Friday, March 25, 2011
Do The Parts Make a Whole?
In Chapter Seven, starting on page 117, Shubin discusses how "a mat of bacteria or a group of skin cells is a very different thing from an array of cells that we would call an individual". This reminded me of our Prokaryotes Unit, where we talked about different cellular types. According to Shubin, would a "complete" individual be qualified as multicellular or unicellullar? Also, use this passage as a chance to review the difference between colonial and multicellular organisms. What are some selective advantages to being multicellular or unicellular?
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As Shubin puts it, “the shift from single-celled animals to animals with bodies reveals a whole new world” (Shubin 119). To stimulate your mind about the prokaryotes unit, the two types of cells are prokaryotes and eukaryotes. Prokaryotes lack a central nucleus, and instead have a “nucleoid region.” The cell wall of a prokaryote is made of peptidogylcan, and inside the cell are ribosomes; one, circular piece of DNA with all of the cell’s genes; and cytoplasm. An example organism of a prokaryote is cyanobacteria, which photosynthesis to get its energy. However, prokaryotes can obtain energy in many different ways: they can be autotrophs or heterotrophs. The second type of cell is a eukaryotic cell. Eukaryotic cells have a central, membrane-bound nucleus with separate membrane-enclosed organelles that have separate functions within the cell. Such organelles are mitochondria, lysosomes, and the Golgi apparatus. Through evolutionary history, it is believed that eukaryotes originated through endosymbiosis. Endosymbiosis is the development of the eukaryotic cell in which an ancestral prokaryote developed a nucleus and endomembrane system, and then engulfed an aerobic heterotrophic prokaryote (which later became a mitochondrion). Some eukaryotes further engulfed photosynthetic prokaryotes (which later became a plastid).
ReplyDeleteTo differentiate between multicellular organisms, unicellular organisms, and colonial organisms: multicellular organisms consist of multiple cells in which all cells function together as a whole (different cells may exist in a multicellular organism, and thus have a different function within the organism); unicellular organisms are organisms that are made up of only one cell that carries out all metabolic functions; and colonial organisms are organisms that consist of cells that function as individual units yet are in association with surrounding cells, i.e. they can benefit from surrounding cells and in some way “work together.” An example of a multicellular organism is the human. As Shubin pointed out, if you were to remove some cells such as brain cells from a human, you could potentially kill or seriously harm that human because those cells are necessary for that human to live. An example of a unicellular organism is cyanobacteria as already discussed. An example of a colonial organism is Volvox, which is a type of green algae.
A selective advantage of a unicellular organism is that it requires little energy. Also, many unicellular organisms can reproduce asexually, which allows for fast reproduction under stable/favorable conditions. An advantage of multicellular organisms is that it has many cells that carry out different, specialized functions. Also, multicellular organisms are able to complete more complex tasks.
I am not sure what you are looking for with regards to being an individual. Both unicellular and multicellular organisms are individuals that function as a whole, only a unicellular organism is made up of one cell. I reread the passage a few times, and since your title is “Do The Parts Make a Whole?,” multicellular organisms have many cells that make up an “individual.” As Shubin explains on page 119, these multicellular organism’s cells “work together” and “’talk’ to each other” to carry out their functions for the organism to survive.
All information from Your Inner Fish, Campbell, and the Biology Wiki.
(Bobby Muttilainen, rmuttilainen@gmail.com)