Give information about ribosomes in short.

(N/A) $\Rightarrow$ Ribosomes are granular structures first observed under the electron microscope as dense particles by George Palade in $1953$.
$\Rightarrow$ Ribosomes are composed of ribonucleic acid $(RNA)$ and proteins and are not surrounded by any membrane.
$\Rightarrow$ Eukaryotic ribosomes are $80S$,while prokaryotic ribosomes are $70S$. Here,'$S$' stands for the sedimentation coefficient,which is an indirect measure of density and size.
$\Rightarrow$ Both $70S$ and $80S$ ribosomes are composed of two subunits.