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Unit-4 Cell Cycle
Answer: The cell cycle includes all the events that occur in a cell from one division to the next, including interphase and the mitotic phase.
Answer: The cell cycle is divided into interphase, where the cell prepares to divide, and the mitotic phase, where division occurs.
Answer: Interphase consists of the G1 (first gap), S (synthesis) and G2 (second gap) phases during which the cell grows and prepares for division.
Answer: In the S (synthesis) phase, the DNA of each chromosome is duplicated so that each chromosome consists of two sister chromatids.
Answer: The G1 phase is typically the longest phase of interphase because the cell grows rapidly and synthesizes proteins and organelles.
Answer: The S phase is called the synthesis phase because DNA is synthesized (replicated) during this phase.
Answer: During the G2 phase, the cell synthesizes proteins and other materials needed for division, such as tubulin for spindle fibers.
Answer: After a cell divides, it enters the G1 phase of interphase, where it grows before starting DNA replication.
Answer: G2 is the last phase of interphase; after G2 the cell enters mitosis.
Answer: Cells in G0 are metabolically active but have exited the cell cycle and do not divide, e.g., mature nerve cells.
Answer: Mitosis is called equational division because it distributes equal numbers of chromosomes to the daughter cells.
Answer: A single mitotic division produces two genetically identical daughter cells.
Answer: The chromosome number is maintained (2n to 2n) in mitosis, so the division is equational.
Answer: During prophase, chromatin condenses into distinct chromosomes, which become visible under a microscope.
Answer: Anaphase is the shortest stage of mitosis because the separation of sister chromatids is completed very quickly.
Answer: In metaphase, the chromosomes align on the equatorial plane, with their centromeres on the equator.
Answer: Spindle fibers attach to a disc-like structure called the kinetochore located at the centromere of each chromosome.
Answer: During prophase, spindle fibers begin to form between the two poles of the cell.
Answer: In animal cells, centrioles move to opposite poles during prophase and help organize the spindle apparatus.
Answer: Since DNA has already replicated in the S phase, each of the 46 chromosomes has 2 chromatids, giving 46 x 2 = 92 chromatids.