Title Ex-2 Cell Cycle and Cell Division (Qs+sol) (1).pdf ✅

30 CELL CYCLE AND CELL DIVISION EXERCISE – 2: Previous Year Completition Questions 1. The centriole undergoes duplication during (NEET 2021) (a) S-phase (b) Prophase (c) Metaphase (d) G2 phase Ans. (a) Sol. In animal cells, the centriole undergoes duplication during S-phase in the cytoplasm. In addition to this, replication of DNA also occurs during S-phase in the nucleus. Hence, the (a) option is correct. Whereas condensation of chromosomes and initiation of mitotic spindle occurs in prophase. During metaphase, spindle fibers attach to kinetochores of chromosomes and chromosomes move to the spindle equator and align along with the metaphase plate. During the G2 phase, protein synthesis occurs and cell growth continues. 2. Which stage of meiotic prophase shows terminalization of chiasmata as its distinctive feature? (NEET 2021) (a) Leptotene (b) Zygotene (c) Diakinesis (d) Pachytene Ans. (c) Sol. Diakinesis is the last stage of prophase I of meiosis I which is marked by the terminalisation of chiasmata. In addition to this, condensation of chromosomes, meiotic spindle formation, the disappearance of the nucleolus and nuclear envelope also occurred in this phase. Hence, the (c) option is correct. Whereas in leptotene, chromosomes became visible. In zygotene, the pairing of chromosomes occurred via a process called synapsis. These chromosomes are termed homologous chromosomes. In pachytene, crossing over between non-sister chromatids of homologous chromosomes occurred. 3. The fruit fly has 8 chromosomes (2n) in each cell. During the interphase of mitosis if the number of chromosomes at the G1 phase is 8, what would be the number of chromosomes after the S phase? (NEET 2021) (a) 8 (b) 16 (c) 4 (d) 32 Ans. (a) Sol. The chromosome number of fruit fly at the G1 phase is 8. So after S-phase, the chromosome number will be the same i.e. 8. After S-phase, the chromosomes get duplicated, hence the amount of DNA is doubled, while the chromosome number remains the same as of the parent cell. Hence, (a) option is correct. 4. Match List-I with List-II. (NEET 2021) List-I List-II (a) S phase (i) Proteins are synthesized (b) G2 phase (ii) Inactive phase (c) Quiescent stage (iii) Interval between mitosis and initiation of DNA replication (d) G1 phase (iv) DNA replication (a) (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii) (b) (a)-(ii), (b)-(iv), (c)-(iii), (d)-(i) (c) (a)-(iii), (b)-(ii), (c)-(i), (d)-(iv) (d) (a)-(iv), (b)-(ii), (c)-(iii), (d)-(i) Ans. (a) Sol. The cell cycle is divided into two phases- The Interphase and mitosis phase. Mitosis is a phase where actual cell division occurs. Interphase is a phase where the cell prepares itself for cell division. The interphase phase is further divided into three phases- G1, S, and G2 phases. -The G1 phase is an interval between mitosis and the initiation of DNA replication. -In the S phase, DNA replication occurs. -In the G2 phase, proteins are synthesized for mitosis division and the cell continues to grow. But there are some cells that divide occasionally to replace injured cells and some do not divide at all. These cells enter into an inactive stage known as the G0 phase or quiescent phase after leaving the cell cycle. Cells in this phase are metabolically active but do not grow at all. Hence, the (a) option is correct.
CELL CYCLE AND CELL DIVISION 31 5. Dissolution of the synaptonemal complex occurs during (NEET 2020) (a) Diplotene (b) Leptotene (c) Pachytene (d) Zygotene Ans. (a) Sol. Dissolution of the synaptonemal complex occurs at the beginning of the diplotene stage of prophase of meiosis I except at the sites of cross-over. Hence, (a) option is correct. Whereas chromosomes become gradually visible during the leptotene phase. The pairing of chromosomes occurs via synapsis to form homologous chromosomes during the zygotene stage. Crossing over occurs between non-sister chromatids of homologous chromosomes during the pachytene stage. 6. Match the following with respect to meiosis. (NEET 2020) (A) Zygotene (i) Terminalization (B) Pachytene (ii) Chiasmata (C) Diplotene (iii) Crossing over (D) Diakinesis (iv) Synapsis Select the correct option from the following. (a) A-(i), B-(ii), C-(iv), D- (iii) (b) A-(ii), B-(iv), C-(iii), D- (i) (c) A-(iii), B-(iv), C-(i), D- (ii) (d) A-(iv), B-(iii), C-(ii), D- (i) Ans. (d) Sol. The prophase I of meiosis I is divided into five sub- stages- Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis. During zygotene, the pairing of chromosomes occurs and this form of association is known as synapsis and such paired chromosomes are known as homologous chromosomes. During the pachytene stage, crossing over occurs between non- sister chromatids of homologous chromosomes with the help of recombinase enzyme. During the diplotene phase, dissolution of the synaptonemal complex occurs except at the cross-over sites. This X- shaped structure is known as chiasmata. During the diakinesis stage, terminalization of chiasmata occurs. Hence, the (d) option is correct. 7. Identify the correct statement with regard to the G1 phase (Gap1) of interphase. (NEET 2020) (a) Cell is metabolically active, grows but does not replicate its DNA (b) Nuclear division takes place (c) DNA synthesis or replication takes place (d) Reorganization of all cell components takes place Ans. (a) Sol. The cell cycle is divided into two phases- The interphase and mitosis phase. The interphase phase is divided into three subphases- the G1, S, and G2 phases. During the G1 phase, the cell is metabolically active and continues to grow but does not replicate its DNA. DNA duplication occurs in S- phase. Nuclear division and reorganization of all cell components take place in the mitotic phase. Hence, (a) option is correct with respect to the G1 phase. 8. Some dividing cells exit the cell cycle and enter the vegetative inactive stage. This is called the quiescent stage (G0). This process occurs at the end of (NEET 2020) (a) S phase (b) G2 phase (c) M phase (d) G1 phase Ans. (d) Sol. Some dividing cells exit the cell cycle and enter the vegetative inactive stage. This is called the quiescent stage (G0). This process occurs at the end of the G1 phase (shown in the figure). Cells in this stage are metabolically active but do not grow at all. Hence, the (d) option is correct. 9. Cells in the G0 phase (NEET 2019) (a) Exit the cell cycle (b) Enter the cell cycle (c) Suspend the cell cycle (d) Terminate the cell cycle Ans. (a) Sol. The cell cycle is divided into two phases- The Interphase and mitosis phase. The interphase phase is divided into three subphases- G1, S, and G2 phases. Interphase is a phase where the cell prepares itself for cell division. Mitosis is a phase where actual cell division occurs. But there are some cells that divide occasionally to replace the injured cells or some do not divide at all (e.g. Heart cells). These types of cells are present in the G0 phase which is also known as the quiescent stage. Cells in this stage are metabolically active but do not grow at all. These cells evade the cell cycle for some time, do not terminate the cell cycle. Hence, (a) option is correct.
32 CELL CYCLE AND CELL DIVISION 10. The stage during which separation of the paired homologous chromosomes begins is (NEET 2018) (a) Diakinesis (b) Diplotene (c) Pachytene (d) Zygotene Ans. (b) Sol. The stage during which the separation of the paired homologous chromosomes begins is diplotene. Diplotene is a stage of meiotic division in prophase I of meiosis I which follows the pachytene stage in which the chiasmata become visible. The actual meaning of diplotene is ‘double thread’ in which synapsed chromosomes separate because of the breakage of the synaptonemal complex except at sites of cross-over. Diplotene is a stage near the end of stage prophase I. 11. Which of the following options gives the CORRECT sequence of events during mitosis? (NEET 2017) (a) Condensation  nuclear membrane disassembly  crossing over  segregation  telophase (b) Condensation  nuclear membrane disassembly  arrangement at equator  centromere division  segregation  telophase (c) Condensation  crossing over  nuclear membrane disassembly  segregation  telophase (d) Condensation  arrangement at equator  centromere division  segregation  telophase Ans. (b) Sol. The initiation of mitotic and meiotic division shows the condensation of chromatin fibers. After condensation, the nuclear membrane disappears, all these events happen during prophase. At the metaphase stage, the chromosomes get aligned at the metaphase plate which is the equator of the cell. The centromere division takes place and the chromatids segregate and go to the opposite poles in anaphase. And lastly, the decondensation of chromosomes, nuclear envelope, and organelles (nucleolus, Golgi complex, and ER) reforms in telophase. 12. Anaphase promoting complex (APC) is protein degradation machinery necessary for proper mitosis of animal cells. If APC is defective in a human cell, which of the following is expected to occur? (NEET 2017) (a) Chromosomes will not condense (b) Chromosomes will be fragmented (c) Chromosomes will not segregate (d) Recombination of chromosome arms will occur Ans. (c) Sol. Anaphase-promoting complex (APC) is a protein degradation machinery necessary for proper mitosis of an animal cell. If this complex is defective in any human cell, then the chromosomes will not segregate. Anaphase-promoting complex helps in the transition of the chromosome from metaphase to anaphase. The APC gets attached to the chromosomes aligned at the metaphase plate and allows the segregation of the chromatids. 13. Spindle fibers attach onto (NEET 2016) (a) Telomere of the chromosome (b) Kinetochore of the chromosome (c) Centromere of the chromosome (d) Kinetosome of the chromosome Ans. (b) Sol. Spindle fibers get attached to the kinetochore of the chromosome. The kinetochore is a protein complex that assembles on the centromeric region of DNA. The kinetochore is responsible for the major attachment point for the spindle microtubule during mitotic or meiotic division to pull the chromosomes apart from each other to the opposite poles of the cell. Kinetochores mediate chromosome segregation at cell division. 14. In meiosis, crossing over is initiated at (NEET 2016) (a) Pachytene (b) Leptotene (c) Zygotene (d) Diplotene Ans. (a) Sol. In meiosis, crossing over is initiated at pachytene. Pachytene referred to as pachynema (thick thread) is one of the five substages of prophase in meiosis I. During the stage of the pachytene, the chromosomes continue to condense. It is the stage by which the synaptonemal complex is already formed and visible as tetrads. During this stage, the homologous chromosomes become thick and the process in which chromosomal crossing over takes place is very crucial for segregation as it holds the maternal and paternal chromosomes. 15. Which of the following is not a characteristic feature during mitosis in somatic cells? (NEET 2016) (a) Spindle fibers (b) Disappearance of the nucleolus
CELL CYCLE AND CELL DIVISION 33 (c) Chromosome movement (d) Synapsis Ans. (d) Sol. Synapsis is not a characteristic feature during mitosis in somatic cells but it is the characteristic feature of the first meiotic division in prophase I. Synapsis is the pairing of two homologous chromosomes that occurs during meiosis. It is the process that takes place during prophase I of meiosis I. Synapses occur when the two recombination sites are brought together by protein-protein interactions with the help of recombinases. 16. When cell has stalled DNA replication fork, which checkpoint should be predominantly activated? (NEET 2016) (a) G1/S (b) G2/M (c) M (d) Both G2/M and M Ans. (a) Sol. The stalled DNA replication forks activate the checkpoint G1/S for signaling and pause replication. Since the G1/S checkpoint checks the damaged DNA for the cells which are prior to S-phase, this checkpoint would be activated by a stalled DNA replication fork. If this checkpoint due to some reason is missed, another checkpoint at the G2 and M phase re-ensures proper replication devoid of any DNA damage prior to initiating the mitosis cycle. Hence, (a) option is correct. 17. Match the stages of meiosis in Column-I to their characteristic features in Column-II and select the correct option using the codes given below. Column-I Column - II 1) Pachytene i) Pairing of homologous chromosomes 2) Metaphase I ii) Terminalization of chaismata 3) Diakinesis iii) Crossing-over takes place 4) Zygotene iv) Chromosomes align at equatorial plate (NEET 2016) (a) 1-iii, 2-iv, 3-ii, 4-i (b) 1-i, 2-iv, 3-ii, 4-iii (c) 1-ii, 2-iv, 3-iii, 4-i (d) 1-iv, 2-iii, 3-ii, 4-i Ans. (a) Sol. Pachytene is the stage where chromatin fibers get condense and the crossing-over of the chromosomes takes place. In metaphase I the chromosomes get aligned at the equatorial plate of the cell. During diakinesis, the chiasmata after crossing over get terminalized. In the zygotene of prophase I, the pairing of homologous chromosomes takes place. 18. During cell growth, DNA synthesis takes place in (NEET 2016) (a) S phase (b) G1 phase (c) G2 phase (d) M phase Ans. (a) Sol. During cell growth, DNA synthesis takes place in the S phase. Cell division takes place in two phases- interphase (G1, S, and G2) and mitotic phase. In the G1 phase, the cell is metabolically active and continuously grows, in the S phase, DNA synthesis takes place and in the G2 phase, the cell prepares itself to go into the M phase and in the M phase, cell division takes place and divides the cell into two parts. 19. Arrange the following events of meiosis in the correct sequence. (i) Crossing over (ii) Synapsis (iii) Terminalisation of chiasmata (iv) Disappearance of nucleolus (NEET 2016) (a) (ii),(iii),(iv),(i) (b) (ii),(i),(iv),(iii) (c) (ii),(i),(iii),(iv) (d) (i),(ii),(iii),(iv) Ans. (c) Sol. Meiosis is basically divided into two- meiosis I and meiosis II. In meiosis I, reduction division takes place while in meiosis II, equational division takes place. The correct order of meiosis I in prophase I are the synapsis (zygotene), crossing over (pachytene), terminalization of chiasmata, and disappearance of the nucleolus by end of diakinesis. 20. During which phase(s) of the cell cycle, amount of DNA in a cell remains at 4C level if the initial amount is denoted as 2C? (NEET 2014) (a) G0 and G1 (b) G1 and S (c) Only G2 (d) G2 and M Ans. (c) Sol. During the S phase, the amount of DNA doubles, after which the 4C content of DNA is present only in the G2 phase because, during the M phase, the cell