No Males Need Apply: Parthenogenesis in Gall Wasps

In some gall wasp species there is reproduction without males!

The title might sound scholarly, but what does it mean?  Parthenogenesis in animals is the development of an embryo from an unfertilized egg cell– in other words, no males involved.  This can happen among some invertebrate species, and even in some reptiles and amphibians.  With gall wasps, the males and females reproduce in the conventional way in the spring, but in the fall the females manage it all by themselves.

Of course, the practice of parthenogenesis decreases genetic diversity, as you would expect, but it has some advantages too.  For one thing, it usually results in production of much larger numbers of offspring, possibly because less energy is expended in looking for a mate.  Imagine being free of those pesky mating rituals!   The time and energy you’d save by not dating!

And here’s a cultural  aspect to consider:  a friend who is a member of the Coast Miwok tribe told me the tribe used to carefully time their controlled burns to hold down populations of these insects.  Clever.

Find out more about gall wasps and all other things related to oak trees in this wonderful book:  “Secrets of the Oak Woodlands” by Kate Marianchild.

Fierce Predators and Sharp Teeth

It’s all about attitude!

So you were expecting maybe –sharks?  Barracuda?  Well, no.  Here you see some creatures to be reckoned with, and they all live in our California kelp forests.

The purple-ringed topshell, Calliostoma annulatum, though tiny, will even rear up on its foot and lunge at its prey!  Of course, its prey might be kelp, a copepod, an anemone, or even some dead fish, but still.

Then there’s the sunflower star, Pycnopodia helianthoides, a giant sea star, as large as 40 inches across, with more than twenty arms at maturity.  It preys on urchins, crabs, sea cucumbers, snails and chitons.

So where do the sharp teeth come in?  The purple sea urchin, Strongylocentrotus purpuratus, has sharp teeth on its underside and is able to use them to erode holes in rocks!

BTW, see the pictured animals, featured as magnetic manipulatives, in Speak Easies’ Kelp Forest Food Web, coming soon on Teachers Pay Teachers.

Sex Change: One of Nature’s Strategies

Here is a picture of a sheephead fish (Semicossyphus pulcher) and he has an interesting story to tell, because, though he’s a male, he used to be a female!  Turns out changing sex is not uncommon among fish; there are many species that do it, and some,  like the                              

A sheephead male on the prowl.

sheephead, go from female to male, while others go from male to female.  In the case of the sheephead it is thought that females reproduce most when they are small, but when the fish gets large, males have the reproductive advantage, thus the change.  This is called serial hermaphrodism.  When it comes to maximizing reproduction, to quote Jeff Goldblum in Jurassic Park, “life will find a way”!

Nitrogen Fixing Bacteria Need Nitrogenase–Why Should You Care?

All us animals need a constant supply of nitrogen for our cells to use to make protein for repair, growth and maintenance.  Good thing the atmosphere is more than 70% elemental nitrogen.  But wait, we can’t use elemental nitrogen!  Uh oh!  How do living things get it then?

There are a few species of bacteria that can “fix” nitrogen, converting it to a form that can enter the food chain and be used by plants and us voracious consumers.  So where does nitrogenase come in?  That “ase” ending is telling us that it is an enzyme, a biological catalyst that makes chemical reactions possible in living things, and the nitrogenase enzyme catalyzes nitrogen fixation reactions in those particular bacteria.  Okay, so what?  Take another look at that bucket…

…Yes, that vitally important enzyme, crucial to life as we know it, could all fit in one bucket.  All of it.  All around the planet.  So this critical ecosystem service, nitrogen fixation, depends on certain bacteria that in turn depend on nitrogenase enzyme.

Makes me want to keep those bacteria very happy, in a clean and healthy environment, with enough good-quality nitrogenase to fill their needs, so they can fill my needs.  (Enlightened self interest at work.)

Fun Fact About Rubisco

But what is rubisco?  Rubisco, ribulose bisphosphate carboxylase, is the enzyme responsible for the regeneration of RuBP as well as for the formation of phosphoglyceric acid, PGA.  In the largest sense, rubisco supplies one of the most important biosphere services–making carbon fixation possible!  We say “give us some sugar” and rubisco goes into action!

You can see it in this photo of the Calvin cycle piece from Speak Easies’ Photosynthesis Kit.  It is shown as a wrench because lots of enzymes catalyze reactions by holding substrate molecules in a certain orientation to each other, you know–sort of like a wrench.

And now for the fun fact:  Rubisco is one of the most abundant enzymes on the planet!  If that isn’t fun, what is?

Where- and What- Is the Z-Scheme?

So, what is this Z-Scheme anyway?  Can you spot it below in the picture of our Speak Easies magnetic Photosynthesis Kit?

    The Z-Scheme is a handy graphic way to think of photosynthesis’ energy profile.

A photon of sunlight (680 nm) blasts an electron out of the chlorophyll in photosystem II and energizes it, propelling it through a series of molecules (the electron transport chain) where it releases its energy step-by-step.  That energy is captured in ATP.  Then another photon (700 nm) energizes an electron from a chlorophyll molecule in photosystem I, and that electron releases its energy in the manufacture of sugar.

This is discussed so clearly in a book by Nick Lane, “Life Ascending–The Ten Great Inventions of Evolution.”  Check it out.  And remember, you can have your students using our hands-on kit to enact the process of photosynthesis till they really get it!!

Did you spot it yet?

Turning the magnetic electron transport chain piece reveals the Z-Scheme.

And there it is!  The Z-Scheme!  Probably you already knew.  But having the separate pieces of this magnetic kit will make it easier to show your students, or better yet, challenge them to show you!

 

 

 

Seeing Stars! The Mystery of the Sea Star

A beautiful example of radial symmetry!

Such a strange, elegant creature—the sea star!  The mystery:  its tiny larva, floating in the plankton, has bilateral symmetry, but its adult form is radially symmetrical—a radical transformation!  How could that happen?  Donald Williamson, an English zoologist, suggested a theory of “larval transfer”, saying that in the past, genes for body shape and for life cycle were exchanged when hybridization occurred between marine species with the two distinct body plans.  This would be possible due to external fertilization, which, in the ocean means millions of sperm and eggs of different species are floating around and bumping into each other.  Williamson demonstrated in the lab that cross-fertilization between species is possible in those circumstances!

Note the radial symmetry in the adult vs. the bilateral symmetry in the larva.

 

See Ryan, Frank, “The Mystery of Metamorphosis—A Scientific Detective Story”, White River Junction, VT, Chelsea Green Publishing, 2011, print

Protein Rescue–Help Is on the Way!

A customer just purchased the Protein Package (consists of the Protein Synthesis Kit, the Macromolecules Kit, and the Enzymes Kit), and it got me thinking about why those kits, in combination, are so helpful for teaching about protein.

Speak Easies’ Protein Package:

  • Accesses “caveman learning”!
  • Overcomes lack of prior knowledge!
  • Shows why protein matters!

 

First:  we’re talking about “caveman learning” here– the most fundamental way of learning, using our hands and movement to explore and find out.  Watch a baby learn–it’s all about hands!  So Speak Easies kits are totally hands-on.  Students hold the pieces and assemble them into structures or move them to enact processes, helping them to understand, and muscle memory helps them remember the concepts involved.  This is especially valuable with the Protein Synthesis Kit, which allows students to enact the translation process.

Protein Synthesis Kit Being Used to Demonstrate Translation

Second:  for such concepts as macromolecules, monomers and polymers, students probably have no prior knowledge at all, so there’s nothing there to hook the concepts to.  That’s where brightly-colored simple shapes and the act of assembling them can help to engage the students and stick those ideas in their minds.  And seeing the simple shape and color of the amino acid monomers in the Macromolecules Kit repeated again in the Protein Synthesis Kit will help students comprehend and remember.

Amino Acid Symbols from Macromolecules Kit

Third:  understanding the basic structure of protein and how it’s assembled is just the beginning.  Students need to understand why protein is so important, and this is where the Enzymes Kit plays a role.  Of course many structures in an organism are made of protein, but all the chemical reactions inside a cell or organism are facilitated by protein in the form of enzymes, and without those enzymes reactions slow down enormously!  The Enzymes Kit helps students see how enzymes function, and the included background information lists some diseases and conditions that result from the absence of certain enzymes.

Images showing an enzyme, substrate, and products
An Enzyme at Work

And finally, using all three kits together reminds students that structure and function are bound together and they see that mistakes in structure can lead to problems with function.  Put the kits on your markerboard, challenge your students with provocative questions, and let them figure it out–the kits provide the clues to help them.

Purchase the Protein Package, consisting of these three kits:  Macromolecules, Protein Synthesis, and Enzymes, to give your students a highly effective learning experience about protein!  And to help cement that knowledge in place, we have Protein Synthesis Desk Kits for students to use working with a partner (discounts available for purchasing a class set).

Biology Models: The Great Blood Vessel Challenge–Hands-On Activity for Your Students

Materials needed for a reusable class set:
1 standard garden hose
1 soaker hose
1 discharge hose (find in pool supply stores)

This is an easy way to have students carefully consider the characteristics of blood vessels. To set it up, you will need three hoses (or lengths of hose) of three different types: a simple garden hose with fairly thick walls (red?), a soaker hose with mesh walls, and a discharge hose (blue?) such as is used to drain the water from swimming pools. The latter can be ordered from a pool supply company. It will flatten when not full of liquid.

Students use common hoses to model blood vessels

Directions:  Simply cut the hoses in lengths of 12 to 18 inches.  Each student or small group is then given one of each type of hose. They are asked to decide which best represents a capillary, vein, or artery. There is not one right answer, although some choices may seem more appropriate than others. Students must consider the properties of each type of blood vessel and make reasoned decisions regarding their choices, citing characteristics to back up their reasoning. It might be helpful to allow them to take the hoses to the sink and run water through them.

Background Information:

Arteries are thick-walled vessels that carry oxygenated blood away from the heart. (Exception: the pulmonary arteries carry deoxygenated blood on its way to the lungs.) The arterial walls contain more smooth muscle and elastic fibers than do the walls of the veins. This makes arterial walls thicker and more elastic, so they retain their circular shape in cross-section, even when emptied of blood on the commercially prepared slides your students may view. The walls are thicker than the walls of veins and more contractile. No valves are present.

Veins are vessels that carry deoxygenated blood on its return trip to the heart. (Exception: the pulmonary veins carry oxygenated blood returning to the heart.) In a tissue sample such as those on commercially prepared slides, the emptied veins may collapse and flatten. Valves are present inside the veins. Contraction of the surrounding skeletal muscles also helps to push the blood back to the heart.

Capillaries are very thin-walled vessels with a very small diameter. Some are only 4 microns across. (Compare this to the diameter of the red blood cell: 8 microns!) They are the site of gas exchange and chemical exchange between the blood and the body’s cells. The capillary walls are only one cell thick, being composed simply of epithelium, and oxygen and carbon dioxide can pass through them readily. They exist in capillary beds in all tissues of the body except epithelial tissue.

Blood vessel illustration by National Cancer Institute, National Institutes of Health – http://training.seer.cancer.gov/anatomy/cardiovascular/blood/classification.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=45154160

 

Biology Models: Consider the Red Blood Cell

It was a pretty good lecture, as lectures go:  brief and to the point, with interesting subject matter– the red blood cell!  All other cells in the body depend on it to bring that life-giving substance, oxygen.  It’s tough and stream-lined to perform its function–zipping through the blood vessels with its payload, bumping into the vessel walls and other blood cells, stacking into rouleaux which reduce wear and tear.  Early on it loses its nucleus and organelles, including mitochondria, so it can transport oxygen with maximum efficiency, traveling by the bulk flow of the blood.  I described its width–8 microns–and the fact that it can fold to fit through capillaries that are only 4 microns in diameter.  A lovely little cell, admirable in every way!

And the next day the class remembered nothing!  I could almost believe we were viewing each other from alternate universes, with no sound and no meaning bridging the gap in between.  Over the summer I thought about it a lot, and finally I went shopping.  In a pet store I found a flexible rubber frisbee.  The fabric store yielded some stretchy red cotton knit and some batting to pad the edges.  Then I went home and sewed a red blood cell, a handsome bi-concave disc, flexible yet strong.

In time, I added to the one red blood cell: an ABO set plus a sickle cell.

In the new school year the day finally arrived when the lesson included blood cells.  This time I tossed the disc to a kid in the middle of the room, asking “What is this?”  They passed it around, looked at it, and came up with the answer.  “Why do you think so?”  “What characteristics do you notice?”  “How can this 8-micron-wide red blood cell fit through capillaries only 4 microns in diameter?”  “What could be the benefit of having no mitochondria?”  At this point I added five minutes worth of further information.  The next class meeting, the students could tell me a lot about red blood cells, without even checking their notes.  Over time that one red blood cell grew to a collection of four, with black and white buttons to represent blood type antigens, plus an appropriately shaped sickle cell.

My conclusion:  an object to hold in the hand, to observe, to bend, and even toss around the room, made quite a positive difference in kids’ receptiveness and retention!  Probably any teacher reading this has already reached this conclusion for her/himself, and I knew this too, even before the red blood cell epiphany.  However, after that I devised even more biology models, and I used them in a more determined and systematic way.  Using them in an introductory lecture, then having students explain key concepts using them, and finally, bringing them out for review prior to tests–this is a powerful strategy to enhance student understanding and recall.

So when and how could a teacher use manipulatives?

  1.   Introduce a topic:   Bring out your biology models to lead into a lecture.
    Question the students:  What do you observe?  What do you suppose it represents?  What is its function?  Comment on the surface area-to-volume ratio– is surface area increased by the way the object is shaped?  How would that affect its function?  How might it interact with what you studied before?
  2.  In your lecture:  Manipulate the biology model yourself as you discuss it.
  3.   Pose a mystery:  Hand out the model and have students examine it to find an answer.    Ex:  How does this red blood cell, 8 microns in diameter, pass through a capillary that’s only 4 microns wide?
  4.   Have students use the object to explain its function to the class.
  5.   For a powerful review:  Put your biology models out in stations with question cards for the students to use, answering  together as they move around the room.
  6. Comply with NGSS:  NGSS calls for use of models.  When there isn’t time for students to create their own, then bring out biology models you have made or purchased, and watch your students get engaged.