What is meant by the beads on a string model of chromatin?

Linker DNA is the string and beads are the nucleosomes

Explanation:

In the eukaryotic cells the chromatin is a complex which is formed of DNA and proteins. Due to the formation of chromatin the long DNA molecule gets packaged into a dense and compact structure. It also prevents DNA from getting damaged. The proteins that help in organization of DNA into chromatin are mainly histone proteins which are positively charged. DNA gets wrapped around these histone proteins in the influence of charge and some other factors. The structure formed by wrapping of DNA around the histone proteins is called nucleosome. These nucleosomes occur at regular intervals in the DNA thread and give it an appearance as 'beads on string'. Here the beaded structure is the nucleosome.

correct answer is option a.

tropopause, stratopause and mesopause have all in common aspect that is point of maximum temperature in its layer of the atmosphere. all layers of atmosphere observe abrupt change in temperature. tropopause is the boundary between troposphere and stratosphere. stratopause is the boundary between stratosphere and mesosphere. mesopause is the boundary between mesosphere and thermosphere. these all boundaries are ranges between altitude of 0 to 80 km.