Question

During mitosis, E.R. and nucleolus begin to disappear at
(a) Early metaphase
(b) Late metaphase
(c) Early prophase
(d) Late prophase

Answer 1

Hint: At a stage of cell division that begins after the interphase in which chromosome condensation occurs, endoplasmic reticulum (E.R) and nucleolus begin to disappear during mitosis. It occurs in the first stage of mitosis.

Complete step by step answer:
Prophase, in mitosis, is the longest period of karyokinesis. Nucleolus membranes begin to disintegrate in the early prophase. The cytoskeleton of the organism, the Golgi complex, the ER, etc., vanish. The nucleus and cell become spheroid during the early prophase of mitosis. Increases in cytoplasm viscosity and refractivity. To shape shortened chromosomes, DNA molecules condense. The endoplasmic reticulum and nucleolus are starting to vanish.

The cell begins to break down some structures and build up others in the early prophase, setting the stage for chromosome division. The chromosomes (making them easier to break apart later on) begin to condense. A portion of the nucleus where ribosomes are produced, the nucleolus (or nucleoli, plural), vanishes. This is a warning that it is getting ready for the nucleus to break down.
So, the correct answer is, ‘Early prophase’.

Additional information: Walther Flemming invented the word mitosis in 1882. The word was derived from the Greek word mitos, which means 'warp thread'. In 1878, Schleicher, or equational division invented in 1887 by August Weismann, introduced the term karyokinesis. The word prophase is a Greek word that means 'before phase’.
Cell division starts to form the mitotic spindle. The spindle fibers are made up of microtubules, they are the strong fibers that make the "skeleton" of the cell. Its role is to arrange the chromosomes during mitosis and transfer them around. When they pass apart, the spindle develops between the centrosomes.

Note: In both mitosis and meiosis of cell division, prophase is the first step. The two copies of identical chromosomes are repeated at interphase to form sister chromatids. Then, along with the endoplasmic reticulum, they enter the prophase and begin chromosome condensation and nucleolus disappearance.