Diffusion & Osmosis Worksheet featuring diagrams and questions about molecular movement across cell membranes.

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 more molecules.

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

Assume sugar molecules can pass through the membrane.

#### Situation 1:
- Cell: 1% sugar
- Outside: 5% sugar

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

✔ Arrow: Into the cell

#### Situation 2:
- Cell: 3% sugar
- Outside: 1% sugar

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

✔ Arrow: Out of the cell

#### Situation 3:
- Cell: 1% sugar
- Outside: 1% sugar

→ Equal concentrations → No net movement

✔ Arrow: No arrow (or bidirectional with equal size)

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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 it to regulate what enters and exits the cell.

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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, while others are blocked.

> Example: Small nonpolar molecules (like oxygen) pass easily; large or charged molecules may need help.

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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

> Diffusion is a passive process — it does not require energy (ATP). Molecules move due to random motion and concentration differences.

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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. They collide with each other and bounce around until they spread evenly.

> Think of it like gas molecules in a room — they move constantly and naturally spread out from crowded areas to less crowded ones.

> So, no spaceship beams or winged monkeys! Just random molecular motion driven by thermal energy.

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✔ Final Answers Summary:

1. A & B: Arrows pointing into the cell
2. Situation 1: Into cell
Situation 2: Out of cell
Situation 3: No net movement (equal)
3. Phospholipid bilayer
4. Selectively permeable — only certain substances can pass through
5. High → Low concentration
6. No, diffusion does not require energy
7. Random motion due to kinetic energy — molecules move and collide until evenly distributed

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