Lesson 4. Diffusion Through a Membrane State Mandated Lab
Estimated Time: 1 period
Objective: To model the selectively permeable nature of the cell membrane.
EQ: How can I model what happens with nutrients that are trying to enter the cell membrane?
Bridge: Define the words on the lab packet (diffusion, selectively permeable, and indicator)
Mini Lesson: Share out from the bridge: use this time to prompt them on what iodine and
Benedict’s solution tested for.
Give expectations for part one of the lab make sure they have their PPE on since they are
working with iodine and the hot plates.
Work Period: Part 1 of the diffusion through a membrane lab.
Summary: Answer the EQ
Closing: Answer the following questions
1. What evidence did you collect that let you know water moved into the artificial
membrane since there is no indicator for water?
2. Where was the starch concentration highest throughout the experiment?
3. Where was the glucose concentration highest at the end of the experiment? How do you
know?
**I have modified parts of this lab based on a few experiences. Since I have had primarily
ESOL and inclusion groups over the past few years, the lab when given to the students at one
time is very daunting and they did not seem to get as much out of it as they should. The
modifications were to make sure they were drawing on class experiences and prior knowledge
more readily, getting the lab in smaller pieces and helping them to map out the connections being
made between each part, and getting more practice with questions that Regents actually asks
about this laboratory. You are more than welcome to use the actual lab, but this aligns with what
the State does and expects.**
SPED and ELL Modifications:
1. Make flashcards of vocabulary words
2. Allow opportunity for students to type responses
Apps or Internet Activities:
1. This site has a good review of flashcards about diffusion:
http://quizlet.com/10444322/diffusion-through-a-membrane-flash-cards/
2. This site is an interactive tutorial:
Diffusion: http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP1903
Diffusion and Osmosis:
http://www.phschool.com/science/biology_place/labbench/lab1/intro.html
3. This is a game that moves molecules from one side of a membrane to another- however
the ads are a bit graphic – thus would need to be a well monitored site.
http://www.dailyfreegames.com/upload/adventure-games/diffusion-naren11-play.html
Name ____________________________________
Living Environment
School
Date ___________________
NYS Mandated Lab: Diffusion Through A Membrane, Modified from its original form
Part I. Diffusion and Selective Permeability
Define the following terms:
Diffusion:
Selectively Permeable:
Indicator:
What is the difference between starch and glucose, since they are both carbohydrates?
Question: Does the size of a molecule affect how it will move through the cell membrane?
Prediction/Hypothesis:
Lugol’s Iodine is an indicator for starch that turns a blue/black/purplish color. If the starch
moves outside of the baggie, what would you expect to see? _________________
Benedict’s Solution is an indicator for glucose, but it only works when heated. It turns
orange/red in color. If glucose moves out of the baggie, what would you expect to see once the
solution is heated? _____________________________
Safety: Wear goggles and coats/aprons at all times (you should have gloves on as well but I do
not have enough so please be very careful with the solutions. Iodine will stain skin and clothing
and is corrosive, so if you spill some on yourself, wash your hands immediately).
Experimental Design:
Materials: string, cup, plastic fold over baggie or dialysis tubing, test tube, hot plate, glass
beaker, water, glucose solution, starch solution, triple beam balance
Procedure:
In your plastic baggie, place 10 mL of starch solution and 10 mL of glucose solution.
Tie off the end with the string as tight as you can. Tip it to make sure it is not leaking and rinse
it off in your sink. Find the mass of the baggie.
Record what you put into the baggie and what it looked like in your data section.
In the cup provided to you, place the baggie and fill it with water up until the baggie is just
barely covered.
Add 10 drops of Lugol’s Iodine solution to the cup.
Record what is in the cup and what it looked like in your data section.
Wait for 20 minutes, recording changes that happen as you notice them in your data section.
Record your final observations after the 20 minutes in the data section.
Once you have completed this, take a pipette and draw off some of the solution outside of the
baggie in the cup. Place it in your test tube and place your test tube in the hot water bath next to
your table. Wait about 5 minutes and record your results.
Data
Beginning of the experiment:
Using the key, record what was placed inside the baggie (dialysis tubing) and what is on the
outside of the baggie at the start of the experiment.
Key:
G= glucose
S= Starch
W= water
I= Iodine
What did the inside of the baggie look like? _______________________
What did the solution outside of the baggie look like? ___________________
What was the original mass of the baggie with solution? ___________ (include unit)
After 20 minutes:
Using the key, record what was placed inside the baggie (dialysis tubing) and what is on the
outside of the baggie at the start of the experiment.
Key:
G= glucose
S= Starch
W= water
I= Iodine
What did the inside of the baggie look like? _______________________
What did the solution outside of the baggie look like? ___________________
What was the final mass of the baggie with solution? ___________ (include unit)
Analysis: Summarize what you found out in your experiment in your own words in the space
below
Evaluation: Once you have completed your evaluation piece, answer the following questions
based on the lab.
Glucose indicator was added to a beaker of an unknown liquid. Starch indicator was added to a
different beaker containing the same unknown liquid. The color of the indicator solutions before
they were added to the beakers and the color of the contents of the beakers after adding the
indicator solution are recorded in the chart below.
1. Which carbohydrate is present in the unknown liquid? Support your answer. [1]
_______________________________________________________________________
_______________________________________________________________________
A laboratory setup of a model cell is shown in the diagram below.
2. Which observation would most likely be made 24 hours later?
(1) The contents of the model cell have changed color.
(2) The diameter of the model cell has increased.
(3) The model cell has become smaller.
(4) The amount of distilled water in the beaker has increased.
The diagram below represents the distribution of some molecules inside and outside of a cell
over time.
3. Which factor prevented the protein molecules (
(1) temperature
(2) pH
(3) molecule size
(4) molecule concentration
) from moving out of the cell?
Base your answers to questions 4 and 5 on the information and table below and on your
knowledge of biology.
A model of a cell is prepared and placed in a beaker of fluid as shown in the diagram below.
The letters A, B, and C represent substances in the initial experimental setup.
The table below summarizes the content and appearance of the cell model and beaker after
20 minutes.
4. Complete the table below to summarize a change in location of substance C in the
experimental setup. [3]
5. Identify substance B and explain why it did not move out of the model cell. [2]
Substance: __________________________________________
_______________________________________________________________________
_______________________________________________________________________
6. A solution containing both starch and glucose was placed inside the model cell represented
below. The model cell was then placed in a beaker containing distilled water.
Identify one specific substance that should have been added to the distilled water so that
observations regarding movement of starch could be made. [1]
_______________________________________________________________________