M Phase Questions in English

(B) The $M-$phase (Mitosis phase) is the phase where the actual cell division occurs.
It consists of four main stages: Prophase,Metaphase,Anaphase,and Telophase.
These stages collectively ensure the equal distribution of chromosomes into the daughter cells.
Interphase $(G_1, S, G_2)$ is the preparatory phase before the $M-$phase,not a part of it.

(A) During cell division,specifically in metaphase,spindle fibers are categorized based on their attachment.
$1$. Chromosomal fibers (also called kinetochore fibers or tractile fibers) extend from the spindle poles and attach directly to the kinetochores of the chromosomes.
$2$. Continuous fibers (or non-kinetochore fibers) extend from pole to pole without attaching to chromosomes.
$3$. Interzonal fibers are found between the separating chromosomes during anaphase.
Therefore,the fibers extending from the pole to the kinetochore are called chromosomal or tractile fibers.

(A) The centromere is a specialized $DNA$ sequence of a chromosome that links a pair of sister chromatids. During cell division,the kinetochore,which is a protein complex,assembles on the centromere. Spindle fibers attach to these kinetochores to pull the sister chromatids towards opposite poles during anaphase. Therefore,the centromere is essential for the movement of chromosomes towards the poles.

(A) During the process of mitosis,the nuclear envelope,nucleolus,Golgi complex,and endoplasmic reticulum disappear at the end of prophase,which is known as late prophase. This allows the spindle fibers to interact with the chromosomes.

(D) During $Anaphase$,the centromere of each chromosome splits,and the chromatids separate.
These separated chromatids,now referred to as daughter chromosomes,move towards opposite poles.
This movement is primarily driven by the shortening of spindle fibers (microtubules) attached to the $Kinetochore$ of the chromosomes.
Therefore,the interaction between the $Kinetochore$ and the spindle fibers is responsible for the chromosomal movement.

(B) During mitosis,the $Anaphase$ stage is characterized by the splitting of the centromere of each chromosome.
This process allows the two sister chromatids to separate.
Once separated,these chromatids are referred to as daughter chromosomes.
These chromosomes then begin to move towards opposite poles of the cell.

(C) During the anaphase stage of cell division,chromosomes split at the centromere and the sister chromatids move towards opposite poles.
Metacentric chromosomes have the centromere in the middle,which results in the formation of two equal arms.
As these chromosomes are pulled towards the poles by spindle fibers,they appear $V$-shaped due to the central position of the centromere.

(D) During $Telophase$,the chromosomes cluster at opposite spindle poles and their identity is lost as discrete elements. The nuclear envelope assembles around the chromosome clusters to form two daughter nuclei. Thus,the nuclear envelope reappears during $Telophase$.

(D) Telophase is the final stage of mitosis. During this phase,the following events take place:
$1$. The chromosomes cluster at opposite spindle poles and their identity is lost as discrete elements.
$2$. The nuclear envelope assembles around the chromosome clusters.
$3$. Nucleolus,Golgi complex,and endoplasmic reticulum reform.
$4$. Spindle fibers depolymerize and disappear.
Therefore,all the given options are correct.

(B) The process of mitosis is divided into four main stages: Prophase, Metaphase, Anaphase, and Telophase.
During $Prophase$, chromatin condenses into visible chromosomes.
During $Metaphase$, the chromosomes align themselves at the $equatorial \text{ } plate$ (also known as the metaphase plate) of the cell.
During $Anaphase$, the sister chromatids separate and move towards opposite poles.
During $Telophase$, the chromosomes arrive at the poles and decondense, and the nuclear envelope reforms.
Therefore, the correct stage is $Metaphase$.

(D) The cell cycle is divided into two main phases: Interphase and $M$-phase (Mitosis).
Interphase is further divided into $G_1$,$S$,and $G_2$ phases.
During the $G_1$ phase,the cell grows and performs metabolic activities.
The $S$ phase is dedicated to $DNA$ replication.
The $G_2$ phase is the second growth phase where the cell continues to grow,synthesizes necessary proteins (like tubulin for spindle fibers),and accumulates energy in the form of $ATP$ to prepare for the energy-intensive process of mitosis.
Therefore,the synthesis and storage of $ATP$ molecules required for cell division occur in the $G_2$ phase.

(A) During $Metaphase$,the chromosomes align themselves at the equator of the cell to form an equatorial plate,also known as the $Metaphase$ plate.
This alignment is facilitated by the attachment of spindle fibers to the kinetochores of the chromosomes.
Therefore,the correct phase is $Metaphase$.

(B) During $Anaphase$,the centromere of each chromosome splits,and the chromatids separate. These chromatids,now referred to as daughter chromosomes,are pulled towards opposite poles by spindle fibers attached to the kinetochores. As they move,the centromere leads the way,causing the chromosomes to take on characteristic shapes such as $V, J, L,$ or $I$ depending on the position of the centromere.

(A) During the $S$-phase of interphase, $DNA$ replication occurs, resulting in each chromosome consisting of two sister chromatids joined at the centromere.
In $Prophase$, the chromosomes condense and remain as two chromatids.
In $Metaphase$, the chromosomes align at the equatorial plate, still consisting of two chromatids.
In $Anaphase$, the centromeres split, and the sister chromatids separate, becoming individual daughter chromosomes.
Therefore, chromosomes consist of two chromatids during $Prophase$ and $Metaphase$.

(A) During the $M$ phase of the cell cycle,specifically during $Prophase$,the chromatin material condenses to form compact mitotic chromosomes.
This condensation process is essential for the orderly separation of chromosomes during cell division.
While condensation begins in $Prophase$,the chromosomes reach their maximum level of condensation during $Metaphase$,making them most visible under a microscope.
However,in the context of the initiation of condensation,$Prophase$ is the correct phase where the process begins and chromosomes become distinct.

(C) The cell cycle consists of $G_1$,$S$,$G_2$,and $M$ phases.
During the $G_2-$ phase (Gap $2$ phase),the cell continues to grow and synthesizes essential proteins,such as tubulin,which are required for the formation of spindle fibers during mitosis ($M-$ phase).
Therefore,the correct answer is $G_2-$ phase.

(B) During the process of cell division,specifically in the anaphase stage,the movement of chromosomes towards opposite poles is facilitated by the shortening of kinetochore microtubules.
This movement is an energy-dependent process.
Experimental studies and biophysical calculations regarding the movement of chromosomes at a velocity of $1 \mu m/min$ indicate that the energy consumption is approximately $30 \, ATP$ molecules per chromosome per minute.
Therefore,the correct option is $B$.

(B) During the $Metaphase$ stage of mitosis,the chromosomes align at the equatorial plate (metaphase plate).
At this stage,the chromosomes are most condensed and clearly visible under a microscope.
Therefore,$Metaphase$ is the best stage to study the morphology of chromosomes and to count them accurately.

(D) During cell division in eukaryotic cells,the spindle apparatus is composed of two main types of spindle fibers:
$1$. Kinetochore microtubules (chromosomal fibers): These attach to the kinetochores of the chromosomes.
$2$. Polar microtubules (non-kinetochore or continuous fibers): These extend from the poles toward the equator but do not attach to chromosomes; they overlap in the center to maintain the shape of the spindle.
Therefore,there are $2$ types of spindle fibers.

(C) Spindle microtubules are primarily composed of the protein tubulin. Specifically,they consist of approximately $95-97\%$ tubulin protein and a small amount of $3-5\% RNA$. These microtubules are essential for the formation of the spindle apparatus during cell division,which facilitates the movement and segregation of chromosomes.

(A) The process of cell division involves several stages.
During the $Prophase$ stage of mitosis,the chromatin material condenses to form compact mitotic chromosomes.
Simultaneously,the centrosomes,which had duplicated during the $S$ phase,begin to move towards opposite poles of the cell.
The radiating microtubules from the centrosomes form structures known as asters.
Therefore,both chromosome condensation and the appearance of asters are characteristic events of $Prophase$.

(D) Colchicine is an alkaloid that acts as a mitotic poison by inhibiting the polymerization of tubulin protein into microtubules.
Since microtubules are essential for the formation of the spindle apparatus during cell division,their absence prevents the chromosomes from aligning at the equatorial plate.
Consequently,the cell is arrested at the metaphase stage of mitosis.

(B) During telophase,the chromosomes decondense and the nuclear envelope reforms around the chromatin.
Simultaneously,the nucleolus,Golgi complex,and endoplasmic reticulum reform.
The nucleolus is specifically organized at the nucleolar organizer region $(NOR)$,which is located at the secondary constriction-$II$ of certain chromosomes.
Therefore,the secondary constriction-$II$ is responsible for the reformation of the nucleolus.

(A) The term 'Mitosis' was coined by the German biologist $Walther \ Flemming$ in $1882$. He was the first to describe the process of cell division in detail and observed the behavior of chromosomes during this process.

(D) During mitosis,the $S$ phase of interphase involves $DNA$ replication,which doubles the amount of $DNA$ per cell. However,the cell remains diploid $(2n)$ because the number of chromosomes does not change. During $Anaphase$,the sister chromatids separate and move toward opposite poles. At this specific moment,each chromatid is considered an individual chromosome. Consequently,the cell temporarily contains double the number of chromosomes $(4n)$ before the cytoplasm divides during cytokinesis. Therefore,the cell becomes tetraploid during $Anaphase$.

(B) During the $Metaphase$ stage of mitosis,the chromosomes align at the equatorial plate (metaphase plate).
At this stage,the chromosomes are most condensed and clearly visible under a light microscope.
Therefore,$Metaphase$ is the best stage to study the morphology of chromosomes.

(A) During the process of cell division,the metabolic activity of the cell decreases significantly as the cell enters the $M$ phase (mitosis).
Specifically,during prophase,the cell focuses on chromatin condensation and the breakdown of the nuclear envelope,leading to a reduction in metabolic rate.
As the cell reaches telophase,the chromosomes decondense,the nuclear envelope reforms,and the cell prepares to return to its normal metabolic state.
Therefore,the metabolic rate begins to increase again during telophase as the cell transitions toward interphase.

(C) During $Anaphase$,the centromere of each chromosome splits,and the chromatids separate.
These separated chromatids,now referred to as daughter chromosomes,begin to move towards opposite poles of the cell.
Therefore,the splitting of the centromere is a characteristic event of $Anaphase$.

(A) During prophase,the chromatin material condenses to form compact mitotic chromosomes. This process of condensation involves the dehydration of chromatin fibers,which makes them visible under a microscope. Simultaneously,the nucleolus and nuclear envelope begin to disintegrate and eventually disappear. Therefore,the hydration of chromatin does not occur; instead,dehydration is a key event.

(C) Mitosis is divided into four main stages: Prophase,Metaphase,Anaphase,and Telophase.
$1$. Prophase is the longest phase of mitosis.
$2$. Anaphase is the shortest phase of mitosis because it involves the rapid separation of sister chromatids towards opposite poles of the cell.
Therefore,the correct answer is $Anaphase$.

(C) Colchicine is an alkaloid that acts as a mitotic poison. It binds to the protein tubulin,thereby preventing the polymerization of microtubules. Since the formation of the spindle apparatus is essential for the alignment of chromosomes at the equatorial plate during metaphase,colchicine effectively arrests the cell cycle at the $Metaphase$ stage. This property is often used in laboratories to induce polyploidy.

(A) The separation of chromosomes during mitosis (specifically anaphase) involves dynamic movements of living structures within the cell.
$1$. $A$ phase contrast microscope is ideal for observing living,unstained cells because it converts phase shifts in light passing through a transparent specimen into brightness changes in the image.
$2$. $TEM$ (Transmission Electron Microscope) and $SEM$ (Scanning Electron Microscope) require fixed,dehydrated,and often metal-coated specimens,making them unsuitable for observing dynamic processes in living cells.
$3$. $X$-ray diffraction is used for determining the molecular structure of crystals,not for observing cellular division processes.
Therefore,the phase contrast microscope is the best choice for studying chromosome separation in living cells.

(C) Interzonal fibers (also known as interzonal microtubules) are a set of spindle fibers that appear between the separating chromosomes during $Anaphase$ of mitosis or meiosis.
These fibers help in the elongation of the cell and ensure the proper separation of chromatids towards opposite poles.

(A) During mitosis,the spindle apparatus is formed by microtubules that extend between the two poles of the cell.
These fibers originate from the centrosomes located at opposite ends of the cell,creating a bipolar structure.
Therefore,the spindle fibers in mitosis are described as bipolar.

(B) In the cell cycle,the $G_1$-phase represents the initial diploid state with $2C$ amount of $DNA$.
During the $S$-phase (Synthesis phase),$DNA$ replication occurs,doubling the amount of $DNA$ from $2C$ to $4C$.
The $G_2$-phase follows the $S$-phase,where the cell maintains the $4C$ amount of $DNA$ before entering mitosis.
$A$ tetraploid cell $(4n)$ also contains $4C$ amount of $DNA$.
Therefore,the amount of $DNA$ in a diploid cell during the $G_2$-phase is equivalent to that of a tetraploid cell.

(B) The morphology of chromosomes is best studied during the $Metaphase$ stage of mitosis. During this stage,chromosomes are most condensed and align at the equatorial plate,making them clearly visible under a microscope.

(D) During the prophase stage of mitosis,the chromatin condenses into chromosomes. Simultaneously,the nuclear envelope and the nucleolus begin to disintegrate and disappear to allow the spindle fibers to interact with the chromosomes. Therefore,both the nuclear envelope and the nucleolus disappear during the early stages of mitosis.

(B) During mitosis, the condensation of chromatin material into compact mitotic chromosomes occurs progressively.
By the end of prophase, chromosomes are clearly visible.
However, the $Metaphase$ stage is characterized by the alignment of chromosomes at the equatorial plate, where they reach their maximum degree of condensation.
This high level of condensation makes chromosomes distinct and easy to study under a microscope during this phase.

(D) In the $Prophase$ stage of mitosis,the following events occur:
$1$. The chromatin material condenses to form compact mitotic chromosomes.
$2$. The nuclear envelope and the nucleolus begin to disintegrate and disappear.
$3$. The centrosomes move towards opposite poles of the cell.
Therefore,the disappearance of the nuclear envelope and nucleolus,along with chromosome condensation,is a hallmark of $Prophase$.

(C) During cell division (specifically in mitosis and meiosis),the movement of chromosomes towards opposite poles is facilitated by the spindle apparatus.
This spindle apparatus is primarily composed of microtubules,which are protein filaments that form the spindle fibers.
The kinetochore microtubules attach to the kinetochores of the chromosomes and,through depolymerization,pull the sister chromatids or homologous chromosomes towards the opposite poles of the cell.

(D) During the $Prophase$ stage of mitosis,the centrosomes,which had duplicated during the $S$-phase of interphase,begin to move towards opposite poles of the cell.
This movement is facilitated by the polymerization of microtubules,which form the mitotic spindle apparatus.
Therefore,the correct answer is $Prophase$.

(B) The kinetochore is a complex protein structure that assembles on the centromere of a chromosome during cell division.
It appears as a disc-shaped structure on the sides of the centromere.
The kinetochore serves as the site where spindle fibers (microtubules) attach to the chromosomes to facilitate their movement during mitosis and meiosis.
Therefore,option $B$ is the correct description.

(A) Microtubules are the primary components of the spindle apparatus formed during cell division (mitosis and meiosis).
They are responsible for the attachment to the kinetochores of chromosomes and their subsequent movement towards the opposite poles of the cell.
Microfilaments and intermediate filaments are primarily involved in maintaining cell shape and motility,while the endoplasmic reticulum is involved in protein and lipid synthesis.

(B) The shape of chromosomes is best observed during $Metaphase$ because the chromosomes are most condensed and aligned at the equatorial plate. However, if the question refers to the study of chromosome morphology (shape and size), $Metaphase$ is the standard answer. If the question specifically asks for the stage where the shape (e.g., $V$, $L$, $J$, or $I$ shape) is clearly visible due to the movement of chromosomes towards poles, $Anaphase$ is often cited. Given the standard biological context for observing chromosome morphology, $Metaphase$ is the most appropriate stage.

(B) During $Metaphase$, the chromosomes are highly condensed and align at the equatorial plate of the cell. This stage is the best time to study the morphology and structure of chromosomes because they are at their maximum level of condensation, making them clearly visible under a microscope.

(C) The $G_2$ phase (Gap $2$ phase) is the second growth phase of the cell cycle,occurring after $S$ phase and before mitosis ($M$ phase).
During the $G_2$ phase,the cell continues to grow,synthesizes proteins (such as tubulin for spindle fibers),and prepares for cell division.
$DNA$ replication occurs exclusively during the $S$ phase (Synthesis phase) of the cell cycle,not during the $G_2$ phase.
Therefore,the statement that $DNA$ replication occurs in the $G_2$ phase is incorrect.

(A) The cell cycle is divided into two main phases: Interphase and $M$ phase (Mitosis).
Interphase is further divided into three sub-phases: $G_1$ phase,$S$ phase,and $G_2$ phase.
The sequence of the cell cycle is $G_1 \rightarrow S \rightarrow G_2 \rightarrow M$.
Therefore,the cell enters the $M$ phase (mitosis) immediately after completing the $G_2$ phase.

(D) The $S$ phase (Synthesis phase) is the period during the cell cycle when $DNA$ replication occurs.
During this phase,the amount of $DNA$ per cell doubles,and each chromosome is duplicated,resulting in two sister chromatids held together at the centromere.
Protein synthesis (specifically histone proteins) also occurs during this phase to package the newly synthesized $DNA$.
However,the separation of chromatids from each chromosome occurs during the Anaphase stage of Mitosis,not during the $S$ phase.
Therefore,option $D$ is not applicable to the $S$ phase.

(D) During the $G_2$ phase (Gap $2$ phase) of the cell cycle,the cell continues to grow and synthesizes various proteins and organelles required for the process of mitosis. Specifically,it synthesizes tubulin proteins,which are essential for the formation of microtubules that make up the spindle apparatus during cell division. $DNA$ replication occurs exclusively during the $S$ phase,not the $G_2$ phase.

(C) The $M$ phase (Mitosis phase) is the phase where the actual cell division occurs.
It consists of two major discrete events:
$1$. Karyokinesis: The division of the nucleus into two daughter nuclei.
$2$. Cytokinesis: The division of the cytoplasm to form two daughter cells.
Therefore,the correct option is $C$.