Worksheet Part 2 Plasma Membrane | PDF | Cell Membrane | Biotechnology - Free Printable

Problem Analysis:

The worksheet focuses on the fluid-mosaic model of the plasma membrane, a fundamental concept in biology. The task involves labeling parts of the diagram and answering questions related to molecular transport across the membrane.

#### Part A: Answer all questions

1. Diagram 1 shows a fluid-mosaic model of a plasma membrane.

- a) On Diagram 1, label structures P, Q, R, S, and T. [5 marks]
- P: This is the phospholipid bilayer, which forms the basic structure of the plasma membrane.
- Q: This is a channel protein or transport protein, which facilitates the movement of molecules across the membrane.
- R: This is the cytoplasmic side of the membrane, facing the interior of the cell.
- S: This is a glycoprotein, which is a protein with attached carbohydrate chains, often involved in cell recognition and signaling.
- T: This is the extracellular matrix or the region outside the cell.

- b) Molecules can pass through structure Q in Diagram 1 by facilitated diffusion.
- (i) State Three characteristics of the molecule that can pass through structure Q. [3 marks]
- Molecules passing through structure Q (a channel protein) via facilitated diffusion typically have the following characteristics:
1. Small size or specific shape: The molecule must be small enough or have a specific shape to fit into the channel protein.
2. Non-lipid-soluble: The molecule is usually non-lipid-soluble and cannot easily pass through the phospholipid bilayer without assistance.
3. Specific affinity for the channel protein: The molecule must bind specifically to the channel protein, which recognizes it based on its chemical properties.

- (ii) Explain how molecules pass through structure Q. [3 marks]
- Facilitated diffusion through a channel protein (structure Q) occurs as follows:
1. Binding: The molecule binds to the channel protein at the extracellular side of the membrane.
2. Channel opening: The binding triggers a conformational change in the channel protein, causing it to open.
3. Passage: The molecule passes through the channel protein from the higher concentration side to the lower concentration side, down its concentration gradient.
4. Release: The molecule is released on the other side of the membrane.
5. Channel closure: After the molecule passes, the channel protein may close or reset to its original conformation, ready to facilitate the passage of another molecule.

- c) State one characteristic of the plasma membrane based on the model in Diagram 1. [1 mark]
- One characteristic of the plasma membrane based on the fluid-mosaic model is that it is fluid and dynamic. The phospholipids and proteins are not fixed in place but can move laterally within the membrane, allowing for flexibility and adaptability.

Final Answers:

1. Labeling:
- P: Phospholipid bilayer
- Q: Channel protein/Transport protein
- R: Cytoplasmic side
- S: Glycoprotein
- T: Extracellular matrix

2. Molecules passing through structure Q:
- (i) Characteristics of the molecule:
- Small size or specific shape.
- Non-lipid-soluble.
- Specific affinity for the channel protein.
- (ii) Explanation of passage:
- Binding → Channel opening → Passage down the concentration gradient → Release → Channel closure.

3. Characteristic of the plasma membrane:
- Fluid and dynamic.

Final Boxed Answer:

\[
\boxed{
\text{P: Phospholipid bilayer, Q: Channel protein, R: Cytoplasmic side, S: Glycoprotein, T: Extracellular matrix}
}
\]
\[
\boxed{
\text{Characteristics of the molecule: Small size, non-lipid-soluble, specific affinity; Passage: Binding, opening, passage, release, closure.}
}
\]
\[
\boxed{
\text{Fluid and dynamic.}
}
\]