The ribosomes are centres (sites) for.

Explanation-
Ribosomes are small and complex structures within cells that are involved in one of the most vital processes needed for life i.e. protein synthesis. They link amino acids together in the order determined by messenger RNA (mRNA) molecules.

• Ribosomes:
Structure: Ribosomes are made up of two subunits: a larger one and a smaller one. Both of these subunits are composed of a special class of RNA known as ribosomal RNA (rRNA) and proteins.
In eukaryotes, the larger subunit is known as the 60S subunit and the smaller one is the 40S subunit, together forming the complete 80S ribosome
In prokaryotes, the smaller subunit is the 30S subunit, and the larger one is the 50S subunit, making an overall smaller 70S ribosome.
 
Function: The main function of ribosomes is to carry out protein synthesis. This process is also known as translation and involves decoding mRNA (which was previously transcribed from the cell's DNA) to build a chain of amino acids, which will become a protein. This means ribosomes are the site where the cell's genetic information is used to create proteins.
Location: Ribosomes are found both in the cytoplasm (free ribosomes) and attached to the endoplasmic reticulum (ER), creating what is known as the rough ER. Free ribosomes typically synthesize proteins that function within the cytoplasm, while those associated with the ER synthesize proteins that are either exported from the cell, incorporated into the cell's membranes, or sent to lysosomes.
Conclusion- Ribosomes are sites for protein synthesis.