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

30 CELL CYCLE AND CELL DIVISION EXERCISE – 1: Basic Objective Questions Cell Cycle: Introduction 1. The sequence of events by which a cell duplicates its genome, synthesizes the other constituents of the cells, and eventually divides into two daughter cells is called (a) Cell division (b) Cell cycle (c) Karyokinesis (d) Cytokinesis Ans. (b) Sol. The sequence of events by which a cell duplicates its genome synthesizes the other constituents of the cells, and eventually divides into two daughter cells is called the cell cycle. It is further divided into interphase and M-phase. Cell division is where the cell is divided into two daughter cells. Karyokinesis is a nuclear division. Cytokinesis is the division of the cytoplasm. 2. A cell cycle includes (a) Interphase and M-phase/divisional phase (b) Prophase, metaphase, anaphase and telophase (c) G1, S and G2 phases (d) Karyokinesis and cytokinesis Ans. (a) Sol. The cell cycle includes the interphase and M- phase/divisional phase. Interphase is the middle stage of the cell cycle because there occurs one interphase between the two-division phases. The interphase cell will grow in size and prepare itself for the next division. The interphase is the most active phase of the cell cycle. The division phase or M-phase is also known as the division phase or mitotic phase. This is the phase of the shortest time in the cell cycle. In this phase, the division of the nucleus occurs which is known as karyokinesis. The division of cytoplasm occurs which is known as cytokinesis. 3. In the 24-hour average duration of the cell cycle of a human cell, cell division properly lasts for about (a) 23 hours (b) An hour (c) Half an hour (d) 90 minutes Ans. (b) Sol. In the 24 hours, the average duration of the cell cycle of a human cell, cell division properly lasts for about an hour. The cell cycle is divided into 2 phases- interphase and M-phase (mitotic phase). In the interphase, the cell prepares itself for division. Interphase is the longest period of the cell cycle. Cell division takes place in the mitotic phase and is of a shorter duration. Out of 24 hours, the interphase is 23 hours long and the mitotic phase is of 1 hour during which cell division takes place. 4. Of the total duration of cell cycle, the interphase lasts more than (a) 95 % (b) 5 % (c) 90 % (d) 92 % Ans. (a) Sol. Out of the total duration of the cell cycle, the interphase lasts more than 95%. The cell cycle is divided into 2 phases- interphase and mitotic phase. Interphase consists of the G1 phase, S phase, and G2 phase in which the cell prepares itself for the division. It is the longest period of the cell cycle and takes almost 23 hours while the mitotic phase is divided into prophase, metaphase, anaphase, and telophase in which cell division takes place. It is the shortest phase and takes about 1 hour for cell division. 5. Read the following statements about cell division and select the correct answer. (i) M phase represents the phase when actual cell division occurs and I phase represents the phase between two successive M phases. (ii) In the 24 hours average duration of the cell cycle of a human cell, cell division properly lasts for only about an hour. (iii) M phase constitutes more than 95 % of the duration of the cell cycle. (a) (i) and (ii) (b) (ii) and (iii) (c) (i) and (iii) (d) (i), (ii) and (iii) Ans. (a) Sol. M phase represents the phase when the actual cell division occurs and the I phase represents the phase between two successive M phases. In the 24 hours average duration of the cell cycle of a human cell, the cell division properly lasts for only about an hour. This is the phase of the shortest time in a cell cycle. In this phase, the division of the nucleus occurs which is known as karyokinesis. The division
CELL CYCLE AND CELL DIVISION 31 of the nucleus occurs by the sequential change in the nucleus and the cytoplasm. 6. Recognise the figure and find out the correct matching. (a) a-G1 , b-S, c-G2, d-M (b) a-M , b-G1, c-S, d-G2 (c) a-G1 , b-S, c-G2, d-G0 (d) a-G0 , b-G1, c-S, d-G2 Ans. (d) Sol. The cell cycle is divided into two phases- interphase and mitotic phase. Here, the G0 phase is also known as the quiescent stage. Non-dividing cells come under the category of the G0 phase. The G1 phase is associated with the aggregation of raw materials required for DNA synthesis. In the S phase, the amount of DNA is doubled but the number of chromosomes remains the same, and in the G2 phase, the cell prepares itself for cell division in M-phase. 7. Four phases of the cell cycle are (a) G1S G2 M (b) S G1 G2 M (c) G1 G2 S M (d) M G1 G2 S Ans. (a) Sol. Four phases of the cell cycle are G1→ S→ G2→ M. G1 phase or pre DNA synthesis phase is the 1st Gap phase. This is the longest phase of the cell's time period of 12 hrs. The cell grows maximum in the G1 stage. S phase is a DNA synthesis phase. Its time period is 6–10 hr. In this phase, the replication of nuclear DNA and the synthesis of histone protein takes place. The G2 phase is the 2nd Gap phase. The time period of this phase is 3-12 hrs. In this phase, the number of cell organelles increases in the cell. The division phase or M-phase is also known as the division phase or mitotic phase. The time period for this phase is 1 hr. This is the phase of the shortest time in the cell cycle. In this phase, the division of the nucleus occurs and the division of the cytoplasm occurs. 8. Which phase corresponds to the interval between mitosis and initiation of DNA replication? (a) Gap 1/G1, phase (b) Gap 2/G2, phase (c) Synthesis/S phase (d) M phase Ans. (a) Sol. The cell cycle runs in two phases- the interphase and the M phase. The phase corresponding to the interval between mitosis and initiation of DNA replication i.e. S phase is Gap 1 or G1 phase. The G1 phase is associated with the aggregation of raw materials required for DNA synthesis. 9. Select the correct statement about the G1 phase. (a) Cell is metabolically inactive. (b) DNA in the cell does not replicate. (c) It is not a phase of synthesis of macromolecules. (d) Cell stops growing. Ans. (b) Sol. In the G1 stage, the DNA in the cell does not replicate. G1 phase or pre DNA synthesis phase is the 1 st Gap phase. This is the longest phase of the cell. Its time period is 12 hr. During the G1 phase, the number of cell organelles increases in the cell and the cell rapidly synthesizes different types of RNA and proteins. Due to the availability of protein, the synthesis of new protoplasm takes place in cells and it starts growing in size. The cell grows maximum in the G1 stage. 10. Assertion: G1 phase is the interval between mitosis and initiation of DNA replication. Reason: The cell is metabolically inactive during the G1 phase. (a) If both assertion and reason are true and reason is the correct explanation of assertion. (b) If both assertion and reason are true but reason is not the correct explanation of assertion. (c) If assertion is true but reason is false. (d) If both assertion and reason are false.
32 CELL CYCLE AND CELL DIVISION Ans. (c) Sol. G1 phase is also known as the first growth phase or post-mitotic gap phase. It is the phase between the end of the mitotic phase of the previous cell and the initiation of the S-phase of the next mitotic phase. During the G1 phase, the cells are metabolically active and continuously grow. In this phase, different types of RNA (mRNA, tRNA, and rRNA) and proteins are synthesized. So, option (c) is correct. 11. In a diploid cell, at which stage of the cell cycle, the amount of DNA is doubled? (a) G1 and G2 phase (b) G0 phase (c) S, G2, and M phase (d) S phase Ans. (d) Sol. In a diploid cell, the amount of DNA is doubled in the S phase of the cell cycle as it is the synthesis phase. The cell cycle has two basic phases- the interphase and the mitotic phase. In the mitotic phase, division of the nucleus and cytoplasm takes place. The interphase cell prepares itself for division. Interphase is further divided into the Gap1 phase, S phase, and Gap 2 phase. 12. In ‘S phase’, the amount of DNA (a) As well as number of chromosomes doubles in each cell (b) Doubles but the number of chromosomes remains the same in each cell (c) And the number of chromosomes remain unchanged in each cell, but the amount of protein doubles (d) Remains the same in each cell but the number of chromosomes doubles Ans. (b) Sol. In the S phase, the amount of DNA doubles but the number of chromosomes remains the same in each cell. S phase is a phase of DNA synthesis. It has a time period of 6-10 hr. In this phase, replication of nuclear DNA and synthesis of histone protein takes place. Centriole replication is semi-conservative, the same as DNA replication. 13. Centriole replicates during (a) Interphase (b) Early prophase (c) Late prophase (d) Late telophase Ans. (a) Sol. The component needed for a particular phase is already synthesized in the previous phase and replication of centriole takes place in the S phase which is a part of the interphase. The centriole is a small set of microtubules. These microtubules then elongate and form spindle fibers along with the centrosome. 14. A somatic cell that has just completed the S phase of its cell cycle as compared to gamete of the same species has (a) Twice the number of chromosomes and four times the amount of DNA (b) Four times the number of chromosomes and twice the amount of DNA (c) Twice the number of chromosomes and twice the amount of DNA (d) Same number of chromosomes and twice the amount of DNA Ans. (a) Sol. For somatic cells, after S-phase, chromosome numbers are twice (2n) and the amount of DNA is four times (due to duplication) as compared to gamete of the same species. In the interphase, the cell grows in size and prepares itself for the next division. The interphase is the most active phase of the cell cycle. S phase of interphase, in this phase the DNA synthesis or replication takes place. During this time, the amount of DNA per cell doubles, but the number of chromosomes remains the same. Somatic cells are diploid (2n) as compared to gametes which are haploid (n). 15. The cells that do not divide further, exit G1 phase to enter an inactive stage called ______ of the cell cycle. (a) G1 stage (b) G2 stage (c) S stage (d) G0 stage Ans. (d) Sol. The cells that do not divide further, exit the G phase to enter an inactive stage called the G0 phase of the cell cycle. The cells of permanent tissue go through the G0 phase which is also called the resting phase of the cell cycle in which cells exist in a quiescent state. G0 phase is an extended G1 phase, where the cell is neither dividing nor preparing to divide. Some types of such cells that continue the quiescent stage when they reach maturity are nerve and heart muscle cells. 16. Which of the following cells in an adult animal do not appear to exhibit division? (a) Bone marrow cells (b) Upper layer of the epidermis (c) Heart cells (d) All of the above
CELL CYCLE AND CELL DIVISION 33 Ans. (c) Sol. The heart cells do not exhibit cell division and do not divide further by exiting the G1 phase to enter the G0 phase which is an inactive stage called the quiescent stage of the cell cycle. The cardiac muscle cells no longer divide after a stage of maturity and they perform their functions, as usual, all through their life. Similarly, the nerve cells are highly specific and they divide once when they get specialized. 17. Assertion: Some cells undergo the G0 phase due to the inactivation of the cell cycle. Reason: G0 phase occurs due to the non-availability of mitogen and energy-rich compounds. (a) If both assertion and reason are true and reason is the correct explanation of assertion. (b) If both assertion and reason are true but reason is not the correct explanation of assertion. (c) If assertion is true but reason is false. (d) If both assertion and reason are false. Ans. (a) Sol. The phase in which cells fail to divide further (do not undergo S-phase after G1-phase) is known as the G0 phase or quiescent stage. It occurs due to the non- availability of mitogen and energy-rich compounds. The cells remain metabolically active but no longer proliferate unless called on to do so depending on the requirement of the organisms. Cell Cycle Checkpoints 18. Cell would normally proceed to mitosis without interruption (a) Once it has entered the G1 Phase (b) Once it has entered the S-phase (c) At any time during cell division activity (d) None of the above Ans. (b) Sol. G1 checkpoint or G1/S checkpoint checks if the cell have enough energy reserves or available nutrients to divide or if the DNA is damaged. Once the check point of G1-S phase is crossed and cell has entered S- phase, cell cycle will go on further division till completion. Mitosis 19. Mitosis is characterized by (a) Reduction division (b) Equational division (c) Both reduction and equational division (d) Pairing of homologous chromosomes. Ans. (b) Sol. Mitosis is characterized by equational division. Mitosis is the process of cell division where the chromosomes replicate and get equally distributed into two identical daughter cells. It is known as the equational division because the number of chromosomes and the amount of DNA in the daughter cells remain equal to the parent cells. 20. Number of mitotic divisions required to produce 128 cells from a single cell is (a) 7 (b) 14 (c) 16 (d) 32 Ans. (a) Sol. One cell gives rise to two daughter cells in one mitotic division. These two cells further divide equationally giving rise to 4 cells, then from these 4 cells to 8 cells. Finally, 7 equation divisions occur which give rise to 128 cells. 21. Bacterium divides every 35 minutes. If a culture containing 10 5 cells per mL is grown for 175 minutes, what will be the cell concentration per mL after 175 minutes? (a) 510 cells 5 (b)3510 cells 5 (c) 3210 cells 5 (d)17510 cells 5 Ans. (c) Sol. The total time given is 175 minutes. One division takes 35 minutes. Total division = 175 min/35 min = 5. One bacterium gives rise to 2 daughter cells from two to four and so on. Here, it has been divided 5 times in 175 min. Hence, cell concentration per ml after 175 min = (2)5×105 = 32×105 cells per ml. 22. What is the proper sequence in mitosis? (a) Metaphase, telophase, prophase, and anaphase (b) Prophase, metaphase, anaphase, and telophase (c) Anaphase, metaphase, telophase, and prophase (d) Telophase, anaphase, metaphase, and prophase Ans. (b) Sol. The proper sequence in mitosis is prophase, metaphase, anaphase, telophase. In prophase, condensation of chromosomes occurred to form compact mitotic chromosomes. In metaphase, the chromosomes get aligned at the metaphase plate in the equator of the cell. In anaphase, the chromatids get separated and move to the opposite poles by spindle fibers. In telophase, the chromosomes disappear, nuclear membrane reforms, centrioles duplicate.