EGG OSMOSIS LAB
10-10-1985
Warm-up
◦List 1 positive thing that happened to you this week
◦List 1 positive thing you look forward to this weekend!
(woohoo!)
Homework Reminders
◦ MasteringBiology: due Monday, October 13 at 10:45 am
◦ Chapter 5 tutorial
◦ Chapter 6 tutorial
◦ Chapter 6 questions
Chapter 6 material may take up to 50 minutes….so do this ahead of time!
◦ Lab Write-up: due Monday, October 13 in beginning of class
The chapter 7 worksheet is yours to work on...bring it 100% completed on
Monday, and 5 extra points will be banked towards the Unit 3 Exam
Unit 3 Exam
Projected to be Thursday, October 16
Topics covered yesterday
◦Cell membrane
◦Diffusion
◦Osmosis
Today’s objectives
◦SWBAT qualitatively investigate osmosis in cells and
explain that external environments can be hypotonic,
hypertonic, or isotonic to internal environments of
cells.
◦Science Practice #6: SWBAT perform data analysis
and evaluation of evidence
Getting through cell membrane
◦ Passive transport
◦ Facilitated transport
◦ Active transport
Cell (plasma) membrane
 Cells need an inside & an outside…

separate cell from its environment

cell membrane is the boundary
Can it be an impenetrable boundary? NO!
OUT
IN
food
carbohydrates
sugars, proteins
amino acids
lipids
salts, O2, H2O
AP Biology
OUT
IN
waste
ammonia
salts
CO2
H2O
products
cell needs materials in & products or waste out 2005-2006
Building a membrane
 How do you build a barrier that keeps
the watery contents of the cell separate
from the watery environment?
Your choices
 carbohydrates?
 proteins?
 nucleic acids?
 lipids?
AP Biology
 LIPIDS 
oil & water
don’t mix!!
Lipids of cell membrane
 Membrane is made of phospholipids

phospholipid bilayer
inside cell
phosphate
hydrophilic
lipid
hydrophobic
outside cell
AP Biology
Phospholipids
AP Biology
It’s like this demented
Rudolph
looking thing
It’s amphipathic!
has a split personality
Semi-permeable membrane
 Need to allow passage through the
membrane
 But need to control what gets in or out

membrane needs to be semi-permeable
sugar
aa
lipid
H 2O
salt
NH3
So how do you build a
semi-permeable membrane?
AP Biology
Phospholipid bilayer
 What molecules can get through directly?
inside cell
NH3
outside cell
AP Biology
lipid
salt
sugar aa
H 2O
fats & other lipids
can slip directly
through the
phospholipid cell
membrane, but…
what about other
stuff?
Simple diffusion across membrane
Which way will
lipid move?
lipid
inside cell
low
lipid
lipid
lipid
lipid
lipid

high
outside cell
lipid
lipid
lipid
lipid
AP Biology
lipid
lipid
lipid
lipid
Permeable cell membrane
 Need to allow more material through

membrane needs to be permeable to…
 all materials a cell needs to bring in
 all waste a cell needs excrete out
 all products a cell needs to export out
inside cell
Haa
sugar
2O
“holes”, or
channels, in cell
membrane allow
material in & out
AP Biology
outside cell
NH
salt3
lipid
Diffusion through a channel
 Movement from high to low
sugar
low
inside cell sugar
sugar sugar
sugar
Which way
will sugar
move?

high
outside cell
sugar
sugar sugar
AP Biology
sugar
sugar
sugar
sugar
Semi-permeable cell membrane
 But the cell still needs control

membrane needs to be semi-permeable
 specific channels allow
specific material in & out
inside cell
salt
outside
NH3 cell
AP Biology
H 2O
aa
sugar
How do you build a semi-permeable
cell membrane?
 What molecule will sit “comfortably” in a
phospholipid bilayer forming channels
bi-lipid
membrane
protein channels
in bi-lipid membrane
what
properties
does it
need?
AP Biology
Why proteins?
 Proteins are mixed molecules

hydrophobic amino acids
 stick in the lipid membrane
 anchors the protein in membrane

hydrophilic amino acids
 stick out in the watery
fluid in & around cell
 specialized “receptor”
for specific molecules
AP Biology
2005-2006
Facilitated Diffusion
 Globular proteins act as doors in membrane

channels to move specific molecules through
cell membrane
open channel = fast transport
high
low
AP Biology
“The Bouncer”
Active Transport
 Globular proteins act as ferry for specific molecules


shape change transports solute from one side of
membrane to other  protein “pump”
“costs” energy
low
high
AP Biology
conformational change
“The Doorman”
Getting through cell membrane
 Passive transport

diffusion of hydrophobic (lipids) molecules
 high  low concentration gradient
 Facilitated transport


diffusion of hydrophilic molecules
through a protein channel
 high  low concentration gradient
 Active transport

diffusion against concentration gradient
 low  high


AP Biology
uses a protein pump
requires ATP
Facilitated diffusion
 Move from HIGH to LOW concentration
through a protein channel
passive transport
 no energy needed
 facilitated = with help

AP Biology
2005-2006
Active transport
 Cells may need molecules to move
against concentration situation
need to pump against concentration
 protein pump
 requires energy
 ATP

Na+/K+ pump
in nerve cell
membranes
AP Biology
2005-2006
Active transport
 Many models & mechanisms
using ATP
AP Biology
using ATP
Osmosis is diffusion of water
 Water is very important, so we talk about water
separately
 Diffusion of water from
high concentration of water to
low concentration of water

AP Biology
across a
semi-permeable
membrane
2005-2006
Concentration of water
 Direction of osmosis is determined by
comparing total solute concentrations
Hypertonic - more solute, less water
 Hypotonic - less solute, more water
 Isotonic - equal solute, equal water

water
hypotonic
hypertonic
net movement of water
AP Biology
Managing water balance
 Cell survival depends on balancing
water uptake & loss
AP Biology
freshwater
balanced
saltwater
Managing water balance
 Isotonic

AP Biology
animal cell immersed in
isotonic solution
 blood cells in blood
 no net movement of water
across plasma membrane
 water flows across
membrane, at same rate in
both directions
 volume of cell is stable
Egg Osmosis Lab
An unfertilized egg is
a very big cell
Purpose of lab
Given two different solutions and an egg as a cell, you will
determine whether the solutions are hypotonic or hypertonic
Methods
Corn syrup
Distilled water
2 replicates
2 replicates
Why is having replicates important in
scientific research?
Methods
Corn syrup
Distilled water
2 replicates
2 replicates
What are our hypotheses & predictions?
Hypothesis and predictions
◦ Hypothesis: The tonicity of a solution will affect the mass of the egg.
◦ Null Hypothesis: The tonicity of a solution will not affect the mass of the egg
◦ Predictions: If a solution is hypertonic, then the eggs will
____________mass over time
If a solution is hypotonic, then the eggs will ________________
mass over time
If a solution is isotonic, then the eggs will
______________________ mass over
time.
Procedures
1. Each group will go back one at a time to record the
final egg mass. When your group is done, please throw
away the egg and thoroughly rinse the beakers and
place them in the spots as directed by Dr. Cao.
2. Please work efficiently so that we can get all the data
collected in a timely manner.
3. Everyone in a group has a role
4. While your group waits to record data, work on your
Chapter 7 (cell membrane) worksheet. It will be
checked for completion on Monday, and an extra 5
points will be banked to the Unit 3 exam…so it is
both a study guide and extra credit.
5. We will pool our data as a class and analyze them
together.
6. Lab write ups are due Monday, October 13 in the
beginning of class.
Group roles:
Person 1: Water 1 Egg
Person 2: Water 2 Egg
Person 3: Syrup 1 Egg
Person 4: Syrup 2 Egg
Person 5: Cleans beakers
Everyone: records data on data
sheet
Class data
https://docs.google.com/a/cms.k12.nc.us/sp
readsheets/d/1OzawI2hsiCfxxlIfpl09u329R9iZp1jhVsT_pA94sQ/edit#gid=0
Data analysis
-In science, it is important to quantify the trends that we see in our data
-Statistics allows us to test our hypotheses and determine whether our
data show a significant relationship in the variables in which we are
studying
-P-values tell us whether a result is significant or not.
-A small p-value (typically ≤ 0.05) indicates strong evidence against the
null hypothesis, so you reject the null hypothesis and accept the other
hypothesis.
Hypothesis and predictions
◦ Hypothesis: The tonicity of a solution will
affect the mass of the egg.
◦ Null Hypothesis: The tonicity of a solution
will not affect the mass of the egg
◦ Predictions: If a solution is hypertonic, then
the eggs will
____________mass
over time
If a solution is hypotonic, then
the eggs will ________________ mass
over time
If a solution is isotonic, then the
eggs will ______________________
mass over
time.
If P > 0.05, then we can reject the null hypothesis.
Simple Linear Regression
◦ Quantifies the linear relationship
between the independent and
dependent variables
ANOVA
df
SS
Regression
MS
1
5356.965659
5356.965659
Residual
29
1766.201438
60.90349785
Total
30
7123.167097
Coefficients
Intercept
0
Standard Error
t Stat
Significanc
eF
F
87.95825934
P-value
2.77E-10
Lower 95% Upper 95%
Lower
95.0%
Upper
95.0%
72.12116476
1.776126889
40.6058628
4.13467E-27
68.48858
75.75375
68.48858
75.75375
-0.010743771
0.001145562
-9.378606471
2.77133E-10
-0.01309
-0.0084
-0.01309
-0.0084
Things to consider in conclusion…
◦ Which solutions were hypertonic and hypotonic? What evidence do
you have in your data that supports this?
◦ Someone observed in class that the water solutions had ‘stuff ’ in
it…what do you think it could be and why is it in the water?
◦ Why is it important to consider the solution tonicity when it comes to
cellular shape?