Question on Cell Cycle And Cell Division (With Answers) - Class 11 PDF Download

 Page 1


Cell Cycle And Cell Division 
Question - 1. What is the average cell cycle span for a mammalian cell? 
Answer: The average cell cycle span of a mammalian cell is 24 hours. 
Question - 2. Distinguish cytokinesis from karyokinesis. 
Answer: The division of cytoplasm is called cytokinesis, while the division of nucleus 
is called karyokinesis. 
Question - 3. Describe the events taking place during interphase. 
Answer: The interphase is divided into three further phases: 
G1 phase (Gap 1): G1 phase corresponds to the interval between mitosis and 
initiation of DNA replication. During G1 phase the cell is metabolically active and 
continuously grows but does not replicate its DNA. 
S phase (Synthesis): S or synthesis phase marks the period during which DNA 
synthesis or replication takes place. During this time the amount of DNA per cell 
doubles. If the initial amount of DNA is denoted as 2C then it increases to 4C. 
However, there is no increase in the chromosome number; if the cell had diploid or 
2n number of chromosomes at G1, even after S phase the number of chromosomes 
remains the same, i.e., 2n. 
G2 phase (Gap 2): In animal cells, during the S phase, DNA replication begins in the 
nucleus, and the centriole duplicates in the cytoplasm. During the G2 phase, proteins 
are synthesised in preparation for mitosis while cell growth continues. 
Question 4. What is Go (quiescent phase) of cell cycle? 
Answer: 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 G1 phase to enter an inactive stage called quiescent stage (G0) of the cell cycle. 
Cells in this stage remain metabolically active but no longer proliferate unless called 
on to do so depending on the requirement of the organism. 
Question 5. Why is mitosis called equational division? 
Answer: Since the number of chromosomes remains same in parent and daughter 
cells so mitosis is also called as equational division. 
Question 6. Name the stage of cell cycle at which one of the following events 
occur: 
(i) Chromosomes are moved to spindle equator. 
Answer: Metaphase 
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Cell Cycle And Cell Division 
Question - 1. What is the average cell cycle span for a mammalian cell? 
Answer: The average cell cycle span of a mammalian cell is 24 hours. 
Question - 2. Distinguish cytokinesis from karyokinesis. 
Answer: The division of cytoplasm is called cytokinesis, while the division of nucleus 
is called karyokinesis. 
Question - 3. Describe the events taking place during interphase. 
Answer: The interphase is divided into three further phases: 
G1 phase (Gap 1): G1 phase corresponds to the interval between mitosis and 
initiation of DNA replication. During G1 phase the cell is metabolically active and 
continuously grows but does not replicate its DNA. 
S phase (Synthesis): S or synthesis phase marks the period during which DNA 
synthesis or replication takes place. During this time the amount of DNA per cell 
doubles. If the initial amount of DNA is denoted as 2C then it increases to 4C. 
However, there is no increase in the chromosome number; if the cell had diploid or 
2n number of chromosomes at G1, even after S phase the number of chromosomes 
remains the same, i.e., 2n. 
G2 phase (Gap 2): In animal cells, during the S phase, DNA replication begins in the 
nucleus, and the centriole duplicates in the cytoplasm. During the G2 phase, proteins 
are synthesised in preparation for mitosis while cell growth continues. 
Question 4. What is Go (quiescent phase) of cell cycle? 
Answer: 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 G1 phase to enter an inactive stage called quiescent stage (G0) of the cell cycle. 
Cells in this stage remain metabolically active but no longer proliferate unless called 
on to do so depending on the requirement of the organism. 
Question 5. Why is mitosis called equational division? 
Answer: Since the number of chromosomes remains same in parent and daughter 
cells so mitosis is also called as equational division. 
Question 6. Name the stage of cell cycle at which one of the following events 
occur: 
(i) Chromosomes are moved to spindle equator. 
Answer: Metaphase 
(ii) Centromere splits and chromatids separate. 
Answer: Anaphase 
(iii) Pairing between homologous chromosomes takes place. 
Answer: Metaphase I of meiosis 
(iv) Crossing over between homologous chromosomes takes place. 
Answer: Prophase I of meiosis 
Question 7. Describe the following: 
(a) synapsis (b) bivalent (c) chiasmata 
Answer: (a) During zygotene of prophase I of meiosis homologous chromosomes 
pair together. This pairing is called synapsis. 
(b) Bivalent: The complex formed by homologous chromosomes during zygotene is 
called a bivalent. 
(c) Chiasmata: During diplotene the paired chromosomes make a x-shaped 
structure. This is called chiasmata. 
Draw a diagram to illustrate your answer. 
 
 
Question 8. How does cytokinesis in plant cells differ from that in animal 
cells? 
Answer: Due to the presence of a cell wall, cytokinesis in plant cells is significantly 
different from that in animal cells. Rather than forming a contractile ring, plant cells 
construct a cell plate in the middle of the cell. The Golgi apparatus releases vesicles 
containing cell wall materials. These vesicles fuse at the equatorial plane and form a 
cell plate. The cell plate begins as a fusion tube network, which then becomes a 
tubulo-vesicular network (TVN) as more components are added. The TVN develops 
Page 3


Cell Cycle And Cell Division 
Question - 1. What is the average cell cycle span for a mammalian cell? 
Answer: The average cell cycle span of a mammalian cell is 24 hours. 
Question - 2. Distinguish cytokinesis from karyokinesis. 
Answer: The division of cytoplasm is called cytokinesis, while the division of nucleus 
is called karyokinesis. 
Question - 3. Describe the events taking place during interphase. 
Answer: The interphase is divided into three further phases: 
G1 phase (Gap 1): G1 phase corresponds to the interval between mitosis and 
initiation of DNA replication. During G1 phase the cell is metabolically active and 
continuously grows but does not replicate its DNA. 
S phase (Synthesis): S or synthesis phase marks the period during which DNA 
synthesis or replication takes place. During this time the amount of DNA per cell 
doubles. If the initial amount of DNA is denoted as 2C then it increases to 4C. 
However, there is no increase in the chromosome number; if the cell had diploid or 
2n number of chromosomes at G1, even after S phase the number of chromosomes 
remains the same, i.e., 2n. 
G2 phase (Gap 2): In animal cells, during the S phase, DNA replication begins in the 
nucleus, and the centriole duplicates in the cytoplasm. During the G2 phase, proteins 
are synthesised in preparation for mitosis while cell growth continues. 
Question 4. What is Go (quiescent phase) of cell cycle? 
Answer: 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 G1 phase to enter an inactive stage called quiescent stage (G0) of the cell cycle. 
Cells in this stage remain metabolically active but no longer proliferate unless called 
on to do so depending on the requirement of the organism. 
Question 5. Why is mitosis called equational division? 
Answer: Since the number of chromosomes remains same in parent and daughter 
cells so mitosis is also called as equational division. 
Question 6. Name the stage of cell cycle at which one of the following events 
occur: 
(i) Chromosomes are moved to spindle equator. 
Answer: Metaphase 
(ii) Centromere splits and chromatids separate. 
Answer: Anaphase 
(iii) Pairing between homologous chromosomes takes place. 
Answer: Metaphase I of meiosis 
(iv) Crossing over between homologous chromosomes takes place. 
Answer: Prophase I of meiosis 
Question 7. Describe the following: 
(a) synapsis (b) bivalent (c) chiasmata 
Answer: (a) During zygotene of prophase I of meiosis homologous chromosomes 
pair together. This pairing is called synapsis. 
(b) Bivalent: The complex formed by homologous chromosomes during zygotene is 
called a bivalent. 
(c) Chiasmata: During diplotene the paired chromosomes make a x-shaped 
structure. This is called chiasmata. 
Draw a diagram to illustrate your answer. 
 
 
Question 8. How does cytokinesis in plant cells differ from that in animal 
cells? 
Answer: Due to the presence of a cell wall, cytokinesis in plant cells is significantly 
different from that in animal cells. Rather than forming a contractile ring, plant cells 
construct a cell plate in the middle of the cell. The Golgi apparatus releases vesicles 
containing cell wall materials. These vesicles fuse at the equatorial plane and form a 
cell plate. The cell plate begins as a fusion tube network, which then becomes a 
tubulo-vesicular network (TVN) as more components are added. The TVN develops 
into a tubular network, which then becomes a fenestrated sheet which adheres to the 
existing plasma membrane. 
Question 9. List the main differences between mitosis and meiosis. 
Answer: Difference Between Mitosis And Meiosis 
 
 
Question 10. What is the significance of meiosis? 
Answer: Significance of Meiosis 
1. Maintaining of genetic identity by maintaining number of chromosomes. 
2. Bringing variations to ensure better species. 
3. Facilitates sexual reproduction.