Biology · Cell biology. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
The nucleus of a cell contains chromosomes, which are made of DNA. Each chromosome carries a large number of genes. In body cells the chromosomes are found in pairs. A human body cell has 23 pairs, which is 46 chromosomes.
Cells divide in a series of stages called the cell cycle. First the cell grows, makes more sub-cellular structures and copies its DNA. Then, in mitosis, one set of chromosomes is pulled to each end of the cell and the nucleus divides. Last, the cytoplasm and cell membrane divide. The result is two identical cells.
A stem cell is an undifferentiated cell. It can divide to make more stem cells and can differentiate into other types of cell.
Students mix up mitosis with meiosis and say that mitosis halves the chromosome number. Mitosis keeps the number the same: 46 in the parent cell, 46 in each new cell.
Answer: About 1.6 hours (96 minutes).
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