Fix the mistake: Growth and Reproduction in Organisms

Cell Division and Growth of Organisms

Multicellular organisms grow because the number of cells increases. Let us learn how cell division works, in which one cell divides into two.

Basic Knowledge

Cell division: The phenomenon in which one cell(parent cell) divides into two cells(daughter cells).
Near the tip of a plant root, cell division occurs actively; this area is called the growth point.
Process of somatic cell division:
① The cell prepares to divide(interphase): DNA in the nucleus isreplicated.
② Prophase: Chromosomes appear in the nucleus. The nuclear membrane disappears.
③ Metaphase: Chromosomes line up at the center of the cell(equatorial plane).
④ Anaphase: Chromosomes split lengthwise and are pulled toward both ends.
⑤ Telophase: Nuclei are re-formed at both ends. The cytoplasm is pinched into two parts(animals)/a partition wall forms in the center(plants).
As a result, two cells with the same number of chromosomes as the original cell are produced. The growth of an organism = an increase in cell number through cell division + an increase in the size of each cell.

Important Terms
Cell division(The division of one cell into two)
Somatic cell division(Division for growth and repair. The chromosome number does not change)
Chromosome(A threadlike structure that appears in the nucleus during cell division. It contains genetic information)
DNA(Deoxyribonucleic acid. The substance of genetic information and the main component of chromosomes)
Replication(The copying of DNA so that it becomes twice as much. It occurs during interphase)
Growth point(A place where cell division is active. In plants, the tip of a root or stem)

Further Exploration (Background and Significance)

The number of chromosomes is determined by the type of organism.
・Humans: 46(23 pairs)
・Onions: 16, peas: 14, horses: 64
In somatic cell division, the chromosome number does not change. DNA is replicated and doubled during interphase, and it is distributed equally to the two daughter cells, maintaining the same chromosome number as the original cell.
The staining solutions used when observing plant roots areacetic orcein andacetic carmine, which stain chromosomes reddish purple. When observing the tip of an onion root, cells in each stage of division can be seen at the same time.
Somatic cell division is also used for repairing injuries and replacing old cells. Human skin and intestinal cells are replaced over several days to several weeks.

Key Points
  • Cell division = 1 cell→2 cells
  • Somatic cell division = the chromosome number does not change
  • Order: interphase(DNA replication)→prophase→metaphase→anaphase→telophase
  • Metaphase = chromosomes line up at the center(equatorial plane)
  • Anaphase = chromosomes split lengthwise and move to both ends
  • Plant growth point = the tip of a root or stem
  • Staining solutions = acetic orcein and acetic carmine
  • Humans have 46 chromosomes(23 pairs)

Points to Note (Often Confused)

① Do not confuse chromosomes(threadlike structures during division) with staining solutions(chemicals used for observation). ② In somatic cell division, the chromosome number does not change(the parent and daughter cells have the same number). ③ Growth includes both an “increase in cell number” and an “increase in the size of the cells themselves.” It is not only an increase in cell number. ④ In animal cytokinesis, the cell constricts; in plant cytokinesis, a partition wall forms.

Practice

  1. Which part of a plant root has the most active cell division?
  2. How does the chromosome number change before and after somatic cell division?
  3. Where do chromosomes line up during metaphase of somatic cell division?

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