2.5a Cell Cycle

23/09/2012 § 1 Comment

All organisms, whether prokaryotic or eukaryotic, need to produce new cells to survive. Prokaryotes use binary fission as their form of cell division that replicates the single circular chromosome, moves the two copies to opposite ends of the cell, and through cytokinesis, divides the cytoplasm to form two new cells.

Eukaryotes’ cell division is much more complicated. Eukaryotic cells go through the cell cycle indefinitely and part of the cell cycle includes mitosis, which is the process by which the nucleus divides to form two genetically identical nuclei, the process eukaryotic cells use to divide. Mitosis is required in cells during growth, embryonic development (as the fetus forms), when damages need reparation, and to reproduce asexually.

Before mitosis, however, cells go through the interphase, which is the longest portion of the cell cycle. There are three stages of the interphase:

  • G1: in which the cell grows, transcribes DNA and synthesizes proteins, as well as produces an increase in the number of mitochondria and other organelle structures
  • S phase: in which all the DNA in the nucleus is replicated
  • G2: in which the cell prepares for division

Afterwards is mitosis, which consists of the stages prophase, metaphase, anaphase, and telophase. This will be covered in more detail in the next blog but these stages essentially take the cell through the process of providing each daughter nucleus with a copy of the DNA (in the form of chromatids) so that the new daughter cells (that will form when the original cell undergoes cytokinesis to split the cytoplasm) have a copy of the original DNA.

There are these things called tumors and all cells are prone to being raided by a tumor – this includes tissues and any organs. Tumors can grow when a cell loses control of the mitosis that it is experiencing and the cells continually reproduce and divide, creating more and more cells – unnecessary cells – too many cells. Tumors are caused by cancer.


1. State the time of day when:

(a) most DNA replication occurs – after midnight, past 24:00

(b) when mitosis is most likely to occur – 03:00

2. Identify the cell cycle stage when most of the increase in cell size is occurring.

—> G1

3. Evaluate the claim that the timing of the cell cycle in Emiliania huxleyi is an adaptation to take advantage of light resources.

It is evident that many of the cells, around 80% and more, are in the G1 stage (when the cell needs to grow and increase its number of organelles) from around noon to when it becomes too dark. From midnight to dawn (24:00 – 06:00), less cells are in G1 and are instead in the S-stage of G2 (or mitosis) stage. This means that during the day, the phytoplankton are adapted to take advantage of the light (especially during the noon, when the light is strongest) to grow. By the time it gets dark, they can switch over to the S-stage (to copy their DNA) or G2+M stage to do mitosis.

§ One Response to 2.5a Cell Cycle

  • Dave Ferguson says:

    Grade 7 A consistent and thorough understanding of the required knowledge and skills, and the ability to apply them almost faultlessly in a wide variety of situations.

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