1. An isolated tissue increases its cell number only when existing cells divide. This observation most directly supports:
ⓐ. enlargement of cells without formation of new cells
ⓑ. genome duplication without formation of cellular progeny
ⓒ. spontaneous production of cells from extracellular material
ⓓ. cellular continuity through division of pre-existing cells
Correct Answer: cellular continuity through division of pre-existing cells
Explanation: Cellular continuity means that new cells arise from cells that already exist. During division, a parental cell passes organised cellular material and genetic information to its daughter cells. An increase in cell size alone may enlarge a tissue temporarily, but it cannot increase the number of cells. Similarly, duplication of DNA is only a preparatory event unless the replicated genetic material is subsequently distributed into cellular progeny. The observation specifically links an increase in cell number with division of existing cells, so it supports continuity through parent-to-daughter cell formation. This principle also explains how tissues maintain themselves: daughter cells may grow, perform specialised functions and, when appropriate, divide again to extend the cellular lineage.
2. One parental cell divides into two daughter cells. Daughter P differentiates and no longer divides, whereas daughter Q completes one further normal division. Which final description is correct?
ⓐ. Three cells are present, and all are descendants of the original parental cell
ⓑ. Four cells are present, because differentiation is equivalent to an additional division
ⓒ. Two cells are present, because only the first division contributes to the lineage
ⓓ. Three cells are present, but the daughters of Q arose without a pre-existing parent cell
Correct Answer: Three cells are present, and all are descendants of the original parental cell
Explanation: The first division produces daughter cells P and Q. Differentiation changes the structure and function of P, but it does not constitute another cell division or remove P from the lineage. When Q subsequently divides, Q gives rise to two new daughter cells. The final population therefore contains differentiated cell P and the two daughters formed from Q, giving a total of three cells. Every one of these cells can be traced through one or more divisions to the original parental cell. The two daughters of Q do not arise independently from extracellular material; they arise by division of a pre-existing cell. The example also shows that cells within the same lineage can follow different developmental paths: one daughter may become specialised and stop dividing, while another may continue the lineage through further division.
3. A zygote develops into an embryo in which the number of cells rises greatly while most individual cells remain microscopic. The increase in organisation is best explained by:
ⓐ. repeated enlargement of the original cell without division
ⓑ. repeated cellular growth followed by successive divisions
ⓒ. formation of cells directly from surrounding nutrients
ⓓ. continuous DNA synthesis without cytoplasmic separation
Correct Answer: repeated cellular growth followed by successive divisions
Explanation: A zygote is a single founding cell, yet a multicellular embryo contains a large population of cells. This transformation requires repeated cycles in which cells grow, prepare their contents and divide. Each division increases the number of cells, and the daughter cells can subsequently enter further cycles. Enlargement of the original zygote alone would produce one large cell rather than an organised multicellular structure. DNA synthesis without division would increase genetic material inside the same cellular boundary but would not generate a population of daughter cells. The important relation is cumulative: successive rounds of growth and division progressively expand cell number, allowing groups of cells to become organised into tissues and developing body structures.
4. Arrange the events in the most appropriate order during expansion of a cell population from one founding cell.
P. The founding cell grows and prepares for division.
Q. It divides to produce daughter cells.
R. The daughter cells grow before their own divisions.
S. Repeated divisions increase the size of the cell population.
ⓐ. Q → P → S → R
ⓑ. P → R → Q → S
ⓒ. P → Q → R → S
ⓓ. R → S → P → Q
Correct Answer: P → Q → R → S
Explanation: A cell ordinarily prepares before it divides. The founding cell first grows and organises the material required for producing viable progeny. Division then generates daughter cells. These newly formed cells are not simply counted as an indefinitely expanding population without preparation; they undergo growth and other cycle events before dividing again. Repetition of this pattern produces a progressive increase in cell number. The order is based on dependency rather than memorisation: daughter-cell growth cannot precede the division that forms those daughters, and repeated population expansion cannot occur before at least one round of division. The sequence represents how one cell can establish a lineage containing many cells while each generation remains connected to the preceding parental generation. The stated start point fixes the direction of the sequence and removes cyclic ambiguity.
5. The cell cycle is most accurately described as:
ⓐ. an ordered sequence limited to DNA synthesis before permanent inactivity
ⓑ. an ordered sequence limited to chromosome condensation and segregation
ⓒ. an ordered sequence limited to cytoplasmic separation after chromosome movement
ⓓ. an ordered sequence of growth, genome duplication, synthesis and division
Correct Answer: an ordered sequence of growth, genome duplication, synthesis and division
Explanation: The cell cycle includes the coordinated events through which one cell prepares for and completes the production of daughter cells. The cell grows, synthesises cellular constituents, duplicates its genome and eventually divides. Nuclear division is only one part of this larger sequence, while cytoplasmic separation is one of its concluding events. DNA replication is essential, but replication alone does not constitute a complete cycle. The term cycle also reflects continuity: after division, suitable daughter cells may grow and enter another round of events. A complete definition must include both preparation and division, since the biological purpose is not merely to copy DNA but to transmit an intact genome and sufficient cellular material to newly formed cells.
6. Evaluate these statements about the cell cycle.
I. It includes duplication of the cellular genome.
II. It includes synthesis of cellular constituents needed by the growing cell.
III. M phase alone represents the complete cell cycle.
IV. It culminates in the production of daughter cells.
ⓐ. I and III only
ⓑ. II and IV only
ⓒ. I, II, III and IV
ⓓ. I, II and IV only
Correct Answer: I, II and IV only
Explanation: Genome duplication is an essential component of the cell cycle, so statement I is valid. Cells also synthesise proteins, membranes and other constituents as they grow and prepare for division, which supports statement II. Statement III is not valid since M phase represents the division phase, not the entire cycle. Interphase occupies the interval in which major preparatory activities, including DNA replication, occur before M phase. Statement IV is valid since successful completion of the sequence produces daughter cells. The accepted combination recognises that a cell cycle integrates preparation with division. Restricting the term to M phase would exclude most growth, constituent synthesis and genome duplication, even though these events are required for successful transmission of cellular organisation.
7. A cell grows, synthesises many proteins and duplicates its genome, but it never undergoes nuclear or cytoplasmic division. Has it completed a cell cycle?
ⓐ. Yes, since genome duplication alone defines completion
ⓑ. No, since division into daughter cells has not occurred
ⓒ. No, but only if synthesis of cellular constituents also stopped
ⓓ. Yes, since cellular growth alone defines completion
Correct Answer: No, since division into daughter cells has not occurred
Explanation: Growth, protein synthesis and genome duplication are major preparatory events, but they do not by themselves complete the cell cycle. Completion requires the replicated genetic material to be organised and distributed during nuclear division, normally followed by separation of the cytoplasm into daughter cells. The described cell has carried out much of interphase but has not completed the division phase. Its DNA content may have increased, yet no new cellular progeny have been produced. This distinction prevents the cell cycle from being reduced to DNA replication alone. Replication prepares genetic information for transmission, whereas division completes that transmission by forming daughter cells capable of continuing the cellular lineage. Until segregation and cytoplasmic partitioning occur, the duplicated genome remains within the original cellular unit.
8. A record begins immediately after one cell division and ends when the same cell completes its next division. Which order best represents the major events during this interval?
ⓐ. Chromosome segregation → genome duplication → cellular growth → division
ⓑ. Cell growth → genome duplication → mitotic preparation → karyokinesis → cytokinesis
ⓒ. Cytoplasmic division → genome duplication → cellular growth → chromosome segregation
ⓓ. Genome duplication → daughter-cell formation → cellular growth → mitotic preparation
Correct Answer: Cell growth → genome duplication → mitotic preparation → karyokinesis → cytokinesis
Explanation: Immediately after division, a daughter cell enters a period of growth and normal activity. Genome duplication then occurs before the cell proceeds to the later preparation required for mitosis. Nuclear division distributes the duplicated chromosomes, and cytoplasmic division usually completes formation of separate daughter cells. The sequence follows biological dependency: chromosome segregation must act on previously duplicated genetic material, and daughter-cell formation is an outcome of division rather than an event preceding preparation. Cellular synthesis can continue across more than one phase, but the broad order remains growth and preparation, DNA replication, further preparation and division. This arrangement captures one complete interval from the end of one division to the end of the next. The order is fixed by dependency: a structure or product must exist before the later event can act on it.
9. Assertion: DNA replication alone cannot ensure that each daughter cell receives an intact genome.
Reason: Replicated chromosomes must also be organised and distributed accurately during cell division.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains the Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not correctly explain the Assertion
ⓒ. Assertion is true and Reason is false, so Reason cannot correctly explain the Assertion
ⓓ. Assertion is false and Reason is true, so Reason cannot correctly explain the Assertion
Correct Answer: Both Assertion and Reason are true, and Reason correctly explains the Assertion
Explanation: The assertion is true since copying DNA creates additional genetic material but does not determine where that material will go. The reason is also true: after replication, chromosomes must be organised and segregated so that each daughter region receives the required chromosome set. This distribution step directly explains why replication alone is insufficient. A cell could duplicate its DNA successfully yet produce abnormal progeny if the chromosomes were not separated appropriately. Growth, replication, segregation and cytoplasmic division must function as a coordinated sequence. The biological outcome being protected is intact-genome transmission, which depends on both accurate copying and orderly allocation of the copied chromosomes. An intact-genome outcome needs accurate copying and accurate allocation. Either process can fail even when the other has occurred normally.
10. Four cell cultures show the following events during one attempted division.
| Culture | DNA duplicated | Chromosome sets segregated equally | Cytokinesis completed |
|---|
| P | Yes | No | Yes |
| Q | No | Yes | Yes |
| R | Yes | Yes | Yes |
| S | Yes | Yes | No |
Which culture is most likely to produce two separate daughter cells, each receiving an intact duplicated genome?
ⓐ. Culture P
ⓑ. Culture Q
ⓒ. Culture R
ⓓ. Culture S
Correct Answer: Culture R
Explanation: The required outcome has two parts: the genome must be duplicated and distributed equally, and the cytoplasm must separate to produce two distinct daughter cells. Culture R satisfies all three observations. Its DNA has been copied, the chromosome sets have moved equally into the two daughter regions, and cytokinesis has physically separated those regions. Culture P completes cytokinesis without equal chromosome segregation, so separate cells could receive incomplete or unequal genetic material. Culture S has accurate duplication and segregation but lacks cytoplasmic separation, leaving the products within one cellular boundary. The table demonstrates why successful cellular reproduction depends on coordination rather than on any single event considered in isolation. Each column represents a separate condition, and the answer must satisfy them simultaneously. The table converts several observations into one stage decision by requiring their biological compatibility.
11. Equal cultures of dividing cells are maintained under identical conditions. One culture receives a treatment that prevents DNA synthesis, while the control culture remains untreated. Treated cells continue increasing in size, but very few complete normal division. The strongest inference is that:
ⓐ. cellular growth automatically duplicates the genome
ⓑ. cytoplasmic enlargement is sufficient to form viable daughter cells
ⓒ. chromosome segregation normally occurs before DNA synthesis
ⓓ. genome duplication precedes reliable chromosome distribution
Correct Answer: genome duplication precedes reliable chromosome distribution
Explanation: The treatment specifically prevents DNA synthesis, while continued increase in cell size shows that at least some growth-related processes remain active. The major difference between the treated and control cultures is the failure to duplicate the genome. Normal division requires genetic material to be copied before it can be organised into equivalent chromosome sets for the daughter cells. The low frequency of completed normal divisions links the replication block with failure of later division events. The experiment does not show that all cellular activity has stopped; instead, it separates growth from genome duplication. Its justified conclusion is limited to the dependency revealed by the treatment: reliable transmission of chromosomes requires prior replication of the genetic material. The absence of a later product is interpreted through the first failed prerequisite, not as evidence that every earlier event also failed.
12. A diploid cell completes normal DNA replication, but its replicated chromosomes are distributed randomly rather than equally during division. The most likely result is:
ⓐ. both daughter cells receive complete identical genomes automatically
ⓑ. chromosome number remains normal solely due to completed cytokinesis
ⓒ. daughter cells may receive unequal or incomplete chromosome complements
ⓓ. the random distribution is corrected by additional cellular growth
Correct Answer: daughter cells may receive unequal or incomplete chromosome complements
Explanation: DNA replication produces copies of the genetic material, but accurate inheritance still depends on orderly chromosome segregation. Random distribution gives no mechanism ensuring that corresponding chromosomes reach opposite daughter regions in balanced sets. One region may receive extra copies of some chromosomes while lacking others, even though the total DNA was duplicated correctly before division. Completion of cytokinesis would only separate the unequal regions into distinct cells; it would not repair the distribution error. Further growth also cannot restore chromosomes that were not inherited. The prediction follows from the coordination requirement: replication supplies duplicated chromosomes, while controlled segregation determines whether each daughter cell receives an intact chromosome complement. The defect is inherited at the moment the unequal chromosome sets are enclosed in separate daughter cells.
13. Evaluate the following statements about coordinated cell-cycle events.
I. Genome duplication must precede distribution of replicated chromosomes.
II. Cytokinesis alone guarantees equal genetic information in daughter cells.
III. Loss of coordination between replication and segregation can impair genome transmission.
IV. Cellular growth by itself produces a second chromosome set.
ⓐ. I and III only
ⓑ. I, II and III only
ⓒ. II and IV only
ⓓ. I, III and IV only
Correct Answer: I and III only
Explanation: Statement I is valid since chromosomes must be duplicated before two equivalent sets can be distributed. Statement II is not valid: cytokinesis divides the cytoplasm, but it cannot guarantee that chromosome segregation was accurate. Statement III follows from the same dependency. A cell may copy DNA but fail to allocate it equally, or it may attempt division without completing replication, and either situation threatens intact-genome transmission. Statement IV is also invalid since an increase in cell mass does not itself copy nuclear DNA. The accepted statements distinguish four related processes—growth, replication, segregation and cytokinesis—and identify the specific contribution of each. Their coordination, rather than mere occurrence, determines whether viable daughter cells inherit complete genetic information.
14. Two cell cultures increase in mass and complete cytokinesis. In culture P, DNA is replicated and the chromosomes are distributed equally. In culture Q, DNA is replicated but chromosome distribution is irregular. The comparison most strongly demonstrates that:
ⓐ. an increase in cell mass proves accurate chromosome segregation
ⓑ. increased cell number alone does not prove genetic continuity
ⓒ. formation of two cellular boundaries ensures equivalent genomes
ⓓ. genome replication becomes unnecessary once cytokinesis begins
Correct Answer: increased cell number alone does not prove genetic continuity
Explanation: Both cultures grow and complete cytoplasmic separation, so each can appear to have produced additional cells. The decisive difference lies in chromosome distribution. Culture P combines replication with equal segregation, while culture Q does not allocate the replicated chromosomes regularly. Two cellular boundaries can form even when the genetic contents enclosed by them are unequal. Cell counting by itself would miss this defect. Genetic continuity requires more than an increase in cell number: each daughter cell must receive an appropriate chromosome complement. The comparison separates the visible outcome of cytokinesis from the less obvious requirement of accurate genome transmission and shows why replication, segregation and cytoplasmic division must be interpreted together. Equal cytokinesis without equal chromosome segregation can therefore create two cells that are numerically separate but genetically abnormal. Such products may differ in chromosome content despite similar cell counts.
15. During a typical proliferative cell cycle, cellular growth may continue through much of interphase, whereas nuclear DNA synthesis is:
ⓐ. restricted to the S phase of interphase
ⓑ. distributed equally across all phases of interphase
ⓒ. completed only during nuclear division
ⓓ. confined to the interval after cytokinesis
Correct Answer: restricted to the S phase of interphase
Explanation: Cellular growth includes increases in cytoplasmic material, proteins, membranes and other constituents. Such growth is not limited to one brief interval and may continue during several parts of interphase. Nuclear DNA replication has a more specific position: it occurs during S phase, where S refers to synthesis of DNA. This distinction is important when interpreting cell-cycle observations. An increase in cell mass does not by itself identify S phase, since a cell can grow while its DNA amount remains unchanged. Evidence of increasing nuclear DNA content, in contrast, directly points to S phase. The cycle coordinates a broadly continuing process of cellular growth with a stage-specific period of genome duplication.
16. A proliferating diploid cell is followed through three consecutive interphase intervals.
| Interval | Cell mass | Nuclear DNA amount |
|---|
| P | Increasing | Remains \(2C\) |
| Q | Increasing | Changes from \(2C\) to \(4C\) |
| R | Increasing | Remains \(4C\) |
Which inference is supported by the complete data?
ⓐ. Cellular growth is restricted to interval Q
ⓑ. Nuclear DNA synthesis occurs throughout P, Q and R
ⓒ. Growth occurs throughout, but DNA synthesis is confined to Q
ⓓ. Both cellular growth and DNA synthesis cease after interval Q
Correct Answer: Growth occurs throughout, but DNA synthesis is confined to Q
Explanation: Cell mass increases during P, Q and R, so the data show that cellular growth continues across all three intervals. Nuclear DNA behaves differently. It remains at \(2C\) during P, rises from \(2C\) to \(4C\) during Q and remains at \(4C\) during R. The increase identifies Q as the DNA-synthesis interval, corresponding to S phase. P is consistent with a pre-replication growth period, while R represents post-replication preparation in which growth continues without another round of DNA synthesis. The table demonstrates that cytoplasmic growth and genome replication are coordinated but not identical processes. One may extend across much of interphase, whereas the other is restricted to a defined phase. The table should be read across each row before comparing rows, since the decisive evidence is the combined pattern rather than any single entry. The inference comes from the complete row pattern; one isolated value could fit more than one stage or process.
17. A graph follows a diploid cell through \(G_1\), S and \(G_2\). At the start of S phase, a treatment blocks nuclear DNA synthesis but leaves cytoplasmic growth and protein synthesis functional. Curve P represents cell mass, and Curve Q represents nuclear DNA amount. Which pattern is expected?
ⓐ. P remains constant, while Q rises from \(2C\) to \(4C\) during S
ⓑ. P continues rising, while Q remains at \(2C\) through S and \(G_2\)
ⓒ. P falls during S, while Q rises from \(4C\) to \(8C\)
ⓓ. Both P and Q rise only after the cell enters \(G_2\)
Correct Answer: P continues rising, while Q remains at \(2C\) through S and \(G_2\)
Explanation: The x-axis fixes the order \(G_1\rightarrow S\rightarrow G_2\), while the two curves represent processes that can be separated experimentally. Cell mass reflects synthesis of cytoplasmic constituents, so it can continue to rise when the treatment leaves growth-related pathways functional. Nuclear DNA amount behaves differently. A block applied at the start of S phase prevents the normal increase from \(2C\) to \(4C\), leaving the DNA curve at the pre-replication level. The cell may continue enlarging, but it cannot be interpreted as having completed a normal S phase or entered a normal post-replication \(G_2\) state. The changed condition demonstrates that growth and genome duplication are coordinated yet distinct events. A rising mass curve alone is not evidence of DNA synthesis; the DNA curve must show the phase-specific increase that marks successful replication. The graph therefore separates continued biomass increase from the S-phase rise in nuclear DNA, showing that the two processes can be uncoupled by a selective block.
18. Which combination correctly evaluates these statements?
I. A rise in cell mass alone is insufficient to identify S phase.
II. An increase in nuclear DNA amount is evidence that the cell is in S phase.
III. Cellular growth may continue outside the period of DNA synthesis.
IV. Nuclear DNA doubles gradually throughout all of interphase.
ⓐ. I, II and III only
ⓑ. I, II and IV only
ⓒ. I, III and IV only
ⓓ. II, III and IV only
Correct Answer: I, II and III only
Explanation: Statement I is valid since cellular growth can occur in \(G_1\), S and \(G_2\); increasing mass is not unique to S phase. Statement II is valid under the stated cell-cycle context since nuclear DNA replication occurs during S phase. Statement III is also valid, as synthesis of cytoplasmic constituents and an increase in cell size may continue before and after genome duplication. Statement IV is not valid. DNA amount remains stable before S, increases during S and stays at the doubled level after replication until division redistributes the genetic material. The valid set distinguishes a broadly continuing cellular process from a phase-specific molecular event and prevents growth from being used as the sole marker of DNA synthesis.
19. Assertion: Chromosome replication and distribution occur through an ordered series of events.
Reason: Genetic control makes every cell type complete its cycle in exactly the same duration.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains the Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not correctly explain the Assertion
ⓒ. Assertion is true and Reason is false, so Reason cannot correctly explain the Assertion
ⓓ. Assertion is false and Reason is true, so Reason cannot correctly explain the Assertion
Correct Answer: Assertion is true and Reason is false, so Reason cannot correctly explain the Assertion
Explanation: The assertion is true. Cell-cycle events occur in an organised order so that DNA replication precedes chromosome segregation and division. This order reflects genetic control of the cellular programme rather than a random collection of unrelated changes. The reason is false, since genetic control does not require all cells to have identical cycle durations. Different organisms and different cell types may complete the cycle at markedly different rates while preserving the same essential dependency between replication and division. Control concerns the coordinated sequence and execution of events, not a universal clock duration. A slow cell and a rapidly dividing cell can both follow an ordered cycle even though the time taken by each phase differs. The conserved feature is the dependency among events, whereas the timing of those events can remain cell-type specific.
20. Consider the following implications of genetic control over the cell cycle.
I. Similar proliferating cells can show a reproducible order of major events.
II. Genetic control does not require equal cycle duration in every cell type.
III. Disruption of event order may interfere with intact-genome transmission.
IV. Random timing of replication and segregation is sufficient for normal daughter cells.
ⓐ. I, II and IV only
ⓑ. II, III and IV only
ⓒ. I, III and IV only
ⓓ. I, II and III only
Correct Answer: I, II and III only
Explanation: Statement I reflects the organised nature of the cycle: growth, DNA replication, preparation and division occur in a reproducible relation rather than in arbitrary order. Statement II is also valid. Cells can differ greatly in cycle duration while still following the required sequence. Statement III follows from the role of control in coordinating replication with chromosome segregation; disturbing that order can prevent equal inheritance of genetic material. Statement IV contradicts this coordination. Random timing would not reliably ensure that the genome had been copied before segregation or that chromosome distribution was complete before daughter-cell formation. Genetic control provides orderly relationships among events while still allowing biological variation in the time taken to complete them. In this way, control permits flexible duration while preserving the order required for reliable daughter-cell formation.
