Unit membrane structure is found in

Options

A. plasma membrane only
B. nuclear membrane only
C. all cell organelles
D. animal membranes only

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks where the unit membrane structure is found. We need to analyze the options provided to determine the correct answer.

2. **Reviewing the Concept of Unit Membrane**: The unit membrane structure was proposed by scientist Robertson in 1959. It describes a specific arrangement of lipids and proteins in biological membranes.

3. **Analyzing the Options**:
- **Plasma Membrane Only**: This option suggests that the unit membrane structure is exclusive to the plasma membrane. However, the unit membrane structure is not limited to just the plasma membrane.
- **Nuclear Membrane Only**: Similar to the previous option, this implies that the unit membrane structure is only found in the nuclear membrane, which is also incorrect.
- **All Cell Organelles**: This option suggests that every cell organelle has a unit membrane structure. However, not all organelles have a membrane (e.g., ribosomes), so this option is not correct.
- **Animal Membranes Only**: This option states that the unit membrane structure is found in all animal membranes, which aligns with Robertson's proposal.

4. **Conclusion**: The correct answer is that the unit membrane structure is found in **animal membranes only**. This includes the plasma membrane, nuclear membrane, and all membrane-bound organelles in animal cells.

5. **Explanation of the Structure**: The unit membrane structure consists of a lipid bilayer with hydrophobic lipids in the center and hydrophilic proteins on both sides. This arrangement is characteristic of all animal membranes.