Can You Answer These Biology MCQs?

Crossing over occurs during Prophase I of meiosis. This is the stage where homologous chromosomes pair up and exchange genetic material through a process called crossing over. This genetic recombination results in the creation of new combinations of alleles on the chromosomes, increasing genetic diversity. Therefore, the correct answer is Prophase |.

During the G1 phase of the cell cycle, the cell's DNA is duplicated. After mitosis, each daughter cell will contain the same amount of DNA as the parent cell. Therefore, each daughter cell will also contain 50 ng of DNA.

During metaphase, the chromosomes align at the equator of the dividing cell. This is an important step in cell division called mitosis. In metaphase, the chromosomes condense and become visible under a microscope. They then line up along the center of the cell, forming what is known as the metaphase plate or equatorial plate. This alignment ensures that each new daughter cell receives an equal and complete set of chromosomes during cell division.

Interphase is the correct answer because it is the longest phase of the cell cycle. It encompasses the G1 phase, S phase, and G2 phase, during which the cell grows, replicates its DNA, and prepares for cell division. This phase accounts for approximately 90% of the cell cycle and is crucial for the cell to perform its normal functions and prepare for division. Mitotic phase, prophase, and telophase are all part of the cell division process but are relatively shorter compared to interphase.

Despiralization refers to the unwinding of the tightly coiled chromosomes that occurred during prophase. This process allows the chromosomes to separate and move towards opposite ends of the cell during anaphase. Therefore, the correct answer is not Telophase, but rather Anaphase.

During mitosis, the chromosomes replicate during the interphase before the first division. This results in two identical sister chromatids held together by a centromere. However, before the second division, there is no further replication of the chromosomes. Instead, the sister chromatids separate and move to opposite poles of the cell. Therefore, the statement that chromosomes don't replicate before the second division in mitosis is true.

During meiosis, the DNA content is halved. In the G2 phase of the cell cycle, the plant cell has 100 ng of DNA. Therefore, at prophase, which is the initial stage of meiosis, the amount of DNA would be reduced by half, resulting in 50 ng of DNA. As meiosis progresses to the second division, the DNA content is halved again, resulting in 25 ng of DNA. Therefore, the correct answer is 50 ng, 25 ng.

During anaphase, the chromosomes will migrate towards the poles of a dividing cell. This is because the microtubules of the spindle apparatus contract, pulling the sister chromatids apart. As a result, each chromatid is now considered a separate chromosome and they move towards opposite poles of the cell. This movement ensures that each new daughter cell will receive the correct number of chromosomes during cell division.

During the S phase of the cell cycle, DNA replication takes place. This is the phase where the cell's DNA is duplicated in preparation for cell division. The S phase is a critical step in the cell cycle as it ensures that each daughter cell receives an identical copy of the genetic material. The G1 and G2 phases are involved in cell growth and preparation for division, while the G0 phase is a resting phase where cells are not actively dividing. Therefore, the correct answer is S phase.

In animal cells, cytokinesis occurs through furrowing, which is the process of the cell membrane pinching inwards to divide the cytoplasm into two daughter cells. In plant cells, cytokinesis occurs through cell plate formation, where a new cell wall is formed in the middle of the cell, dividing it into two daughter cells.

During anaphase, the homologous chromosomes, which are pairs of chromosomes that carry the same genes, are separated and move towards opposite ends of the cell. This process ensures that each resulting daughter cell receives one copy of each chromosome, maintaining the correct number of chromosomes in the offspring. Therefore, the correct answer is "Anaphase |".

Cytokinesis is the correct answer because it refers to the process of dividing the cytoplasm of a cell during cell division. It occurs after the nuclear division (either mitosis or meiosis) and results in the formation of two separate daughter cells. Cytokinesis ensures that each daughter cell receives a complete set of genetic material and necessary organelles.

The G1 checkpoint is responsible for ensuring that all conditions are met before the cell enters the S phase of DNA duplication. This checkpoint assesses factors such as cell size, nutrient availability, DNA damage, and the presence of growth factors. If any of these conditions are not met, the cell will not proceed to the S phase. Therefore, the G1 checkpoint is crucial in ensuring that everything is ready for DNA duplication in the S phase.

The G2 checkpoint is the control point that determines if the cell can proceed to the M phase for division. At this checkpoint, the cell checks for DNA damage and ensures that DNA replication has been completed accurately during the S phase. If any errors or damage are detected, the cell will pause and attempt to repair the DNA before proceeding to division. Therefore, the G2 checkpoint plays a crucial role in maintaining the integrity of the cell's DNA and ensuring the proper progression of the cell cycle.

G0 is not part of the cell cycle. The cell cycle consists of four main phases - G1, S, G2, and M. G0 is a resting phase in which cells exit the cell cycle and temporarily stop dividing. It is a non-dividing state that cells enter when they are not actively proliferating or preparing to divide. Therefore, G0 is not considered as part of the cell cycle.

During Prophase, homologous chromosomes arrange along their length as pairs in a process called synapsis and form what is called a tetrad.

Mitosis is the process by which a cell divides into two identical daughter cells. Before mitosis can occur, the DNA in the cell must be duplicated. This ensures that each daughter cell receives a complete set of genetic information. Therefore, it is true that mitosis should be preceded by DNA duplication.

During meiosis, homologous pairs of chromosomes are separated in a process called "segregation" or "disjunction." This occurs during the first division of meiosis, known as meiosis I. The separation of homologous chromosomes results in the formation of two haploid cells, each containing one set of chromosomes. Therefore, the correct answer is "Meiosis |."