Cell Cycle and Chromosomes

Eukaryotic chromosomes are made of chromatin, a nucleoprotein - DNA coiled around histone proteins while prokaryotic chromosomes are circular chromosome attached to the inside of the cell membrane. They are single chromosome plus plasmids

12, 36, 24; because pollen grains are haploid while endosperm has triploid chromosome number and integument is diploid in nature.

The root of a flowering plant is diploid (2n = 24). Gametes are haploid (n), so they contain half the number of chromosomes, which is 12.

The nucellus is a diploid tissue (2n). The microspore mother cell (MMC) is also a diploid cell derived from the sporophytic tissue, so it has the same chromosome number.

Pollen grains are haploid (n) structures containing half the somatic chromosome number. If the pollen grain has 6 chromosomes (n = 6), the leaf tip cells, which are diploid (2n), will have 2 * 6 = 12 chromosomes.

Root cells are diploid (2n = 14). Synergids are part of the embryo sac and are haploid (n). Thus, n = 7.

A zone of inactive cells is present in the central part of the root apex called quiescent centre.

Every somatic cell in the human body contains the complete genome, including the gene for insulin, although it is only expressed in the beta cells of the pancreas.

In mitosis DNA content is doubled during S phase resulting in 2n chromosomes having two chromatids. These 2 chromatids of 2n get arranged at metaphase plate in metaphase. And in anaphase, the 2 chromatids of 2n chromosomes are separated from each other . so the cell during this phase becomes 4n.

Early in the history of biology, scientists believed cells arose spontaneously. With the development of cell theory, people finally realized that only cells can beget other cells. In fact, two categories that define something as living or not are growth and reproduction, both of which cell division accomplishes. Cell division, also called mitosis, occurs in all living things. As living things grow, some cells die or become damaged and need replacements. Some single-celled organisms use a type of mitosis as their only form of reproduction. In multicellular organisms, cell division allows individuals to grow and change by expanding the number of total cells. The division of the nucleus is equal during cell division. This ensures the characteristic of both parent cell in daughter cells and restores the size of the nucleus.

Mitosis is equational division and meiosis is reductional division. Both consists of 4 phases, namely prophase, metaphase, anaphase and telophase. Prophase is the first phase of both mitosis and meiosis I. During this phase, the chromatin condenses and forms visible chromosomes. The mitotic spindle begins to form, nucleolus disappears, the nuclear envelope disappears. 

1. In G$ _1$  phase the amount of DNA is the same as 40 because the cell is metabolically active but no division of DNA is observed.
   
2. In G$ _2$ phase the DNA gets doubled as it has gone through the synthesis phase which is characterized by the replication of DNA.
3. In mitosis since equational division occurs the DNA content remain 4C through the process before the transfer of DNA into daughter cells.

G$ _1$ , S , G$ _2$, M , cytokinesis. The correct sequence has G$ _1$ as a preparation for S and G$ _2$ as the time between the completion of S and entry into M. Cytokinesis occurs after the other stages to create two daughter cells.