Cell Cycle Questions in English

(B) The correct answer is $G_{0}$-phase.
Some cells in the adult animal do not appear to exhibit division (e.g.,heart cells) and many other cells divide only occasionally,as needed to replace cells that have been lost because of 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 $G_{0}$ stage remain metabolically active but no longer proliferate unless called on to do so,depending on the requirement of the organism.

(C) The cell cycle is divided into two basic phases:
$(i)$ Interphase
$(ii)$ $M$-phase (mitosis phase)
The interphase is further divided into three phases:
$(i)$ $G_{1}$-phase (Gap $1$)
$(ii)$ $S$-phase (Synthesis)
$(iii)$ $G_{2}$-phase (Gap $2$)
The correct sequence of a cell cycle is $G_{1} \rightarrow S \rightarrow G_{2} \rightarrow M$.

(C) Interphase is the phase of the cell cycle between two successive $M$-phases. It is a period of intense metabolic activity and growth.
Interphase is divided into three sub-phases:
$1$. $G_{1}$-phase (First Gap phase): The cell grows and performs normal metabolic functions.
$2$. $S$-phase (Synthesis phase): $DNA$ replication occurs.
$3$. $G_{2}$-phase (Second Gap phase): The cell prepares for mitosis by synthesizing proteins and organelles.
Therefore,the correct sequence is $G_{1}$-phase,$S$-phase,and $G_{2}$-phase.

(B) The cell cycle was described by Howard and Pelc in $1953$.
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 as the cell cycle.

(A) The cell cycle is divided into two main phases: Interphase and $M$-phase (Mitosis). Interphase is further divided into $G_{1}$ phase,$S$ phase,and $G_{2}$ phase.
Some cells in the adult animals do not appear to exhibit division (e.g.,heart cells) and many other cells divide only occasionally,as needed to replace cells that have been lost because of injury or cell death. These cells that do not divide further exit $G_{1}$ phase to enter an inactive stage called quiescent stage $(G_{0})$ of the cell cycle.
Based on the provided diagram:
$A$ represents the quiescent stage $(G_{0})$,
$B$ represents the $G_{1}$ phase,
$C$ represents the $S$ phase,
$D$ represents the $G_{2}$ phase.
Therefore,the correct sequence is $A=G_{0}, B=G_{1}, C=S, D=G_{2}$.

(C) The interphase is also called the resting phase.
It is the period during which the cell prepares for division by undergoing cell growth and $DNA$ replication in an orderly manner.

(A) During the $G_{1}$-phase of the cell cycle,the cell prepares for $DNA$ replication by synthesizing various biochemicals.
These include $RNAs$,regulatory proteins,and essential enzymes such as $DNA$ polymerase,which are required for the subsequent $S$-phase.
Histone proteins are synthesized during the $S$-phase along with $DNA$ replication.
Tubulin proteins are primarily synthesized during the $G_{2}$-phase to facilitate spindle fiber formation.

(B) During interphase,the chromosome material ($DNA$ of chromosome) replicates and becomes doubled.
Chromosome material in the form of very loosely coiled threads is called chromatin.

(D) $S$-phase is the sub-phase between $G_{1}$-phase and $G_{2}$-phase,during which $DNA$ synthesis or replication takes place.
In animal cells,during the $S$-phase,$DNA$ replication begins in the nucleus and centriole duplication occurs in the cytoplasm.
The amount of $DNA$ per cell doubles in the nucleus. If the initial amount of $DNA$ is denoted as $2C$,it increases to $4C$.
However,there is no increase in the chromosome number; the number of chromosomes remains the same as it was in the $G_{1}$-phase.
Therefore,statements $I, II,$ and $III$ are correct,while statement $IV$ is incorrect.

(B) The $G_{1}$-phase (Gap $1$) is the first phase of interphase,not the last. Therefore,statement $I$ is incorrect.
During the $G_{1}$-phase,the cell is metabolically active and continuously grows. Cell organelles increase in number,so statement $II$ is incorrect.
The cell grows in size and content,making statement $III$ correct.
In this phase,the cell synthesizes $RNAs$,proteins,and other biochemicals required for cell growth and the subsequent replication of $DNA$ in the $S$-phase. Thus,statement $IV$ is correct.
Since statements $III$ and $IV$ are correct,the correct option is $B$.

(A) The provided diagram shows a cell with a distinct nuclear envelope,a prominent nucleolus,and chromatin material in the form of a network of threads. The centrioles are present outside the nucleus. These features are characteristic of the interphase stage of the cell cycle,specifically the $G_2$ phase,where the cell prepares for division. During this period,the $DNA$ of chromosomes replicates. Chromosome material is in the form of very loosely coiled threads called chromatin. Centrioles have already replicated.

(C) The cell cycle is regulated by enzymes known as cyclin-dependent kinases $(CdKs)$.
$CdKs$ phosphorylate specific amino acids, such as serine and threonine, which either initiate or inhibit activities related to the cell cycle.
Key checkpoints in the cell cycle include:
$1.$ The $G_{1}$ checkpoint (entry into the $S$ or synthesis phase) is controlled by $CdK_{4} / \text{Cyclin } D$ and $CdK_{6} / \text{Cyclin } D$.
$2.$ The $G_{2}$ checkpoint (entry into the $M$ phase or maturation-promoting factor) is controlled by $CdK_{2} / \text{Cyclin } B$.
$3.$ The metaphase checkpoint is controlled by the degradation of $\text{Cyclin } B$.

(C) The sequence of events by which a cell duplicates its genome, synthesizes other constituents of the cell, and eventually divides into two daughter cells is termed the $Cell \ cycle$.
$A$. $Quiescent \ stage$ ($G_0$ phase): In this phase, cells remain metabolically active but do not proliferate unless called upon to do so.
$B$. $Generation \ time$: The time taken by a cell to complete one cell cycle, i.e., the time required for the number of cells to double.
$C$. $Cell \ cycle$: The correct term for the entire process of genome duplication and cell division.
$D$. $Kinetochore$: $A$ trilamellar proteinaceous structure present at the centromere, which serves as the attachment site for spindle fibers.

(A) $DNA$ replication occurs during the $S$ phase (Synthesis phase) of the cell cycle.
$G_{1}$ phase: In this phase,the cell grows and organelles duplicate.
$S$ phase: $DNA$ replication and histone protein synthesis occur.
$G_{2}$ phase: Tubulin protein synthesis and preparation for mitosis occur.
$M$ phase: Mitotic phase where cell division takes place.

(C) The cell cycle is divided into two main phases: the $M$ phase (Mitosis) and the Interphase.
Interphase is the period between two successive $M$ phases.
During Interphase,the cell prepares for division by undergoing growth,$DNA$ replication,and protein synthesis.
Therefore,the phase between two successive $M$ phases is known as Interphase.

(A) The biosynthetic phase is the $G_1$ phase,$S$ phase,and $G_2$ phase,which collectively constitute the $Interphase$.
During $Interphase$,the cell prepares for division by synthesizing proteins,replicating $DNA$,and duplicating cell organelles.
$Prophase$: Chromatin condenses into chromosomes.
$Anaphase$: Centromeres split and sister chromatids separate.
$Metaphase$: Chromosomes align at the equatorial plate.

(B) The cell cycle is the series of events that take place in a cell leading to its division and duplication of its $DNA$ to produce two daughter cells.
In the case of yeast $(Saccharomyces \text{ } cerevisiae)$, the entire cell cycle is completed in approximately $90$ minutes under optimal growth conditions.

(D) Interphase is considered the most active stage of the cell cycle because the cell undergoes intense metabolic activity,$DNA$ replication,and synthesis of proteins and organelles to prepare itself for cell division. During this phase,the cell grows in size and duplicates its genetic material,which is essential for the subsequent division phases.

(B) Interphase is known as the resting phase because,although the cell is metabolically very active and undergoes growth,there is no visible or apparent activity related to the actual process of cell division (mitosis or meiosis) during this stage. The cell is preparing for division by replicating its $DNA$ and synthesizing proteins,but the morphological changes associated with division are absent.

(D) The $G_1$ phase (Gap $1$ phase) is the first growth phase of the cell cycle.
During this phase,the cell is metabolically active and continuously grows.
It synthesizes the necessary enzymes,proteins,and $RNA$ required for $DNA$ replication,which occurs in the subsequent $S$ phase.
Therefore,the $G_1$ phase prepares the cell for $DNA$ synthesis.

(C) Cells that do not divide further exit the $G_1$ phase to enter an inactive stage called the $G_0$ phase ($G_0$ phase),also known as the Quiescent phase. In this stage,cells remain metabolically active but do not proliferate unless called upon to do so depending on the requirement of the organism.

(D) 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. In this phase,cells exit the cell cycle and start differentiating into specific types of cells to perform specialized functions in the organism.

(D) During the $S$ phase (Synthesis phase) of the cell cycle,the $DNA$ content of the cell doubles.
If the initial amount of $DNA$ is $8$ $C$,then after the replication process in the $S$ phase,the amount of $DNA$ will become $8 \times 2 = 16$ $C$.

(A) During the $S$ phase (Synthesis phase) of the cell cycle,the $DNA$ content of the cell doubles,but the number of chromosomes remains the same.
In the $G_1$ phase,the cell has $36$ chromosomes.
Since the $S$ phase involves $DNA$ replication but not the separation of centromeres,the number of chromosomes remains $36$ throughout the $S$ phase.
Each chromosome will consist of two sister chromatids after replication.

(B) The cell cycle consists of two main phases: Interphase and $M$-phase. Interphase is the phase of preparation where the cell grows,replicates its $DNA$,and synthesizes proteins required for division. It is the longest phase of the cell cycle,accounting for more than $95\%$ of the total duration of the cell cycle.

(A) The cell cycle is regulated by specific control points known as checkpoints.
The most critical checkpoint,often referred to as the 'restriction point' or 'start',occurs at the $G_1 \rightarrow S$ transition.
At this stage,the cell commits to $DNA$ replication and division based on internal and external signals.
Another significant checkpoint exists at the $G_2 \rightarrow M$ transition,which ensures that $DNA$ replication is complete and accurate before the cell enters mitosis.

(D) The transition from the $G_1$ phase to the $S$ phase in the cell cycle is a critical checkpoint. This transition is primarily regulated by the formation of a complex between $G_1$ cyclins and cyclin-dependent kinases (specifically cdc$2$ kinase or its homologs). These complexes phosphorylate target proteins that initiate $DNA$ replication,thereby allowing the cell to progress from the $G_1$ phase into the $S$ phase.

(C) Cyclin Dependent Kinases ($CDK$s) are a family of protein kinases that are activated by binding to specific cyclins. They play a crucial role in regulating the progression of the cell cycle by phosphorylating target proteins that drive the cell through various checkpoints and phases (such as $G_1/S$ and $G_2/M$ transitions). Therefore,they control the various phases of the cell cycle.

(C) In the $S$-phase (synthesis phase) of the cell cycle,the amount of $DNA$ per cell doubles,but the chromosome number remains the same.
- Statement $a$ is true: $G_1$ phase involves metabolic activity and protein synthesis without $DNA$ replication.
- Statement $b$ is true: $S$-phase involves $DNA$ replication,resulting in sister chromatids carrying duplicate genes.
- Statement $c$ is true: After $S$-phase,the $DNA$ content becomes $4C$ compared to the initial $2C$.
- Statement $d$ is false: The chromosome number does not double during the $S$-phase; it remains $2n$ because the sister chromatids remain attached at the centromere.
Therefore,only statement $d$ is incorrect.

(A) The $G_1$ phase (Gap $1$) is the most critical checkpoint in the cell cycle. During this phase,the cell assesses its internal and external environment to determine whether to proceed with $DNA$ replication ($S$ phase) or exit the cycle and enter the $G_0$ phase (quiescent stage). In the $G_0$ phase,cells remain metabolically active but do not proliferate unless signaled to re-enter the cell cycle.

(D) Based on the cell cycle diagram:
$A$ represents the $M$-phase (Mitosis),which starts with karyokinesis and ends with cytokinesis.
$B$ represents the $G_0$ phase (Quiescent stage). In this stage,cells remain metabolically active but do not proliferate unless called upon to do so.
$C$ represents the $G_1$ phase,where the cell grows and carries out normal metabolism.
$D$ represents the $S$ phase (Synthesis phase),where $DNA$ replication occurs,not cytoplasmic growth (which occurs primarily in $G_1$ and $G_2$).
Therefore,the statement '$D$ - Period of cytoplasmic growth' is incorrect as it typically refers to the $G_1$ or $G_2$ phases,making option $D$ the mismatched pair.

(C) The synthesis $(S)$ phase of the cell cycle is characterized by the following events:
$1$. $DNA$ replication: The amount of $DNA$ per cell doubles (from $2C$ to $4C$).
$2$. Chromatin fibre duplication: As $DNA$ replicates,the chromatin fibres also duplicate.
$3$. Histone protein synthesis: Histones are synthesized in the cytoplasm and transported to the nucleus to package the newly replicated $DNA$.
$4$. Centriole duplication: In animal cells,the centriole duplicates in the cytoplasm during the $S$ phase.
Membranous organelle duplication (like mitochondria and Golgi bodies) typically occurs during the $G_1$ and $G_2$ phases,not the $S$ phase.
Therefore,the features associated with the $S$ phase are: $DNA$ replication,chromatin fibre duplication,histone protein synthesis,and centriole duplication. This makes a total of four features.

(D) cell undergoes mitotic division where one cell produces $2$ daughter cells in each generation.
This follows the formula $2^n = N$,where $n$ is the number of generations and $N$ is the total number of cells.
Given $N = 128$,we have $2^n = 128$.
Since $128 = 2^7$,it follows that $n = 7$.
Therefore,$7$ generations are required to produce $128$ cells.
$1 \xrightarrow{1} 2 \xrightarrow{2} 4 \xrightarrow{3} 8 \xrightarrow{4} 16 \xrightarrow{5} 32 \xrightarrow{6} 64 \xrightarrow{7} 128$

(D) An egg is a haploid cell $(n)$,and its $DNA$ content is represented as $C$.
Given that the egg has $10 \; pg$ of $DNA$,we have $C = 10 \; pg$.
$A$ diploid cell $(2n)$ in the $G_1$ phase has $2C$ amount of $DNA$.
During the $S$ phase of the cell cycle,$DNA$ replication occurs,doubling the $DNA$ content.
Therefore,in the $G_2$ phase,the $DNA$ content of a diploid cell becomes $4C$.
Substituting the value of $C$: $4 \times 10 \; pg = 40 \; pg$.

(C) Meiotic products (gametes) are haploid $(n)$ and contain $C$ amount of $DNA$. Given that $C = 20 \; pg$.
$A$ somatic cell is diploid $(2n)$ and contains $2C$ amount of $DNA$ in the $G_1$ phase.
During the $S$ phase,the $DNA$ content doubles,so in the $G_2$ phase,the cell contains $4C$ amount of $DNA$.
Therefore,the $DNA$ content in the $G_2$ phase = $4 \times 20 \; pg = 80 \; pg$.

(A) During the $G_1$-phase (Gap $1$ phase),the cell grows in size and synthesizes various proteins and $RNA$. Most of the cell organelles,such as mitochondria,chloroplasts,and the endoplasmic reticulum,undergo duplication during this phase to prepare for cell division.

(C) The $G_2$-phase is known as the pre-mitotic phase or the second growth phase,during which the cell prepares for mitosis by synthesizing proteins and duplicating organelles like mitochondria and chloroplasts.
Chromosome condensation does not occur in the $G_2$-phase; it is a characteristic feature of the prophase stage of mitosis.
Therefore,the Assertion is correct,but the Reason is incorrect.

(C) During the cell cycle,the synthesis phase ($S$ phase) is the period where $DNA$ replication occurs. In this phase,the amount of $DNA$ per cell doubles,although the number of chromosomes remains the same. This ensures that each daughter cell receives an identical set of genetic material after mitosis.

(A) In animal cells,the centriole is a crucial organelle involved in the formation of the spindle apparatus during cell division.
During the $S-$phase (Synthesis phase) of the cell cycle,$DNA$ replication occurs in the nucleus.
Simultaneously,the centriole pair in the cytoplasm also undergoes duplication to ensure that each daughter cell receives a pair of centrioles.
Therefore,the correct phase for centriole duplication is the $S-$phase.

(A) In the cell cycle,the $S$ phase (Synthesis phase) is characterized by the replication of $DNA$.
During this phase,the amount of $DNA$ per cell doubles (from $2C$ to $4C$),but the number of chromosomes remains the same.
Since the number of chromosomes at the $G_1$ phase is $8$,after the $S$ phase,the number of chromosomes remains $8$ because the sister chromatids remain attached at the centromere.
Therefore,the correct answer is $8$.

(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.
During the $S$ phase (Synthesis phase),$DNA$ replication occurs,which means the amount of genetic material $(DNA)$ in the cell doubles.
If the initial amount of $DNA$ is denoted as $2C$,it becomes $4C$ at the end of the $S$ phase,although the chromosome number remains the same.

(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.
In the provided diagram,$P$ represents the $G_1$ phase,$Q$ represents the $S$ phase (Synthesis phase),$R$ represents the $G_2$ phase,and $S$ represents the $M$-phase.
$DNA$ polymerase is the primary enzyme responsible for $DNA$ replication.
$DNA$ replication occurs specifically during the $S$ phase (Synthesis phase) of the cell cycle.
Therefore,the enzyme is required in phase $Q$.

(A) The cell cycle is divided into two main phases: $Interphase$ and $M$ phase (Mitotic phase).
$Interphase$ is the preparatory phase where the cell grows, replicates its $DNA$, and prepares for division.
It occupies more than $95\%$ of the total duration of the cell cycle.
In contrast, the $M$ phase is the actual division phase, which is relatively short.
Therefore, $Interphase$ lasts for the longest duration.

(B) The cell cycle duration varies significantly among different organisms:
$1$. Yeast ($Saccharomyces$ $cerevisiae$) typically completes its cell cycle in approximately $90$ minutes or $1.5$ hours.
$2$. $E. coli$ (a bacterium) has a very rapid cell cycle,often dividing every $20$ minutes under optimal conditions.
$3$. Human cells in culture typically have a cell cycle duration of about $24$ hours.
Matching these:
$P$ (Yeast) matches with $II$ ($1.5$ hours).
$Q$ $(E. coli)$ matches with $I$ ($20$ minutes).
$R$ (Human cell) matches with $III$ ($24$ hours).
Therefore,the correct sequence is $(P-II), (Q-I), (R-III)$.

(D) The cell cycle is divided into two main phases: the $M$ phase (Mitosis) and the Interphase.
Interphase is the period between two successive $M$ phases.
It is further divided into three sub-phases: $G_1$ phase (Gap $1$),$S$ phase (Synthesis),and $G_2$ phase (Gap $2$).
Since Interphase encompasses the entire duration between two $M$ phases,it is the correct representation of the stage between them.

(D) The interphase is the phase of the cell cycle in which a typical cell spends most of its life.
It is divided into three distinct subphases:
$1$. $G_1$ phase (Gap $1$): The cell grows and performs its normal metabolic functions.
$2$. $S$ phase (Synthesis): $DNA$ replication occurs.
$3$. $G_2$ phase (Gap $2$): The cell prepares for mitosis by synthesizing proteins and organelles.
Therefore,all the listed options are subphases of interphase.

(C) In the cell cycle,the $G_1$ phase represents the initial growth phase where the $DNA$ content is $2C$ and the chromosome number is $2n$.
During the $S$ phase (Synthesis phase),$DNA$ replication occurs,which doubles the $DNA$ content from $2C$ to $4C$,while the chromosome number remains $2n$ because the sister chromatids remain attached at the centromere.
Following the $S$ phase,the cell enters the $G_2$ phase.
Therefore,in the $G_2$ phase,the $DNA$ content is $4C$ and the chromosome number remains $2n$.
Thus,the transition from $G_1$ to $G_2$ involves a change in $DNA$ content from $2C$ to $4C$,while the ploidy $(2n)$ remains constant.

(B) In animal cells,the centriole duplicates during the $S$ phase (Synthesis phase) of the cell cycle,alongside the replication of nuclear $DNA$. This ensures that each daughter cell receives a pair of centrioles during cell division.

(B) 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.
During the $S$ phase (Synthesis phase),the replication of $DNA$ takes place.
In this phase,the amount of $DNA$ per cell doubles,although the chromosome number remains the same.

(C) In eukaryotes,the replication of $DNA$ occurs during the $S$ phase (Synthesis phase) of the cell cycle.
During this phase,the amount of $DNA$ per cell doubles,although the chromosome number remains the same.
In contrast,the $G_1$ phase involves cell growth and the duplication of most cell organelles,while the $G_2$ phase involves protein synthesis and preparation for mitosis.