MadSci Network: Cell Biology
Query:

Re: How does a Stentor Reproduce?

Date: Wed Nov 29 20:52:01 2000
Posted By: John Carlson, Medical student, MD/PhD (parasitology) , Tulane University, School of Medicine
Area of science: Cell Biology
ID: 974391487.Cb
Message:

Dear Ryan,

Thank you for your question to MadSci Network! Protists are interesting creatures. They have only one cell, like bacteria. The one cell of the protist is much more complicated than the one cell of a bacteria. Inside a protist cell there are more structures than inside a bacteria cell. These structures work on keeping the protist functioning at a higher level. There are many kinds of structures that do different things. The structures are called organelles. One kind of organelle that you might have heard of is the mitochondria.

The group of protists that Stentor is in is called the Ciliates. Ciliates have a very unique kind of organelle. This unique organelle is called a macronucleus. The macronucleus is a copy of the Stentor's DNA. The DNA of the macronucleus acts like the DNA of most other organisms, except for one major difference. The macronucleus is not directly involved in reproduction!

Instead, Stentor uses a micronucleus for reproduction. When two Stentor run into each other, they may latch on and decide to mate. Before mating takes place, the macronucleus is destroyed and the micronucleus copies itself, and becomes ready for the exchange. The micronucleus is the DNA that is exchanged between organisms when Stentor species mate.

Once two Stentor species have exchanged their micronuclei, the micronuclei reorganize themselves. Once the micronucleus is reorganized, copies are made which become macronuclei. Then the protist divides many times by asexual reproduction. After dividing many times, the Stentor will be ready to mate again.


Summary:

It is common for protozoa to reproduce both sexually and asexually. When they reproduce, it is always the micronuclei that is passed on. The macronuclei are interesting organelles that are made by the micronuclei. The macronuclei control the cell like DNA of other organisms, but they are not used to pass on genetics to their offspring. Usually organisms only have one kind of nucleus. The genus Stentor is in the phylum Ciliophora, more commonly called the Ciliates. It is the Ciliates that have developed a system of having a macronucleus for running the cell and a micronucleus to pass on genetic material.

Unfortunately, there are not many places on the Internet that discuss the biology of Stentor, so I have no diagrams for you to look at. The only source of information on these interesting animals I was able to find was a college-level text book entitled Invertebrate Zoology by Robert D. Barnes. If you live near a college campus, you should have someone take you there and show you how you can find a copy of this book. In it there are diagrams that illustrate the reproduction cycle that I have explained.

Another MAD Scientist, Allison Gong has answered the question, How does Vorticella reproduce? Vorticella is another genus of Ciliate. This answer describes the asexual portion of Ciliate reproduction.


If you are curious about why Ciliates have two kinds of nuclei, what other organelles protists have, or anything else, please ask us another question!

John Carlson
MAD Scientist


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