Diffusion Recap by Amoeba Sisters | PDF | Diffusion | Cell Membrane - Free Printable

Problem Overview:

The task involves answering questions related to the concept of diffusion and its variations, such as simple diffusion and facilitated diffusion. The worksheet provides images and scenarios to help explain these concepts.

Solution and Explanation:

#### 1. In diffusion, the net movement of a substance travels down its concentration gradient. Explain using the image below.

- Explanation: Diffusion is the process by which molecules move from an area of high concentration to an area of low concentration. This movement occurs naturally due to the random motion of molecules.
- Image Analysis:
- On the left side of the image, there is a high concentration of molecules (many purple dots).
- On the right side of the image, there is a low concentration of molecules (fewer purple dots).
- Over time, molecules will move from the left (high concentration) to the right (low concentration) until the concentration becomes equal on both sides.
- Answer: Molecules move from high to low concentration. In this case, the molecules on the left (high concentration) will move to the ones in the right (low concentration).

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#### 2. When diffusion has reached equilibrium, we say that the net movement of the molecules is zero. Does this mean these molecules below would stop moving? Explain using the image below.

- Explanation: At equilibrium, the net movement of molecules is zero because the number of molecules moving in one direction is balanced by the number moving in the opposite direction. However, this does not mean the molecules stop moving altogether.
- Image Analysis:
- Even after reaching equilibrium, molecules continue to move randomly.
- The dashed line represents the boundary where the concentration is equal on both sides.
- Although the net movement is zero, individual molecules still cross the boundary in both directions.
- Answer: Molecules don't stop moving. They are always moving, just not going to the other side in a net sense.

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#### 3. Simple diffusion can occur through a cell membrane! According to the video, what are some cell membrane characteristics that can affect the diffusion rate?

- Explanation: The cell membrane's structure and composition play a crucial role in determining how easily substances can diffuse across it.
- Key Characteristics:
1. Thickness of the Cell Membrane: Thicker membranes slow down diffusion because molecules have to travel a longer distance.
2. Presence of Proteins: Certain proteins (e.g., channels or carriers) can facilitate the movement of specific molecules, affecting diffusion rates.
3. Lipid Bilayer Composition: The phospholipid bilayer is hydrophobic, so only small, nonpolar molecules can pass through easily.
- Answer: Cell membrane characteristics that can affect the diffusion rate include the cell membrane's thickness, the presence of proteins, and the lipid bilayer composition.

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#### 4. Does simple diffusion require an input of energy?

- Explanation: Simple diffusion is a passive process, meaning it does not require any energy input from the cell. It relies solely on the random motion of molecules and the concentration gradient.
- Answer: No, simple diffusion does not require an input of energy.

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#### 5. Is simple diffusion passive or active transport?

- Explanation: Simple diffusion is classified as passive transport because it occurs without the use of cellular energy (ATP). It relies on the natural movement of molecules down their concentration gradient.
- Answer: Simple diffusion is passive transport.

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#### 6. Sometimes, a substance can only travel across a cell membrane via facilitated diffusion. What is facilitated diffusion?

- Explanation: Facilitated diffusion is a type of passive transport where molecules move across the cell membrane with the help of transport proteins (e.g., channels or carriers). These proteins assist in the movement of molecules that cannot easily cross the lipid bilayer on their own.
- Image Analysis:
- The image shows a protein (purple structure) embedded in the cell membrane.
- Molecules (green dots) are moving from a high concentration to a low concentration with the help of the protein.
- Answer: Facilitated diffusion is when a molecule gets help from a protein to move from a high concentration to a low concentration.

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#### 7. Does facilitated diffusion require an input of energy?

- Explanation: Facilitated diffusion is also a passive process, meaning it does not require energy input from the cell. The transport proteins simply facilitate the movement of molecules down their concentration gradient.
- Answer: No, facilitated diffusion does not require an input of energy.

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#### 8. Is facilitated diffusion passive or active transport?

- Explanation: Facilitated diffusion is classified as passive transport because it occurs without the use of cellular energy (ATP). It relies on the concentration gradient and the assistance of transport proteins.
- Answer: Facilitated diffusion is passive transport.

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Final Answers:

1. Molecules move from high to low concentration. In this case, the molecules on the left (high concentration) will move to the ones in the right (low concentration).
2. Molecules don't stop moving. They are always moving, just not going to the other side in a net sense.
3. Cell membrane characteristics that can affect the diffusion rate include the cell membrane's thickness, the presence of proteins, and the lipid bilayer composition.
4. No, simple diffusion does not require an input of energy.
5. Simple diffusion is passive transport.
6. Facilitated diffusion is when a molecule gets help from a protein to move from a high concentration to a low concentration.
7. No, facilitated diffusion does not require an input of energy.
8. Facilitated diffusion is passive transport.

Final Answer Box:

\[
\boxed{
\begin{array}{l}
1. \text{Molecules move from high to low concentration.} \\
2. \text{Molecules don't stop moving; they are always moving.} \\
3. \text{Thickness, presence of proteins, lipid bilayer composition.} \\
4. \text{No, simple diffusion does not require energy.} \\
5. \text{Simple diffusion is passive transport.} \\
6. \text{Facilitated diffusion uses proteins to help molecules move.} \\
7. \text{No, facilitated diffusion does not require energy.} \\
8. \text{Facilitated diffusion is passive transport.}
\end{array}
}
\]