Diffusion student worksheet | PDF - Free Printable

Let's go through each question on the Diffusion Worksheet step by step and provide clear answers with explanations.

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

> O = a molecule that can pass through the cell membrane
> □ = a cell membrane

We are given two diagrams (A and B), showing molecules (O) outside and inside a cell membrane (□). Diffusion moves molecules from areas of higher concentration to areas of lower concentration.

#### A)
- Outside the cell: many O molecules
- Inside the cell: fewer O molecules
→ Molecules will diffuse into the cell.

✔ Arrow pointing into the cell (from outside to inside)

#### B)
- Outside the cell: many O molecules
- Inside the cell: only one O molecule
→ High concentration outside, low inside → molecules move into the cell.

✔ Arrow pointing into the cell

> ✔ In both A and B, the net movement is into the cell due to higher concentration outside.

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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 can pass through the membrane.)

We have three scenarios:

#### a) Cell: 1% sugar | Outside: 5% sugar
- Higher concentration outside → sugar diffuses into the cell
→ Arrow: Into the cell

#### b) Cell: 3% sugar | Outside: 1% sugar
- Higher concentration inside → sugar diffuses out of the cell
→ Arrow: Out of the cell

#### c) Cell: 1% sugar | Outside: 1% sugar
- Equal concentrations → no net movement
→ No arrow (or "equilibrium")

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3. The cell membrane is made of a _________________________.

✔ Phospholipid bilayer
> Explanation: The cell membrane is primarily composed of a double layer of phospholipids, with hydrophilic heads facing outward and hydrophobic tails inward.

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

✔ Selective permeability
This means that only certain substances can pass through the membrane easily, while others are blocked or require assistance.

> Example: Small nonpolar molecules (like O₂) pass easily; ions and large polar 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.

✔ High → Low
> Diffusion is the passive movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached.

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

✔ No
> Diffusion is a passive process — it does not require energy (ATP). It occurs naturally due to random molecular motion and concentration gradients.

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✔ Final Answers Summary:

1. A: Arrow into the cell
B: Arrow into the cell

2.
- 1% inside / 5% outside → Arrow into cell
- 3% inside / 1% outside → Arrow out of cell
- 1% inside / 1% outside → No net movement (equilibrium)

3. Phospholipid bilayer

4. Selective permeable. This means that only certain substances can pass through the membrane freely.

5. From a region of high concentration to a region of low concentration.

6. No, the cell does not expend energy during diffusion.

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