 M
Etc.
What elements are needed in a good graph?
Discuss trends, errors.
Your lab group should be prepared to
use the terms hypertonic,
hypotonic, isotonic as they report to the class.
To Calculate Ψs
Ψs = -iCRT
i= Ionization constant (sucrose is 1.0
because it does not ionize).
C= Molar Concentration (from line of best fit
where the line crosses the x axis)
R= Pressure Constant (0.0831 liter
bars/mole °K
T= Temperature °K (273 + °C)
An example
• Ψs = -iCRT
• Ψs= -(1.0)(0.36 mole/liter)(0.0831 liter
bar/mole °K)(295 °K)
• -8.83 bars
• This equals the entire Ψ of the cell.