DNA is packed with help of packing proteins such as histone into the compact form so as to get accommodated into the nucleus. The thread-like structures formed by DNA and the packing proteins are called chromosomes. Chromosomes are visible during cell division only.
In a resting cell, chromosomes are present in the form of decondensed indistinct chromatin. Each unreplicated chromosome has a single chromatid and two arms that are held together by a centromere.
Energy decreases as it moves up trophic levels because energy is lost as metabolic heat when the organisms from one trophic level are consumed by organisms from the next level.
