Diffusion worksheet illustrating the movement of molecules across a membrane, with instructions to draw and label concentration gradients and equilibrium.

Let's solve this step-by-step based on the worksheet titled "DIFFUSION". We'll fill in the blanks, complete the diagrams, and explain each part clearly.

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✔ Part 1: Definition

Fill in the blanks using the words provided:
*partially, high, membrane, low, net*

> Diffusion is the net movement of a substance, from an area of high concentration, to an area of low concentration, across a partially permeable membrane.

✔ Explanation:
- "Net" movement means the overall direction of particles.
- Particles move from high to low concentration (down the concentration gradient).
- This occurs across a partially permeable membrane, which allows certain molecules through but not others.

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✔ Part 2: Diagrams

#### 🔹 Diagram 1:
We are given:
- Left side has many circles (representing molecules).
- A partially permeable membrane (vertical grey bars).

Instructions:
1. Draw molecules on the right-hand side showing lower concentration than left.
2. Draw arrows showing net movement.

Solution:
- On the right side, draw fewer circles (e.g., 2–3) compared to the left (which has 8).
- Draw arrows pointing from left to right across the membrane — this shows the net movement of molecules from high to low concentration.

> ⚠️ Note: Molecules move randomly, but the net flow is from high → low.

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#### 🔹 Diagram 2:
Instruction: Show that equilibrium has been reached.

Solution:
- Draw equal numbers of molecules on both sides of the membrane (e.g., 4 on each side).
- No net movement — so no arrows or perhaps small bidirectional arrows (but no net direction).

> ✔ At equilibrium, concentration is equal on both sides. Molecules still move randomly, but there’s no net movement.

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✔ Part 3: Key Points – Fill in the Blanks

Use these words:
*blood, equilibrium, oxygen, permeable, passive, low, high, energy, randomly*

> Diffusion is a passive process, meaning it does not require energy.
> Molecules move around randomly, but their net movement will be from high to low concentration, until an equilibrium is reached.
> This movement occurs across a partially permeable membrane.
> Diffusion is important for the movement of substances in the body. For example, the movement of oxygen from the lungs to the blood, and carbon dioxide in the opposite direction.

✔ Explanation:
- Passive: No energy required (unlike active transport).
- Random motion: Molecules move due to kinetic energy, but the net effect is down the gradient.
- High → low: The driving force for diffusion.
- Equilibrium: When concentrations are equal on both sides.
- Partially permeable membrane: Allows selective passage (e.g., cell membranes).
- Oxygen & blood: In respiration, O₂ diffuses from alveoli (lungs) into capillaries (blood), while CO₂ moves out.

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🧠 Summary of Concepts

| Concept | Explanation |
|--------|-------------|
| Diffusion | Net movement of molecules from high → low concentration |
| Passive process | No energy needed |
| Partial permeability | Membrane allows only certain molecules through |
| Net movement | Overall direction; even if individual molecules go both ways |
| Equilibrium | Equal concentrations on both sides; no net movement |

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✔ Final Answer (Completed Worksheet)

#### Definition:
> Diffusion is the net movement of a substance, from an area of high concentration, to an area of low concentration, across a partially permeable membrane.

#### Diagram 1:
- Right side: Fewer circles (e.g., 3)
- Arrows: From left to right (→)

#### Diagram 2:
- Equal number of circles on both sides
- No net arrow (or balanced arrows)

#### Key Points:
> Diffusion is a passive process, meaning it does not require energy.
> Molecules move around randomly, but their net movement will be from high to low concentration, until an equilibrium is reached.
> This movement occurs across a partially permeable membrane.
> Diffusion is important for the movement of substances in the body. For example, the movement of oxygen from the lungs to the blood, and carbon dioxide in the opposite direction.

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