Which one of the following is not considered as a part of the endomembrane system
Or
Which of the following has a single unit membrane?
(a) Ribosome
(b) Peroxisome
(c) Nucleus
(d) Centrosome

Options

A. Ribosome
B. Peroxisome
C. Nucleus
D. Centrosome

Answer

To solve the question regarding which of the following is not considered a part of the endomembrane system or which of the following has a single unit membrane, we can analyze each option step by step.

### Step 1: Understand the Endomembrane System
The endomembrane system in a cell includes various organelles that work together in the synthesis, modification, and transport of proteins and lipids. Key components include the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and vesicles.

### Step 2: Analyze Each Option
- **(a) Ribosome**: Ribosomes are not membrane-bound organelles; they are involved in protein synthesis and are often found on the rough endoplasmic reticulum (RER), which is part of the endomembrane system. Therefore, ribosomes are associated with the endomembrane system.

- **(b) Peroxisome**: Peroxisomes are single-membrane-bound organelles that are involved in various metabolic processes, including the breakdown of fatty acids and detoxification of hydrogen peroxide. Importantly, peroxisomes are not part of the endomembrane system.

- **(c) Nucleus**: The nucleus, with its nuclear envelope, is a central part of the endomembrane system as it is involved in the synthesis and modification of RNA and ribosome assembly.

- **(d) Centrosome**: The centrosome is not a membrane-bound organelle; it is involved in organizing microtubules and is not considered part of the endomembrane system.

### Step 3: Identify the Correct Answers
- For the first part of the question, which asks for the component not considered part of the endomembrane system, the correct answer is **(b) Peroxisome**.
- For the second part of the question, which asks for the organelle with a single unit membrane, the correct answer is also **(b) Peroxisome**.

### Final Answer
The correct answer for both parts of the question is **(b) Peroxisome**.

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