Discriminating examination

If you really want to find out how good students are, how well they are learning, how well they are mastering the material, all you have to do is push them just past their comfort zone, stress the system a little, and the results will be very discriminating, and quite discouraging.  My last botany exam covered too much material, that is, too much material to be easily reviewed just before the exam.  Not only that but the lecture material involved a couple of key concepts that are rather beyond a textbook to explain (a classic textbook weakness).  And without any particular intent to create more of a problem, the exam asked students to demonstrate their understanding of the land plant life cycle, a topic the Phactor has been beating his head against the wall for decades to teach effectively.  This subject has the ability to separate the memorizers from the conceptualizers.  Now as freshmen about 70% of college students are memorizers (concrete thinkers) and 15% conceptualizers with the remaining 15% sort of transitional.  By the time they get to be 3d and 4th year students you certainly expect a larger percent of conceptualizers, but my class breaks down almost exactly like 1st year students which indicates that we, a collective we, are doing a very poor job of changing the way they learn.  From the view of the concrete thinkers, the Phactor is a poor teacher and gave them an unfair exam.  However at the other end of the class, the exam was considered easy with two nearly perfect papers (out of 22).  The Phactor was unaware of how drastic the problem was because it was not readily apparent until the system was stressed by the amount and nature of the material covered.
Here's an example.  The diagram is a typical moss.  Here are the questions asked.  1. In terms of its life cycle, what does the leafy bottom half represent?  2. What is the ploidy level of the portion indicated by D?  3. What type of cell is produced by the organ labeled A?  4. What cellular process produces these cells (ref. #3)?  5. What sex organ is/was located at the position indicated by B?
Their answers exposed a lot of conceptual misunderstandings when they mismatch their answers to 1-4 with ploidy level or process.  To get B correct they have to think backwards in the process to understand what took place before this stage in the life cycle.  And for those who grasp the concept, it was so easy.  The problem is that no matter how you present the material, concrete thinkers resort to memorization, even when the lab endeavors to create an investigatory approach.  When the Phactor first encountered such material as a freshman biology major, the professor, Dr. Marsh, aptly named because he studied cattails, deducted for logical inconsistencies because it was evidence you were guessing.  Even then there were howls of protest and indignation.  
Some things just don't seem to change, but Marsh is proud of me.  And the exam did one thing it was supposed to do; it discriminated among my students and will make the final grading relatively easy even if the memorizers must be cut some slack.  Sadly this was just too difficult for most of our students.  Sorry, kids; sorry, world.  You try, but sometimes you fail.  However, you may be guaranteed that those top students are quite impressive, and really understand the land plant life cycle.  
Have at it readers.  

What is a seed?

Seeds are perhaps the most misunderstood and misinterpreted of botanical subjects. You plant a radish seed, a radish grows, flowers, gets pollinated, fruits, and the seeds within contain an embryonic radish plant. This seems simple enough, rather like chickens. In fact the traditional name for an immature seed at the time of pollination is an ovule, literally an egg. So of course the floral structure that houses ovules must be an ovary. Oh so very like an animal, NOT!

An ovule is actually a sporangium, a jacketed, unopening sporangium that produces 1 spore via meiosis thus reducing the chromosome number from diploid to haploid. The spore develops into a female organism, a gametophyte, that ultimately produces a real egg. Pollen is also a spore at its inception, and it too develops into a haploid male organism, albeit a very tiny and reduced fellow. Having a small dispersible male solves the swimming-sperm problem that land plants with free-living gametophytes have, e.g., ferns.

Pollination is the completion of the male’s dispersal trip. A pollen tube that grows from him to her delivers the sperm, fertilizes the egg, and results in a new embryo. When the entire kit and caboodle is mature, the jacketed sporangium, what’s left of the female, and the resulting embryo of a new diploid plant (a sporophyte) gets dispersed as a seed.

The seed plant life cycle only makes sense as an evolutionary solution to a reproductive problem that limited the distribution of land plants.

Here are some great false color images of seeds and pollen complements of the Royal Botanical Garden at Kew. HT to DD at Neuron Culture.

Gneater (neater) than all get out!

Visits to our teaching greenhouse still manage to deliver surprises even thought I have been doing it regularly for years.

This is something the Phactor had never seen before: the ovulate strobilus (cone) of Gnetum (knee-tum). Hmm, that's pretty funny, telling you how to pronouce a silent G with a silent K.

Gnetum is a tropical liana, and that's one of the reasons I've never seen strobili before. They're usually way, up, there. The closest I've come before is the seeds, mature ovules, which are about 4 cm long. They have a fleshy, reddish outer seed coat that attract and reward an animal disperser. Finding these seeds on the rain forest floor means that somewhere far above where the vine clamors along in the canopy, a strobilus just like the one above got pollinated.


The strobilus consists of several whorls of small bracts (modified leaves) above which is a whorl of ovules. Ovules are not eggs so their name is a misnomer. Ovules are jacketed, indehiscent megasporangia. The single megaspore produced develops into a haploid female (a gametophyte) who then produces an egg. The jacket prevents the pollen access except through a small hole. The ovules shown here are ready to receive pollen. The ovule has exuded a a drop of sticky liquid out through this small opening and any pollen grains (endosporic males) that adher to the surface of this pollen drop get pulled inside the ovule when the ovule reabsorbs the liquid.

This is not the work of a passive female. She reaches out, grabs passing males, and pulls them into her lair.

Now if the foregoing description wasn't a tipoff, what makes Gnetum so Gneat is that this is a gymnosperm, a relative of conifers, albeit a fairly distant one. Yet as you can see, this vine has broad leaves, and it has vessel elements in its wood, both features usually associated with flowering plants. And of course there is a certain flower like quality to the strobilus.

Do flowering plants share a common ancestry with Gnetum? The jury is still out. For many years data suggested that the answer might be yes, but most recent studies suggest this strange plant is more closely related to conifers, and not in a gymnosperm lineage having a common ancestry with flowering plants.

Ever seen a fern this pretty?

Here's a pretty image of a fern. Have you ever seen a fern like this one? No question about it, this fern is pretty small, about the same size as a neatly trimmed nail on your little finger, and at that size, a fern can be over looked pretty easily.

You may think that this fern doesn't look very fern-like, but in this you are wrong. Your experience with ferns is just too limited. Granted this fern has no ferny fronds, and no vascular tissue either, but I assure you it is quite typical. The most interesting thing about this fern is that it is haploid. The nucleus in each of its cells has only a single set of chromosomes. All of the ferns with which you are familiar have two sets of chromosomes. And what a difference this makes.

This haploid fern is the sexual phase of its life cycle. It makes sex cells, eggs and sperm, and after fertilization, it nutures, for a short while, an embryonic fern, which can grow into a typical appearing fern. So this haploid fern is not some strange, exotic beast, but just the alternate phase of the fern life cycle, the gametophyte phase, the gamete (sex cell) producing plant. Like all other vascular land plants, the familiar fern is the diploid phase, the sporophyte phase, the spore producing plant. And with that I am off to sow some spores and raise some haploid ferns.