Problem 1 - Campbell Biology

Question

In what way do the membranes of a eukaryotic cell vary? \begin{equation}\begin{array}{l}{\text { (A) Phospholipids are found only in certain }} \\ {\text { membranes. }} \\ {\text { (B) Certain proteins are unique to each membrane. }} \\ {\text { (C) Only certain membranes of the cell are }} \\ {\text { selectively permeable. }} \\ {\text { (D) Only certain membranes are constructed from amphipathic }} \\ {\text { molecules. }}\end{array}\end{equation}

Step-by-Step Solution

Answer

B

Step 1: Clarify the question

Understand that the question is asking how the membranes in a eukaryotic cell differ from each other.

Step 2: Analyze Option A

Option A states that phospholipids are found only in certain membranes. This is incorrect since phospholipids are a fundamental component of all cell membranes in eukaryotes.

Step 3: Analyze Option B

Option B states that certain proteins are unique to each membrane. This is correct as different membranes in a cell have specific proteins that contribute to their unique functions.

Step 4: Analyze Option C

Option C suggests only certain membranes are selectively permeable. This is incorrect since selective permeability is a characteristic of all cell membranes.

Step 5: Analyze Option D

Option D claims that only certain membranes are constructed from amphipathic molecules. This is incorrect because all cell membranes are made of amphipathic molecules like phospholipids.

Step 6: Conclusion

After analyzing each option, determine that the correct answer is B.

Key Concepts

membrane proteins

Membrane proteins play vital roles in the functioning of eukaryotic cells. They are embedded within or attached to the cell membrane and come in several types:

• Integral proteins, which span the membrane and are involved in transport.
• Peripheral proteins, which are attached to the surface and help with signaling and maintaining cell shape.

Some proteins allow specific substances to pass through the membrane, while others serve as receptors for signaling molecules. Membrane proteins also help in cell recognition and adhesion, contributing to the unique identity of each cell membrane within different cellular compartments.
Each membrane within a eukaryotic cell has a unique set of proteins tailored to its particular function. For instance,
the inner mitochondrial membrane contains proteins involved in ATP production, while the plasma membrane has proteins for nutrient transport and cell communication.
Understanding membrane proteins' specific roles and locations helps explain their critical contribution to cellular functions.

cell membrane structure

The cell membrane, also known as the plasma membrane, is fundamental to the life of a eukaryotic cell. Its structure is based on a phospholipid bilayer, which is made up of two layers of phospholipids.
Phospholipids have a hydrophilic (water-attracting) 'head' and two hydrophobic (water-repelling) 'tails.' This arrangement causes the hydrophobic tails to face inward, away from water, while the hydrophilic heads face outward.
In addition to phospholipids, cell membranes contain cholesterol, which helps maintain fluidity and stability, and various proteins and carbohydrates.
The fluid mosaic model describes this structure, emphasizing the flexible, dynamic nature of the membrane, where proteins can move laterally within the lipid bilayer. This flexibility is crucial for various functions such as cell signaling, transport of molecules, and cell division.
Overall, the cell membrane's unique structure allows it to perform its role as a selective barrier and communicator between the cell's internal and external environments.

selective permeability

Selective permeability is a key feature of eukaryotic cell membranes. This property means that the membrane allows certain molecules or ions to pass through while blocking others. It is critical for maintaining homeostasis within the cell.
Selective permeability is achieved through several mechanisms:

• Simple diffusion, where small, nonpolar molecules like oxygen and carbon dioxide move across the membrane without assistance.
• Facilitated diffusion, where larger or polar molecules move through the membrane with the help of transport proteins such as channels or carriers.
• Active transport, which uses energy (ATP) to move molecules against their concentration gradient through transport proteins.

This ability to control what enters and exits the cell ensures that the internal environment remains stable, allowing the cell to function properly despite changes in the external environment. For example, cells can intake essential nutrients while expelling waste, and maintain ion gradients necessary for processes like nerve impulse transmission.
Selective permeability is essential for various cellular processes and functions, making it a fundamental feature of eukaryotic cell membranes.