M Phase Questions in English

(A) The image shows the $Anaphase$ stage of mitosis.
Key features observed are the presence of centrioles at the poles and the characteristic $V$-shaped or $J$-shaped chromosomes being pulled towards opposite poles.
Centrioles are present in animal cells but are absent in higher plant cells.
Therefore,the presence of centrioles indicates that this is an animal cell undergoing $Anaphase$.

(C) During metaphase,the nuclear envelope completely disintegrates,allowing the spindle fibers to interact with the chromosomes.
Chromosomes are at their most condensed state during this phase.
Chromosomes align at the equatorial plate of the cell.
Each metaphase chromosome consists of two sister chromatids held together by a centromere,not four. Therefore,the statement that they are made up of four sister chromatids is incorrect.

(A) During the process of cell division,the spindle fibers attach to the kinetochores of the chromosomes specifically during the $Metaphase$ stage. This attachment is crucial for the alignment of chromosomes at the equatorial plate (metaphase plate) before they are pulled apart in the subsequent $Anaphase$ stage.

(A) During mitosis,the spindle fibers are composed of microtubules that attach to the kinetochores of the chromosomes.
Their primary function is to pull the sister chromatids apart toward opposite poles of the cell during anaphase.
This ensures that each daughter cell receives an identical set of chromosomes.
Therefore,the correct function is to separate the chromosomes.

(B) In $S$-phase (Synthesis phase), $DNA$ replication occurs, but the number of chromosomes remains the same; only the amount of $DNA$ doubles.
In Metaphase, chromosomes align at the equatorial plate and are maximally condensed.
In Anaphase, the centromere of each chromosome splits, and chromatids separate to move towards opposite poles.
In Telophase, chromosomes decondense to form chromatin, and the nuclear envelope reforms.
Therefore, the correct match is $Anaphase - \text{Splitting of centromere}$.

(B) The process of mitosis is divided into four main stages: $Prophase$,$Metaphase$,$Anaphase$,and $Telophase$.
During $Prophase$,the chromatin condenses into chromosomes,and the nuclear envelope begins to break down.
By the end of $Prophase$ (or the transition to $Prometaphase$),the nuclear envelope completely disintegrates.
This event allows the spindle fibers to attach to the kinetochores of the chromosomes,marking the beginning of $Metaphase$ where chromosomes align at the equatorial plate.
Therefore,the complete disintegration of the nuclear envelope is the hallmark transition that leads into $Metaphase$.

(B) During the $S$ phase of interphase,$DNA$ replication occurs,resulting in the duplication of the genetic material.
Each chromosome,which consisted of a single chromatid before replication,now consists of two identical sister chromatids held together at the centromere.
Since prophase occurs after the $S$ phase and $G_2$ phase,each chromosome in the prophase stage contains $2$ sister chromatids.
Therefore,the correct answer is $2$.

(C) During $Anaphase$,the centromere of each chromosome splits,and the sister chromatids (now referred to as chromosomes of the daughter nuclei) separate.
These chromatids are then pulled towards the opposite poles of the cell by the shortening of spindle fibers attached to the kinetochores.
Therefore,the movement of chromatids to opposite poles is a characteristic feature of $Anaphase$.

(B) Free nuclear division, also known as $free nuclear mitosis$, is a process where the nucleus undergoes repeated divisions without being followed by cytokinesis (division of the cytoplasm).
This results in a multinucleated cell or a $coenocytic$ condition.
A classic example is the formation of the liquid endosperm in coconut, where the primary endosperm nucleus undergoes several rounds of free nuclear division.

(D) In mitosis,the $Anaphase$ stage is characterized by the splitting of the centromere of each chromosome,allowing the sister chromatids to separate. These separated chromatids,now referred to as daughter chromosomes,are pulled towards the opposite poles of the cell by the spindle fibers. Therefore,observing chromosomes at the opposite poles indicates that the cell is in the $Anaphase$ stage.