Module 12
Passive Transport Lab
Date: ____________________
Completed By: Suzette McLean-Fletcher
SBI 3U
Name: ____________________
PASSIVE TRANSPORT LAB
BACKGROUND/INTRODUCTION:
Our cells carry out a myriad of reactions which require different substances and produce several
substances. These substances must be delivered to or removed from the cells. Cells have a
membrane which separates the inside of the cell from the outside environment. Therefore these
substances move into and out of cells across the cell membrane. It is said to be permeable.
Substances move across the membrane in different ways and are affected by different factors
such as properties of the phospholipid by-layer of the cell membrane and properties of the
substance e.g. size, charge. Some substances move easily based on differences in concentration
(concentration gradient) inside and outside of the cell. Others require help such as special
transport molecules and energy.
For this lab, the movement of substances across a membrane will be investigated. An indicator,
iodine, will be used to track the movement as it changes colour in the presence of starch.
PURPOSE: To observe passive transport of a substance across a permeable membrane.
HYPOTHESES:
1. Iodine molecules will travel from the beaker into the zip-lock bag and turn cornstarch
blue-black.
2. Cornstarch molecules will travel from the zip-lock bag into the iodine solution in the
beaker and turn blue-black.
3. Iodine molecules will travel from the beaker into the zip-lock bag and turn cornstarch
blue-black and cornstarch molecules will travel from the zip-lock bag into the beaker and
turn blue-black in the iodine solution.
MATERIALS:
o Beaker
o Plastic zip lock bag
o Scoopula
o Corn starch
o Iodine
o Water
SAFETY/PRECAUTION INSTRUCTIONS:
1. Do not eat the cornstarch
2. Be careful with iodine. DO NOT let any spill on your hands, clothing or notebooks. They
will turn blue-black!
3. Ensure you close the zip-lock bag tightly/properly
4. Lower zip-lock bag, bottom first, into beaker. Ensure that the top (closure) of the zip-lock
bag is above the iodine solution.
Module 12
Passive Transport Lab
Completed By: Suzette McLean-Fletcher
METHOD:
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Put 1 scoop of corn starch into the bag.
Put 200mL of water into the bag.
Close bag.
Add water to a beaker until it is half full
Put 10 drops of iodine into the beaker.
Submerge the bag in the beaker.
Wait for 15 minutes.
Record observations.
OBSERVATIONS:
Table showing observations of colour changes before and after zip-lock bag containing
cornstarch solution was submerged in a beaker of iodine solution.
Condition
Cornstarch
BEFORE submersion of bag
into beaker
White suspension/solution
Iodine solution
Volume of
solutions
Yellow-brown
Beaker was half-full with
iodine solution
AFTER submersion of bag
into beaker
Streaks of blue-black colour
began forming in the
cornstarch solution which
became increasingly more
blue-black as time passed
Yellow-brown
Iodine solution decreased and
zip-lock bag with cornstarch
looked swollen.
ANALYSIS:
1. Compare and contrast diffusion and osmosis.
Both diffusion and osmosis involve the movement of substances from an area of high
concentration to an area of low concentration (down a concentration gradient). They will both
occur until an equilibrium is reached at which time there will be no net movement of substances.
Diffusion does not require a membrane (whether fully permeable or semi-permeable) to occur
and it involves molecules of gases, solids, liquids. Osmosis, on the other hand, involves the
movement of water molecules from a region where they are in high concentration (hypotonic
solution) to a region where they are in lower concentration (hypertonic solution) across a semipermeable membrane.
Module 12
Passive Transport Lab
Completed By: Suzette McLean-Fletcher
2. Describe what happened to the iodine. Be sure to use the words “hypertonic”,
“hypotonic”, “high concentration”, “low concentration” and “concentration gradient” in
your answer.
The iodine solution remained yellow-brown after submersion. This means that no cornstarch
molecules diffused/moved into the beaker. It also decreased in volume. The iodine solution was
hypotonic (had more water molecules) to the cornstarch solution which was hypertonic (less
water molecules). Water molecules therefore moved down the concentration gradient from its
high concentration in the iodine solution across the zip-lock bag membrane to the cornstarch
solution where it was in low concentration.
3. Describe what happened to the starch. Be sure to use the words “hypertonic”,
“hypotonic”, “high concentration”, “low concentration” and “concentration gradient” in
your answer.
The cornstarch solution became blue-black as iodine molecules moved down the concentration
gradient into it from their region of high concentration (hypertonic iodine solution) to a low
concentration (hypotonic cornstarch solution). The starch molecules did not move as the iodine
solution did not change to blue-black.
4. Conclude whether the bag is a permeable or semi-permeable membrane. Support your
answer with evidence.
The zip-lock bag was a semi-permeable membrane as small molecules of iodine and water were
able to move across it but the larger starch molecules could not. This was evidenced by
(i) the blue- black colour to which cornstarch changed indicating that iodine diffused into it
(ii) the decrease in volume of the iodine solution and the subsequent swollen zip-lock bag
indicating that water molecules moved from iodine solution into the cornstarch solution and
(iii) the lack of colour change of the iodine solution (did not turn blue-black) indicating that
starch molecules did not diffuse into it.
5. Conclude whether diffusion or osmosis occurred in this experiment. Support your answer
with evidence.
Both diffusion and osmosis occurred in this experiment. Iodine molecules moved by diffusion
from its high concentration in the iodine solution to the cornstarch solution where it was in low
concentration as evidenced by the blue-black colour change of the cornstarch. Water molecules
moved by osmosis across the semi-permeable membrane of the zip-lock bag from the hypotonic
iodine solution where they were in high concentration to the hypertonic cornstarch solution
where they were in low concentration.