9th Biology Chapter5 Cell Cycle

Question 1. What is Crossing Over and When Does it Occur?
Answer:

Crossing over is the exchange of genetic material between homologous chromosomes during prophase I of meiosis. It results in the shuffling and recombination of genes, leading to genetic variation among offspring.

Question 2. Describe the Anaphase Stage of Mitosis.
Answer:

Anaphase is the third stage of mitosis marked by the separation of sister chromatids and their movement towards opposite poles of the cell. Motor proteins associated with spindle fibers pull the chromatids apart, ensuring that each daughter cell receives a complete set of chromosomes.

Question 3. Explain Metaphase II in Meiosis.
Answer:

Metaphase II is the stage of meiosis II where individual chromosomes line up along the equatorial plane of the cell, attached to spindle fibers. This alignment ensures that each daughter cell receives a complete set of chromosomes.

Question 4. Explain Mitosis and its Role in Cell Division.
Answer:

Mitosis is the process of nuclear division in eukaryotic cells that results in the formation of two genetically identical daughter nuclei. It ensures the accurate distribution of replicated DNA to daughter cells during cell division, maintaining chromosome number and genetic stability.

Question 5. Describe Interphase and its Significance in the Cell Cycle.
Answer:

Interphase is the longest phase of the cell cycle and comprises three sub-phases: G1, S, and G2. During interphase, the cell grows, carries out normal cellular functions, and duplicates its DNA in preparation for cell division. It is essential for ensuring that the cell has enough resources and genetic material to divide successfully.

Question 6. Explain the Role of Meiosis in the Production of Variations in the Next Generation.
Answer:

Meiosis introduces genetic variation through processes such as crossing over and independent assortment. Crossing over results in the exchange of genetic material between homologous chromosomes, while independent assortment leads to the random distribution of chromosomes during cell division. These mechanisms increase genetic diversity among offspring, enhancing their adaptability to changing environments.

Question 7. Explain the Replacement of Cells in the Body.
Answer:

The replacement of cells in the body is a continuous process involving the renewal and regeneration of tissues. Cells are constantly being shed or damaged and need to be replaced to maintain proper tissue function. Mitosis allows for the production of new cells to replace those that are lost or damaged.

Question 8. What are the Phases of Mitosis and What Happens in Each Phase?
Answer:

Mitosis consists of four phases: prophase, metaphase, anaphase, and telophase. During prophase, chromatin condenses into visible chromosomes, the nuclear envelope breaks down, and the mitotic spindle forms. In metaphase, chromosomes align at the metaphase plate. In anaphase, sister chromatids separate and move towards opposite poles of the cell. Finally, in telophase, chromosomes decondense, nuclear envelopes reform around each set of chromosomes, and the spindle apparatus disassembles.

Question 9. What is Cell Division and Why Does it Occur?
Answer:

Cell division is the process by which a parent cell divides into two or more daughter cells. It is necessary for growth, repair, and reproduction in organisms. Cell division ensures that each daughter cell receives a complete set of genetic material (DNA) and organelles to maintain proper cellular functions.

Question 10. Compare and Contrast Mitosis and Meiosis.
Answer:

Mitosis and meiosis are both processes of cell division, but they have distinct differences:

– Mitosis produces two genetically identical diploid daughter cells, while meiosis produces four genetically diverse haploid daughter cells.

– Mitosis occurs in somatic cells for growth, repair, and asexual reproduction, whereas meiosis occurs in germ cells for the production of gametes.

– Mitosis consists of one division (mitotic division), while meiosis consists of two divisions (meiosis I and meiosis II).

– Mitosis results in identical daughter cells with the same chromosome number as the parent cell, while meiosis reduces the chromosome number by half.

Question 11. What are Genetically Identical Cells?
Answer:

Genetically identical cells refer to cells that have the same genetic material (DNA) and genetic makeup. They are produced through processes such as mitosis, where a parent cell divides to produce two daughter cells with identical sets of chromosomes and genes.

Question 12. How Does Growth Occur in Multicellular Organisms?
Answer:

Growth in multicellular organisms occurs through an increase in the number and size of cells. Cells divide through processes like mitosis, leading to the formation of new cells, which contribute to tissue growth and overall organismal growth.

Question 13. Explain the Telophase Stage of Mitosis.
Answer:

Telophase is the final stage of mitosis in which chromosomes decondense, nuclear envelopes reassemble around each set of chromosomes, and the mitotic spindle apparatus disassembles. This stage prepares for the division of the cytoplasm during cytokinesis.

Question 14. What is Asexual Reproduction?
Answer:

Asexual reproduction is a type of reproduction where offspring are produced from a single parent without the involvement of gametes or the fusion of genetic material from two individuals. It often involves processes like mitosis, budding, or fragmentation, resulting in genetically identical offspring.

Question 15. Describe Prophase I of Meiosis and its Significance.
Answer:

Prophase I is the longest and most complex phase of meiosis. It is characterized by the pairing of homologous chromosomes (synapsis) and the exchange of genetic material between non-sister chromatids (crossing over), which increases genetic diversity.

Question 16. Describe Anaphase II of Meiosis.
Answer:

Anaphase II is the stage of meiosis II where sister chromatids separate and move towards opposite poles of the cell, facilitated by the shortening of spindle fibers.

Question 17. Explain Metaphase I in Meiosis.
Answer:

Metaphase I is the stage of meiosis I where homologous chromosomes line up along the equatorial plane of the cell, attached to spindle fibers. This alignment allows for independent assortment of chromosomes, contributing to genetic diversity.

Question 18. Describe the Prophase Stage of Mitosis.
Answer:

Prophase is the first stage of mitosis characterized by the condensation of chromatin into visible chromosomes, the breakdown of the nuclear envelope, and the formation of the mitotic spindle apparatus. Sister chromatids become attached to spindle fibers, preparing for their movement towards opposite poles of the cell.

Question 19. Explain the First Meiotic Division.
Answer:

The first meiotic division is the initial stage of meiosis, during which homologous chromosomes separate. It consists of prophase I, metaphase I, anaphase I, and telophase I.

Question 20. What are the Phases of the Cell Cycle?
Answer:

The cell cycle consists of four main phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitotic phase). The G1, S, and G2 phases together make up interphase, while the M phase includes mitosis and cytokinesis.

Question 21. Explain Interphase II in Meiosis.
Answer:

Interphase II is a brief phase between meiosis I and meiosis II where the two daughter cells produced in meiosis I undergo minimal growth and preparation for the second meiotic division.

Question 22. Define Karyokinesis and Explain its Significance.
Answer:

Karyokinesis refers to the division of the nucleus during cell division. It ensures that each daughter cell receives an identical set of chromosomes, maintaining genetic continuity between parent and daughter cells.

Question 23. What is the Cell Cycle and Why is it Important?
Answer:

The cell cycle is the series of events that occur in a cell leading to its division and duplication. It is crucial for growth, development, and repair in organisms, as it ensures the accurate transmission of genetic material (DNA) to daughter cells.

Question 24. What is the Significance of Meiosis in Sexual Reproduction?
Answer:

Meiosis is essential for sexual reproduction as it produces haploid gametes (sperm and egg cells) with half the number of chromosomes as the parent cell. When gametes fuse during fertilization, the resulting zygote has the correct chromosome number for the species, ensuring genetic diversity in offspring.

Question 25. What Happens During Telophase I of Meiosis?
Answer:

Telophase I is the stage of meiosis I where homologous chromosomes reach the opposite poles of the cell. Nuclear envelopes may reform around the chromosomes, and cytokinesis occurs, resulting in the formation of two haploid daughter cells.

Question 26. What is the Significance of Mitosis in Organisms?
Answer:

Mitosis plays a crucial role in growth, development, and repair in multicellular organisms by producing genetically identical daughter cells with the same number of chromosomes as the parent cell. It ensures tissue renewal, regeneration, and maintenance of proper chromosome number and genetic stability.

Question 27. Discuss Errors in Mitosis and their Consequences.
Answer:

Errors in mitosis can lead to abnormalities in chromosome number or structure, resulting in genetic mutations or chromosomal disorders. These errors may occur due to mistakes during chromosome segregation, chromosome duplication, or spindle fiber formation. Examples of consequences include genetic disorders such as Down syndrome, Turner syndrome, or cancer.

Question 28. Describe Prophase II of Meiosis.
Answer:

Prophase II is the stage of meiosis II where the nuclear envelope breaks down, and spindle fibers form. Chromosomes condense, and sister chromatids become visible.

Question 29. What is the Second Meiotic Division?
Answer:

The second meiotic division is similar to mitosis but involves haploid cells. It separates sister chromatids, resulting in the formation of four haploid daughter cells, each with half the number of chromosomes as the parent cell.

Question 30. What are the Phases of Meiosis?
Answer:

Meiosis consists of two main stages: meiosis I and meiosis II. Each stage is further divided into phases, resulting in a total of eight phases.

Question 31. What is Meiosis and Why is it Important?
Answer:

Meiosis is a type of cell division that occurs in sexually reproducing organisms to produce gametes (sperm and egg cells). It reduces the chromosome number by half, ensuring that when gametes fuse during fertilization, the resulting zygote has the correct chromosome number for the species.

Question 32. What Happens During Telophase II of Meiosis?
Answer:

Telophase II is the final stage of meiosis II where chromosomes reach the opposite poles of the cell, and nuclear envelopes begin to reform around them. Cytokinesis occurs, resulting in the formation of four haploid daughter cells, each genetically distinct from the others.

Question 33. Explain the Metaphase Stage of Mitosis.
Answer:

Metaphase is the second stage of mitosis in which chromosomes align along the metaphase plate, an imaginary plane equidistant between the two poles of the cell. This alignment ensures that each daughter cell receives an equal number of chromosomes during cell division.

Question 34. What are Errors in Meiosis and How Do They Occur?
Answer:

Errors in meiosis, such as nondisjunction or chromosome misalignment, can lead to chromosomal abnormalities in offspring. Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate properly during meiosis, resulting in an abnormal distribution of chromosomes in daughter cells. These errors can lead to conditions such as Down syndrome or Turner syndrome.

Question 35. How Does Meiosis Contribute to the Maintenance of Chromosome Number in the Next Generation?
Answer:

Meiosis reduces the chromosome number by half, ensuring that the next generation of organisms receives the correct number of chromosomes. This prevents doubling of chromosome number with each generation and maintains genetic stability within a species.

Question 36. Describe Interphase I in Meiosis.
Answer:

Interphase I is the phase preceding meiosis I, during which the cell undergoes normal growth and prepares for division. DNA replication occurs, resulting in the duplication of chromosomes.

Question 37. Differentiate Between Necrosis and Apoptosis.
Answer:

Necrosis and apoptosis are two different types of cell death:

– Necrosis is a form of cell death caused by external factors such as injury, infection, or toxins. It is characterized by cell swelling, rupture of the cell membrane, and release of cellular contents, which can trigger inflammation in surrounding tissues.

– Apoptosis, also known as programmed cell death, is a controlled process of cellular self-destruction that occurs in response to internal signals or developmental cues. It involves orderly dismantling of the cell, condensation of chromatin, fragmentation of the nucleus, and formation of apoptotic bodies, which are engulfed by neighboring cells without causing inflammation. Apoptosis plays a crucial role in tissue remodeling, immune response, and elimination of damaged or unwanted cells.

Question 38. Define Cytokinesis and its Role in Cell Division.
Answer:

Cytokinesis is the division of the cytoplasm following nuclear division (mitosis), resulting in the formation of two daughter cells. It completes the process of cell division, ensuring that each daughter cell receives a complete set of organelles and cytoplasm necessary for cellular functions.

Question 39. Describe Anaphase I of Meiosis.
Answer:

Anaphase I is the stage of meiosis I where homologous chromosomes separate and move towards opposite poles of the cell. Unlike in mitosis, sister chromatids remain attached at their centromeres during this phase.