From the following pairs determine the correctly described cellular parts.

Options

A. Thylakoids - Flattened membranous sacs forming the grana of chloroplast.
B. Centrioles - Sites for active RNA synthesis
C. Ribosomes - Those in chloroplasts are large (80 s) while those in the cytoplasm are smaller (70 s)
D. Lysosomes - Optically active at a pH of about 8.5

Answer

To solve the question regarding the correctly described cellular parts, we will analyze each pair provided in the question step by step.

### Step-by-Step Solution:

1. **Identify the First Pair: Thylakoid and Flattened Membranous Sac**
- Thylakoids are indeed flattened membranous sacs that are part of the chloroplast. They are organized in stacks known as grana, which are crucial for the photosynthesis process.
- **Conclusion**: This pair is correctly described.

2. **Identify the Second Pair: Centrioles and Sites for Active RNA Synthesis**
- Centrioles are cylindrical structures found in the centrosome and are involved in cell division and the formation of cilia and flagella. They do not function as sites for RNA synthesis; that role is primarily served by the nucleus and ribosomes.
- **Conclusion**: This pair is incorrectly described.

3. **Identify the Third Pair: Ribosomes and 80s Ribosomes**
- Ribosomes are indeed involved in protein synthesis, but they come in two types: 70s ribosomes found in prokaryotes and organelles like mitochondria and chloroplasts, and 80s ribosomes found in eukaryotic cytoplasm. The statement is misleading because it incorrectly associates ribosomes in chloroplasts with 80s.
- **Conclusion**: This pair is incorrectly described.

4. **Identify the Fourth Pair: Lysosomes and pH of about 8.5**
- Lysosomes contain hydrolytic enzymes that function optimally at an acidic pH (around 4.5 to 5). The statement that they are active at a pH of 8.5 is incorrect.
- **Conclusion**: This pair is incorrectly described.

### Final Conclusion:
The only correctly described cellular part is the first pair: **Thylakoid and Flattened Membranous Sac forming the Grana of Chloroplast**.

### Answer:
The correct answer is option number 1.

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