Cell Cycle and Cell Division Test - 14

DNA replication occurs during S phase of interphase. Prophase is the stage of mitosis which is characterized by spindle formation, shortening and thickening of chromosomes, disintegration of nuclear envelope and disappearance of nucleolus. Metaphase proceeds prophase and is marked by movement of chromosomes towards the equator of cell mediated by kinetochore microtubules of spindle fibres. Telophase is the last phase of mitosis wherein daughter chromosomes are now at opposite poles. Cytokinesis refers to division of cytoplasm after telophase of mitosis leading to formation of two daughter cells. 

G$$_2$$ phase is also called post-DNA synthesis phase. This phase comes after S phase. In S-phase synthesis of DNA and histone protein and also replication of chromosomes take place. Thus option B is the correct answer.

The S phase of a cell cycle occurs during interphase, before mitosis or meiosis, and is responsible for the synthesis or replication of DNA.

Meiosis is a reductional division where each daughter cell gains half the number of the chromosome from the parent cell. For meiosis, the cell needs to have a diploid set of chromosome. So, the correct answer is option B.

A cell that differentiates into a gamete through the process of meiosis is known as meiocyte. The resulting cell is a haploid.

Mitosis is shown by eukaryotes. It is not observed in E. coli. This is a prokaryote as it lacks a well-defined nucleus. In these organisms the nuclear membrane is absent and the genetic material is present floating in the cytoplasm. Hence these organisms divide by binary fission in which the parent body divides to form the daughter cells in which the genetic material and cytoplasm is divided between the offsprings. Thus the correct answer is option B.

Metaphase is the best stage to count the total number of chromosomes in any species and to establish a detailed study of the morphology of the chromosomes. As mitotic cells are easy to obtain, morphological studies are generally based on mitotic metaphase chromosomes. In this stage, the centrioles are at opposite poles of the cell. The homologous chromosome pairs (the bivalents), are tightly coiled and condensed and become arranged on a plane called the metaphase plate or equatorial plate. This plate is equidistant from the poles. Discontinuous fibres radiate out from the two poles and get connected to kinetochores at the surface of the centromere. A kinetochore is complex protein structure and a point where microtubules attach themselves to the chromosome. When the chromosomes get arranged at the metaphase plate, smaller chromosomes get directed towards the centre while the larger ones are peripheral in position on the equator. The centromeres of all the chromosomes lie on the equator forming an apparent plate called metaphasic or equatorial plate while arms are directed towards the poles.

The correct answer is option C.

Cytokinesis is the process whereby the cytoplasm of a parent cell is divided between two daughter cells produced either via mitosis or meiosis. This is also often known as cytoplasmic division or cell cleavage. Cytokinesis occurs in the late telophase of mitosis in an animal cell.

• The cell cycle has 2 phases the M phase and the Interphase.
• The interphase is made up of G1, S and G2 phase.
• The G1 phase is present after the M phase where the cell divides and in G1 phase the cell is provided time to rest before it can start to prepare for another cell division. Here it performs the normal functions of the cell.
• The S phase takes place after the G1 phase where the DNA/genetic material is replicated and it becomes 2 times of the genetic material of the mother cell so that it can be equally distributed among the daughter cells in the cell division.
• The G2 phase is where the cell is prepared for the cell division where the protein and the enzymes required for the cell division are prepared or synthesized. 
• Therefore the correct answer is option S phase.