### Cell Structure And Function-Cell Cycle And Cell Division Topic

**JEE Main Numerical Questions**

**Problem:**A normal human somatic cell has 46 chromosomes. How many chromatids are present in a cell entering mitosis?

**Solution:** Chromosomes condense and become visible during mitosis. Each chromosome is made up of two chromatids, which are identical copies of each other. Since there are 46 chromosomes in a normal human somatic cell, there will be 46 x 2 = 92 chromatids present in a cell entering mitosis.

**Problem:**A cell is observed to have 16 chromosomes in its nucleus. How many daughter cells will be produced after mitosis?

**Solution:** Mitosis is a process by which a single cell divides into two identical daughter cells. Since the cell in question has 16 chromosomes, each daughter cell will also have 16 chromosomes. Therefore, mitosis will produce two daughter cells, each with 16 chromosomes.

**Problem:**If the DNA content of a cell in the G1 phase is ‘x’, what will be its content during the prophase of the next mitosis?

**Solution:** During the G1 phase of the cell cycle, the DNA content is ‘x’. In the S phase, DNA replication occurs, and the DNA content doubles. Therefore, the DNA content during the prophase of the next mitosis will be 2x.

**Problem:**A plant cell has 12 chromosomes in its somatic cells. How many chromosomes will be present in its germ cells?

**Solution:** Germ cells are reproductive cells, such as eggs and sperm, which contain half the number of chromosomes as somatic cells. Since the plant cell in question has 12 chromosomes in its somatic cells, its germ cells will have 12/2 = 6 chromosomes.

**Problem:**If the DNA replication time in a cell cycle is 8 hours, what would be the duration of the S phase if the total duration of the cell cycle is 24 hours?

**Solution:** The S phase is the phase of the cell cycle during which DNA replication occurs. If the DNA replication time is 8 hours and the total duration of the cell cycle is 24 hours, then the duration of the S phase will be 8/24 x 100 = 33.33% of the cell cycle.

**Problem:**A cell takes 24 hours to complete one cell cycle. If the interphase lasts for 18 hours, calculate the duration of the mitotic phase.

**Solution:** The mitotic phase is the phase of the cell cycle during which cell division occurs. If the interphase lasts for 18 hours and the total duration of the cell cycle is 24 hours, then the duration of the mitotic phase will be 24 - 18 = 6 hours.

**Problem:**A dividing cell completes mitosis in 30 minutes. Calculate the number of hours required for the completion of 20 rounds of mitosis by this cell.

**Solution:** If the cell takes 30 minutes to complete one round of mitosis, then the number of hours required for the completion of 20 rounds of mitosis will be 20/60 x 30 = 10 hours.

**Problem:**A cell has a diploid number of 2n = 32. What will be the number of chromatids present in a metaphase plate during mitosis?

**Solution:** During metaphase, the chromosomes line up at the metaphase plate. Each chromosome consists of two chromatids. Since the cell in question has a diploid number of 2n = 32, there will be 32 chromosomes at the metaphase plate, each with two chromatids, resulting in a total of 32 x 2 = 64 chromatids.

**Problem:**A scientist observes a cell with 4 chromatids in each chromosome. At what stage of the cell cycle is the cell present?

**Solution:** A cell with 4 chromatids in each chromosome is in the metaphase stage of mitosis. During metaphase, the chromosomes line up at the metaphase plate, and each chromosome consists of two sister chromatids.

**Problem:**A cell has a DNA content of 2 pg (picograms) during the G1 phase of the cell cycle. What will be the DNA content of this cell during the G2 phase?

**Solution:** During the G1 phase, the cell has a DNA content of 2 pg. In the S phase, DNA replication occurs, and the DNA content doubles. Therefore, the DNA content of the cell during the G2 phase will be 2 pg x 2 = 4 pg.

**CBSE Board Exam Numerical Questions**

**Problem:**A cell with 20 chromosomes undergoes mitosis. What is the total number of chromosomes and chromatids present at the metaphase stage of mitosis?

**Solution:** At the metaphase stage of mitosis, all the chromosomes are aligned at the equator of the cell. Each chromosome consists of two sister chromatids. Since the cell has 20 chromosomes, there will be 20 chromosomes and 20 x 2 = 40 chromatids present at the metaphase stage of mitosis.

**Problem:**A cell has a diploid number of 14 chromosomes. Calculate the number of chromatids present in a cell about to enter the prophase of mitosis.

**Solution:** A cell about to enter the prophase of mitosis has replicated its DNA. Each chromosome now consists of two sister chromatids. Since the cell has a diploid number of 14 chromosomes, there will be 14 chromosomes and 14 x 2 = 28 chromatids present in a cell about to enter the prophase of mitosis.

**Problem:**A cell takes 24 hours to complete one cell cycle. If the S phase occupies one-half of the total interphase duration, what is the length of the S phase?

**Solution:** The interphase is the phase of the cell cycle between two successive divisions. If the cell takes 24 hours to complete one cell cycle and the S phase occupies one-half of the total interphase duration, then the length of the S phase will be 24/2 = 12 hours.

**Problem:**A plant cell with 16 chromosomes undergoes meiosis. How many daughter cells will be produced at the end of meiosis II?

**Solution:** Meiosis is a type of cell division that reduces the chromosome number by half. Meiosis consists of two rounds of division, meiosis I, and meiosis II. At the end of meiosis II, four daughter cells will be produced, each with half the number of chromosomes as the parent cell. Therefore, the plant cell with 16 chromosomes will produce 4 daughter cells with 16/2 = 8 chromosomes each at the end of meiosis II.

**Problem:**A cell has a DNA complement of 1.8 pg (picograms) in the G1 phase of the cell cycle. What would be the DNA complement of the same cell in the metaphase stage of mitosis?

**Solution:** In the G1 phase of the cell cycle, the cell has a DNA complement of 1.8 pg. In the S phase, DNA replication occurs, and the DNA content doubles. Therefore, the DNA complement of the same cell in the metaphase stage of mitosis will be 1.8 pg x 2 = 3.6 pg.