Ch 10Cell Cycle and Cell Division — Class 11 Biology, concept-first.

Every organism, however large, begins life as a single cell. That one cell is somehow capable of giving rise to an enormous, complex body made of millions of cells — so how does this happen? The answe…

Every living organism relies on cell division to grow, to replace worn-out or damaged cells, and to produce offspring.

A convenient way to understand a typical eukaryotic cell cycle is to look at human cells grown in culture. Such cells divide roughly once every 24 hours.

The M Phase is the most dramatic period of the whole cell cycle. During it, almost every component of the cell undergoes a major reorganisation as the cell prepares to physically split in two.

Prophase is the first stage of karyokinesis in mitosis. It follows directly after the S and G2 phases of interphase.

Metaphase is the second phase of mitosis, and its onset is marked by the complete disintegration of the nuclear envelope.

Anaphase is the mitotic stage in which the two halves of every chromosome finally part company and travel to opposite ends of the cell.

Telophase is the last stage of karyokinesis — the division of the nucleus. By the time telophase begins, the daughter chromosomes have already finished their journey and have gathered at their respect…

Mitosis does more than just share out the duplicated chromosomes into two nuclei — that part is karyokinesis.

Mitosis is also called the equational division because each daughter cell ends up with exactly the same chromosome number and the same genetic content as the parent cell.

Meiosis is a special kind of cell division that halves the chromosome number, producing haploid cells from a diploid parent.

Meiosis I is the first of the two divisions that together make up meiosis, and it is the division that actually reduces the chromosome number.

Meiosis II is the second meiotic division, and it follows meiosis I very closely. It sets in almost at once after cytokinesis of the first division, often even before the chromosomes have had time to…

Meiosis carries a significance out of all proportion to the simple fact that it halves the chromosome number.

Every cell arises from a cell that existed before it — this is the heart of the cell theory, and the event by which one cell gives rise to others is called cell division.

Higher-order thinking problems from the NCERT Exemplar.