Cell Cycle Questions in English

(D) The cell cycle is divided into two main phases: Interphase and $M$-phase (Mitosis/Meiosis).
Interphase is further divided into three sub-phases: $G_1$ phase (Gap $1$),$S$ phase (Synthesis),and $G_2$ phase (Gap $2$).
$G_1$ is the first phase,followed by the $S$ phase,and finally the $G_2$ phase.
Therefore,the $G_2$ phase is the last phase of interphase before the cell enters the $M$-phase.

(D) The $G_0$ phase,also known as the quiescent stage,is a period in the cell cycle where cells exist in a quiescent state.
Cells in this stage remain metabolically active but do not proliferate unless called upon to do so depending on the requirement of the organism.
Therefore,it is often referred to as the inactive stage of cell division.

(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.
$G_1$ phase (Gap $1$) is the period between the end of mitosis ($M$ phase) and the beginning of $DNA$ replication ($S$ phase).
During this phase,the cell is metabolically active and continuously grows in size but does not replicate its $DNA$.

(C) The $G_0$ phase,also known as the quiescent stage,is a state where cells remain metabolically active but do not proliferate unless called upon to do so depending on the requirement of the organism.
In this phase,cells exit the cell cycle from the $G_1$ phase and enter an inactive stage.
They continue to perform their specific functions but do not undergo $DNA$ replication or division.

(D) The cell cycle is defined as the series of events that take place in a cell leading to its duplication and division.
It involves the replication of $DNA$ and the synthesis of other cell constituents,followed by the division of the cell into two daughter cells.
Option $D$ correctly describes this process as a series of events occurring inside the cell that result in cell division and duplication.

(A) Interphase is the phase between two successive $M$ phases. Although it is historically called the 'resting phase',it is actually a period of intense metabolic activity. During this phase,the cell prepares for division by replicating its $DNA$,synthesizing proteins,and accumulating the necessary components required for the subsequent cell division process.

(B) During the $S$ phase (Synthesis phase) of the cell cycle,the amount of $DNA$ per cell doubles.
In eukaryotic cells,including animal cells,$DNA$ replication occurs within the nucleus.
Simultaneously,the centriole pair,which is located in the cytoplasm near the nucleus,undergoes duplication to ensure proper spindle formation during mitosis.

(B) The cell cycle consists of two main phases: Interphase and $M$-phase (Mitosis).
Interphase is further divided into $G_1$,$S$,and $G_2$ phases.
$1$. $G_1$ phase (Gap $1$): The cell grows and prepares for $DNA$ replication.
$2$. $S$ phase (Synthesis): $DNA$ replication occurs,doubling the amount of $DNA$ per cell.
$3$. $G_2$ phase (Gap $2$): The cell prepares for mitosis by synthesizing proteins and organelles.
$4$. $M$-phase: The actual division of the nucleus and cytoplasm occurs.
Therefore,the statement that $DNA$ replication occurs in the $S$ phase is correct.

(A) The $S$ phase (Synthesis phase) is a critical stage of the cell cycle occurring during interphase. During this phase,$DNA$ replication takes place. As a result,the amount of $DNA$ per cell doubles,although the number of chromosomes remains the same (the sister chromatids are formed).

(C) In the cell cycle,the $S$ phase (Synthesis phase) is the period during which $DNA$ replication occurs.
During this phase,the amount of $DNA$ per cell doubles.
If the initial amount of $DNA$ is $2C$,it replicates during the $S$ phase to become $4C$.
Therefore,the amount of $DNA$ becomes $4C$ during the $S$ phase.

(B) The cell cycle consists of interphase and $M$ phase. Interphase is further divided into $G_1$,$S$,and $G_2$ phases.
During the $S$ phase (Synthesis phase),the replication of $DNA$ takes place.
Along with $DNA$ replication,the synthesis of histone proteins also occurs in the nucleus to package the newly synthesized $DNA$.
Therefore,the correct option is $B$.

(D) The cell cycle is a series of events that take place in a cell leading to its division and duplication of its $DNA$ to produce two daughter cells.
It is divided into two main phases: Interphase and $M$-phase (Mitosis).
Interphase is further divided into three sub-phases: $G_{1}$ phase (Gap $1$),$S$ phase (Synthesis),and $G_{2}$ phase (Gap $2$).
The sequence starts with $G_{1}$ phase,where the cell grows and prepares for $DNA$ replication.
This is followed by the $S$ phase,where $DNA$ replication occurs.
Next is the $G_{2}$ phase,where the cell prepares for mitosis.
Finally,the $M$ phase (Mitosis) occurs,where the cell divides.
Therefore,the correct sequence is $G_{1} \rightarrow S \rightarrow G_{2} \rightarrow M$.

(A) The $G_0$ phase,also known as the quiescent stage,is a state where cells exit the cell cycle.
In this phase,cells remain metabolically active but do not proliferate unless called upon to do so depending on the requirement of the organism.
Therefore,cells in the $G_0$ phase are considered to have exited the cell cycle.

(D) Previously,interphase was called the resting stage because there is no apparent morphological activity related to cell division.
However,the interphase cell is metabolically quite active.
Interphase consists of three subphases ($G_1$,$S$,and $G_2$).
Synthesis of $DNA$ occurs in the $S$ phase.
$G_1$ is the period between the end of mitosis and the start of the $S$ phase.
$G_2$ is the phase between the $S$ phase and the next mitosis.
As the synthesis of $DNA$ and proteins occurs during interphase,it is considered a metabolically active phase.
Therefore,the Assertion is incorrect because it is not a resting stage,and the Reason is incorrect because the cell is metabolically active.

(B) The average cell cycle span for a typical cultured mammalian cell is approximately $24$ hours.
This duration includes the interphase ($G_1$,$S$,and $G_2$ phases) and the $M$ phase (mitosis).

(N/A) Interphase involves a series of changes that prepare a cell for division. It is the period during which the cell experiences growth and $DNA$ replication in an orderly manner. Interphase is divided into three phases:
$G_{1}$ phase
$S$ phase
$G_{2}$ phase
$G_{1}$ phase: It is the stage during which the cell grows and prepares its $DNA$ for replication. In this phase,the cell is metabolically active.
$S$ phase: It is the stage during which $DNA$ synthesis occurs. In this phase,the amount of $DNA$ (per cell) doubles,but the chromosome number remains the same.
$G_{2}$ phase: In this phase,the cell continues to grow and prepares itself for division. The proteins and $RNA$ required for mitosis are synthesised during this stage.

(C) $G_{0}$ or quiescent phase is the stage wherein cells remain metabolically active,but do not proliferate unless called to do so.
Such cells are used for replacing the cells lost during injury or tissue damage.

(B) Mitotic cell division cannot take place without $DNA$ replication in the $S$ phase.
Two important events take place during the $S$ phase: one is the synthesis or duplication of $DNA$,and the other is the duplication of the centriole.
$DNA$ duplication is essential because it maintains the chromosome number in the daughter cells.
Mitosis is an equational division,meaning the chromosome number remains the same as the parent cell.
Therefore,the duplication of $DNA$ is a mandatory prerequisite for mitosis.

(A) Yes,there can be $DNA$ replication without cell division.
During normal cell division,the parent cell divides into two daughter cells.
However,if $DNA$ replication occurs repeatedly without subsequent cell division,the $DNA$ content accumulates within the nucleus.
This leads to an increase in the volume of the nucleus and the overall size of the cell.
$A$ classic example of this phenomenon is observed in the salivary glands of $Drosophila$ (fruit fly).
The chromosomes formed due to repeated $DNA$ replication without cell division are known as polytene chromosomes.

(N/A) $\Rightarrow$ Cell division is a very important process in all living organisms.
$\Rightarrow$ $DNA$ replication and cell growth take place during cell division.
$\Rightarrow$ All processes like cell division,$DNA$ replication,and cell growth must occur in a coordinated manner to ensure correct division and the formation of progeny cells containing intact genomes.
$\Rightarrow$ Cell Cycle: The sequence of events by which a cell duplicates its genome,synthesizes the other constituents of the cell,and eventually divides into two daughter cells is termed the cell cycle.
$\Rightarrow$ Although cell growth (in terms of cytoplasmic increase) is a continuous process,$DNA$ synthesis occurs only during one specific stage in the cell cycle.
$\Rightarrow$ The replicated chromosomes $(2n)$ $(DNA)$ are then distributed to daughter nuclei by a complex series of events during cell division.
$\Rightarrow$ These events are under genetic control.

(N/A) $ \Rightarrow $ $ A $ typical eukaryotic cell is illustrated by human cells in culture.
$ \Rightarrow $ The duration of the cell cycle can vary from organism to organism and also from cell type to cell type.
$ \Rightarrow $ $ A $ cell cycle is completed every $ 24 $ hours in human beings.
$ \Rightarrow $ Yeast can progress through the cell cycle in about $ 90 $ minutes.
$ \Rightarrow $ The cell cycle is divided into two basic phases:
$ (1) $ Interphase
$ (2) $ $ M $-Phase (Mitosis phase)
$ \Rightarrow $ The $ M $-Phase represents the phase when the actual cell division or mitosis occurs.
$ \Rightarrow $ The interphase represents the phase between two successive $ M $-phases.
$ \Rightarrow $ It is significant to note that in the $ 24 $ hours average duration of the cell cycle of a human cell, cell division lasts for only about an hour.
$ \Rightarrow $ The interphase lasts for more than $ 95\% $ of the duration of the cell cycle.
$ \Rightarrow $ The $ M $-Phase starts with nuclear division, corresponding to the separation of daughter chromosomes (Karyokinesis), and usually ends with the division of the cytoplasm (Cytokinesis).
$ \Rightarrow $ The interphase, though called the resting phase, is the time during which the cell is preparing for division by undergoing both cell growth and $ DNA $ replication in an orderly manner. It is further divided into $ G_1 $, $ S $, and $ G_2 $ phases.

(N/A) $\Rightarrow$ $G_{1}$ phase is the initial stage of interphase.
$\Rightarrow$ This phase corresponds to the interval between mitosis and the initiation of $DNA$ replication.
$\Rightarrow$ During the $G_{1}$ phase,necessary enzymes,$RNA$,and proteins are synthesized for the synthesis of $DNA$.
$\Rightarrow$ $DNA$ replication does not occur in this phase.
$\Rightarrow$ In the $G_{1}$ phase,cells are metabolically active and grow continuously.

(N/A) $\Rightarrow$ Some cells in adult animals do not appear to exhibit division (e.g.,heart cells,nerve cells),and many other cells divide only occasionally as needed to replace cells lost due to injury or cell death.
$\Rightarrow$ These cells that do not divide further exit the $G_{1}$ phase to enter an inactive stage called the quiescent stage $(G_{0})$ of the cell cycle.
$\Rightarrow$ Cells in this stage remain metabolically active but no longer proliferate unless called upon to do so,depending on the requirements of the organism.
$\Rightarrow$ Note: In animals,mitotic cell division is only seen in diploid somatic cells. Plants can show mitotic divisions in both haploid $(n)$ and diploid $(2n)$ cells.

(N/A) $(1)$ The sequence of events by which a cell duplicates its genome,synthesizes the other constituents of the cell,and eventually divides into two daughter cells is called the cell cycle.
$(2)$ Interphase is the phase between two successive $M$ phases. It is the period of preparation where the cell undergoes growth,$DNA$ replication,and synthesis of required materials for the subsequent cell division.

(C) $\Rightarrow$ Replication of $DNA$ takes place in the nucleus,and the doubling (duplication) of the centriole is seen in the cytoplasm.
Centrioles are cylindrical structures that form spindle fibers during cell division in animal cells,which control chromosomal movement.
The $DNA$ is contained within the nucleus,hence its replication occurs there,while centrioles are organelles located in the cytoplasm near the nucleus.

(A) Prokaryotic cells have a significantly shorter cell division time compared to eukaryotic cells.
For example,the bacterium $E. coli$ can divide in approximately $20$ minutes under optimal conditions.
In contrast,typical eukaryotic cells,such as those in humans,take about $24$ hours to complete a cell cycle.
Therefore,prokaryotes exhibit a much faster rate of cell division.

(D) The cell cycle is divided into two main phases: $Interphase$ and $M$ phase (Mitosis/Meiosis).
$Interphase$ is the phase during which the cell prepares for division by growing and replicating its $DNA$.
It occupies more than $95\%$ of the total duration of the cell cycle.
Therefore, $Interphase$ is the longest phase of the cell cycle.

(A) chromatid is a single $DNA$ molecule that forms one-half of a duplicated chromosome.
During the cell cycle,specifically after $DNA$ replication,two identical chromatids are joined together at a region called the centromere.
Once these chromatids separate during cell division (such as in anaphase),each individual chromatid is then independently referred to as a chromosome.
Therefore,the primary attribute required for a chromatid to be classified as a chromosome is the presence of its own functional centromere,which allows it to be moved by spindle fibers.

(B) $DNA$ synthesis occurs during the $S$ (synthetic) phase of the interphase of the cell cycle.
During this phase,the amount of $DNA$ per cell doubles,although the chromosome number remains the same.

(A) The total duration of the cell cycle in human cells is approximately $24$ hours.
Interphase is the phase of the cell cycle during which the cell prepares for division by growing and replicating its $DNA$.
It is the longest phase of the cell cycle,occupying about $95 \%$ of the total time.
Therefore,the correct answer is Interphase.

(A) Heart cells are specialized cells that do not undergo further division once they reach maturity.
These cells exit the $G_{1}$ phase of the cell cycle and enter an inactive stage known as the $G_{0}$ phase (also called the quiescent stage).
In the $G_{0}$ phase,cells remain metabolically active but do not proliferate unless called upon to do so by specific signals.

(D) The $G_{1}$ phase,also known as the first gap phase,is the interval between mitosis and the initiation of $DNA$ replication. During this phase,the cell is metabolically active and continuously grows in size,but it does not replicate its $DNA$.

(B) Cells that do not divide further exit the $G_{1}$ phase to enter an inactive stage called the quiescent stage $(G_{0})$ of the cell cycle.
In this stage,cells remain metabolically active but no longer proliferate unless called upon to do so depending on the requirement of the organism.

(C) The cell cycle is divided into two main phases: Interphase and $M$-phase.
Interphase is further divided into $G_1$ phase,$S$ phase,and $G_2$ phase.
In the $G_1$ phase (Gap $1$),the cell is metabolically active and continuously grows in size.
However,$DNA$ replication does not occur during this phase; $DNA$ replication takes place specifically during the $S$ phase (Synthesis phase).
Therefore,the correct statement is that the cell is metabolically active and grows,but does not replicate its $DNA$.

(D) The cell cycle consists of the $G_{1}$ phase,$S$ phase,$G_{2}$ phase,and $M$ phase.
Cells that do not divide further exit the $G_{1}$ phase to enter an inactive stage called the quiescent stage $(G_{0})$.
Therefore,the $G_{0}$ stage occurs at the end of the $G_{1}$ phase.

(B) The formation of tissues from a single cell (like a zygote) requires two fundamental processes: cell division (to increase the number of cells) and cell differentiation (where cells specialize to perform specific functions). Among the given options,cell division is the primary and essential process that provides the necessary cellular mass for tissue formation.

(C) The cell cycle is divided into two main phases: Interphase and $M$-phase (Mitosis).
Interphase is further subdivided into three stages: $G_{1}$ phase (Gap $1$),$S$ phase (Synthesis),and $G_{2}$ phase (Gap $2$).
Following Interphase,the cell enters the $M$-phase.
Therefore,the correct sequence is $G_{1} \rightarrow S \rightarrow G_{2} \rightarrow M$.

(B) The $G_{1}$-phase is the first gap phase of the cell cycle,occurring before the $S$-phase (Synthesis phase).
During the $S$-phase,$DNA$ replication occurs,which doubles the amount of $DNA$ per cell,but the number of chromosomes remains the same.
Since the cell has $14$ chromosomes during interphase,and the $G_{1}$-phase is a part of interphase,the number of chromosomes remains $14$ in the $G_{1}$-phase.
The chromosome number only changes during the $M$-phase (Mitosis or Meiosis) when sister chromatids or homologous chromosomes separate.

(B) $G_{1}$-phase is known as the pre-synthetic phase or post-mitotic phase.
It is the longest phase of the cell cycle.
During the $G_{1}$-phase,the cell undergoes metabolic activities,grows in size,and performs its normal physiological functions.
After this phase,the cell has two options:
$1.$ It continues the cell cycle and enters the $S$-phase for $DNA$ replication.
$2.$ It stops the cell cycle and enters the $G_{0}$-phase (quiescent stage) for differentiation or to remain metabolically active without dividing.

(C) Cells that do not divide further do not proceed beyond the $G_{1}$ phase. Instead,they exit the cell cycle and enter an inactive stage called the quiescent stage or $G_{0}$ phase. In this stage,cells remain metabolically active but do not proliferate unless called upon to do so,often undergoing differentiation to perform specific functions in the organism.

(B) During the $S$-phase (Synthesis phase) of the cell cycle,$DNA$ replication occurs,which doubles the amount of $DNA$ per chromosome.
In the $G_{1}$-phase,each chromosome consists of a single chromatid (one $DNA$ molecule).
After $DNA$ replication in the $S$-phase,each chromosome consists of two sister chromatids,each containing one $DNA$ molecule.
Therefore,at the $G_{2}$-stage,each chromosome contains two $DNA$ strands (chromatids) held together by a centromere.

(D) Some cells in adult animals do not appear to exhibit division (e.g.,nerve cells,heart cells). Many other cells divide only occasionally,for example,when there is a need to replace cells that have been lost due to injury or cell death.
These cells that do not divide further exit the $G_{1}$-phase to enter an inactive stage called the quiescent stage $(G_{0})$ of the cell cycle.
Cells in this stage remain metabolically active but no longer proliferate.

(C) The synthesis phase or $S-$phase is the period in the cell cycle during which $DNA$ replication occurs.
During this phase,the amount of $DNA$ per cell doubles,but the chromosome number remains the same.
Additionally,the synthesis of histone proteins occurs in this phase,and each chromosome consists of two sister chromatids.

(C) Mitosis results in two daughter cells,each having the same number of chromosomes as the parent cell. If the cell has $12$ chromosomes at the end of mitosis,it means the diploid number $(2n)$ is $12$.
During the $S$-phase of the next cell cycle,the $DNA$ content doubles,but the number of chromosomes remains the same.
In the $G_{2}$-phase,the cell still contains the same number of chromosomes as it did after mitosis,although each chromosome now consists of two sister chromatids.
Therefore,the number of chromosomes in the $G_{2}$-phase remains $12$.

(B) $DNA$ replication occurs only once during the $S$-phase (Synthesis phase) of the cell cycle. This ensures that the genetic material is duplicated exactly once before the cell undergoes division,whether it is mitosis or meiosis.

(C) The $G_{0}$ phase,also known as the quiescent stage,is a state where cells exit the cell cycle.
During this phase,cells remain metabolically active,meaning they continue to perform essential cellular functions such as protein synthesis and respiration.
However,they do not undergo further division or proliferation unless called upon to do so by specific signals in response to injury or other physiological requirements.

(D) $G_{1}$-phase corresponds to the interval between mitosis and the initiation of $DNA$ replication.
During the $G_{1}$-phase,the cell is metabolically active and continuously grows in size,but it does not replicate its $DNA$.
Therefore,the amount of $DNA$ remains the same as it was at the end of the previous cell division.

(A) The cell cycle is divided into two main phases: Interphase and $M$-phase (Mitosis).
Interphase consists of three sub-phases: $G_{1}$ (Gap $1$),$S$ (Synthesis),and $G_{2}$ (Gap $2$).
Following Interphase,the cell enters the $M$-phase.
Therefore,the correct chronological sequence is $G_{1} \rightarrow S \rightarrow G_{2} \rightarrow M$.

(A) During the $S$-phase (Synthesis phase) of the cell cycle,$DNA$ replication occurs.
Although the amount of $DNA$ per cell doubles (from $2C$ to $4C$),the number of chromosomes remains the same.
This is because the sister chromatids remain attached at the centromere.
If a cell has $2n$ chromosomes at the $G_1$ phase,it will still have $2n$ chromosomes after the $S$-phase.