Osmosis and Diffusion Worksheet- Practice with Answers

🧪 Why These Worksheets Actually Matter

Most students bomb the osmosis and diffusion unit because they memorize definitions and skip the practice. That is a mistake.

These processes run everything from how your cells breathe to why your fingers wrinkle in water. If you cannot apply the concepts, you will fail the exam. Period.

This worksheet gives you real practice problems with answers. Work through them. Check your mistakes. Move on.

📋 Diffusion vs. Osmosis: The Basics

Before you touch the problems, lock down the difference.

Diffusion is the movement of any particles from high concentration to low concentration. No membrane required. No energy needed.

Osmosis is the movement of water across a selectively permeable membrane from low solute concentration to high solute concentration. Again, no energy needed.

Key point: All osmosis is diffusion, but not all diffusion is osmosis. Osmosis is just the water-specific version.

📝 Practice Worksheet

Do not scroll to the answers yet. That defeats the purpose.

Part 1: Multiple Choice

1. During osmosis, water moves toward the area with:
   • A) Higher water concentration
   • B) Lower solute concentration
   • C) Higher solute concentration
   • D) Equal solute and water concentration
2. A cell is placed in pure water. The cell swells and bursts. This happens because:
   • A) Water left the cell
   • B) The cell is hypertonic to its environment
   • C) The environment is hypotonic to the cell
   • D) Solutes moved into the cell
3. Which of these is not an example of diffusion?
   • A) Oxygen entering blood cells in the lungs
   • B) A drop of food coloring spreading in water
   • C) Water moving into a plant root
   • D) The smell of baking bread traveling through a house
4. A selectively permeable membrane allows:
   • A) All substances to pass freely
   • B) Only water to pass
   • C) Certain substances to pass while blocking others
   • D) Only solutes to pass

Part 2: Fill in the Blank

5. Osmosis is the diffusion of __________ across a selectively permeable membrane.
6. If the concentration of solute is equal inside and outside the cell, the solutions are __________.
7. A solution with a lower solute concentration than the cell is called __________.
8. When a plant cell is placed in a hypertonic solution, the cell membrane pulls away from the cell wall in a process called __________.

Part 3: Short Answer

9. Explain what happens to a red blood cell placed in a 10% salt solution. Use the terms hypertonic, water, and shrivel.
10. Describe why a freshwater fish cannot survive in saltwater. Focus on osmosis and water movement across its gills.
11. A bag made of dialysis tubing (selectively permeable) is filled with 20% starch solution and placed in a beaker of pure water. Predict what happens to the mass of the bag over 30 minutes and explain why.

Part 4: Diagram Analysis

Imagine a U-tube separated by a selectively permeable membrane.

• Side A: 5% salt solution
• Side B: 15% salt solution

12. In which direction will the water move?
13. Which side has the higher water concentration?
14. After equilibrium is reached, will the water stop moving entirely? Explain.

🔑 Answer Key

Check your work. If you got it wrong, figure out why.

Part 1 Answers

1. C — Water moves toward higher solute concentration.
2. C — The pure water is hypotonic relative to the cell, so water rushes in.
3. C — Water moving into a root is osmosis, not general diffusion.
4. C — Selectively permeable means it picks and chooses what gets through.

Part 2 Answers

5. water
6. isotonic
7. hypotonic
8. plasmolysis

Part 3 Answers

9. The 10% salt solution is hypertonic compared to the inside of the red blood cell. Water leaves the cell by osmosis, causing it to shrivel (crenate).
10. Seawater is hypertonic to a freshwater fish. Water leaves the fish's body through its gills via osmosis. The fish dehydrates and dies.
11. The bag will gain mass. Water moves from the beaker (low solute) into the bag (high solute) by osmosis. Starch molecules are too large to pass through the membrane.

Part 4 Answers

12. Water moves from Side A to Side B.
13. Side A has the higher water concentration because it has less dissolved salt.
14. No, water does not stop moving entirely. At equilibrium, water molecules move at equal rates in both directions. There is no net movement, but the molecules keep crossing.

🛠️ How To Actually Use This Worksheet

Here is a no-nonsense study plan that works:

• Step 1: Do the problems without looking at your notes. Struggling is part of learning.
• Step 2: Grade yourself using the answer key. Mark every single wrong answer.
• Step 3: For every mistake, write one sentence explaining why you got it wrong. Do not skip this.
• Step 4: Re-do the missed questions in 24 hours. If you still miss them, you do not understand the concept.
• Step 5: Teach the U-tube problem to someone else. If you cannot explain it simply, you do not know it.

⚠️ Common Mistakes Students Make

• Confusing hypertonic and hypotonic. Hyper = more solute. Hypo = less solute. Remember: the prefix refers to the solution, not the cell.
• Saying water moves to "low concentration." Be specific. Water moves to high solute concentration (or low water concentration).
• Thinking diffusion and osmosis stop at equilibrium. They do not. Net movement stops. Molecular movement continues.
• Forgetting that osmosis requires a membrane. Diffusion does not.

📥 Downloadable PDF Version

Want to print this? You can copy the questions above into a document, or search for "osmosis and diffusion worksheet PDF" to find formatted versions. Most biology textbooks also have practice problem sets in the back.

If your teacher gave you a specific worksheet, use that one first. This page is a backup for extra reps.

🎯 Final Word

Diffusion and osmosis are not hard. Students just refuse to do enough practice problems. Do this worksheet twice. Understand every wrong answer. You will be fine on the test.