2.1b Cell Theory: Differentiation

28/08/2012 § Leave a comment

I’d first like to point out that I found an editing error in the IB Biology Course Companion textbook (p. 16, section Multicellular organisms and cell differentiation, para. 3, line 3). It prides me to know this. That is all.

The next topic of discussion in this season of IB Biology is multicellular organisms and cell differentiation. To start off, cell differentiation is [quote] the development of cells in different ways to perform different functions [end quote], or the method in which cells alter themselves and branch out in order to accomplish different tasks for the body, which is how I understand it. Cells in a multicellular organism can do this by using the information programmed into the organism’s genome (or set of information in their DNA). Different cell types use different parts of the genes in its nucleus but omits the rest of the information. Note that when cells are using information from certain genes, those genes are being expressed. Furthermore, when genes are expressed, it’s like a switch goes off that instructs the cell to produce a particular protein or other product that the cell will need.

There are unicellular and multicellular organisms. An example of a unicellular organism is a toe of alga called Volvox aureus, which live together in spherical colonies. Though they live in colonies, the volvox aureus is still a unicellular organism because they are not fused to form one single mass of cells, like humans are. (Spoilers: humans are multicellular organisms, if our something-trillion number of cells are of any indication.)

Now we’re getting into how these cells change and, overall, stem cells. Because I had a little trouble (just a little) getting my head around the concept of stem cells, I looked up the root word, stem, which generally means “to originate” or “be caused by” or even “the root” or “main body of something.” This makes sense because, at its early stages, a human embryo consists entirely of stem cells and later those stem cells alter themselves to become different kinds of cells that will work different jobs for the embryo-turned-human.

Stem cells are known to be exceptionally capable of regenerating and repairing damaged parts of the human tissue, such as bone marrow, skin, and liver. In other notably more sensitive organs, like the brain, kidney, and heart, the presence of stem cells only allow limited repair.

Because of stem cells’ regenerative abilities, there is a large interest in learning how to use them to replace or repair missing and damaged cells. An example in which stem cells are greatly therapeutic is their role in bone marrow transplants. The hematopoietic stem cells (HS cells – no, not High School cells) are the ones necessary for the job. Because only a small number of HS cells (just 100, which, compared to a trillion cells, is a really small amount) are needed to completely replace an entire blood system, they’ve been used to treat several disorders like leukemia, SCID (sever combined immune deficiency), multiple myeloma, and lymphoma. We can take a look at lymphoma as an example:

  • a lymphoma is a cancer of the lymphatic system, where the individual lacks in energy and body mass
  • the cells are removed from the patient’s bone marrow
  • chemotherapy drugs kill the dividing cells in the body (including that bone marrow), including both cancer cells and normal cells
  • HS cells step into to regenerate a new line of blood cells in the bone marrow

The only risk in stem cell therapy is if one stem cell loses control and doesn’t stop dividing, which will only create a tumor, consequently harming the patient rather than saving them.


1. There were 13 cells in the nervous system when the larva hatched from the egg.

2. a) 7-8 hours, b) ~33 hours

3. Apoptosis occurs nine times during the development of the nervous system. I now know what apoptosis is thanks to Mr. Ferguson – it’s what happens when the cells that make up the webbing on our hands are programmed to die off and give us our normal, flexible hands.

4. The maximum number of times cell division occurred = 74 times.

5. 78 cells in the adult nervous system ÷ 959 total cells in the entire adult body = 0.081… * 100% = 8.13% of the cells of an adult C. elegans worm is part of the nervous system.

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