Cells 11 - BIOLOGY JUNCTION

Potato Osmosis Bi Lab

Potato Osmosis

Introduction:

A shipwrecked sailor is stranded on a small desert island with no fresh water to drink. She knows she could last without food for up to a month, but if she didn’t have water to drink she would be dead within a week. Hoping to postpone the inevitable, her thirst drove her to drink the salty seawater. She was dead in two days. Why do you think drinking seawater killed the sailor faster than not drinking any water at all? Today we explore the cause of the sailor’s death. We’ll prepare solutions of salt water to represent the sea, and we’ll cut up slices of potato to represent the sailor. Potatoes are made of cells, as is the sailor!

Objective:

The concentration of solute in a solution will affect the movement of water across potato cell membranes.

Materials:

potato, corer, 3 plastic cups, marker, salt, sugar, distilled water, paper, pencil, electronic balance, clock with second hand or timer, metric ruler, small ziplock plastic bag, foil or plastic wrap

Procedure:

Day 1

Use a knife to square off the ends of your potato. Your potato’s cells will act like the sailor’s cells.
Stand your potato on end & use your cork borers to bore 3 vertical holes.

Remove the potato cylinders from the cork borer & measure their length in centimeters.
Cut the 3 potato cylinders to the same length (about 4 -5 centimeters long).
Record the length & turgidity of the potato cylinders in your data table (day 1).
Place the 3 potato cylinders in a small ziplock bag to prevent them from dehydrating before they’re used.
Take 3 plastic cups and label them with the solution that will be placed in each one — sugar, salt, distilled water.
Prepare a saturated solution of salt by mixing as much salt as you can with water.
Repeat this step by making a saturated sugar solution.
Now fill each cup 2/3’s full of the correct solution —- sugar water, salt water, or distilled water.
Mass each of the potato cylinders & record this mass in grams on your data table.
Place one of your potato cylinders into each cup and cover the top of the cup with foil or plastic.
Leave the potato cylinders in the solution for 24 hours.

Day 2

Carefully remove the potato cylinder from the distilled water solution & pat it dry on a paper towel.
Measure the length of the potato cylinder & record this length & the appearance of the cylinder on your data table. (day 2)
Measure & record the mass of this cylinder.
Repeat steps 13-15 for the potato cylinders in the salt solution & the sugar solution.
Clean up your equipment & area and return materials to their proper place.

Data:

Results of Osmosis in Potato Cells
Solution	Initial length cm (day1)	Final length cm (day2)	Change in length cm	Initial Mass g (day1)	Final Mass g (day2)	Change in mass g	Initial Turgidity (flaccid or crisp)	Final Turgidity (flaccid or crisp)	Tonicity of Solution (iso-, hypo-, or hpertonic)
Distilled water
Salt Solution
Sugar Solution

Results & Conclusions:

1. Did any of the potato cylinders change in their turgidity (flexibility), and if so, which ones changed?

2. Explain why the flexibility of the potato slices changed.

3. Define isotonic, hypotonic, & hypertonic solutions.

4. If potato slices changed in length or turgidity, what process was responsible for this?

5. Make a sketch of your potato cylinder in the distilled water and use arrows to show the direction of water movement across the potato cell membranes.

6. What type of solutions were the salt & sugar solutions. Explain how you know this.

7. Which solution served as the control for this experiment & why?

8. In which solutions was their a greater solute concentration outside of the cells?

9. In which direction did water move through these cell membranes?

10. In what type of solution do plant cells do best & why?

11. Using the information you’ve discovered from this experiment, explain why the sailor died that drank saltwater.

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Preap Cell Study Guide

Cell Structure & Function Review

1. The first Person to describe microscopic organisms and living cells was
________________________________.

2. The maximum size to which a cell may grow is limited mainly by the cell’s ___________________________ ____________________________.

3. Short, hair-like organelles that can move and may cover a unicellular organism or line the respiratory tract are called ______________________________________.

4. Some Ribosomes are free in the cytoplasm, while others line the membrane of the
_________________ __________________ __________________________.

5. Everything between the cell membrane and the nucleus, is the cell’s
____________________________________.

6. All cells, from all organisms, are surrounded by a _______________ _____________________.

7. Membranes are _______________________ and have the consistency of vegetable oil.

8. The organelle that stores DNA and synthesizes RNA _________________________.

9. The organelle that processes and packages substances produced by the cell ______________________ _________________________.

10. The ____________________________ is the control center of the cell.

11. The DNA in the form of a long strand is called ______________________________.

12. Cytoplasm consists of two main components: ____________________________ and
______________________________.

13. The cell membrane functions like a ______________________, controlling what
__________________ and _______________________ the cell.

14. A lipid is a simple form of ________________________________.

15. There are many kinds of ______________________ in cell membranes; they help to move material into and out of the cell.

16. Scientist call the modern view of the cell membrane structure the
______________________________ ____________________ _________________.

17. The nucleus is surrounded by a double layer membrane called the
__________________________ _________________________________.

18. During cell division, _________________________ strands coil and condense into thick structures called _____________________________________.

19. The nucleoli make ___________________________. Which in turn build proteins.

20. Membranes are made mostly of ___________________ and ______________________.

21. The _________________ is the smallest unit that can carry out all of the processes of life. The basic unit of life.

22. The maximum size to which a cell may grow is limited mainly by the cell’s ___________________ ____________________.

23. The discovery of cells is linked most directly the development of the __________________________.

24. Organisms whose cells never contain a membrane bound nucleus are called _____________________________________.

24. Suspended in the cell’s cytosol are tiny ___________________________________.

25. Cell membranes consist of two phospholipid layers called a ___________________.

26. The chromosomes in the nucleus contain coded _____________________ that control all cellular activity.

27. When a cell prepares to reproduce the _______________________ disappears.

28. Cytosol is a jelylike mixture that consists mostly of _____________________.

29. The nucleus is one ______________________________.

30. In Eukaryotic cells, most organelles are surrounded by a _____________________.

31. Organisms whose cells always or usually contain a nucleus or nuclei are called
____________________________________.

32. ________________________ are structures that carry out specific functions in the cell.

33. Most cells have a single ______________________; some cells have more than one.

34. Unicellular organisms such as bacteria and their relatives are ___________________________.

35. The Fluid Mosaic Model presents the modern view of a
__________________ ___________________________.

36. The “Blueprints” in a Cell that controls all its activity are the ___________________.

37. Where are poisons and waste detoxified in a cell? _________________________ _________________________________.

38. A cell synthesizes protein by using organelles called _______________________________.

39. The Mitochondria of a cell contain an inner membrane called _____________________________.

40. What are the membrane-bound sacs that package and secrete cell products?
___________________________ ___________________________.

41. Unlike animal cells, plant cells have ______________ ________________.

42. A Chloroplast can convert _________________, __________________________, and ____________________________ into ________________________.

43. What are Flagella? ___________________________________________________.

44. In animal cells, the Cytoskeleton maintains three-dimensional structure and helps the cell ___________________________.

45. The organelle that digest molecules, old organelles, and foreign substances in the cell _______________________________________.

46. A pigment that absorbs energy in sunlight ________________________________.

47. The organelle that prepares proteins for export and synthesizes steroids is ________________________ ________________________.

48. Ribosomes differ from most organelles because they have no ___________________________.

49. What type of cells would you expect to find large numbers of mitochondria? _______________________ _________________.

50. The “Powerhouse” of the cell _______________________________.

51. Short, hairlike organelles that can move and may cover a unicellular organism or line the respiratory tract are called _______________________________.

52. The first cells on Earth were likely _______________________ that did __________ make their own _________________.

53. Microfilaments and microtubules function in cell _______________________ and ____________________________.

54. What is the correct order of structures in living things, from simplest to the most complex? ______________________, __________________________, ______________________________, ______________________________.

55. The is the organelle that transfers energy in ATP _______________________________.

56. What word means “Water Fearing”? ____________________________.

57. What word means “Water Loving”? _____________________________.

58. What is cell specialization? Give an example.
59. Distinguish between the structure of rough ER and that of smooth ER.

60. Explain how ribosomes, endoplasmic reticulum, Golgi apparatus function together in protein synthesis.

61. Explain the difference between a tissue and an organ.

62. Why is the cell membrane said to be selectively permeable?

63. If a cell has a high energy requirement, would you expect it to have many or few mitochondria? Explain your answer.

64. Describe TWO differences between prokaryotic cells and eukaryotic cells.

65. How can you determine whether a unicellular organism is a prokaryote or a eukaryote?

66. Plant cells have cell walls, but animal cells do not. Why do you think that is so?

67. What are the THREE Parts of the Cell Theory?

68. Describe three differences between plant and animal cells.

69. Name the TWO different kinds of animal cells, and describe how their shape is related to their function.

70. What is the difference between chromatin and chromosomes?

71. What are the major roles of the nucleus, and what parts of the nucleus carry out these roles?

72. What is a colonial organism, and what does it have in common with multicellular organisms?

Osmosis and Diffusion in an Egg Lab: Measure Water Movement

Cells and Transport Teaching Resources · High school biology; AP extensions where noted.

A shell-less egg can model net water movement across a barrier. Its remaining shell membranes are not a living cell’s plasma membrane, and mass change alone does not identify every substance that crossed. Use this investigation to practice measurement and evaluate a model’s limits.

Objectives and preparation

Students will predict water movement, measure mass change consistently, calculate percentage change, and distinguish observations from explanations. Prerequisites: osmosis, tonicity, variables, and balance use. Teacher preparation takes several days; allow brief observation sessions over an additional day or more. Pilot the timing with the available eggs and refrigeration before class.

Materials and safety

Per group: two intact eggs or access to a class set, labeled lidded containers, household vinegar, distilled water, plain corn syrup, a balance readable to 0.1 g, a weighing boat, disposable towels, and a scoop or spoon. Use equal exposure times and enough liquid to cover each egg.

Raw eggs can carry Salmonella even with clean shells. Prefer pasteurized shell eggs when available; they still require safe handling. Follow school approval, allergy, eye-protection, and sanitation procedures. Keep containers in a designated refrigerator at 4°C/40°F or below, labeled “experiment—do not eat,” within secondary containment and separated from food. Never taste materials. Wash hands and clean contaminated surfaces and balance trays. Do not seal a gas-producing vinegar reaction in an airtight container. The teacher manages preparation, disposal, and any damaged eggs. Use a teacher demonstration or a non-egg alternative if safe refrigeration or allergy controls are unavailable.

Teacher preparation

Cover eggs with vinegar in loosely covered containers under the approved refrigerated protocol. Allow the calcium-carbonate shell to dissolve; replace vinegar if needed. Cold conditions may slow the reaction.
When shells are removed, gently rinse the intact membranes. Discard ruptured or suspect eggs. The shell-removal reaction is preparation, not the measured osmosis treatment.
Assign intact eggs to water and syrup groups. Use several eggs per treatment across the class. Record the shell-less starting mass immediately before treatment.

Student procedure

Predict each treatment’s mass-change direction and explain your assumptions. Label egg identity, treatment, and start time.
Gently blot each shell-less egg using the same method and duration. Weigh in a tared boat and record starting mass in grams.
Place one egg in distilled water and the other in syrup. Keep temperature, exposure time, container conditions, and liquid volume consistent across groups. Refrigerate between measurements.
After the teacher-selected interval, lift with a spoon, remove surface liquid consistently, and reweigh. For syrup, the teacher should standardize any brief rinse because rinsing can change results.
Record final mass, time, appearance, and any membrane damage. Do not silently omit a leaking egg; document it as an invalid replicate.
Clean up under teacher direction and wash hands.

Record and calculate

Use columns for egg ID, treatment, starting mass (g), final mass (g), exposure time (h), temperature, observations, and percentage mass change. Calculate: 100 × (final mass − starting mass) ÷ starting mass. An egg changing from 60.0 g to 66.0 g has a +10.0% change. Compare replicate values and report variability as well as a mean.

Analysis

Did the mass-change direction match the prediction? Use measurements, not just appearance.
Why is the shell-less starting mass a better baseline than the intact egg mass?
How might syrup left on the surface, a damaged membrane, or different blotting affect the result?
Why are separate parallel treatments easier to compare than sending one egg through water and syrup in sequence?
What would you need to measure to show that a particular solute diffused across the membrane?

Teaching note: Water commonly increases egg mass and concentrated syrup commonly decreases it, but do not alter data to match that pattern. Water movement is an interpretation supported by the treatment and observations, not proof that only water moved. An AP extension can examine water potential and explain why pressure and permeability limit simple concentration comparisons.

Continue the unit

Sources and further reading

Homeostasis & Transport

HOMEOSTASIS AND TRANSPORT
All Materials © Cmassengale

I. Cell Membranes

A. Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave cells

B. Some substances can cross the cell membrane without any input of energy by the cell

C. The movement of such substances across the membrane is known as passive transport

D. To stay alive, a cell must exchange materials such as food, water, & wastes with its environment

E. These materials must cross the cell or plasma membrane

F. Small molecules like water, oxygen, & carbon dioxide can move in and out freely

G. Large molecules like proteins & carbohydrates cannot move easily across the plasma membrane

H. The Cell Membrane is semipermeable or selectively permeable only allowing certain molecules to pass through

II. Diffusion

A. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration

B. Small molecules can pass through the cell membrane by a process called diffusion

C. Diffusion across a membrane is a type of passive transport because it does not require energy

D. This difference in the concentration of molecules across a membrane is called a concentration gradient

E. Diffusion is driven by the kinetic energy of the molecules

F. Kinetic energy keeps molecules in constant motion causing the molecules to move randomly away from each other in a liquid or a gas

G. The rate of diffusion depends on temperature, size of the molecules, & type of molecules diffusing

H. Molecules diffuse faster at higher temperatures than at lower temperatures

I. Smaller molecules diffuse faster than larger molecules

J. Most short-distance transport of materials into & out of cells occurs by diffusion

K. Solutions have two parts — the solute which is being dissolved in the solvent

L. Water serves as the main solvent in living things

M. Diffusion always occurs down a concentration gradient (water moves from an area where it is more concentrated to an area where it is less concentrated)

N. Diffusion continues until the concentration of the molecules is the same on both sides of a membrane

O. When a concentration gradient no longer exists, equilibrium has been reached but molecules will continue to move equally back & forth across a membrane

III. Osmosis

A. The diffusion of water across a semipermeable membrane is called osmosis

B. Diffusion occurs from an area of high water concentration (less solute) to an area of lower water concentration (more solute)

C. Movement of water is down its concentration gradient & doesn’t require extra energy

D. Cytoplasm is mostly water containing dissolved solutes

E. Concentrated solutions have many solute molecules & fewer water molecules

F. Water moves from areas of low solute concentration to areas of high solute concentration

G. Water molecules will cross membranes until the concentrations of water & solutes is equal on both sides of the membrane; called equilibrium

H. At equilibrium, molecules continue to move across membranes evenly so there is no net movement

I. Hypertonic Solution
1. Solute concentration outside the cell is higher (less water)
2. Water diffuses out of the cell until equilibrium is reached
3. Cells will shrink & die if too much water is lost
4. Plant cells become flaccid (wilt); called plasmolysis

J. Hypotonic Solution
1. Solute concentration greater inside the cell (less water)
2. Water moves into the cell until equilibrium is reached
3. Animal cells swell & burst (lyse) if they take in too much water
4. Cytolysis is the bursting of cells
5. Plant cells become turgid due to water pressing outward against cell wall
6. Turgor pressure in plant cells helps them keep their shape
7. Plant cells do best in hypotonic solutions

K. Isotonic Solutions
1. Concentration of solutes same inside & outside the cell
2. Water moves into & out of cell at an equal rate so there is no net movement of water
3. Animal cells do best in isotonic solutions

IV. How Cells Deal With Osmosis

A. The cells of animals on land are usually in isotonic environment (equilibrium)

B. Freshwater organisms live in hypotonic environments so water constantly moves into their cells

C. Unicellular freshwater organisms use energy to pump out excess water by contractile vacuoles

D. Plant cell walls prevent plant cells from bursting in hypotonic environments

E. Some marine organisms can pump out excess salt

V. Facilitated Diffusion

A. Faster than simple diffusion

B. Considered passive transport because extra energy not used

C. Occurs down a concentration gradient

D. Involves carrier proteins embedded in a cell’s membrane to help move across certain solutes such as glucose

E. Carrier molecules change shape when solute attaches to them

F. Change in carrier protein shape helps move solute across the membrane

G. Channel proteins in the cell membrane form tunnels across the membrane to move materials

H. Channel proteins may always be open or have gates that open & close to control the movement of materials; called gated channels

I. Gates open & close in response to concentration inside & outside the cell

VI. Active Transport

A. Requires the use of ATP or energy

B. Moves materials against their concentration gradient from an area of lower to higher concentration

C. May also involve membrane proteins

D. Used to move ions such as Na+, Ca+, and K+ across the cell membrane

E. Sodium-Potassium pump moves 3 Na+ out for every 2 K+ into the cell
1. Causes a difference in charge inside and outside the cell
2. Difference in charge is called membrane potential

F. Ion pumps help muscle & nerve cells work

G. Plants use active transport to help roots absorb nutrients from the soil (plant nutrients are more concentrated inside the root than outside)

VII. Bulk Transport

A. Moves large, complex molecules such as proteins across the cell membrane

B. Large molecules, food, or fluid droplets are packaged in membrane-bound sacs called vesicles

C. Endocytosis moves large particles into a cell

D. Phagocytosis is one type of endocytosis
1. Cell membrane extends out forming pseudopods (fingerlike projections) that surround the particle
2. Membrane pouch encloses the material & pinches off inside the cell making a vesicle
3. Vesicle can fuse with lysosomes (digestive organelles) or release their contents in the cytoplasm
4. Used by ameba to feed & white blood cells to kill bacteria
5. Known as “cell eating”

E. Pinocytosis is another type of endocytosis
1. Cell membrane surrounds fluid droplets
2. Fluids taken into membrane-bound vesicle
3. Known as “cell drinking”

F. Exocytosis is used to remove large products from the cell such as wastes, mucus, & cell products

G. Proteins made by ribosomes in a cell are packaged into transport vesicles by the Golgi Apparatus

H. Transport vesicles fuse with the cell membrane and then the proteins are secreted out of the cell (e.g. insulin)

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Homeostasis Worksheet Ch5 BI

Homeostasis & Transport

Section 5-1 Passive Transport

1. What is the purpose of the cell membrane?

2. Explain passive transport.

3. What is the simplest type of passive transport?

4. In which direction does diffusion occur?

5. What is a concentration gradient?

6. Sugar dissolving in water is an example of _______________________.

7. What supplies the energy for diffusion?

8. Molecules are constantly _____________________.

9. What is meant by equilibrium?

10. Do molecules stop moving when equilibrium is reached? Explain.

11. List three things that determine if a molecule will be able to diffuse across a membrane.

12. Name the 2 parts of a solution.

13. Define osmosis. Is it passive or active transport?

14. The direction water moves across a cell membrane depends on the concentration of what on either side of the cell membrane?

15. Explain what is true about solutes if the outside of the cell is hypotonic to the cytosol? Which way does water move?

16. Explain the solute conditions if the outside is hypertonic to the cytosol. Which way does water move?

17. What occurs if the solute concentration on each side of the cell membrane is isotonic?

18. If the inside & outside of a cell are both isotonic, does water still move across the cell membrane? Explain.

19. If the inside of the cell is hypotonic, the outside will be _________________________.

20. Water tends to diffuse from ____________________ to ___________________ solutions.

21. How does a unicellular paramecium get rid of its excess water? Is energy used?

22. Many cells in multicellular organisms have _________________ pumps to prevent them from taking in too much water in hypotonic solutions.

23. What structure around the outside of plant cells keeps hem from rupturing from too much water?

24. What is turgor pressure & how does it help plant cells?

25. What happens to plant cells placed in a hypertonic solution? Name this process.

26. What is cytolysis & what causes it?

27. Another type of passive transport is __________________________ diffusion.

28. Explain how carrier proteins help in facilitated.

29. Sketch the changes that take place in a carrier protein as it helps molecules move across the cell membrane.

30. What sugar moves across the cell membrane by facilitated diffusion?

31. What are ion channels & are they used in passive or active transport?

32. Name 4 ions that cross the cell membrane through ion channels.

33. Why can’t these ions diffuse across the lipid bilayer of the cell membrane?

34. Ion channels may be always ________________ or have ___________________.

35. Name 3 stimuli that open & close gated channels.

Section 5-2 Active Transport

36. Define active transport.

37. Why are carrier proteins in the cell membrane that are used for active transport called “pumps”?

38. What is the best-known carrier protein pump in animal cells?

39. What 2 ions move up their concentration gradient in this pump?

40. ___________________ ions are pumped out, while ______________ ions are pumped into the cell.

41. Is energy required for active transport? Explain.

42. Sodium ions are exchanged for potassium ions at a ____________ to ____________ ratio.

43. Name 2 processes used to move macromolecules & food particles across the cell membrane. Is energy required?

44. Explain how cells move large particles into the cell by endocytosis.

45. Name & describe the 2 types of endocytosis.

46. How do phagocytes protect cells?

47. What process moves large materials such as wastes & proteins out of the cell?

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