Homeschool World Forum

The old five kingdom system of classification disappeared from college texts a number of years ago, but I suspect that it is still being taught in some high schools, and I don't know what you have in the resources that you are using.

The three domain system of classification - Bacteria, Archaea, and Eukarya - is the current system. There has been a blending of a three- domain/six-kingdom classifcation system for awhile now, but the six-kingdom system is about to kick the bucket, too. I attended a conference this weekend where there is also a push to eliminate the use of the term "prokaryote", because it is basically as bad as the old grouping of whatever wasn't a eukaryote into the kingdom Monera. (The Monerans were divided into the domains of Bacteria and Archaea, and the other 4 kingdoms were grouped into the Eukarya.) Also, there has been talk for some time about dividing the kingdom of Protista into at least three different kingdoms, because that is also a hodge-podge group of distantly related organisms.

The last universal common ancestor (LUCA) to all living things was not a member of any of these three domains. The Bacteria diverged from the lineage that led to to the Archaea and Eukarya, which last shared a common ancestor more recently in time. Genes have been passed between the three lines by viruses and other mechanisms. Also, it has been well established for some time now that the mitochondrion and chloroplast were originally bacteria that lived inside a host cell and later degenerated into organelles. (This is called the endosymbiotic theory, if you want to look it up.)

I just wanted to let you know that these are exciting times in the life sciences. I also wanted to let you know what you might expect your kids to learn if/when they get to college.

knobren

Is it heresy to say that anyone outside of a Biology major probably isn't going to care? I could discuss the shift from Pascal to C++ to Java, but I'm sad to say that only computer programmers would even know what I'm talking about.

That's fine. Like I said, I'm just throwing the information out there for whoever might be interested.

I DO NOT want to debate evolutionary relationships or belief systems.

Personally, I'd like more emphasis on things large enough to see. Tiny organisms are all well and good, but very little use to anyone not specializing in biology, while the entire rest of the spectrum is given just a token once-over. Read any standardized test for biology and you'll see what I mean - there are probably more questions on Mendellian genetics than there are for plants or animals.

If you want to talk about how antibiotics work, it helps to understand how the drugs affect bacterial cells and not ours because bacterial cells are different than our cells. For example, penicillin interferes with forming new cell walls, but our cells don't have cell walls, so it doesn't affect our cells. (People can have an allergy to penicillin, but that is an immune response.) Streptomycin affects certain bacterial ribosomes, and therefore, inhibits protein production, but we have a different kind of ribosome, so it doesn't inhibit our ribosomes.

Do you go over cell structure? Bacteria and Archaea don't have membrane-bound organelles, such as chloroplasts and mitochondria. And yet, some bacteria and Archaeans can do photosynthesis and/or cellular respiration.

Plants wouldn't have a source of nitrogen that they could use if it weren't for nitrogen-fixing bacteria. Do you live in a place that has crop rotations of soybeans and corn? Legumes (peas, beans, peanuts, clover) have nitrogen-fixing bacteria in root nodules. Some of the ammonium and nitrates leak out into the soil and enrich it for the corn the next year.

Do you discuss nutrient cycling of nitrogen, phosphorus, and carbon through food chains? Do you discuss the roles of decomposer bacteria and nitrogen-fixing bacteria?

Do you talk about the normal flora in and on our bodies that act as a first line of defense against harmful bacteria?

Do you talk about how cheese, yogurt, and saurerkraut are made and the role of bacteria in these processes? Do you discuss "active cultures" in yogurt?

Did you know that animals can't digest the cellulose that makes up the cell walls of plants and that bacteria (and protists) digest it for termites and ruminants like cows and then the cows, etc. digest the bacteria?