Free Cell Cycle And Cell Division (Daily Quiz: 7) NEET Biology Questions & Answers with Detailed Explanation & Full Review

Answer: (b)

Spindle is microtubular apparatus that appears in many eukaryotic cells at the beginning of nuclear division and is responsible for the ordered separation of the chromosomes, chromosomes being attached to the spindle fibres by their centromeres. Two types of spindle fibres can be distinguished as the interpolar fibre, which stretches continuously from pole to pole of the spindle; the kinetochore fibre, which stretches from the pole to the centromere (kinetochore) of an individual chromosome. The mechanism by which the chromosomes move and the spindle fibres contract remains unclear. Cells of animals and lower plants possess centrioles, which act as organizer regions for spindle microtubule formation, but centrioles are absent from the cells of higher plants.

Answer: (a)

Prophase is the stage of mitosis in which the following events takes place like,

(i) The nucleolus disappears.

(ii) In the cytoplasm, the mitotic spindle, consisting of microtubules and other proteins, forms between the two pairs of centrioles as they migrate to opposite poles of the cell.

(iii) The nuclear envelope disappears at the end of prophase. Which indicates the beginning of the sub-stage called prometaphase.

(iv) Chromosomes become more coiled and can be viewed under a light microscope.

(v) Each duplicated chromosome is seen as a pair of sister chromatids joined by the duplicated but unseparated centromere.