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Q1. In a cell cycle, DNA replication takes place in 

• 1) G₁ phase
• 2) G₂ phase
• 3) Mitotic metaphase
• 4) S phase

Solution

In the S phase, replication of chromosomes and their DNA occurs with the help of DNA polymerase. Maximum histone protein is synthesised in the S phase. The number of chromosomes remains the same as was present in the cell but each chromosome becomes double stranded. 

Q2. In a cell cycle, during which phase are chromosomes arranged on the equatorial plate?

• 1) Anaphase
• 2) Telophase
• 3) Metaphase
• 4) Prophase

Solution

During metaphase, the chromosomes get arranged in the form of a plate called the equatorial plate or metaphase plate at the equator of the spindle. This plate is at right angles to the axis of the spindle and is formed of the kinetochores, the arms of chromatids trailing away. The centromeres are drawn to the equator by the equal pull of two chromosomal fibres which connect the sister kinetochores to the opposite poles. The process of drawing the chromosomes onto the equator of the spindle is known as congression.

Q3. Which stages of cell division do the figures A and B represent?              

• 1) A: Late anaphase; B: Prophase  
• 2) A: Prophase; B: Anaphase  
• 3) A: Metaphase; B: Telophase  
• 4) A: Telophase; B: Metaphase  

Solution

During anaphase, the sister chromatids move towards the opposite poles. The anaphase ends when all the chromatids reach the opposite poles.     During prophase, the chromosomes become visible and the nucleolus disappears. The mitotic spindle forms and the nuclear envelope disappears.    

Q4. The point at which polytene chromosomes appear to be attached together is called 

• 1) Centriole
• 2) Centromere
• 3) Chromocentre
• 4) Chromomere

Solution

Polytene chromosomes are formed by pairing of two somatic homologous chromosomes which undergo endomitosis forming a number of strands. These strands remain attached to a large chromocentre and are rich in heterochromatin.   

Q5. How many mitotic divisions are needed for a single cell to make 128 cells? 

• 1) 28
• 2) 14
• 3) 64
• 4) 7

Solution

A single mitotic division results in the production of two cells from a single cell. Therefore, it will be 1, 2, 4, 8, 16, 32, 64, 128.... 

Q6. Sanjay observes a cell in the metaphase stage under a microscope. Describe the structure or appearance of chromosomes which he may have observed.

Solution

Chromosomes are thick and clearly visible. Their two sister chromatids are visible. The sister chromatids are held together by the centromere. Small disc-shaped structures are visible at the surface of the centromeres. These structures are called kinetochores, and they provide the surface of attachment of spindle fibres to chromosomes.

Q7. Where can we study mitosis?  

• 1) Legs  
• 2) Kidneys  
• 3) Nail base  
• 4) Brain  

Solution

Mitosis takes place in the nail root at the base of the nail.  

Q8. Define meiosis.

Solution

Meiosis is a specialised kind of cell division which reduces the chromosome number by half resulting in the formation of haploid daughter cells.

Q9. Define crossing over.

Solution

Crossing over is the exchange of genetic material between two homologous chromosomes.

Q10. Label the diagram and also determine the stage at which the contents of a cell appear like the following diagram.

Solution

Metaphase:  

Q11. What is the function of kinetochores?

Solution

Kinetochores provide the surface for the attachment of spindle fibres to the chromosomes.

Q12. The yeast cell can progress through the cell cycle in about

• 1) 30 minutes
• 2) 90 minutes
• 3) 120 minutes
• 4) 60 minutes

Solution

The duration of the cell cycle depends on the type of cell and external factors such as temperature, food and oxygen supplies. The bacterial cell can divide every 20 minutes, while onion root tips may take 20 hours. The mammalian cell divides once in every 24 hours, and a yeast cell may take about 90 minutes.

Q13. At which stage of the cell cycle are histone proteins synthesised in a eukaryotic cell? 

• 1) S phase
• 2) G₂ stage of prophase
• 3) Entire prophase
• 4) Telophase

Solution

The synthesis of histone proteins takes place during the S phase of the cell cycle because the number of chromosomes is double the somatic number. 

Q14. Name the four stages of mitosis.

Solution

The four stages of mitosis are Prophase Metaphase Telophase Anaphase

Q15. Identify the stage which the following diagram represents.      

Solution

Prophase I  

Q16. Write the events which occur during the metaphase stage.

Solution

Metaphase: Spindle fibres attach to kinetochores of chromosomes. Chromosomes get aligned in the middle of the cell on the equatorial plane or metaphase plate.

Q17. State the event which marks the beginning of prophase during mitosis.

Solution

Initiation of condensation of chromatin material marks the beginning of prophase during mitosis.

Q18. Which is the longest phase of the cell cycle?  

Solution

Interphase is the longest phase of the cell cycle.  

Q19. What is the proper sequence in mitosis?

• 1) Prophase, metaphase, anaphase and telophase
• 2) Metaphase, telophase, prophase and anaphase
• 3) Telophase, anaphase, metaphase and prophase
• 4) Anaphase, metaphase, telophase and prophase

Solution

There are two main events in mitosis - karyokinesis or duplication of the nucleus, followed by cytokinesis or division of the cytoplasm. This is followed by the separation of the daughter cells. Karyokinesis is divided into four stages - prophase, metaphase, anaphase and telophase.

Q20. Identify the meiotic stage in which the homologous chromosomes separate while the sister chromatids remain associated at their centromeres.  

• 1) Anaphase II  
• 2) Metaphase II  
• 3) Anaphase I  
• 4) Metaphase I  

Solution

During anaphase I, two out of each tetrad of chromatids of a chromosome move as a unit to one of the poles of the spindle. The other two chromatids of its homologue migrate to the opposite pole. Therefore, rather than the chromatids of a chromosome, the homologous chromosomes of each pair are separated.  

Q21. State the duration of the cell cycle in yeast.  

Solution

The duration of the cell cycle in yeast is 90 minutes.  

Q22. Explain the events which occur during a pachytene stage.  

Solution

The following events occur during the pachytene stage:     Recombination nodules appear.   Homologous chromosomes cross over at the recombination nodules for the exchange of genetic material.

Q23. Meiosis results in

• 1) All of the above
• 2) Production of gametes
• 3) Maintenance in the number of chromosomes
• 4) Introduction of variation

Solution

Meiosis has the following significance: 1. Formation of gametes 2. Formation of spores 3. Maintenance of chromosome number 4. Introduction of variation 5. Mutation 6. Evidence of basic relationship of organisms 

Q24. Match List I and List II, and select the correct answer.     List I (Phase of Meiosis)     List II (Event which occurs)     1. Prophase I     Crossing over occurs     2. Metaphase II     Sister chromatids migrate to opposite poles     3. Anaphase I     Homologous chromosomes line up at the equator in pairs     4. Telophase II     Condensation of chromatin fibres        

• 1) 2 and 4 are correct.  
• 2) 1 and 3 are correct.  
• 3) 1 and 2 are correct.  
• 4) 1, 2 and 3 are correct.  

Solution

Crossing over or recombination occurs during the pachytene stage of prophase I of meiosis. During metaphase II, sister chromatids migrate to opposite poles forming a single metaphase plate. In metaphase I, homologous pairs of chromosomes are spread across the metaphase plate. Progressive condensation and coiling of chromosome fibres occur during the leptotene stage of prophase I of meiosis.  

Q25. The best stage to observe the shape, size and number of chromosomes is 

• 1) Metaphase
• 2) Interphase
• 3) Prophase
• 4) Telophase

Solution

During the stage of metaphase, the following characteristics can be easily studied:  1. Least coiled chromosomes  2. Show maximum condensation  3. Chromosomes are shortest in length 

Q26. State the events which take place during prophase.

Solution

Events which occur during prophase: Chromosomal material condenses into chromosomes. Chromatids and centromeres are visible. The mitotic spindle starts forming in the cytoplasmic microtubules and proteinaceous components of the cytoplasm.

Q27. A mitotic spindle is mainly composed of which protein? 

• 1) Myoglobin
• 2) Myosin
• 3) Actin
• 4) Actomyosin

Solution

Mitotic spindles are nothing but microtubules made of small units of tubulin which have amino acid composition similar to actin. 

Q28. Synapsis occurs in which of the following stages of meiosis?

• 1) Diakinesis
• 2) Zygotene
• 3) Leptotene
• 4) Pachytene

Solution

Synapsis is the pairing of homologous chromosomes. It allows matching of homologous pairs of chromosomes before their segregation and possible chromosomal crossover between them. Synapsis occurs during the zygotene stage of prophase I of meiosis.

Q29. At which stage of mitosis do chromatids separate and pass to different poles?  

• 1) Prophase  
• 2) Telophase  
• 3) Metaphase  
• 4) Anaphase  

Solution

During anaphase of mitosis, the chromosomes split and the sister chromatids of each chromosome move towards the opposite poles. The separation of chromatids begins at the kinetochore and the arms trail behind. Therefore, the chromosomes are pulled into V, L, J and I shapes based on the position of the kinetochore.  

Q30. Define bivalents.

Solution

Bivalents are the homologous chromosomes which are paired during the zygotene stage of prophase I in meiosis.

Q31. Distinguish between the cytokinesis of plant cell and animal cell.

Solution

Cytokinesis of Animal Cell Cytokinesis of Plant Cell A furrow appears in the plasma membrane. Cytokinesis begins with the formation of the cell plate in the middle of the cell. The furrow deepens and joins the centre dividing the cell into two daughter cells. The cell plate grows from the centre outwards, dividing the cell into two daughter cells.

Q32. Draw the diagrams of     Transition to metaphase   Anaphase  

Solution

Transition to Metaphase:         Anaphase:      

Q33. Name the stage during which chromatids start moving to the opposite poles.

Solution

Anaphase

Q34. Draw a diagram of the cell cycle indicating the formation of two new daughter cells from the parent cell.

Solution

 

Q35. During meiosis, crossover occurs between  

• 1) Non-sister chromatids of homologous chromosomes  
• 2) Sister chromatids of homologous chromosomes  
• 3) Non-sister chromatids of non-homologous chromosomes  
• 4) Sister chromatids of non-homologous chromosomes  

Solution

Some of the essential features of meiosis include:     1. Two consecutive divisions without DNA replication between them     2. Synapsis of homologous chromosomes     3. Crossing over of segments between non-sister chromatids of homologous chromosomes     4. Segregation of homologous chromosomes     5. Separation of sister chromatids   

Q36. Name the enzyme involved in crossing over.

Solution

Recombinase

Q37. Identify the phase shown in the following diagram.

Solution

Late Prophase:  

Q38. Describe the quiescent stage of the cell cycle.

Solution

Some cells do not exhibit cell division or some cells divide only when the body has lost cells during an injury. Such cells enter the quiescent stage. In this stage, the cells are metabolically active. However, the cells do not divide. They undergo division only when there is a requirement by the body under certain conditions.

Q39. What does the cell plate represent?

Solution

The cell plate represents the middle lamella between the walls of the adjacent cells.

Q40. Define cell cycle.

Solution

The sequence of events during which a cell duplicates its genome, synthesises its other constituents and eventually divides into two daughter cells is called the cell cycle.

Q41. Identify the stages during which the following events occur in M phase: Spindle fibres attach to the kinetochores of chromosomes. Golgi complex and endoplasmic reticulum disappear. Daughter chromosomes begin their migration towards the opposite poles. Centromere splits.

Solution

Spindle fibres attach to the kinetochores of chromosomes - Metaphase Golgi complex and endoplasmic reticulum disappear - Prophase Daughter chromosomes begin their migration towards opposite poles - Anaphase Centromere split - Anaphase

Q42. Why is mitosis also called equational division?

Solution

During mitosis, the number of chromosomes in the parent and progeny cells is the same. Hence, it is also called equational division.

Q43. Write the three phases which are collectively known as interphase.

Solution

Three phases which are collectively known as the interphase are G₁ phase S phase G₂ phase

Q44. Name the following: Complex structure formed during synapsis The stage between two meiotic divisions The sites at which the homologous chromosomes remain unseparated during prophase I Enzyme involved in crossing over

Solution

Complex structure formed during synapsis - Synaptonemal complex The stage between the two meiotic divisions - Interkinesis The sites at which the homologous chromosomes remain unseparated during prophase I - Chiasmata Enzyme involved in crossing over - Recombinase

Q45. What are recombination nodules?

Solution

Recombination nodules are the sites at which crossing over occurs between two non-sister chromatids of the homologous chromosomes during the pachytene stage.

Q46. Diagrammatically represent the chromosomal arrangement during the M phase of a cell with four chromosomes of organism X.  

Solution

Early Prophase:                 Late Prophase:                 Metaphase:                 Anaphase:                 Telophase and Cytokinesis:              

Q47. Describe the process of cytokinesis in plant cells.

Solution

In plant cells, the precursors of the cell wall, i.e. the cell plate, are formed in the centre of the cell. The cell plate grows from the middle of the cell outwards, dividing the cell into two daughter cells. The cell plate represents the middle lamella between the walls of two adjacent cells.

Q48. Distinguish between anaphase I of meiosis and anaphase of mitosis.  

Solution

Anaphase I of Meiosis     Anaphase of Mitosis     Centromeres split and chromatids separate.   Homologous chromosomes separate.   Chromatids move to opposite poles.   Sister chromatids remain associated at their centromeres.  

Q49. Differentiate between mitosis and meiosis.

Solution

Mitosis Meiosis Two daughter cells are formed. Four daughter cells are formed. Cytoplasm and nucleus divide once during cell division. Cytoplasm and nucleus divide twice during cell division. Number of chromosomes in daughter cells and parent cell is the same. Number of chromosomes in daughter cells is half the number of chromosomes in parent cell. Mitosis occurs in diploid cells, but it also occurs in some haploid cells. It occurs in diploid cells. It helps in growth and cell repair in organisms. It helps maintain a constant number of chromosomes in a species.

Q50. Name the stage at which the morphology of chromosomes can be studied.

Solution

The morphology of chromosomes can be studied at metaphase.

Q51. State the events which occur during interphase.

Solution

Events which occur during the interphase are as follows: The cells grow. DNA replication takes place.

Q52. State the significance of mitosis.

Solution

Significance of mitosis: Growth of organisms occurs due to mitosis. The cells of the upper layer of the epidermis, blood cells and cells of the gut lining are continuously replaced by mitosis. Mitosis in apical meristem and lateral cambium in plants allows continuous growth throughout life.

Q53. Distinguish between interphase and M phase.

Solution

Interphase M phase It the phase between two successive M phases. It is the phase during which actual cell division takes place. It is the longest phase of the cell cycle. It is the short phase of the cell cycle. Chromosomes are in the form of chromatin. Chromosomes are thick and rod-like.

Q54. State the significance of fertilisation.

Solution

Fertilisation restores the diploid phase in the life cycle.

Q55. State the two phases of the cell cycle.

Solution

The two phases of the cell cycle are Interphase Mitosis phases

Q56. How many chromosomes are present in an onion cell?  

Solution

14 chromosomes are present in an onion cell.  

Q57. Define the following:     M phase   Interphase  

Solution

M phase - It is the phase of the cell cycle during which actual cell division occurs.   Interphase - It is the phase of the cell cycle which occurs between the two successive M phases.  

Q58. Name the cell in which the diplotene phase lasts for years.  

Solution

Oocytes of some vertebrates  

Q59. Name the following: Division of cytoplasm Division of nucleus

Solution

Division of cytoplasm - Karyokinesis Division of nucleus - Cytokinesis

Q60. State the events which occur during the S phase in animal cells.  

Solution

During the S phase in animal cells, DNA replicates in the chromosome and centrioles duplicate in the cytoplasm.  

Q61. State the five phases of meiosis I.

Solution

The five phases of meiosis I are Leptotene Zygotene Pachytene Diplotene Diakinesis

Q62. Give one example of syncytium.

Solution

Liquid endosperm of coconut.

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