Don't believe the hype

It's amazing what that one extra grape chromosome can do for you.

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A Positive Definition for Prokaryotes

This article highlights some of the current thought behind the need for a positive definition of "prokaryote." The current definition is negative: Cells that don't have a nucleus (nuclear membrane) are not eukaryotes, so they are prokaryotes. Negative definitions are not scientifically useful, since they only allow members to be excluded from the group, not included in another group. You have a nucleus, you don't belong in this group.

This new positive definition is based on molecular data rather than morphological observations. The old format has two major groups, the prokaryotes and the eukaryotes.

The current textbook paradigm for biological diversity and evolution is based on what I will call the prokaryote/eukaryote model. This posits that there are two kinds of cells: prokaryotic, those without nuclei (specifically, without nuclear membranes) and eukaryotic, those with a classical membrane-bounded nucleus. The model further posits that the former gave rise to the latter.

This "textbook" definition states that prokaryotes appeared first, and slowly evolved into eukaryotes. However, modern molecular analysis does not support this.

Molecular-sequence comparisons, first of ribosomal RNA genes in the late 1970s and of many other genes since, replaced analyses based on morphological subjectivities (such as the presence or absence of a nuclear membrane) with credible maps of evolutionary relationships between genes. These sequence comparisons have rendered the prokaryote/eukaryote model obsolete.

Analysis of the rRNA sequences results in the following evolutionary tree:



This illustrates that eukaryotes and archaea are more closely related than archaea and (eu)bacteria. So putting archaea and bacteria together in a group does not make evolutionary sense when the molecular biology is taken into account.

The article concludes with a call to remove the term "prokaryote" from the textbooks.

I believe it is critical to shake loose from the prokaryote/eukaryote concept. It is outdated, a guesswork solution to an articulation of biological diversity and an incorrect model for the course of evolution. Because it has long been used by all texts of biology, it is hard to stop using the word, prokaryote. But the next time you are inclined to do so, think what you teach your students: a wrong idea.

Our textbook has chapters on prokaryotes. I will do my best to refer to them as arcaea and bacteria.

Macromolecule powerpoint

If you have any questions/concerns about the test material, I will be online until 10.30 tonight. Post your questions as a comment and I will respond as quickly as possible.

Water PowerPoint

Found it.

Enzyme PowerPoint

PowerPoint for sections 8.4 and 8.5.



I will post the water review PowerPoint as soon as I find the CD where I have it saved. Hopefully it is in my computer at home.

Change in test material

The material to be covered on the test on Thursday has been adjusted. The test will only cover chapters 1 -4 and sections 8.4 and 8.5. Chapter 5 (Structure and Function of Macromolecules) will NOT be on the test Thursday. Chapter 5 will be presented in class on Wednesday, and we will finish chapter 5 after the test. There will be a test on chapter 5 sometime next week, most likely Tuesday or Wednesday.

McCain and science

As promised, here are John McCain's answers to the 14 top science questions facing the next President of the United States. For a side-by-side comparison of the two candidates, click here.

Jury duty and schedule changes

So I was able to get off with only one day of jury duty (Friday), since the court of New Jersey allows teachers to claim a "hardship" and be excused from three weeks of service. The case actually sounded sort of interesting (man murders girlfriend, claims self-defense. Not sure how the dismemberment part fits as self-defense...) but missing three weeks of school would have been a little much.

In order to get back on track, we are going to have to make a few adjustments to the schedule for this week. The new schedule will be as follows:

Monday - Enzymes and energy
Tuesday - Enzyme activity lab
Wednesday - Macromolecules review
Thursday - Test on Unit 1 (Chapters 1 - 5)
Friday - Microscope review

The review day scheduled for Tuesday was cut out, so that we will only be one day behind the original schedule. If you want extra review before the test, I will be in room 216 after school on Tuesday.

New Poll

New poll on the left. Be sure to vote and make your voice heard.

Obama and Science

Barack Obama responds to questions on US science policy. John McCain has said he will also provide answers to these questions. When McCain's responses are posted, they will be linked.

Summer ecology review PowerPoint

Here is the PowerPoint to review the summer ecology packet. Test is on Thursday.