Diffusion & Osmosis Worksheet - Free Printable

Let's go through each question on the Diffusion & Osmosis Worksheet step by step, providing answers and explanations.

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1. Use arrows to indicate the direction of diffusion in each case:

> O is a molecule that can pass through the cell membrane. ▭ is a cell membrane.

We are given two diagrams (A and B), showing molecules (O) outside and inside a cell (represented by a rectangle).

#### A)
```
Outside: O O O O
| |
| |
[ ] [ ]
| |
O O O O
```

- The concentration of molecules outside the cell is higher than inside.
- Diffusion moves from high to low concentration.
- So, molecules will move into the cell.

✔ Answer: Draw arrows pointing into the cell.

#### B)
```
Outside: O O O O O O
| |
| |
[ ] [ ]
| |
O O
```

- Concentration is higher outside than inside.
- Again, molecules will diffuse into the cell.

✔ Answer: Draw arrows pointing into the cell.

> Note: In both A and B, molecules are moving into the cell because the outside has a higher concentration.

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2. For each situation below, use an arrow to indicate the net movement of sugar into or out of the cell.

Assume sugar molecules can pass through the membrane.

#### First Diagram:
- Cell: 1% sugar
- Outside: 5% sugar

→ Higher concentration outside, so sugar moves into the cell.

✔ Arrow: Into the cell

#### Second Diagram:
- Cell: 3% sugar
- Outside: 1% sugar

→ Higher concentration inside, so sugar moves out of the cell.

✔ Arrow: Out of the cell

#### Third Diagram:
- Cell: 1% sugar
- Outside: 1% sugar

→ Equal concentration → No net movement

✔ Arrow: No arrow (or "no net movement")

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3. The cell membrane is made of a _________________________.

✔ Answer: Phospholipid bilayer

> Explanation: The cell membrane is composed of two layers of phospholipids, with hydrophilic heads facing outward and hydrophobic tails inward. This structure allows selective permeability.

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4. The cell membrane is ___________ permeable. This means that _________________

✔ Answer:
- Selectively permeable
- This means that only certain substances can pass through it easily, while others are blocked or require assistance.

> Example: Small nonpolar molecules (like oxygen) pass easily; ions and large polar molecules may need transport proteins.

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5. Diffusion always causes particles to move from a region of _________ concentration to a region of _________ concentration.

✔ Answer:
- From a region of high concentration to a region of low concentration.

> This is the definition of diffusion — movement down the concentration gradient.

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6. Does a cell expend energy when molecules diffuse in or out of the cell?

✔ Answer: No

> Explanation: Diffusion is a passive process. It does not require energy (ATP). Molecules move due to random motion and concentration gradients.

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7. During diffusion, how do the molecules physically get from one place to the other? (Spaceship tractor beam? Winged monkeys?)

✔ Answer:
Molecules move randomly due to their kinetic energy (thermal motion). They collide with each other and bounce around. Over time, they spread out from areas of high concentration to areas of low concentration simply due to this random movement.

> Think of it like gas molecules spreading in a room — no "beam" or "monkeys," just constant, random motion.

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✔ Final Answers Summary:

1. A & B: Arrows point into the cell
2. Sugar movement:
- 1% inside / 5% outside → Into cell
- 3% inside / 1% outside → Out of cell
- 1% inside / 1% outside → No net movement
3. Phospholipid bilayer
4. Selectively permeable – only certain substances can pass through
5. High → Low concentration
6. No, cells do not expend energy
7. Molecules move via random thermal motion (kinetic energy), colliding and spreading out naturally

Let me know if you'd like a visual version or help drawing the arrows!