How do you divide the eukaryotes? September 19 2019, 0 Comments
If I asked you how you would divide the eukaryotes into groups, what would you say? Many people would say protists, fungi, animals, and plants. This is the idea presented in Five (or Six) Kingdoms classification. There is a more enlightening way to divide the eukaryotes, one that students currently see in introductory college courses.
The DNA revolution and the development of systematics rather than plain classification have given us a new view. Systematics includes the relationships between taxonomic categories instead of listing them with no information about their shared ancestors. It is a young science that has produced many changes and will likely produce many more.
This is not to say that we don’t have useable information right now. The largest categories of eukaryotes have been defined, and they are called the eukaryotic supergroups. There are four of them presently, and so the eukaryotes can be divided into four groups. Here’s an introduction to the archaeplastida, SAR, excavata, and unikonts aka Amorphea.
Archaeplastida is the lineage that acquired the first chloroplast. Its name means “ancient plastids.” A plastid is a type of organelle in a eukaryotic cell, and the category includes the chloroplast, whose name means “green body.” The archaeplastida lineage includes red algae and green algae, along with the embryophytes or land plants, which evolved from a green alga. This lineage is the only one that incorporated an ancient cyanobacterium into its cells. The origin of the chloroplasts in other lineages is a more complicated story.
The SAR lineage is named for the three main branches within it, stramenopiles, alveolates, and rhizarians. These lineages were defined independently and then researchers gathered enough evidence to conclude that they share a common ancestor. The stramenopiles (aka chromists or heterokonts) include brown algae, golden algae, diatoms, and water molds. Alveolates include dinoflagellates, apicomplexans (parasites such as malaria), and ciliates. The rhizarians include foraminiferans and radiolarians, single cell organisms that build amazing outer shells called tests.
And where did these branches of life get their chloroplasts? It seems that chloroplasts are NOT easy to acquire. Apparently, it is easier to take one from another cell than to acquire one by eating a cyanobacterium. An ancestor of the stramenopiles and alveolates probably ate a red alga and kept its chloroplasts. Euglenas, which we meet below, got their chloroplasts from a green alga.
The third eukaryotic supergroup is the excavata, also called the excavates, but I see potential for confusion between the word as a noun vs. a verb. The lineage is named for a groove that looks like it has been excavated from the cells of some members. The excavata include the euglenas, which are free-living, and the trypanosomes, which are parasites. Other members of this group include the parasite Giardia and organisms that live in the guts of termites and help them break down cellulose. These have reduced mitochondria, so small that they were first described as lacking mitochondria.
I know you have been waiting for the last of the four supergroups, our own lineage, the unikonts (“single flagellum”) also known as the Amorphea (“having no form”). “Wait a minute,” you may be thinking, “we definitely have form.” The amoebas that belong to this lineage do not, however. The Amoebozoa lineage includes most of the slime molds or social amoebas as well as the single cell ones. Some of the latter build hard coverings (tests) for themselves. The other members of the unikonts are the fungus kingdom and the animal kingdom, which are sister kingdoms, having shared a common ancestor right before they branched off. There are other single cell organisms that are related to animals and fungi as well.
As you can see, the old protist kingdom had many different lineages of life shoe-horned into it, and the kingdoms that developed from its members were chopped off and boxed separately from it in the Five (or Six) Kingdoms scheme.
Why should you or your children learn about the supergroups of eukaryotes? It gives you a richer view of life and one that your children will see in their future studies. Will the names stay the same? Maybe, or maybe not, but these are the names in current college biology books, and it is worthwhile to learn about them and their members now.
Enjoy your explorations of the living world!
How do you know it's right? Resources for fact-checking October 21 2018, 0 CommentsFact-checking... is an important part of preparing the classroom environment. Here are some tips on how to do it.
Why is the horse the example of a mammal? January 30 2018, 1 Comment
Certain materials are “classic” in Montessori classrooms. The external parts of the vertebrate animals are one of those essential materials. This set traditionally has a horse as the example of a mammal, and almost all commercially available card sets for study of the vertebrates uses the horse.
My question is “why?” Unless we try to understand Maria Montessori’s purpose in the design of her materials, we can easily get caught in a web of tradition that keeps us from serving children’s learning needs to the best of our ability.
Here is my best guess on the horse as the mammal example. The horse was present in the lives of children all over the world until about 1920. It didn’t matter if they lived in a city or on a farm. When Maria Montessori first created her materials, the mammal that most children would see in their everyday lives was a horse. That has changed for most children. The horse is still used for transportation in some rural areas, but this animal is now more likely to be seen in a hobby or leisure situation. Most children in the United States do not see a live horse with any regularity.
What mammals do children see today? Dogs and cats would likely top the list. Classroom pets like gerbils, guinea pigs, or hamsters are common enough. Why don’t we use one of these for the example mammal? Children are more likely to be interested in learning about an animal they can experience, and learning about the care of that animal may also be very relevant to them.
Should we get rid of the “Parts of a Horse” cards? Probably not. There is nothing to keep you from having additional examples after you study the first one. Some children do see horses regularly and will be very interested in learning their parts. Others could have their horizons expanded by seeing additional examples.
What about the other vertebrate examples? The frog as an amphibian is about as good an example as a newt or salamander. The latter two are harder to observe in nature, but they can be kept in the classroom, probably with fewer problems than keeping a frog. It depends on the frog. Some can be escape artists – voice of experience here.
The turtle probably became the reptile of choice because it is less intimidating than a snake or a lizard, but a lizard gives a better look at the basic reptile body. Turtles are quite derived – they have changed a lot from their ancestors. They still have the scaly skin and lay eggs, so they work.
At some point, the crocodilians (crocodiles, alligators, caimans) need their own category. They are more closely related to birds than they are to the squamates (snakes and lizards). Both crocodilians and birds belong to the archosaur branch of the reptiles. Now that this is known, even children’s books point out the similarities. Both birds and crocodilians make nests, vocalize, and care for their young. They both have four-chambered hearts as well.
These two are closer cousins than either is to a lizard.
Using a perching bird for the example of the feathered vertebrates works well. It is worth asking, however, what birds children see. Maybe they see chickens on the school grounds. Maybe it is song birds that come to a feeder. Maybe it is a pigeon in the city. Maybe it is caged bird in the classroom. Going back to a real bird is an important step to make learning the parts into living knowledge.
Finally, the whole collection of vertebrates should be called the groups of vertebrates, NOT the classes of vertebrates. Biologists haven’t placed fishes into a single class since about 1850. The former classes were jawless fishes, cartilaginous fishes, ray-finned fishes, and lobe-finned fishes. That’s much more than children need at the beginning of their studies. The classroom fish tank can house valuable examples of ray-finned fishes, and that’s a great launching point. After all, ray-finned fishes are more than 99% of all fishes.
You can look that fish in the eye and say to it, “You and I shared a common ancestor, back in the beginning of the Paleozoic Era.” You can tell the amphibian that you shared a common ancestor with it back in the Devonian Period. Not long (geologically speaking) after that in the Carboniferous Period you shared a common ancestor with birds and reptiles, the other animals that reproduce on dry land, which are known as the amniotes.
It’s all in the ancestors and the great evolutionary journey. Enjoy the trip.
Help with studies of flowering plant families June 01 2017, 1 Comment
For many years, I have promoted the idea of structuring botany around the flowering plant families. It’s a practical way of addressing the diversity of the angiosperms, and it is knowledge that works in many places and at many levels. For instance, organic gardeners need to know the families of vegetables so that they can do the proper crop rotation and fertilizing. Plant identification is much easier if one can determine the family. Flowers in the same family share certain features, so it is quite possible to recognize the family even if you have never seen that species before.
To help you with your botany studies, I’ve just revised and expanded my PowerPoint slides on flowering plant families. This file is a pdf that can be printed to make letter-sized posters of 20 flowering plant families. The slides include text that describes the features of the flowers, and they show photos of family members. To round out this material, I’ve added a representative photo of 48 other families or subfamilies from all branches of the angiosperms.
Perhaps you would like to do a Tree of Life diagram for the flowering plants. There is a good one in the book, Botanicum by Katie Scott and Kathy Willis. It is part of the Welcome to the Museum series from Big Picture Press (no relation to Big Picture Science), and it was published in 2016. The branches are correct on the diagram (pages 2 and 3), but they have just one example for each branch, and the orders are not stated. The example represents a whole order, which leaves out a lot. For example, the rose order, Rosales, is represented by a mulberry leaf. Mulberries and figs belong to family Moraceae, which is in the rose order, along with rose, elm, buckthorn, hemp, and nettle families. On the other hand, the diagram fits on two pages. It have to be much larger to be more comprehensive. All-in-all, the book is delightful and will provide lots of fun browsing. You will have to tell children that the page on fungi is a holdover from earlier definitions of botany.
The photos of families from my newly revised Flowering Plant Families Slides can be used to create a Tree of Life that has many orders. It gives a broader look at the families than its predecessor, and it is still centered on the families of North America. There are over 400 families of angiosperms worldwide. You don’t need to worry about being anywhere near comprehensive when you introduce children to flower families. Select the main ones for which you have examples from your school landscape, in areas near the school, or as cut flowers. If you or your children want to see the full list, go to the Wikipedia article on APG IV system (Angiosperm Phylogeny Group IV).
I’m not the only one that advocates structuring botany studies around flowering plant families. Thomas Elpel has written a highly successful book called Botany in a Day: The Pattern Method of Plant Identification. It is further described as “An Herbal Field Guide to Plant Families of North America.” This book is in its sixth edition. It has color drawings as well as black and white ones, and these could be useful in classrooms. I have not recommended placing this book in the elementary classroom, however, because it includes many food and medicinal uses for wild plants. I do not want to encourage children to eat wild plants or use them as medicine.
Botany in a Day is available from Mountain Press Publishing in Missoula, Montana, which also carries Elpel’s flower family book for children, Shanleya’s Quest. This book is a great one for elementary classrooms, and I strongly recommend it.
Enjoy exploring and identifying the flowers!
The Tree of Life versus the Timeline of Life March 29 2017, 0 Comments
Someone has posted my Tree of Life chart on Pinterest and suggested in the caption that it could be a substitute for the Timeline of Life. NOT SO! These are two different materials with two different uses.
The Tree of Life does not show details of life through time. It shows extant animals and their lineages. People may be confused because classification has an element of time now. We group organisms by their common ancestors. You can’t show relatives without some reference to time. My cousins and I share a set of grandparents, so we have a recent common ancestor. That’s what makes us closely related.
Classification has become systematics (more on that in a later post). Biologists do not show rows of evenly spaced boxes with no connections when they diagram a kingdom or other related life. Instead, they connect the boxes (or names) with a branching diagram to show which organisms share more recent common ancestors.
The Tree of Life chart is used much like a Five Kingdoms chart was. If you are still using a Five Kingdoms, Six Kingdoms, or heaven forbid, a Two Kingdoms chart, you need to change to a different kind of chart. A Tree of Life chart is used to introduce children to the diversity of life. When I give this lesson, I tell children that this chart has a branch for all the major kinds of life on Earth. (And you may have one precocious child who asks “What about viruses?” No, they don’t belong on the organisms’ Tree of Life. They have their own.)
I can envision directing children’s attention to the big, black branches and noting that they are all connected, and they all share a common origin. I would also say that there are many, many varieties of life, and we would have a hard time studying it all at once. Instead, we put certain branches together for the purpose of focusing on them. Three of these major branches are called kingdoms because they are all the descendants of a common ancestor. They are outlined with color rectangles – yellow for fungi, red for animals, and green for land plants. The other two rectangles show organisms that we put together for the purposes of study – purple for prokaryotes and blue for protists.
The Tree of Life is used for children ages 6-9 to show them the big overview of life. They enjoy putting the cards on the solid, colored rectangles. The text on the back of the illustrations helps children place the picture of the organism. To help them find the right place, the major section and the name of the branch are in bold typeface. Older children and even secondary level students can still use the Tree of Life, and they should have an opportunity to place the cards and discuss this chart. Do they see that animals and fungi are sister kingdoms? This is why treating fungal infections is so hard.
On the other hand, the Timeline of Life shows the organisms that have lived during the time periods of the Phanerozoic Eon. A few timelines may have a bit of the previous Late Proterozoic, but the major emphasis is on life since the beginning of the Cambrian Period. There is nothing other than a timeline of life that can show this. Unfortunately the traditional Montessori Timeline of Life is riddled with mistakes – omission of the five major extinctions, all extinctions shown as ice ages, indistinct organisms, no grouping of related organisms, and my worst pet peeve, converging red lines that seem to show several lineages being fused into one.
OK, enough attacks on the Timeline of Life. It is still an important material for children, and I think it is important to use one that is updated and corrected, either by the teacher or by a company that has carefully researched its product. The Timeline of Life helps children understand how life has changed through time. (One last rant – add the Devonian explosion of plants! During that period, the land turned green as plants changed from a low green fuzz to trees that bore seeds. The Devonian – It’s not just for fishes!)
As a reminder of what is available on my website to aid you, my Outline of Geologic Time and the History of Life has lots of information that will help you make an accurate, up-to-date Timeline of Life. The Tree of Life chart is still a free download – my gift to the Montessori community. My book, Kingdoms of Life Connected, is a teacher’s guide to the tree of life. I updated it in the fall of 2016.
May you and your children enjoy exploring the living world, both its diversity and its history.
The New Edition of Kingdoms of Life Connected is here! October 30 2016, 0 Comments
The second edition of my book, Kingdoms of Life Connected: A Teacher’s Guide to the Tree of Life, is available now. I wrote the first edition in 2008, and it was already time for an update this year. New information keeps coming in all fields of science. This leads to gradually evolving ideas, but change has been exceptionally rapid in the field of systematics, the study of the diversity of life.
The flood of DNA information continues, and we must bear that in mind in our presentations. It would be better to state that the story you tell is based on the evidence scientists have gathered for now. In the future, there could be adjustments. This doesn’t mean that all the information about the Tree of Life will change. Instead there will be small alterations. The potential for change certainly doesn’t excuse the presentation of obsolete classifications as anything other than history.
One of the hardest tasks for my book revision was finding up-to-date children’s books about the diversity of life. I had to leave many older, but valuable, books on the resource lists. At least it is easier to find out-of-print books now than it was a decade ago. I also found that publishers have reprinted some valuable older books. They include Peter Loewer’s Pond Water Zoo: An Introduction to Microscopic Life. Jean Jenkins illustrated this book in black and white, and it has attractive, clear drawings of many protists, bacteria, and microscopic animals, along with text that upper elementary children can read. You will have to warn your children that the classification scheme presented, the Five Kingdoms, is obsolete, but the information about the groups of organisms is still quite good.
A forty-year-old book by Alvin and Virginia Silverstein, Metamorphosis: Nature’s Magical Transformations, has been reprinted by Dover Books. It has a chapter on sea squirts that shows the tadpole-like larval stage and tells about the life cycle of these chordates. I haven’t found another children’s book that tells this story. The black and white illustrations show how old the book is, but there didn’t seem to be a good alternative.
I know the pain of having to purchase a new edition of a reference book. My favorite biology textbook cost nearly $200, and I see the new edition, just published this month, is priced at $244. Yikes, that’s hard on the budget. If you own the first edition of Kingdoms of Life Connected, you will be able to purchase the ebook version – the pdf file – of the book at a reduced price. Please email info (at) bigpicturescience (dot) biz for information about how to do this.
Tweaking the Tree of Life - Again! August 19 2016, 0 Comments
If you look closely at my Tree of Life chart, you may notice changes. Knowledge about the early branches of the eukaryotes has grown, and it was time for another adjustment in the protists. This time I changed the label on the unikonts to also include a newer term for them, the Amorphea. Some biologists wanted this change because the original hypothesis about what makes the unikonts unique failed. The unikonts do not always have one flagellum, and they have two basal bodies (the part from which flagella grow), like other eukaryotes. What they do have is a unique fusion of three genes. This condition is so rare that it is unlikely to arise twice. The lineage of amoebas, animals, and fungi is still called the unikonts by many biologists, so I left that name on the chart.
The other main branch of eukaryotes, known informally as the bikonts, has a fusion of two different genes, another rare feature. The branch that includes chromalveolates (brown algae, diatoms, ciliates, etc.) and rhizarians (foraminiferans, radiolarians, etc.) has a much less wieldy name. It is now known as SAR (or Sar), an abbreviation for stramenopiles, alveolates, and rhizarians, and I added this to the chart. The evidence now points to some associations that I wanted to include on my Tree of Life. It appears that the Archaeplastida and SAR are more closely related to each other than they are to the Excavata (euglenas, Giardia, etc.). I’ve moved the branch positions on the chart to show this.
I like a newer term for the main branches of the eukaryotes. They are called the eukaryotic supergroups, which is a good descriptor for them.
You may be wondering what to do with your Tree of Life chart if you printed it from the older files. At lower elementary, I would do little more than adding the SAR and Amorphea labels. At that level, it is about showing a broad sweep of life, not the more exacting details. At upper elementary, you may wish to briefly explain about the changes since your chart was printed. Secondary students can learn more about these changes and modify their chart if they are interested.
And then there is that little fact we like to ignore. There are at least as many organisms not shown on our charts (even the more sophisticated scientific ones) as we show there. DNA studies show as many or more bacteria that have never been cultured or named as known bacteria. There are many named, but unplaced protists. Life isn’t simple! Is this the last version of the Tree of Life? Not likely, but it works for now.
You may also be wondering why I bothered to change the chart. Why not start new users of it with the most up-to-date information? As the flood of information continues, it will be best to go forward, not back. The most important thing is that children understand the Tree of Life and the evolutionary history it reflects. As a recent article in Nature Microbiology (2016, article number 16048) states “The tree of life is one of the most important organizing principles in biology.”
New ways to look at the Tree of Life November 21 2015, 1 Comment
I have two new posters that do a good job showing the history and diversity of life. The first is just out from Fairhope Graphics, and it is called “A History of Existing Angiosperms.” The many branches of flowering plants show up very well on this poster. You can see why there’s more to flowering plant lineages than monocots and dicots. The timescale on the left of this poster could lead to confusion, so you will need to explain to your children that all the pictures show flowering plants that still exist. Each illustration is placed at the time when we think its lineage originated.
An important qualifier for this information – plant fossils are so much harder to find than large vertebrate fossils. Paleobotanists have to piece the story together from small, hard-to-preserve fragments, not large bones, so it could well be that a number of these plants will have a different age of origin as scientists obtain more fossil data. That should not detract from the information show here, however.
You can see from this poster that the plants had developed their major lineages before the K-Pg (K-T) extinction, and these lineages survived much better than the large vertebrates. The poster has the number of species and the common names of a few members for each lineage.
Look for the three main branches of angiosperms, the magnoliids, the monocots, and the eudicots, on the poster. You can also find two large branches of the eudicots, the rosids and the asterids. The rosids split into the fabids and the malvids. The asterid subdivisions are the lamiids and campanulids. These seem like a bunch of big meaningless names until you put a flower image with them, so this Fairhope Graphics poster will help make the lineages more memorable.
Fairhope Graphics also has useful posters on the lineages of birds, the Tree of Life at a simple and more advanced level, and the history of the Earth.
My second recently acquired poster is from a company called Evogeneao, which they explain on their website is short for evolutionary genealogy. The motto of this organization is “Life on Earth is one big extended family.” Their “Evolution Cousin” poster shows their branching diagram for all of life, along with several familiar organisms and a number that reflects their relationship to us. For instance, your cat is your 27 millionth cousin. You can also get a larger poster that features the Tree of Life as the main graphic and gives information about it. These posters would be great for an impressionistic lesson on the Tree of Life. If you decide to use one of these posters in your classroom (or even if you do not) you will find it useful to read the Tree of Life page under the “Learn” menu on the Evogeneao website.
Under the “Explore” menu there, you can select “Tree of Life Explorer.” When you can click on an organism, you will see lines appear from humans and the selected organism. These lines meet at the most recent common ancestor. It is a very cool illustration of our relation to all of life.
Name That Flower! January 31 2015, 0 Comments
As we strive to reconnect children with nature, learning the names of plants can be a valuable first step. It certainly is an excellent measure to fight plant blindness, that malady that hides the marvelous details and identities of plants. All plants that children encounter are good subjects for learning names, whether the plant is a cut flower, a garden vegetable, a wildflower, or a weed.
Spring is coming extra early to the Willamette Valley, and although I realize that is not the case in most of the US, it is never too early to start thinking about spring and the opportunities for botany studies it presents. The crocuses are blooming here, as well as snowdrops and violets. When spring comes to your school, will the children know the names of the flowers that appear?
My “Study Starter Cards for Early Spring Flowers” can help your children start learning about the local flowers in the US, especially in moderate climates. This material is a print-it-yourself file that has half-page sized cards for 20 flowers and four full pages on early blooming trees. The trees are red maple, bigleaf maple, alder, and hazelnut, all of which have inconspicuous flowers. The flowers in this set include bulbs, perennials, and shrubs.
These cards have more than just the common and scientific names of the flowers. That information is enough for beginners, but elementary children are able to learn more. These and older children need names that will open doors to further learning.The cards include the family, order, and major branches of the angiosperms to which the plant belongs.
The major branches of the angiosperms are the magnoliids, the monocots, and the eudicots. The largest branch, the eudicots, has several branches including the asterids and the fabids. The names of these branches are not capitalized, nor do they carry a rank such as order or class. This is the new world of plant classification, the phylogenetic system that is currently used by botanists. With a little practice, it isn’t hard to learn or understand. My book, Kingdoms of Life Connected can help you. In case you are wondering, the former dicots included eudicots and magnoliids, which are two different lineages. "Eudicots" means "the true dicots."
The photo shows crocuses that were blooming in my garden early last March. They are at about the same stage this year at the end of January. Yes, the weather is strange, as usual. Enjoy your early spring plants, whenever they come.
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