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Q1. In a cell cycle, during which phase are chromosomes arranged on the equatorial plate?

• Metaphase
• Anaphase
• Telophase
• 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.

Q2. A mitotic spindle is mainly composed of which protein? 

• Actin
• Myosin
• Actomyosin
• Myoglobin

Solution

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

Q3. The yeast cell can progress through the cell cycle in about

• 30 minutes
• 60 minutes
• 90 minutes
• 120 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.

Q4. Meiosis results in

• Production of gametes
• Maintenance in the number of chromosomes
• Introduction of variation
• All of the above

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 

Q5. Centromere is required for  

• Transcription  
• Crossing over  
• Cytoplasmic cleavage  
• Movement of chromosomes towards poles  

Solution

Centromeres are required for chromosome separation during cell division. They are the attachment points for microtubules which pull duplicate chromosomes towards the opposite poles of the cell before it divides. This separation ensures that each daughter cell will receive a full set of chromosomes.  

Q6. Identify the meiotic stage in which the homologous chromosomes separate while the sister chromatids remain associated at their centromeres.  

• Metaphase I  
• Metaphase II  
• Anaphase I  
• Anaphase II  

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.  

Q7. Which phase comes in between the G₁ and G₂ phases of the cell cycle?

• M phase
• G₀ phase
• S phase
• Interphase

Solution

Interphase involves a series of changes which a newly formed cell and its nucleus undergo to become fit for cell division. It is divided into three phases - the first gap or G₁ phase, followed by the synthetic or S phase and the second gap or G₂ phase.

Q8. G₁, G₂ and S phases are seen in which phase of the cell cycle?

• Metaphase
• Prophase
• Anaphase
• Interphase

Solution

Interphase involves a series of changes which a newly formed cell and its nucleus undergo to become ready for cell division. It is divided into three phases - G₁ phase, S phase and G₂ phase. The duration of these phases varies in different organisms.

Q9. At which stage of mitosis do chromatids separate and pass to different poles?  

• Metaphase  
• Prophase  
• Telophase  
• 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.  

Q10. How many mitotic divisions are needed for a single cell to make 128 cells? 

• 7
• 14
• 28
• 64

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.... 

Q11. In mitosis, the number of chromosome sets in daughter cells will be

• Different from parent cells
• Half of parent cells
• Double of parent cells
• Same as in parent cells

Solution

Mitosis is the division of the parent cell into two identical daughter cells, each with a nucleus which has the same amount of DNA, same number and kind of chromosomes and same hereditary information as in the parent cell. Hence, mitosis is regarded as equational division.

Q12. When energy is stored and the cell undergoes differentiation in adverse conditions, the stage is called  

• G₁  
• G₀  
• S  
• Anaphase  

Solution

Cells which cannot divide further do not proceed beyond the G₁ phase and begin to differentiate into specific cell types. Such cells are said to be in the G₀ phase. The cells remain metabolically active but do not proliferate. Example: Fibroblast cells help in the healing of wounds, grow and divide again depending on the requirement of the body.  

Q13. During meiosis, crossover occurs between  

• Sister chromatids of non-homologous chromosomes  
• Sister chromatids of homologous chromosomes  
• Non-sister chromatids of homologous chromosomes  
• Non-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   

Q14. 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 3 are correct.  
• 1 and 2 are correct.  
• 2 and 4 are correct.  
• 1 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.  

Q15. Cross-like configurations when non-sister chromatids of a bivalent come in contact during the first meiotic division are  

• Chiasmata  
• Chromomeres  
• Centromeres  
• Bivalents  

Solution

Chiasma is the point where two homologous non-sister chromatids exchange genetic material during chromosomal crossover which occurs during meiosis. The chiasmata become visible during the diplotene stage of prophase I of meiosis. However, crossing over of genetic material occurs during the pachytene stage.  

Q16. A cell plate is laid during  

• Cytokinesis  
• Karyokinesis  
• Interphase  
• None of the above  

Solution

Cytokinesis involves cytoplasmic movements which bring about equal distribution of mitochondria and other cell organelles in the two halves of the cell. Due to the presence of a rigid cell wall, a plant cell cannot undergo cytokinesis by an invaginating cleavage furrow. Hence, plant cells divide by cell plate formation which begins during late anaphase or early telophase.  

Q17. Synaptonemal complex is observed during cell division in  

• Meiotic prophase  
• Mitotic prophase  
• Meiotic metaphase  
• Mitotic telophase  

Solution

Synapsis occurs during the zygotene stage of prophase I of meiosis. A fibrillar, ladder-like organelle called synaptonemal complex develops between the synapsed homologous chromosomes. It functions to stabilise the paired condition of chromosomes till crossing over is completed.  

Q18. Crossing over may result in

• Addition of genetic material
• Deletion of genetic material
• Exchange of genetic material
• All of the above

Solution

Crossing over is the exchange of genetic material between homologous chromosomes which results in recombination. It occurs during the pachytene stage of prophase I of meiosis during a process called synapsis.

Q19. Where can we study mitosis?  

• Nail base  
• Brain  
• Legs  
• Kidneys  

Solution

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

Q20. The major events which occur during the anaphase of mitosis which bring about equal distribution of chromosomes is

• Replication of the genetic material
• Splitting of the chromatids
• Splitting of the centromeres
• Condensation of the chromatin

Solution

Before cell division, each chromosome duplicates to form two identical parts called sister chromatids attached to each other at a region called the centromere. During anaphase, the division of the centromere releases two daughter chromosomes, one for each daughter cell.

Q21. Cell division is initiated in plants by

• Cytokinin
• Auxin
• Gibberellin
• Abscisic acid

Solution

Cytokinins are a class of plant growth hormones which promote cell division or cytokinesis in plant roots and shoots. They are involved primarily in cell growth and differentiation, but they also affect apical dominance, axillary bud growth and leaf senescence.

Q22. The point at which polytene chromosomes appear to be attached together is called 

• Centriole
• Centromere
• Chromomere
• Chromocentre

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.   

Q23. The best stage to observe the shape, size and number of chromosomes is 

• Interphase
• Metaphase
• Prophase
• 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 

Q24. In a cell cycle, DNA replication takes place in 

• G₁ phase
• G₂ phase
• Mitotic metaphase
• 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. 

Q25. When synapsis is complete all along the chromosome, the cell is said to have entered a stage called

• Zygotene
• Pachytene
• Diplotene
• Diakinesis

Solution

Synapsis occurs during the zygotene stage of prophase I of meiosis. A synaptonemal complex develops between the synapsed homologous chromosomes. During the pachytene stage, the synapsed chromosomes slightly separate and become visible.

Q26. Which of the phases of mitosis is the longest?

• Prophase
• Metaphase
• Anaphase
• Telophase

Solution

Metaphase

Q27. What is the proper sequence in mitosis?

• Metaphase, telophase, prophase and anaphase
• Prophase, metaphase, anaphase and telophase
• Anaphase, metaphase, telophase and prophase
• Telophase, anaphase, metaphase 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.

Q28. In meiosis, the daughter cells are not similar to the parent because of

• Crossing over
• Synapsis
• Both 1 and 2 above
• None of the above

Solution

Meiosis introduces variation by forming new gene combinations through crossing over and random assortment of paternal and maternal chromosomes. So, the daughter cells produced through meiosis are not similar to the parent.

Q29. At which stage of the cell cycle are histone proteins synthesised in a eukaryotic cell? 

• G₂ stage of prophase
• S phase
• Entire prophase
• 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. 

Q30. Which of the following statements is incorrect about the G₀ phase?  

• Mitosis occurs after the G₀ phase.  
• Biocatalysts can be used to exit the G₀ phase.  
• Cell volume goes on increasing during the G₀ phase.  
• Cell metabolism occurs continuously in the G₀ phase.  

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