Our challenge this week was inspired by the images uploaded by the Bangkok contingent. We’d like all of you to:
1. Practice separating plant tissue into layers
2. Learn to recognize the overall quality of plant cells when they are observed under a microscope
3. Connect the operation of a microscopic plant structure to a process that is essential to plant survival.
You may remember that many plant cells contain a type of green pigment, or coloring, called chlorophyll. You may even know that there are several types of colored pigments in plants and these pigments help the plant convert energy from the sun into different types of sugars. Chlorophyll’s chemical “cousin” is a red pigment in plants called beta carotene. A bit of chemistry: Chlorophyll particles are made up of atoms, and one of these atoms is a metal called magnesium (strong, lightweight silvery metal used in mixtures of metals called alloys). The plant’s pigment, chlorophyll, contains a particle of metal, just as your blood’s pigment contains a particle of a different metal (you may know from science class that the metal in your blood is iron). Just as you need to have a source of iron in a healthy diet, plants often need soil that contains magnesium to help them stay healthy as well.
In this segment, Dan is handling a type of lettuce called Romaine, which we have chosen for its availability and high water content. For our first examination of plant cell structures, we wanted plant tissue that has a high water content because light can easily pass through the plant cell’s fluid interior (called cytoplasm) and help reveal why some of the first cell biologists once compared plant cells to crystals. Here we can see that they have a rather uniform geometry and they are highly translucent (allow light to pass through). In future challenges, we plan to examine the components of a plant cell, yet today we focus on structures called stomata (singular: stoma from the Latin word meaning “mouth”).
Separating the plant tissue into layers is quite easy in plants with soft tissue that contains a lot of moisture (called herbaceous, as opposed to “woody”tougher, dryer plant tissue forming fibers an a tough outer bark). Here we can “snap” and peel a layer of cells from the central “rib” of the lettuce leaf. You can tell it’s thin enough when light passes through your sample. Dan’s sample is actually quite thick (you can tell because it’s a pale green color). If you practice, you can separate a thinner layer, and you will see that when it is thin enough, the sample appears clear instead of pale green.
EXTENSION: Try “painting” a small area of the plant tissue with clear nail polish or liquid band-aid, then “peel” off the clear coating to examine with your digital microscope. Here you will see perhaps one or two layers of plant tissue, instead of the 10+ layers you may see in a sample that is peeled in the way demonstrated in our video.
The stomata structures we are hunting for in this MicroGlobalScope challenge aren’t actually cells, they are really openings between two special crescent shaped cells called “Guard Cells”. We like to think they are called “guard” cells because they “guard” the level of moisture in the plant tissue. Can you predict what would happen if too much moisture left a plant’s tissue? What if the plant was unable to release extra moisture into the atmosphere? Dan mentions how plants open and close their stoma to trap and release moisture, yet they also use the same methods to release gasses as well. In one sense, it’s a bit like the plant uses stomata to perspire (or sweat) and also to “breathe” gases in and out. If you’d like to catch the plant in action, try placing a clear plastic bag over it during the night. In the morning, you may see droplets of water vapor that have been released into the air, then gathered on the inner surface of the bag changing from a gas (water vapor) to a liquid (droplets) through a process called condensation.
- Why do some plants have more stoma than others?
- Where on a plant’s leaf may we commonly find more stomata?
- Brain Drain: What structures in the guard cells allow them to change position, opening and closing the stoma depending on conditions in the environment?
- What would you call the openings in your skin that allow moisture to move into and out of your body?
We think of steel as one of the strongest, most versatile materials in our arsenal of building resources. Yet in this MicroGlobalScope challenge, we witness steel’s weakness under the influence of one of the universe’s tiny, invisible yet strangely powerful fundamental particles: The Electron. You may know from science class that the electron is one of three main particles inside an atom (atoms are the smallest particle of matter that is still has the properties of an element; Think if you were to divide a nugget of gold until you were no longer able to divide it. Each piece of gold, separated from all other pieces of the sample, would be an atom).
The behavior of elements like oxygen, carbon, sulfur and all others that we know of, is determined by the arrangement of the electrons, or tiny negatively charged particles that moved in cloudlike spaces around the atom’s center, or nucleus. In a neutral atom (one with no electrical charge), the number of negative electrons is “balanced out” by the number of positively charged protons. That’s why we consider atoms in a pure sample of an element such as gold or copper, to be “neutral”, meaning neither negative nor positive.
Yet often electrons in one atom are more attracted to another atom. When electrons move between atoms, the materials involved change properties. We know this as a chemical reaction. In our challenge this week, we are seeing atoms of iron lose electrons to atoms of oxygen, to form particles of another substance called iron oxide. While iron in its uncharged, neutral form is normally a gray solid particle, it changes to a reddish brown scaly, crumbly material when it combines chemically with oxygen atoms (it does this when the atoms of oxygen “snatch away” electrons from the iron. There are potentially sixteen different forms of iron compounds that can form as the electrons of iron atoms are removed by atoms of other elements.
In this segment, Dan wet mounts fibers of “steel wool”. Steel wool is made up of very fine threads of steel, a substance that is composed mostly or iron. Dan uses tap water, which contains dissolved oxygen, as well as many salts, which can “snatch” electrons from the iron in the steel wool.
As the electrons move between the atoms in the water and the atoms of iron, we can see new matter forming. With careful focusing, you may see layers of the iron reacting. When filming this segment, out fibers appeared to be “shedding” layers of new chemicals (called oxides). Try to capture the process in stages, and share your images with us on our MicroGlobalScope blog.
1. Do you think this experiment occur faster or slower if we used thicker fibers of steel wool? Why?
2. Why do we use steel wool that has no other materials added to it, such as soap? How would the presence of soap affect our results?
3. Can you think of another material to substitute for the steel wool fibers? Would this experiment work well with fibers of gold? Why or why not?
An exciting and important aspect of microscopy is the ability to examine the structure of matter up close and to see aspects of it another way. In our next MicroGlobalScope challenge, we want you to consider the structure of crystalline solids. In the segment, we discuss one obstacle in examining crystals under an optical microscope such as our Celestrons. As you know, many crystals dissolve in water, which is sometimes called “the universal solvent” because of its ability to dissolve so many things. In attempting to wet mount common but interesting crystals like salt (sodium chloride) and sugar (called by chemists sucrose or saccharose), we find that they quickly dissolve in the water we typically use in our wet mounting procedure. Our solution was to consider other clear liquids to allow us to suspend the crystals under the lenses and allow us to magnify them with bending rays of light.
We have selected two options as clear liquids to suspend our crystals in as we study them under magnification. Our first effort using an astringent (that’s the name we use for material that causes tissue to shrink or contract) called witch hazel. As you may see in the accompanying video, we use it here because it allows light to pass through it and it does not quickly dissolve the crystals (here salt and sugar). You may know from camping trips that we sometimes use witch hazel to help soothe your skin after an insect bite or exposure to poison ivy. It helps by reducing the swelling that happens when your body is exposed to toxic chemicals from insects or plants. We also have good luck with rubbing alcohol, called isopropyl alcohol or isopropanol by chemists. In fact, in both cases (witch hazel and isopropanol), we are simply using alcohol in place of water in mounting our crystals on a slide, because the witch hazel is dissolved in another form of alcohol called ethyl alcohol.
In examining samples of your own crystals, compare what you see with your eyes alone, with a hand lens, and then under lower and higher powers of magnification. Using a sharp pencil, practice sketching what you observe under the microscope to help prepare for our upcoming challenges involving lab drawings.
Tip: If you use a nice, sharp pencil and angle your lines correctly, you may be able to make your lab sketches of the crystals appear three-dimensional. We are planning a segment to share with you some lab drawing techniques in the future, but for now, hold your sharp pencil at an angle and “shade” lightly away from a dark border to make your image look three dimensional. I call this “counter-shading” and use it often in my own lab drawings to show the shape of things. It takes a bit of practice, but it’s actually kind of fun.
You may know from science class that the crystals appear somewhat uniform in shape and light passes through them because the particles of salt are arranged in a pattern. Other matter, called “amorphous” or shapeless matter, doesn’t normally allow light to pass through it because its particles are arranged more randomly and also often change position (think of a lump of clay or the silly putty from our VideoScience segment on polymers).
Upload some images of salt and sugar crystals to our blog. In the coming weeks, we are planning a segment on growing your own large crystals from specially prepared “supersaturated” solutions. But for now, let’s take a look at the crystals we already have at hand. If you find another crystalline solid to study (perhaps colored sugars or powdered soaps), suggest them to the MGS team and show us what you find.
Remember, as always, to use only materials that are safe to handle from the kitchen and wash your hands with warm soapy water after any lab work.
Fibers are one of several forms we plan to examine in our journey together through the microscopic universe. We’ve selected a simple study of fibers as an early MicroGlobalScope task because everyone, everywhere has access to some form of fiber, and most fibers are safe and easy to handle.
In our video segment, Dan gathers a piece of red cotton/polyester thread from a sewing kit. He selects a piece that is long enough to comfortably handle, then ties it into a single knot. After, he trims away the excess thread on each side of the knot, and then wet mounts the knotted thread on a slide. In trying it, you will see that adding the water to the slide first may make the process easier. Placing the knot by itself on the center of the slide seems like a good idea, yet when you add water to the slide, you may find that the knot is “washed” aside by the water droplet. On the other hand, placing a good sized drop of water onto the slide and then laying the knot on the top surface of the water may stabilize the knot when it is mounted. This happens because thread quickly absorbs the water on contact, and the process “glues” the knot into position. If you are clumsy or have large thumbs, you may want to use a pair of tweezers or forceps to handle the knot during the wet mounting process.
After allowing the thread to absorb the water, position your coverslip on top of the specimen. If your thread is thicker than most, you may want to add a bit more water to create a smooth surface for the coverslip to rest upon. If some water leaks over the edge of the slide, simply place a piece of paper towel or tissue beside the slide and it will absorb the excess water through a process called “capillary action”, or a form of wicking.
Depending on the position of the knot on the slide, you may be able to see light passing through its center. Dan’s sample is very loosely knotted, so he was able to see light coming through the center of the knot in a shape that resembled a donut hole, yet much smaller.
Before mounting any specimen on a microscope slide, try to observe it macroscopically, or with the naked eye. Before Dan mounts the thread on the slide, he studies its structure unmagnified. To him, it looks like a single fiber. Yet even under the lowest power of magnification, Dan is able to see that the thread is in fact composed of smaller threads. Further, observing for a few moments, he notices that some of the fibers in the thread appear to become larger, while others do not. Can you think of a reason why?
Since his specimen is a mixture of cotton and polyester, he is able to see on a higher power of magnification that the cotton fibers in the thread appear to enlarge, yet the polyester fibers to not. Can you think of the properties of these materials that may explain this phenomenon? If not, try to find a sample of pure cotton and one of pure polyester (sometimes sports clothing is made of 100% polyester). You can try two things:
1. Pour two equal volume water samples onto a laminate or stone surface, then rest the cotton cloth on one, and the polyester swath on the other. After a moment, remove each cloth. Can you predict which sample with have water remaining?
2. You may simply pour a small volume of water on to each of the cloths. Can you envision which cloth will absorb the water and which will allow it to roll off?
If you find the cotton has absorbed the water, it’s because fibers like these are hydrophilic, meaning they attract and capture particles of water. Polyester, a man-made long chained molecule, is composed of plastics, which tend to repel water particles. So it’s not unusual that the cotton fibers in our sample are expanding faster than the polyester fibers. If these suffixes are new to you, remember that “philos” comes from the Latin word to “love”, as a philosopher is a “lover of knowledge”. Similarly, “phobic” means “afraid of”, as in “arachnophobic” means “afraid of spiders”, or arachnids. So here we have two fibers in a thread, some absorb water, others do not. Further, if you find a thread that specifies the percentage of cotton and polyester in it, you may be able to check the composition by counting how many threads of each are present. In a thread specifying 40% cotton, expect to find 4 threads expanding in the wetmount for every six that do not.
Join us on a fiber hunt! Find and examine different fibers under your Celestron scope. As you notice similarities, disparities and anything unusual or interesting, share it with us on MicroGlobalScope.org.
the Biobus, who will be traveling around New York and the USA sending images and video as they go!
If you’re reading this post it means you’ve received your equipment and have logged in to the website. You’re ready to go! So let’s get started!
For your first project, can you find 5 different plants, flowers, insects, bugs, or materials that are unique or iconic to your area and take a photo of each one with your MiScope?
To get your microscopes set up, follow these setup instructions. Once you’ve completed the setup process, learn how to use the microscopes, take photos and video, and upload your findings to the blog by watching these instructional videos.
Visit each city’s blog by clicking on the city names above, or see everyone’s posts by visiting the activity.
Can’t wait to see what you find!