Which one of the following organelles is enclosed by a single membrane?a)Ribosomeb)Mitochondriac)Endoplasmic reticulumd)CentrosomeCorrect answer is option 'C'. Can you explain this answer?

Question

Answer

Correct answer: C: Endoplasmic reticulum

Endoplasmic reticulum (ER) is an organelle enclosed by a single membrane.

Here is an explanation for each option:

A: Ribosome
- Ribosomes are not enclosed by any membrane.
- They are responsible for protein synthesis.
- Ribosomes are found either freely floating in the cytoplasm or attached to the endoplasmic reticulum.

B: Mitochondria
- Mitochondria are enclosed by two membranes – an outer membrane and an inner membrane.
- They are known as the "powerhouse of the cell" as they produce adenosine triphosphate (ATP) through cellular respiration.

C: Endoplasmic reticulum
- The endoplasmic reticulum is a network of membranous tubules and flattened sacs.
- It is enclosed by a single membrane called the endoplasmic reticulum membrane.
- The ER is classified into two types: smooth endoplasmic reticulum (SER) and rough endoplasmic reticulum (RER).
- The RER is involved in protein synthesis and has ribosomes attached to its surface, while the SER is involved in lipid synthesis and detoxification.

D: Centrosome
- The centrosome is not enclosed by any membrane.
- It is an organelle composed of two centrioles, which play a crucial role in cell division.
- The centrosome helps in the organization of microtubules and provides structure to the cell.

Answer

Correct answer: C: Endoplasmic reticulum

Endoplasmic reticulum (ER) is an organelle enclosed by a single membrane.

Here is an explanation for each option:

A: Ribosome
- Ribosomes are not enclosed by any membrane.
- They are responsible for protein synthesis.
- Ribosomes are found either freely floating in the cytoplasm or attached to the endoplasmic reticulum.

B: Mitochondria
- Mitochondria are enclosed by two membranes – an outer membrane and an inner membrane.
- They are known as the "powerhouse of the cell" as they produce adenosine triphosphate (ATP) through cellular respiration.

C: Endoplasmic reticulum
- The endoplasmic reticulum is a network of membranous tubules and flattened sacs.
- It is enclosed by a single membrane called the endoplasmic reticulum membrane.
- The ER is classified into two types: smooth endoplasmic reticulum (SER) and rough endoplasmic reticulum (RER).
- The RER is involved in protein synthesis and has ribosomes attached to its surface, while the SER is involved in lipid synthesis and detoxification.

D: Centrosome
- The centrosome is not enclosed by any membrane.
- It is an organelle composed of two centrioles, which play a crucial role in cell division.
- The centrosome helps in the organization of microtubules and provides structure to the cell.

Answer

The correct answer is option 'C' - Endoplasmic reticulum.

The endoplasmic reticulum (ER) is an organelle found in eukaryotic cells that is responsible for the synthesis, folding, and transport of proteins and lipids. It is composed of a network of membranes that are interconnected, forming a complex system of tubules and sacs throughout the cytoplasm of the cell. The ER can be divided into two regions: the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER).

1. Rough endoplasmic reticulum (RER):
- The RER is called 'rough' due to the presence of ribosomes attached to its surface. These ribosomes are responsible for protein synthesis.
- The RER plays a crucial role in the folding and modification of proteins. As the newly synthesized proteins enter the RER, they undergo various modifications such as glycosylation (addition of sugar molecules) and formation of disulfide bonds.
- Once the proteins are properly folded and modified, they are transported to their final destinations within the cell or outside the cell via vesicles.

2. Smooth endoplasmic reticulum (SER):
- The SER does not have ribosomes attached to its surface, hence the name 'smooth.'
- The SER is involved in various functions, including lipid synthesis, detoxification of drugs and toxins, and calcium ion storage.
- Lipids synthesized in the SER are important for the construction of cell membranes and for the production of steroid hormones.
- The SER also plays a role in the metabolism and detoxification of drugs and toxins by modifying them to make them more water-soluble and easier to eliminate from the body.
- In muscle cells, the SER stores calcium ions and releases them when the cell needs to contract.

In summary, the endoplasmic reticulum is an organelle enclosed by a single membrane. It consists of two regions: the rough endoplasmic reticulum (RER) and the smooth endoplasmic reticulum (SER). The RER is responsible for protein synthesis and modification, while the SER is involved in lipid synthesis, detoxification, and calcium ion storage.

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