(a) : Ribosomes are very small organelles having a diameter of 150AA−250AA. Each ribosome is made up of two subunits, a smaller subunit and another larger subunit. These two subunits are associated with the help of Mg2+ ions (at 0.001M concentration). If the Mg2+ ions concentration is less in cytoplasm, the two units of ribosome separate but when the Mg2+ ions concentration is increased ten times, the two unites and form a dimer.