BIOLOGY L2

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Hands On Lab 2: Cells and Membrane Transport (3 Activities)

Submission instructions

• Type your answers and copy all pictures directly into this Word document.
Submit it via the blackboard submission link in Word format (docx).

Introduction:
Cells are the basic structural and functional units of life. Your entire body is composed
of cells and the substances produced by them. Each type of cell you possess has a
unique structure based on its overall function, but they all share a set of common
organelles that fulfill the basic needs every cell has. We will look at each of these
organelles, identify them, and define their functions.

One of the universal activities within the body is the movement of substances into and
out of cells. Gases, nutrients, wastes, chemicals, and water must all be transported in a
controlled manner for cells to maintain homeostasis. For example, if a cell contains too
much or too little salt, then it will die.

The plasma membrane is the major regulator of cellular transport. In this lab you will
demonstrate the two simplest transport mechanisms used by the plasma membrane,
diffusion and osmosis.

Watch This:
This video on tonicity is particularly helpful and clear on explaining this concept that
many find a bit tricky. It will be quite helpful when working on activity 3 in this lab. Khan
Academy Tonicity (opens in new window: 6min:30sec)

Activity 1: Cellular Structure
Complete the table by identifying each part of the cell (diagram on next page) and give
the function of each. Both columns must be correct for credit.

Structure Function

1. Goigi Apparatus

2.Cilia

2.

3. Peroxisome

4. Nucleus

5. Nucleolus

6. Nuclear Envelope

7. Ribosome

8. Smooth ER

9. Centrrioles

10. Lysosome

11. Plasma Membrane

12. Mitochondrion

13. Microvilli

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Activity 1 Conclusion Questions
All parts of the question must be correct for credit.

14. Many of what small organelles give #7 it’s studded appearance AND what is the

function of these?

15. What organelle is not visible on the cell above because in humans it is present only
on sperm?

16. What are the loose strands of DNA with associated proteins found in the nucleus
AND what form do these strands coil tightly into as the cell begins to divide?

17. Name the 3 types of proteins that make up the cytoskeleton in order from largest to
smallest.

18. A double-layer of what molecules are the main component of #11?
Membrane Transport Pre-Activity Questions

19. To facilitate transport, the plasma membrane of a cell is selectively permeable.

Define selective permeability.

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20. Define solution and give examples of the two major components of solutions.

21. Watch this 3 minute video about concentration gradients (link opens in new window).
How would you describe a concentration gradient?

22. Define diffusion

23. Define osmosis

24-27. Compare and contrast diffusion and osmosis. Give at least 2 differences and 2
similarities (1pt. for each difference and 1pt for each similarity).

Activity 2: Diffusion
In this activity, you will observe a substance diffusing through a selectively permeable
membrane. As evidence of diffusion, we will use iodine, an indicator that turns blue-
black the presence of starch.

Materials

• 2-cup clear glass container
o Size does not have to be exact,

but it should be taller than it is
wide

o Drinking glasses or measuring
cups work fine.

• 1 sandwich size resealable bag
o The cheaper the bag, the better

this experiment will work
• ~10 drops liquid Iodine

o Warning: Handle with care, toxic
if ingested and can stain!

o Can be obtained in any
drugstore

▪ Do NOT purchase
colorless iodine! It will not
work. Iodine should be
brownish-yellow in color.

• ~2 tablespoons Cornstarch
• Water
• Camera

Procedure
1. Fill the glass container with 200 mL (~1 cup) of water and add 10 drops of iodine
2. Place 2-4 tablespoons of cornstarch in a plastic bag and add 100 mL of water.
3. Carefully close the bag and gently squeeze to mix the cornstarch and water.

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4. Gently place the bag into the container so that the cornstarch solution is submerged
in the iodine solution.

5. Gather data
a. Take a picture at the start (0min) and end of your experiment (60min). Post

these pictures in the results section.
b. In the provided data table, record the starting color of the solution in the

beaker and bag, then observe and record color changes every 15 minutes for
1 hour.

Results
28. 0min Picture

29. 60min Picture

30. Data Table

Solution 0 min 15min 30min 45min 60min

Color in
Container

Color in
Bag

Activity 2 Conclusion Questions

31. Based on your observations, which substance moved, the iodine or the cornstarch?
How can you tell?

32. What would happen if you did an experiment in which the iodine solution was in the
plastic bag and the cornstarch solution was in the beaker?

Activity 3: Osmosis
In this activity, you will observe osmosis through a selectively permeable membrane.
Osmosis is easily observed in plants, as the osmotic pressure of the water is what
provides support (this is why plants wilt when they need water). In this lab you will
observe the effect of osmosis using a very familiar plant, the potato.

Materials

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• 2 clear glass containers
o Size does not have to be exact, but shallow bowls work best

• 1 Potato

• Salt

• Water

• Camera

Procedure
1. Label or mark your containers #1 and #2—Any method works, as long as you can

tell them apart.
2. In container 1, mix 15 m (one tablespoon) of salt with 100 ml (~1/2 cup) of water and

stir until the salt is completely dissolved.
3. In container 2, fill with 100ml (~1/2 cup) of pure water.
4. Cut 2 strips of potato about the size of a French fry. They should be no thicker than

0.5 cm (~⅓ in). Make sure to remove all of the skin from the potato.
5. Gather preliminary data

c. Take a picture of both potato strips at the start (0min) of your experiment.
Post this picture in the results section.

d. Examine each strip and record your observations of the firmness of the strips
in the provided data table

6. Place one of the strips in container #1 (salt water) and the other strip in the container
#2 (pure water). Make sure that both potato strips are completely submerged.

7. Leave the strips in the water for 60 minutes.
8. Gather Results

e. Take a picture of both potato strips at the end (60min) of your experiment.
Post this picture in the results section.

f. Examine each strip and record your observations of the firmness of the strips
in the provided data table

33. 0min Picture

34. 60min Picture

35. Data Table

Container Firmness @ 0 min Firmness @ 60min

1 (salt water)

2 (Pure water)

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Activity 3 Conclusion Questions

36. This experiment showed osmosis. Based on your results would you classify the salt
water as hypertonic or hypotonic? Why?

37. This experiment showed osmosis. Based on your results would you classify the pure
water as hypertonic or hypotonic? Why?

38-46: Hypothetically, use red blood cells to explain osmosis and states of tonicity. Red
blood cells naturally are approximately 0.9% salt in content. We introduced red blood
cells to the following solutions:

A. 100% water
B. 0.9% saline
C. 10% saline

Match solutions A, B, or C with the criteria (each letter used 3x):

Solution
Type

Solution A,
B, or C

Net Water
Movement

Solution A,
B, or C

Cell Change Solution
A, B, or C

Hypertonic 38. Into Cell 41. No Change 44.

Hypotonic 39. No Water
Movement

42. Crenation 45.

Isotonic 40. Out Of Cell 43. Swelling/
Lysis

46.