Dna coils tightly during division and assembles into visible

chromosomes

Explanation:

DNA of organisms is organized into one or more thread-like structures called chromosomes. Chromosomes are made of DNA and its packing proteins.  During cell division, the thin mass of chromatin which in turn is made of DNA and its packing protein condense and becomes visible as individual chromosomes. The DNA molecule is wrapped around histone proteins to form nucleosomes which in turn become compact into chromatin fibers.

The further condensation of looped domains formed by the coiling of chromatin fiber forms chromosomes. The part of a chromosome that holds its two arms together is called centromere. Chromosome becomes visible during the prophase stage only when condensation of chromatin takes place.

answer: land bridge theory. land bridge theory held that shifting portions of dry land explained the finding of identical species on different continents. plate tectonic theory eventually eliminated the land bridge theory.

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]